Category: cacti

Bioinvaders on Puerto Rico: More Complete Information

Spathodea campanulata (one of the most common invasive plant species in moist or wet forests on Puerto Rico); photo by Annika Lindqvist via EasyScape

America’s Caribbean islands have received much less attention that Hawai`i with regard to either their biological importance or level of biological invasion. I posted a blog three years ago about invasive tree species. I rejoice that the silence might be starting to change – thanks in large part to Julissa Rojas-Sandoval.

The West Indies

The Caribbean islands – including but not limited to Puerto Rico and the U.S. Virgin Islands – are considered one of 35 global BD hotspots on Earth (Castro, Quinones, and Gould 2016; Zimmerman et al. 2021). The most comprehensive descriptions are a decade old. Castro, Quinones, and Gould (2016) report that the Caribbean islands are home to ~14,526 plant and terrestrial vertebrate species, half of which are endemic to the region. At that time more than 900 species were on the IUCN Red List. The West Indies are characterized by exceptionally high levels of plant endemism, with more than 70% of seed plants considered endemic to the region (Rojas-Sandoval et al. 2017, citing earlier floristic assessments).

The Caribbean islands have a long history of anthropogenic disturbance – especially since Europeans arrived in 1492 — and intentional or accidental introductions of non-native species. Available sources differ on the number of species that should be categorized as “invasive”.

Potter et al. (2022) report that 17% of the flora of the islands of the Caribbean archipelago are not native. Rojas-Sandoval et al. (2017) identified 516 invasive non-indigenous plant species, representing about 4% of the total West Indian flora, and concluded that the incidence of invasive plants in the region is high compared with other island groups. Interestingly, each island group has its own suite of invasive species. More than 60% of these taxa occur on a single island. Thirty-eight percent belong to one of three families — Fabaceae, Poaceae, and Asteraceae. Thirty-four families are represented by a single species; 78 families by fewer than five.

Leucaena lecocephala; photo by Agnieszka Kwiecien-Nova via WikiMedia

They report that the most widely distributed species is river tamarind, Leucaena leucocephala (Fabaceae); it occurs on all nine islands. Another seven species are found on seven of the islands: Casuarina equisetifolia (Casuarinaceae); Eichhornia crasssipes (Pontederiaceae); Megathyrsus maximus (Poaceae); Melaleuca quinquenervia (Myrtacea); Ricinus communis (Euphorbiaceae); Spathodea campanulata (Bignoniaceae), Terminalia catappa (Combretaceae).

The density of invasive plants per square kilometer varies considerably among the islands. The Virgin Islands (US and British) rank second highest at 0.245 / km2. Puerto Rico doesn’t stand out. As noted above, each island has a distinct invasive flora. The pair of islands which share the highest number of species (122) is Puerto Rico and the Virgin Islands (Rojas-Sandoval et al. 2017). I suggest it might be informative to explore whether these islands’ century-long ties to the United States influenced trade pathways and planting choices, thereby leading to this similarity.  

Rojas-Sandoval et al. (2017) report that 31% of the invasive plants (162 species) are herbs; 20% (102 species) are trees; 16% (80 species) are shrubs; 15% (77 species) are grasses; 13% (67 species) are vines; 3% (15 species) are succulents; 2.5% (13 species) are aquatics. Three-quarters are perennials. These plants occur primarily in human-altered habitats: 98% (506 species) in ruderal areas; 61% (314 species) in seminatural areas; 35% (138 species) in agricultural areas. Only 5% (27 species) are found in mature forests.

Nineteen of the species are listed among the “world’s worst alien invasive species”. For example, six of the eight most widely distributed species (above) are invasive in Florida also.

Seventy-five percent of the invasive plant species have escaped from cultivation. According to Rojas-Sandoval et al. (2017), half of these were introduced as ornamentals; another third were introduced for various agriculture and forestry purposes. Finally, 7% were deliberately planted in natural ecosystems for some purpose such as erosion control. They suggest that repeated introduction of some of these species – especially the ornamentals – might increase propagule pressure and thus their probability of establishing.

Generalities About Biology on Puerto Rico

Puerto Rico is the smallest island of the Greater Antilles at ~ 9100  km2 (5,325 mi² / 1,379,000 ha) (Rojas-Sandoval, Presley, and Willig 2026). It is 39% forest, 32% grassland, 13% woodland and shrubland, 11% urban, 3% herbaceous wetlands, 1% forested wetlands, 1% inland water, < 1% natural barrens (Castro, Quinones, and Gould 2016).

Puerto Rico is relatively poor in species richness compared to mainland tropical areas. In one example, a plot in a Puerto Rican wet forest had half the number of freestanding woody species as a comparably-sized area in central Panama. Puerto Rico lacks large herbivores and predators. Still, Puerto Rico is much more diverse than other more isolated islands, e.g., the Hawaiian Islands (Zimmerman, Rojas-Sandoval, and Shiels 2021). There are 2,780 species of plants and 361 native vertebrates, including 277 birds, 52 reptiles, 19 amphibians, and 13 mammals (Castro, Quinones, and Gould 2016).

This biodiversity reflects the island’s highly varied topography – elevations range from sea level to 1338 m – and rainfall. Areas in the south and southwest receive ~800 mm while the high-elevation areas in the northeast are drenched by more than 4000 mm.

Unlike in most tropical areas, forests on Puerto Rico are regrowing due to abandonment of agriculture. Forest cover has increased from less than 6% in the 1950s to more than 55% by 2014. These regenerating forests contain a mixture of native and non-native species in a mosaic of forest at various stages of succession (Rojas-Sandoval, Presley, and Willig 2026). Potter et al. (2022) reported that two-thirds of Puerto Rico’s forests comprised novel tree assemblages.

Invasive species

A decade ago, Puerto Rico had 176 invasive plant species – 32% of the island’s flora. They comprised 44 herbs, 35 grasses, 33 trees, 28 vines, 19 shrubs, and 5 succulents. In this category, Puerto Rico ranks higher than other islands in the Greater Antilles e.g. Jamaica (21%), Dominican Republic (18%), and Cuba (12%) (Rojas-Sandoval et al. 2017; Rojas-Sandoval and Acevedo-Rodríguez 2015).

Three studies have addressed invasive species on “la Isla del Encanto”. They differ in in geographic scope, data, and study objectives.

Zimmerman, Rojas-Sandoval, and Shiels (2021) addressed biological invaders in all taxonomic groups, not just vascular plants. However, their analysis was limited geographically to the Caribbean National Forest (CNF; popularly known as El Yunque). This study was based on published literature, museum and herbarium collections, local and academic experts’ experience, and personal field observations. They concluded that there were some worrisome trends but no strong evidence that the National Forest’s ecosystem was in danger of fundamental change as a result of invasive species. However, they admit data were limited and called for systematic surveys and detailed studies. This need is particularly acute because of the ecological importance of El Yunque, which is one of the few (and the most important) remnants of original native forest on Puerto Rico.

Potter et al. (2022) relied on data collected as part of the USFS Forest Inventory and Analysis (FIA) survey. The survey evaluates 341 permanent plots every 5 years. They assessed trees (no other kinds of plants) in forested areas across the island, not just in the CNF. They usually attribute invasive trees’ prevalence largely to the land-use history, i.e., reforestation of formerly agricultural lands. These scientists emphasize the importance of recent land-use history in determining where non-native tree species occur. They do not offer an overall assessment of the trajectory of invasions.

A more recent analysis by Rojas-Sandoval, Presley, and Willig (2026) was also island-wide and included all woody plants with dbh ≥ 2.5 cm, i.e., trees and shrubs. Noting that invasion intensity is steadily increasing in Puerto Rico’s forests, they concluded that the threat to Puerto Rico’s native biological diversity is greater than did the earlier studies.

Relying on the FIA surveys has the advantage of providing statistically valid data. However, this survey has two drawbacks as regards assessing plant invasions. First, the FIA inventory data don’t evaluate species in the understory, i.e., herbs, small shrubs, or vines. These species might also alter long-term successional trajectories (Rojas-Sandoval, Presley, and Willig (2026). Second, the FIA inventory is not designed to detect even woody plant species in the early stage of invasion, i.e., those that occur only as small seedlings on a few inventory plots (Potter et al. 2022). 

El Yunque

Invasive Plants

Zimmerman et al. (2021) report that 168 non-native plant species from 135 genera and 57 families are established in the National Forest  – at varying levels from “naturalized” to fully invasive. Of these, 77 species (~46%) had previously been listed as invasive on Puerto Rico. Twelve were hangers-on from crops planted in the past (e.g., coffee, mango, and breadfruit). They considered most of these non-invasive because they hadn’t increased strongly during a 10-year study. They named one possible exception, Simarouba amara, a timber tree, which had increased in numbers in areas of less intense land use after hurricanes in late 1990s. However, this species has not been mentioned as problematic by any other study.

El Yunque (CNF) is home to 37 of the non-indigenous plant species, including 14 vines, nine herbs, and eight grasses. These plants are described as colonizing primarily disturbed areas (e.g., landslides), wastelands, river edges, and roadsides.

The non-native species present in the regrowing forests vary by forest type – as would be expected given the large differences in rainfall. In the subtropical dry forest the principal invasive plants are river tamarind (Leucaena leucocephala) and Prosopis juliflora (Rojas-Sandoval, Presley, and Willig (2026). The former is one of the most widespread and common of the highly invasive non-native tree species throughout the Caribbean. On Puerto Rico, L. leucocephala is documented on 12.6% of 294 forested plots, 40% of plots in this biome. P. pallida (algarroba) is recorded on 10.9% of all survey plots, 27.1% of plots in the biome. Invasions in the dry forest are sometimes arrested by chronic disturbance – presumably fire (Potter et al. 2022). However, the authors do not report which species – native or introduced – come in after the disturbance.

The subtropical moist forest is presumably the biome most affected by previous agricultural efforts.  African tuliptree (Spathodea campanulata) occupies 41.8% of survey plots in this biome. Rose apple (Syzygium jambos) is found on 36.4% of these survey plots (Potter et al. 2022).

Invasive trees in the subtropical wet and rain forests biome included Erythrina poeppigiana and two species also found in the moist biome – Spathodea campanulate, and Syzygium jambos. S. campanulata is found on 33.9% of the plots in this biome (Potter et al. 2022). Zimmerman et al. (2021) call our attention to an herb, Selaginella willdenowii. They call this ornamental spikemoss one of most aggressive plant invaders in the CNF.

There is a difference of opinion on the threats posed by Spathodea campanulata. Potter et al. report that S. campanulata is found on 6.1% of all plots surveyed – half or less of plots invaded by the dryland species Leucaena leucocephala and Prosopis juliflora (and the S. campanulata plots are spread across two much larger biomes – moist and wet forests). S. campanulata is also shade intolerant so Potter et al. believe it might decline in the future as other species overtop it. The conflicting opinion is offered by Rojas-Sandoval, Presley, and Willig (2026). They call Spathodea campanulata a key driver of native biodiversity loss and homogenization in moist and wet forests. They note that the species has broad ecological tolerance and can proliferate after hurricanes. They found the species to already be significantly influencing native forest distinctiveness and composition – and to be increasing in abundance.

Potter et al. (2022) considered rose apple (Syzygium jambos) to pose a higher threat since it is shade tolerant and can form dense, monotypic stands under closed canopies – which S. campanulata cannot. Zimmerman, Rojas-Sandoval, and Shiels (2021) agree that where it occurs in areas of secondary forest near stream beds, S. jambos outcompetes other species. Rojas-Sandoval, Presley, and Willig (2026) note the species might potentially contribute to homogenizing biodiversity. A new development might counter this threat: the accidental introduction of guava/ohia rust (Austropuccinia psidii); it has been highly fatal to rose apple populations in Hawai`i.  Both Zimmerman et al. and Rojas et al. mention this possibility but I have not seen a more recent discussion of whether this is occurring.

myrtle rust on Syzygium jambos; photo by Smallbiologie via Wikimedia

Zimmerman et al. (2021) say several invasive vines are established in El Yunque. The vines respond quickly to the disturbances caused by the region’s frequent hurricanes. Seven of the 14 species in the CNF are morning glories in the Ipomoea genus. Other locally abundant non-native vines are Epipremnum pinnatum, Pueraria phaseoloides, Dioscorea alata, Thunbergia alata, and Thunbergia fragrans.m

Potter et al. (2022) defined invasive tree species as those exhibiting 60 – 75% of stems in the “small” diameter categories (less than 12.5 cm dbh). Fifty-seven non-native tree species in old-growth and regenerating forests it this definition. They considered 17 of them as highly invasive, 16 as potentially highly invasive, and two as moderately invasive. That is, 35 of 57 nonnative tree species, or 60%, are actually or potentially bioinvaders. While on the continent only seven non-native tree species occurred on at least 2% of FIA plots across the ecoregions in which they were inventoried, on Puerto Rico 21 species (38%) occurred on at least 2% of the FIA plots. Potter et al. (2022) could not assess the invasiveness of eight additional species that occurred only as small stems on a couple of survey plots.

Potter et al. (2022) note the possibility of conflicting views about the invaders: some of the moderately to highly invasive species provide timber and non-timber forest products. These include S. campanulata, L. leucocephala, Syzgium jambos, and Mangifera indica (mango).

Rojas-Sandoval, Presley, and Willig (2026) also analyzed FIA data to assess how non-native tree species affect the biodiversity and composition in three forest types: dry, moist, and wet forests. Unlike Potter et al. (2022), they found that non-native tree species are reshaping native tree assemblages in Puerto Rican forests, leading to significant declines in native species abundance, richness, evenness, and diversity.

The transformation is greatest in the dry forest; there, native richness has declined by more than 90% by some measures. Native communities have become depauperate, dominated by a few species. In subtropical moist forest, native richness peaked at low to moderate invasion levels, then declined. S. campanulata is the dominant non-native species; as noted above, it is found on 41.8% of survey plots in this biome. In subtropical wet forests, native species richness and diversity were highest in uninvaded and lightly invaded plots, followed by marked declines at higher levels of invasion. This is largely driven by that one species, S. campanulata (found on a third of the survey plots in this biome).

The dry forest suffered the greatest proportional loss of biodiversity, including the largest proportional declines in native species richness. Wet forests also experienced strong declines in native richness & abundance. However, since wet forests had much higher initial diversity & structural complexity, their proportional decline in biodiversity is less. Thus, invasion effects differ among forest types depending on initial diversity, resource availability, land-use history, successional stage, and community composition.

Invasion can make individual plots diverge locally through loss of some rare species or gain of different non-native species. If this happens across the study site, the compositional heterogeneity at broader scales is simultaneously reduced. This results in landscape-level biotic homogenization.

Rojas-Sandoval, Presley, and Willig (2026) say homogenization effects are particularly concerning in insular ecosystems, where high endemism and ecological specialization make native biotas especially vulnerable to displacement.

To their surprise, the key driver on Puerto Rico is the increasing abundance of the non-native trees, rather than non-native species richness (Rojas-Sandoval, Presley, and Willig. 2026).

RECOMMENDATIONS

Potter et al. (2022) advise limited efforts to eradicate or control the eight species that occurred only as small stems on a couple of survey plots. These are probably incipient invasives. They name specifically Schinus terebinthifolius (Brazilian pepper) – a species already recognized as moderately invasive in Hawai`i and seriously invasive in peninsular Florida. In 2019 USDA APHIS approved release of two biocontrol insects in Florida targetting Brazilian pepper.

infestation of Brazilian pepper in the Florida Everglades; photo courtesy of Tony Pernas, National Park Service

I recommend that, in order to avoid having to consider importing those biocontrol agents to Puerto Rico, island conservation stakeholders should focus eradication efforts on this species now while it is still – apparently – not widespread.  

Rojas-Sandoval, Presley, and Willig (2026) are bolder. They call for implementation of more effective policies to prevent additional introductions and spread of the invasives already on Puerto Rico or nearby islands. They suggest that officials focus on the species named in their dataset. In addition, scientists should also collect data on understory dynamics to get a more comprehensive assessment of bioinvasion in the forest. Rojas-Sandoval et al. (2026) also urge implementation of policies aimed at reducing anthropogenic disturbances in these fragile ecosystems. One component of this program is for those responsible for forest management, conservation, and climate adaptation to incorporate invasion dynamics into their strategies. They remind us that Caribbean islands host extraordinary species richness – many of which are endemic. So protecting these biological riches is of global importance.

Preventing anthropogenic disturbance is likely to aid control of invasive plants. Zimmerman et al. (2021) found that the better-protected forests of the Caribbean National Forest was less invaded by vascular plants than were similar areas that had higher levels of human disturbance. However, this was not the case regarding invasive mammals and some invertebrates. Other than the passing reference to Austropuccinia psidii on Syzygium jambos, none of the studies considered pests or pathogens hosted by trees or other plants. 

Other Taxa

Zimmerman et al. (2021) also evaluated invasive animal species. They report that six species of vertebrates are invasive in Caribbean National Forest. Black rats (Rattus rattus), mongoose (Herpestes auropunctatus), and feral cats (Felis catus) are widespread through both disturbed and undisturbed mature forest. Each threatens many native species. The black rat also preys on seeds of several native tree species. House mouse (Mus musculus) is also very common, but restricted to roadside habitats. Cane toad (Rhinella marina) and green iguana (Iguana iguana) are also present. The green iguanas was introduced relatively recently and is rarely observed in CNF. Cane toads have been established much longer. Zimmerman et al. (2021) report no impacts.

Surprisingly, they report no introduced bird or fish species in El Yunque, even the species are common on the island and in parts of the Forest having a history of anthropogenic disturbance.

Two invertebrate bioinvaders are reported as ubiquitous in the National Forest: a hybrid honeybee and Aedes aegypti mosquito. The Africanized honeybee has evolved gentle behaviors and is no longer a great threat to cavity nesting birds, including the endangered Puerto Rico Parrot (Amazona vittata). Two species of introduced earthworms, Pontoscolex corethrurus and Ocnerodrilus occidentalis, are widespread in El Yunque; a third, Drawida barwelli, is found only in lower-elevation forest areas outside NF. The earthworms alter biogeochemical cycling in the soil, which might further influence plant community dynamics. Non-native slugs and snails do not appear to be spreading rapidly or damaging native plant species. Zimmerman, Rojas-Sandoval, and Shiels (2021) warn that additional invertebrates might be of concern in the future, since they can expand rapidly after forest destructions caused by hurricanes.

See also the brief summary of invasive species on Puerto Rico included in the Regional Summary Appendix for the Southeast in Poland et al. (2019). I note mentions of the South American Harrisia cactus mealybug (Hypogeococcus pungens, which is killing columnar cacti in the islands’ dry forests.  

SOURCES

Lugo, A.E., J.E. Smith, K.M. Potter, H. Marcano Vega, C.M. Kurtz. 2022. The Contribution of Non-native Tree Species to the Structure and Composition of Forests in the Conterminous United States in Comparison with Tropical Islands in the Pacific and Caribbean. USFS International Institute of Tropical Forestry General Technical Report IITF-54.

Poland, T.M., Patel-Weynand, T., Finch, D., Miniat, C. F., and Lopez, V. (Eds) (2019), Invasive Species in Forests and Grasslands of the United States: A Comprehensive Science Synthesis for the United States Forest Sector. Especially the Appendix on the Southeast and Caribbean. Springer Verlag. Available gratis at https://link.springer.com/book/10.1007/978-3-030-45367-1

Potter K.M., Riitters, K.H. and Guo. Q. 2022. Non-native tree regeneration indicates regional and national risks from current invasions. Frontiers in Forests and Global Change Front. For. Glob. Change 5:966407. doi: 10.3389/ffgc.2022.966407

Rojas-Sandoval, J., R.L. Tremblay, P. Acevedo-Rodriquez, H.D. Soltero. 2017. IAS plant species in the West Indies: geog, ecological and floristic insights. Ecology and Evolution 2017; 1-12

Rojas-Sandoval, J., Presley, S.J. and Willig, M.R. 2026. Increasing non‑native tree abundance reshapes biodiversity and composition of tropical forests. Biol Invasions 28, 84 (2026). https://doi.org/10.1007/s10530-026-03802-w

Zimmerman, J.K., J. Rojas-Sandoval, and A.B. Shiels. 2021. IAS in PR: The View From El Yunque. Front. Ecol. Evol. 9:640121. doi: 10.3389/fevo.2021.640121

Posted by Faith Campbell

We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.

For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm

Or

https://fadingforests.org

Bioinvader Threat to Caribbean cacti – Who is Protecting Them?

Photo of infested cactus at Cabo Rojo National Wildlife Refuge, Puerto Rico. Taken August 20, 2018 by Yorelyz Rodríguez-Reyes

For 15 years I have maintained a profile of the Harrisia cactus mealybug Hypogeococcus pungens because it threatens columnar cacti in the subfamily Cactoideae from the Caribbean basin and possibly in the American Southwest and Mexico. My recent attempts to clarify the current situation have been frustrated by the apparent collapse of funding support for scientists trying to conserve these cactus species.

The dry regions of the Caribbean Islands are home to about 100 native cacti, 75% of which are endemic. According to the Center for Plant Conservation, 20 species are listed as threatened by the IUCN. Puerto Rico specifically is home to 14 cactus species, at least three of which are endemic.

How and when the mealybug first invaded the Caribbean and North America is unknown. The presence of the insect now known as H. pungens Hyp-C on Puerto Rico was detected in the Guánica Commonwealth Forest and Biosphere Reserve on the island’s southern coast in 2005 (Zimmerman et al. 2010). However, the actual introduction probably occurred about ten years earlier, in about 1996 (Poveda-Martinez et al. 2022).  See map of locations below.

In the 20 years since then, the mealybug has spread across the island’s dry districts. By 2010, it was estimated to be present on about 1,400 km2. By 2014 – nine years after detection — the mealybug had reached the small island of Caja de Muertos. The most recent survey of which I am aware (date unclear) detected the mealybug on 268 out of 445 cactus plants examined (60%) in 12 out of 39 sites examined (Poveda-Martinez et al. 2022). The mealybug is also killing native cacti on the nearby U.S. Virgin Islands (Poland et al. 2019), although I have found no data on this invasion or its impact.

Below – columnar cacti on St. John, US Virgin Islands; photos by F.T. Campbell

H. pungens Hyp‑C threatens seven of 14 native cactus species in Puerto Rico. Three of the cacti are endemic; two are federally listed as endangered species: Harrisia portoricensis and Leptocereus grantianus (USDA ARS). Since the mealybug’s detection in Puerto Rico, it has caused extensive damage to Pilosocereus royenii (Royen’s tree cactus), Leptocereus qaudricostatus (pitaya), Melocactus intortus (turk’s cap), and an introduced cultivar, Cereus hexagonus. It has caused minor damage to Stenocereus fimbriatus (Zimmerman et al. 2010). These cacti provide food or shelter for endemic bats, birds, moths and other pollinators (Segarra and Ramirez; USDA ARS).

The insect’s attack promotes abnormal gall-like growth on the stem and deformed flowers. These deformations severely affect infested plants’ reproduction and eventually survival (Poveda-Martinez et al. 2022).

Biological Control

When the mealybug was first detected Commonwealth and federal agencies tried to counter it. A search for possible biocontrol agents in the insect’s native range in Argentina began the 2010. While no funds have ever been appropriated for this activity, for several years the U.S. Department of Agriculture supported the work by allocating funds to the Agriculture Research Service Insect Behavior and Biocontrol laboratory in Gainesville, Florida, from broader programs. Dr. Stephen Hight took the lead, working with colleagues in South America. According to Dr. Hilda Diaz-Soltero, then a USDA official, these funds came primarily from the USDA Invasive Species Coordination Program and APHIS Eastern Region. In fiscal years 2017 and 2019, an additional ~$550,000 came in the form of grants under APHIS’ Plant Pest and Disease Management and Disaster Prevention Program. Link Scientists at the Center for Excellence in Quarantine and Invasive Species at the University of Puerto Rico devoted at least a decade to the search.

Scientists focused on two parasitoid wasps, Anagyrus cachamai and A. lapachosus (Hymenoptera: Encyrtidae). A third candidate, the predator Hyperaspis conclusa, was also assessed (Aguire et al.).

Research on the mealybug-wasps interaction uncovered troubling patterns. First, it has long been known that some mealybugs believed to be belong to the species Hypogeococcus pungens feed on columnar cacti while others feed on plants in two unrelated families, Amaranthaceae and Portulacaceae (USDA ARS; Zimmerman et al. 2010). Would the introduced wasps attack the cactus-feeding mealybug in sufficient numbers?

The confusion over how many mealybug species have been introduced – and where – severely hampered development of a program. (The mealybug has been introduced to control invasive cactus in Australia and South Africa. Most sources say it has been highly effective – prompting the initial concern when it appeared on Puerto Rico.) I have been unable to find any information about the status of the candidate biocontrol agents more recent than 2022.

Genetic Conservation

The USDA also partnered with the Naples (Florida) Botanical Garden to collect fruits and vegetative material for ex situ conservation. Rigorous phytosanitary procedures were followed to ensure the absence of the mealybug. Collections of fruits and vegetative material provided 1,298 cacti samples from 13 species, representing 1,173 maternal lines from 91 sites throughout Puerto Rico. A total of 90,720 seeds representing 8 species are banked at the NBG for long-term storage. Propagation of the vegetative material has 56% success, and plants are incorporated into the NBG’s living collections. (These figures include Opuntia cacti that are hosts of a second invasive insect, Cactoblastis cactorum.)  

Genetic Concerns

Scientists now consider Hypogeococcus pungens (Hemiptera: Pseudococcidae) to be a species complex composed of at least five putative species. The species are separated in part by the plants they use as hosts. Two of the complex have apparently been introduced to Puerto Rico: H. pungens Hyp‑C feeds on cacti; H. pungens Hyp‑AP feeds on hosts in the Portulacaceae & Amaranthaceae. Both evolved from putative source populations in Brazil (Poveda-Martinez et al. 2022).

The two species H. pungens Hyp-C and Hyp-AP are currently separated on Puerto Rico by host preferences and climatic niches. They also occupy different geographic areas. Scientists fear that ongoing climate change could allow H. pungens Hyp-C to establish farther into the island’s interior and in a large area in the north. Such range expansion would end the geographic separation. Overlapping of the two species is likely to exacerbate the threat to Puerto Rico’s cacti. Most directly, it would complicate implementation of management strategies, especially biological control. Intermixing of the two species could also facilitate hybridization which might result in more vigorous attacks or a broadened host range. Hybridization is frequent in closely related species (Poveda-Martinez et al. 2022).

The Mealybug is Frequently Introduced

Mealybugs that feed on cacti and believed to be in the species Hypogeococcus pungens made multiple appearances in southern California between 2000 and 2018 – in gardens and in nurseries. Confusingly, CDFA reports interception of the mealybug on alternanthera and ludwigia plants shipped from Florida (CDFA 2018). I have no more recent data. The population in Florida was reported to be present in 16 counties in 2009); it might be the species that feeds on plants other than cacti (Poveda-Martinez et al. 2022). Other populations has been reported in the Dominican Republic (no date) (CDFA 2018); and in Hawai`i in 2005 (Hawaii Department of Agriculture new pest report). A mealybug that feeds on Amaranthaceae and Portulacaceae was detected in 2000 in San Juan, Puerto Rico (Poveda-Martinez et al. 2022).

In the absence of control measures, scientists expect H. pungens Hyp-C to continue decimating Puerto Rican cactus diversity and threaten other cactus rich ecosystems across the Caribbean islands, Central America and, potentially, North America (Poveda-Martinez et al. 2022).

saguaro and organ pipe cacti in Organ Pipe Cactus National Monument; photo by F.T. Campbell

North America has more than 500 columnar cactus species in the Cactoideae (Zimmerman et al. 2010). Some of these cacti are already endangered, e.g., several Pediocactus. Others are totems of the desert, e.g., the saguaro (Carnegiea gigantea) and organ pipe (Stenocereus thurberi) cacti. Picture The larger ones, particularly, play important ecological roles. It is not known how vulnerable individual species are to the mealybug (Golubov pers. comm. January 2011). In Mexico several mealybugs in the same genus are already present. The natural enemies of these mealybugs might be able to attack H. pungens Hyp-C if it invades the country (Zimmerman et al. 2010). Despite the well-founded concern, apparently no funds have been allocated by governments or conservation organizations to studying the vulnerability of these cacti to one or more mealybugs in the Hypogeococcus genus.

The most likely pathway by which the mealybug is spread is the trade in plants for planting (the horticultural trade) (Zimmerman et al. 2010). A decade ago APHIS reported intercepting mealybugs on cactus (primarily on roots) imported from Germany, Peru, and Puerto Rico. APHIS has also intercepted several other mealybugs in the same genus – on plants (including orchids and bromeliads as well as cacti) from Belize, Costa Rica, Ecuador, Guatemala, Honduras, Mexico, Panama, Peru, and Venezuela (USDA APHIS alert).

A decade ago NatureServe and IUCN found that 31% of Earth’s cactus species were threatened with extinction. They named overharvesting (often for the illegal horticultural trade) and destruction of habitat by smallholder livestock ranching and farming. Did not mention predation by introduced insects – although that is now manifest not only in the cactus mealybug but also the cactus moth.

Sources

Aguirre, M. G. Logarzo, S. Triapitsyn, H. Diaz-Soltero, S. Hight, O. Bruzzone. 2023? Effect of egg production dynamics on the functional response of parasitoids

California Plant Pest and Disease Report. 2005. Vol. 22 No. 1. Covering Period from July 2002 through July 2005.California Department of Food and Agriculture. 2018.California Pest Rating for Hypogeococcus pungens Granara de Willink | Harrisia cactus mealybug Hemiptera: Pseudococcidae Pest Rating: A California Pest Rating for Hypogeococcus pungens Granara de Willink | Harrisia cactus mealybug Hemiptera: Pseudococcidae Pest Rating: A

Hawaii Department of Agriculture. 2006. https://hawaii.gov/hdoa/pi/ppc/2006-annual-report/new-pest-detections  (accessed 11/1/10)

Poland, T.M., Patel-Weynand, T., Finch, D., Miniat, C. F., and Lopez, V. (Eds) (2019), Invasive Species in Forests and Grasslands of the United States: A Comprehensive Science Synthesis for the United States Forest Sector.  Springer Verlag.

Poveda-Martinez, D. N.A. Salinas, M. Belen Aguirre, A.F. Sanchez-Restrepo, S. Hight, H. Diaz-Soltero, G. Logarzo,  and E. Hasson. 2022 Geonomic & ecol evidence shed light on the recent demographic history of two related invasive insects. Scientific Reports.

Segarra-Carmona, A.E., A. Ramirez-Lluch. No date. Hypogeococcus pungens (Hemiptera: Pseudococcidae): A new threat to biodiversity in fragile dry tropical forests.

Segarra-Carmona, A.E., A. Ramírez-Lluch, I. Cabrera-Asencio and A.N. Jiménez-López. 2010. First Report of a New Invasive Mealybug, the Harrisia Cactus mealybug Hypogeococcus pungens (Hemiptera: Pseudococcidae). J. Agrie. Univ. RR. 94(1-2):183-187 (2010)

Srivastava, M., P. Srivastava,  R. Karan, A. Jeyaprakash, L. Whilby, E. Rohrig, A.C. Howe,  S.D. Hight, and L. Varone. 2019. Molecular detection method developed to track the koinobiont larval parasitoid Apanteles opuntiarum (Hymenoptera: Braconidae) imported from Argentina to control Cactoblastis cactorum (Lepidoptera: Pyralidae). Florida Entomologist 102(2): 329-335.

Triapitsyn, Aguirre, Logarzo, Hight, Ciomperlik, Rugman-Jones, Rodriguez. 2018. Complex of primary and secondary parasitoids (Hymenoptera: Encyrtidae and Signiphoridae) of Hypogeococcus species. mealybugs (Hemiptera: Pseudococcidae) in the New World. Florida Entomologist Volume 101, No. 3 411

USDA Agriculture Research Service, Research Project: Biological Control of the Harrisia Cactus Mealybug, Hypogeococcus pungens (Hemiptera:pseudococcidae) in Puerto Rico Project Number: 0211-22000-006-10 Project Type: Reimbursable

Zimmermann, H.G., M.P.S. Cuen, M.C. Mandujano, and J. Golubov. 2010. The South American mealybug that threatens North American cacti. Cactus and Succulent Journal. 2010 Volume 82 Number 3

Invasive species cost more than extreme weather attributable to climate change; 17 times more than previously estimated!

ash tree killed by emerald ash borer; photo courtesy of (then) Mayor of Ann Arbor John Hieftje

Since the 1990s, scientists have been trying to the determine costs imposed by invasive species. They hope that measuring monetary costs will motivate political decision-makers to take more assertive actions to counter this ecological treat. As Daigne et al. (2021) point out, too few countries are implementing effective control and mitigation strategies. They say this inaction stems, largely, from undervaluing bioinvasions’ impacts by the general public, stakeholders and decision-makers.

A major step in this effort was creation of the InvaCost database. The goal was to provide a reliable, comprehensive, standardized and easily updatable synthesis of bioinvasions’ monetary costs worldwide.

Several publications based on this database appeared. I have blogged about studies published in 2021 or 2022: a) the costs of bioinvasions generally (Cuthbert et al. 2022);  b) the costs imposed by invasive species in protected areas (Moodley et al. 2022; c) a focus on the “worst” 100 invasives (as determined by the IUCN) (Ahmed et al. 2022); and d) assessing costs associated with various pathways of introduction (Turbelin et al. 2022).

The InvaCost database, as applied in these studies, demonstrated that bioinvasions impose tremendous costs –a minimum of US $1.288 trillion for the period 1970 – 2017. These costs increased on average three times per decade (Daigne et al. 2022).

Still, everyone has recognized that InvaCost data have significant limitations. First, three-quarters of the records in the original database came from North America, Oceania and Europe; and referred to animal taxa, even though plants are a major group of invaders. Also, a large proportion of total invasion costs – for all taxa – probably is undetected. Finally, the many non-market values of species and ecosystems are extremely difficult to calculate (Daigne et al. 2022).

As a result of these deficiencies, the earlier studies discussed in the blogs referenced above substantially underestimated the true costs associated with bioinvasion (Cuthbert et al. 2022).

Now a new study, led by Ismael Soto, finds that the underestimate is huge. Global costs associated with a subset of 162 species (17% of all the species in the InvaCost database) is nearly 17 times higher than reported in the InvaCost database.

Soto et al. (2025) applied species distribution models and macroeconomic data to interpolate these 162 species’ probable impacts in 172 countries  

Japanese knotweed – one of the invasive plants proving very costly in Europe, according to I. Soto

The newly identified costs were greatest in Europe; second place fell to North America. This is because both higher damage costs and management expenditures are linked to higher gross domestic product and extent of agricultural area, in addition to environmental suitability. Analysis of monetary costs per unit area revealed that ‘cost hot spots’ are predominantly located in densely populated urban areas and locations hosting key industries. These tend to be in coastal zones, i.e., Europe, the east coast of China, and the east and west coasts of the US.

cypress aphid Cinara cupressi – a threat to both native & plantation trees in Africa; photo by Blackman & Eastop via Wikimedia

The authors found that the greatest increase in estimated costs for countries in Africa and Asia. These countries had not previously recorded any economic costs arising from invasions by these 162 species. I have blogged about forest pest threats in Africa.

The authors also significantly increased estimated costs linked to invasive plants. Daigne et al. found that invasive insects caused ~90% of reported costs in the InvaCost database as of 2022. Vertebrates ranked second, plants third. In contrast, Soto et al. determined that invasive plants had the highest average estimated damage costs (US $42.10 billion) and management expenditures ($0.81 billion).

Substantial total costs were also reported for arthropods, mammals and birds. Reported damage and management costs were much lower for molluscs, fish, reptiles and amphibians. Daigne et al. suggest this might be due to their lower (observable) damage to human infrastructure, research biases leading to fewer studies, or disparities resulting from the filtering process used in their own study.

Williams et al. (2023) focus on insects, which cause damage primarily to agriculture, human health, and forestry. Insects constitute the highest number of species introduced as ‘Contaminants’ (n = 74) and ‘Stowaways’ (n = 43). They also impose the highest costs among species using these two pathways.

Forest insects and pathogens account for less than 1% of the records in the InvaCost database. I believe that this figure reflects significant under-reporting of these invasion events. Even at this paltry level of reported invasions, forest insects and pathogens were responsible for causing 25% of total annual costs ($43.4 billion) (Williams et al. 2023). This discrepancy illustrates the huge economic cost associated with widespread mortality of trees. Yet authorities in most countries continue to provide completely inadequate resources to counter this threat.

The authors of these publications examining economic losses associated with bioinvasion all note that ecological damage is additional. Soto et al. note that bioinvasions contribute to 60% of already recorded global extinctions. Interestingly, the species ranked third using the criterion of monetary damage is the cactus moth Cactoblastis cactorum. This insect threatens flat-padded Opuntia cacti across the United States and in the center of endemism, Mexico.

a flat-padded Opuntia — vulnerable to the cactus moth; photo by F.T. Campbell

Soto et al. found a lag of ~46 years between first (reported) detection of an introduced species and the peak of damage costs. They suggest that the rising monetary cost reflects the species becoming more abundant or occupying a larger area. The authors also say this finding demonstrates the value of implementing mitigation measures as soon as possible. Their finding thus validates others’ advocacy for investing in prevention and rapid response measures (see Cuthbert et al. and Daigne et al.). Soto et al. were cheered by the fact that spending on management measures – when it was reported – often followed soon after a species’ detection – or even before (e.g., prevention).

But Decision-Makers Usually Delay – Why?

Prevention is a hard sell. Decision-makers find it difficult to justify management expenditures before impacts become obvious. By that time, of course, management of the invasion is extremely difficult and expensive – if it is possible at all. Ahmed et al. found particularly effective wording to describe this problem: bioinvasion costs can be deceitfully slow to accrue, so policy makers don’t appreciate the urgency of taking action. Another contributing factor is that when efficient proactive management succeeds in preventing any impact, it paradoxically undermines evidence of the value of this action!

Programs to minimize the economic and ecological consequences of bioinvasion are severely obstructed – if not doomed! – by the following difficulties:

  • Resources are in short supply. Experts find that demands to address other threats to agriculture or natural systems outcompete appeals to ramp up invasive species efforts.
  • Prediction is uncertain. Cuthbert et al. found that none of the species with the highest pre-invasion investment was among the top 10 costliest invaders in terms of damages. Cuthbert et al. do not discuss whether this is evidence that the prevention efforts were effective? Or, alternatively, that prevention efforts target the wrong species.
  • Harm is in the eye of the beholder. Stakeholders’ perceptions of whether an introduced species causes a detrimental impact vary. For example, Moodley et al. point out that species imposing the highest economic costs might not be the ones causing the greatest ecological harm.
  • Externalities. Those harmed by a bioinvasion often are different from those that decide whether to act. Ahmed et al. argue that this creates a moral dilemma.

These decisions are political — influenced by citizens’ expressed wishes. Changing decision-makers’ perceptions of what is important is up to us!!! Start a parade!!!

SOURCES

Ahmed, D.A., E.J. Hudgins, R.N. Cuthbert, .M. Kourantidou, C. Diagne, P.J. Haubrock, B. Leung, C. Liu, B. Leroy, S. Petrovskii, A. Beidas, F. Courchamp. 2022. Managing biological invasions: the cost of inaction. Biol Invasions (2022) 24:1927–1946 https://doi.org/10.1007/s10530-022-02755-0

Cuthbert, R.N., C. Diagne, E.J. Hudgins, A. Turbelin, D.A. Ahmed, C. Albert, T.W. Bodey, E. Briski, F. Essl, P. J. Haubrock, R.E. Gozlan, N. Kirichenko, M. Kourantidou, A.M. Kramer, F. Courchamp. 2022. Bioinvasion costs reveal insufficient proactive management worldwide. Science of The Total Environment Volume 819, 1 May 2022, 153404

Diagne, C., B Leroy, A-C. Vaissière, R.E. Gozlan,  D. Roiz, I. Jaric,  J-M. Salles, C.A. Bradshaw, and F. Courchamp. 2021. High and rising econ costs of bioinvasions worldwide Published online: 31 March 2021

Moodley, D., E. Angulo, R.N. Cuthbert, B. Leung, A. Turbelin, A. Novoa, M. Kourantidou, G. Heringer, P.J. Haubrock, D. Renault, M. Robuchon, J. Fantle-Lepczyk, F. Courchamp, C. Diagne. 2022. Surprisingly high economic costs of bioinvasions in protected areas. Biol Invasions. https://doi.org/10.1007/s10530-022-02732-7

Soto, I., P. Courtois, A. Pili, E. Tordoni, E. Manfrini, E. Angulo, C. Bellard, E. Briski, M. Buric, R.N. Cuthbert, A. Kouba, M. Kourantidou, R.L. Macêdo, B. Leroy, P.J. Haubrock, F. Courchamp and B. Leung. 2025.  Using species ranges and macroeconomic data to fill gap in costs of biological invasions. Nat Ecol Evol doi: 10.1038/s41559-025-02697-5

Turbelin, A.J., C. Diagne, E.J. Hudgins, D. Moodley, M. Kourantidou, A. Novoa, P.J. Haubrock, C. Bernery, R.E. Gozlan, R.A. Francis, F. Courchamp. 2022. Introduction pathways of economically costly invasive alien spp. Biol Invasions (2022) 24:2061–2079 https://doi.org/10.1007/s10530-022-02796-5

Williams, G.M., M.D. Ginzel, Z. Ma, D.C. Adams, F.T. Campbell, G.M. Lovett, M. Belén Pildain, K.F. Raffa, K.J.K. Gandhi, A. Santini, R.A. Sniezko, M.J. Wingfield, and P. Bonello. 2023. The Global Forest Health Crisis: A Public Good Social Dilemma in Need of International Collective Action. Annual Review of Phytopathology Vol. 61, 2023

Posted by Faith Campbell

We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.

For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at  https://treeimprovement.tennessee.edu/

or

www.fadingforests.org

APHIS funding for pests that kill trees (& cacti)

emerald ash borer; some of PPA grants are funding evaluation of biocontrol efficacy

USDA APHIS has released information about its most recent annual allocation of funds under the Plant Pest and Disease Management & Disaster Prevention Program under §7721 of the Plant Protection Act. (Also see Fading Forests II and III; links provided at the end of this blog.) These funds support both critical needs and opportunities to strengthen the nation’s infrastructure for pest detection, surveillance, identification, and threat mitigation. Since 2009, this USDA program has provided nearly $940 million to more than 5,890 projects.

For FY25 APHIS allocated $62.725 million to fund 339 projects, about 58% of the proposals submitted. About $10 million has reserved for responding to pest and plant health emergencies throughout the year.

According to APHIS’ press release, the highest amount of funds (almost $16 million) is allocated to the category “Enhanced Plant Pest/Disease Survey.” Projects on “Enhanced Mitigation Capabilities” received $13.6 million. “Targetting Domestic Inspection Efforts to Vulnerable Points” received nearly $6 million. “Improving Pest Identification and Detection Technology” was funded at $5 million. Outreach & education received $4 million.  I am not sure why these do not total $63 million.

Funding for States and Specific Pests

Wood-boring insects received about $2.3 million. These included more than $869,800 to assess the efficacy of biocontrol for controlling emerald ash borer (EAB) Agrilus planipennis, $687,410 was provided for various detection projects, and $450,000 for outreach efforts related to various pests. Ohio State received $93,000 to optimize traps for the detection of non-native scolytines (bark beetles).

Biocontrol efficacy will also be assessed for hemlock woolly adelgid, invasive shot hole borers, cactus moth, and several invasive plants (including Brazilian pepper). (Contact me to obtain a copy of CISP’s comments on this biocontrol program.)

Opuntia basilaris in Anza Boreggo; one of flat-padded Opuntia vulnerable to the cactus moth; photo by F.T. Campbell

Funding for other pests exceeded $1 million for spotted lanternfly (nearly $1.4 million), Asian defoliators ($1.2 million) and box tree moth (just over $1 million).

$630,000 was provided for detection surveys and studies of the sudden oak death pathogen Phytophthora ramorum, especially how it infects nursery stock. Nursery surveys are funded in Alabama, Louisiana, North Carolina, Ohio, Oklahoma, Pennsylvania, South Carolina, Tennessee, Virginia, and West Virginia. Most of these states are in regions considered most at risk to SOD infection of wildland plants.    

sudden oak mortality of tanoak trees in southern Oregon; photo by Oregon Department of Forestry

Oregon received much-deserved $41,000 to evaluate the threat of the NA2 and EU2 lineages of P. ramorum to nurseries and forests Oregon also received $104,000 to respond to the detection of Phytophthora austrocedri in nurseries in the state. The Oregon outbreak has been traced to Ohio, but I see no record of funds to assist that state in determining how it was introduced.

Asian defoliator (e.g., Lymantrid moths) surveys have been funded for several years. This year’s projects are in Alaska, Arkansas, California, Kentucky, Maryland, Massachusetts, Mississippi, Montana, Nevada, North Carolina, Oregon, Tennessee, Texas, Washington, and West Virginia. While I agree that the introduction risk is not limited to coastal states with maritime ports, I don’t what criteria were applied in choosing the non-coastal states which are funded to search for these insects

Spotted lanternfly surveys (including technological improvements) or related outreach are funded in Alabama, Connecticut, Delaware, Kentucky, New Hampshire, New Jersey, North Carolina, Oregon, Pennsylvania, and Tennessee. California’s project is focused on postharvest treatments.

The Don’t Move Firewood project continues to be funded by APHIS. Several states also direct attention specifically to the firewood pathway: Kentucky, Maine, and Michigan.

I applaud the precautionary funding of the Agriculture Research Service to generate of high-quality genomic resources for managing the causal agent of Japanese oak wilt Dryadomyces quercivorous

Florida Department of Agriculture, North Carolina State University, and West Virginia University each received more than $100,000 to improve detection and management of invasive hornets.

Tennessee State University got $100,000 to continue efforts to detect and understand Vascular Streak Dieback in redbud Cercis canadensis.

Posted by Faith Campbell

We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.

For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at  https://treeimprovement.tennessee.edu/

or

www.fadingforests.org

What do “Self-Introduced” & “Door-Knocker” Species Tell Us?

Woldstedtius flavolineatus – one of at least 13 taxa of non-native ichneumonid wasps established in restoration forests in Hawaiian Forest National wildlife rfefuge; photo by Torgrim Breiehagen for the Norwegian Biodiversity Information Centre; via Wikipedia

As we know, non-native insects and pathogens pose a significant and accelerating threat to biodiversity in forests and other ecosystems. They undermine some conservation programs and reduce ecosystem services and quality of life in urban areas. Nevertheless, damaging introductions continue.  

Two recent articles have advocated accelerating biocontrol programs. These articles have reminded us  of ongoing failures of international and national biosecurity programs, including that of the US. The articles also make interesting suggestions regarding ways to be more pro-active in preventing introductions.

1. “Self-introductions” of invaders’ enemies

Weber et al. (full citation at end of blog) provide many examples of unintentional “self-introductions” of natural enemies of arthropod pests and invasive plants. In fact, “self-introductions” of natural enemies of arthropod pests might exceed the number of species introduced intentionally. These introductions have been facilitated by the usual factors: the general surge in international trade; lack of surveillance for species that are not associated with live plants or animals; inability to detect or intercept microorganisms; huge invasive host populations that allow rapid establishment of their accidentally introduced natural enemies; and lack of aggressive screening for pests already established.

Among the examples illustrating failures of biosecurity programs:

  • Across six global regions, nearly two-thirds of parasitoid Hymenoptera species were introduced unintentionally. The proportion varies significantly by region. For example, four-fifths of these insects in New Zealand arrived accidentally.
  • The  unintentional spread of the glassy-winged sharpshooter (Homalodisca vitripennis) and a biocontrol agent Cosmocomoidea ashmeadi has been so rapid among islands in the Pacific Ocean (including Hawai`i) they are considered ‘biomarkers’ of biosecurity failures.
  • Regarding the United States specifically, an estimated 67% of beneficial insects introduced to Hawai`i and 64% of parasitoid Hymenoptera introduced to the mainland U.S. were accidental “self-introductions.”

Weber et al. consider their figures to be underestimates. The situation is particularly uncertain regarding pathogens that kill arthropods. Many microbial species are not yet described.

spotted lanternfly; photo by Stephen Ausmus, USDA

In some cases, these “self-introduced” arthropods have proved beneficial. Two examples are Entomophaga maimaiga and Lymantria dispar nucleopolyhedrovirus (LdNPV), which help control the spongy moth (Lymantria dispar). In other cases the “self-introduced” creatures are pests themselves. A prominent example is the invasion by the spotted lanternfly (Lycorma delicatula). This was facilitated by the widespread presence of the highly invasive plant Ailanthus altissima. It illustrates what Weber et al. call “receptive bridgehead effects.” That is, once an invasive pest is well-established, the chance that its natural enemies will find a suitable host and also establish in the pest’s invaded range is much higher.

Weber et al. reaffirm that there are many good reasons not to allow such random invasions of diverse non-native species – including their natural enemies. Deliberately introduced biocontrol agents are chosen after determining their efficacy, host-specificity, and climatic suitability. Random introductions, on the other hand, might favor generalist species, which could threaten non-target species. Accidental introductions might also be accompanied by pathogens and hyperparasitoids that could compromise the efficacy of biocontrol agents.

In short, unintentionally introduced natural enemies might have about the same level of success in controlling the target pest’s populations as do intentionally introduced agents. However, unintentional introductions of both pests and pathogens carry additional risks of non-target impacts and contamination with their own natural enemies that would hamper the efficacy of the biocontrol agent. Weber et al. conclude that delays in releasing a deliberately chosen and evaluated biocontrol agent reduce the probability that it will successfully establish instead of an unintentionally introduced organism.

cactus moth larva on Opuntia; photo by Doug Beckers via Flickr

It is especially likely that an arthropod – whether or not a biocontrol agent – will spread within a geographic region. Weber et al. say both the U.S. and Canada have received more than a dozen species intentionally introduced into the other country. They also cite spread of the cactus moth, Cactoblastis cactorum, into Florida from several Caribbean countries. The cactus moth has spread and now threatens the center of diversity of flat-padded Opuntia cacti in the American southwest and Mexico.

Another example is California: 44% of invading terrestrial macroinvertebrates that have established in the state came from populations established elsewhere in the US and Canada (Hoddle 2023). This number exceeds the total number of invasive macroinvertebrates in the state that originated anywhere in Eurasia (Weber et al.).

True, it is very difficult to prevent natural spread. But a lot of this spread is facilitated by human activities, e.g., transporting vectors such as living plants, firewood, outdoor furniture or storage “pods.” I have complained often — here and here and here — that interstate movement of invasive plant pests is particularly poorly controlled.

Some scientists and regulators have responded to these situations by improving phytosanitary programs. California officials, in 2019, set up a program to fund projects aimed at developing integrated pest management strategies for species thought to have a high invasion potential before they arrive. I urge other states to do the same. This would probably be most effective in controlling the target species – and in relation to cost — if developed by regional consortia.

Weber et al. suggest that given continuing unintentional introductions of non-native species, phytosanitary agencies need to focus on those invasion pathways that are particularly likely to result in invasions, e.g. live plants, raw lumber (including wood packaging), and bulk commodities e.g. quarried rock. 

The authors also suggest research opportunities that arise from biocontrol agents’ “self-introductions”. These include:

  • Comparing actual host ranges to those predicted by laboratory and other studies;
  • Quantifying the role of Allee effects, for example by studying the spread of the glassy-winged sharpshooter and its biocontrol agent across the Pacific region;
  •  Using molecular analyses to disentangle multiple routes of entry (e.g., the “invasive bridgehead effect”) and hybridization.

2. Door-knocker species

Hoddle (2023) suggests further that early detection programs should focus on “door-knocker” species — those likely to enter and cause significant negative impacts. In an earlier article (Hoddle, Mace and Steggall 2018) argued that the benefits of a pro-active biocontrol program outweigh the costs. The authors say the information gained would cut the time needed to deploy effective biocontrol. Ultimately, this could reduce the prolonged and even irreversible ecological and economic disruption from invasive pests, associated pesticide applications, and lost ecological services.

Asian citrus psyllid  (Diaphorina citri); USDA photo by Justin Wendell; Hoddle cites this species as one that a pro-active biocontrol program should have targetted

Hoddle calls funding pro-active biocontrol research programs before they’re needed as analogous to buying insurance. The owners of insurance policies hope not to need them but benefit when catastrophe strikes. Furthermore, the information gained from early research might identify natural enemy species that could “self-introduce” along with the invading host. Finally, proactive research might clarify whether the increasing number of natural enemy species that are “self-introducing” pose a threat to non-target organisms.

Recognizing the difficulty of identifying an “emerging invasive species” before its introduction, Hoddle endorses other components of prevention programs:

  • Collaborating with non-U.S. scientists to identify and mitigate invasion bridgeheads. Such efforts would both lessen bioinvasion threats and possibly aid in determining native ranges and facilitating location of natural enemies.
  • Sentinel plantings, such as those established under the International Plant Sentinel Network. These plantings can also support research on natural enemies of key pests.
  • Integrating online platforms, networks, professional meetings, and incursion monitoring programs into “horizon scans” for potential invasive species. He mentions specifically PestLens; online community science platforms, e.g., iNaturalist; international symposia; and official pest surveillance, e.g., U.S. Forest Service’s bark beetles survey and surveys done by the California Department of Food and Agriculture and border protection stations.
date palm mealybug (Pseudaspidoproctus hyphaeniacus); threat to native Washingtonia palms of California; one of pests tracked by PestLens

Weber et al. also support the concept of sentinel plant nurseries – especially because accidental plant and herbivore invasions often occur at the same points of entry.

Both Weber et al. and Hoddle urge authorities not to strengthen regulations governing biocontrol introductions. Weber et al. say that would be to make perfect the enemy of the good. The need is to balance solving problems with avoiding creation of new problems.

SOURCES

Hoddle, M.S., K. Mace, J. Steggall. 2018.   Proactive biological control: A cost-effective management option for invasive pests. California Agriculture. Volume 72, No. 3

Hoddle. M.S. 2023. A new paradigm: proactive biological control of invasive insect pests. BioControl https://doi.org/10.1007/s10526-023-10206-5

Weber, D.C. A.E. Hajek, K.A. Hoelmer, U. Schaffner, P.G. Mason, R. Stouthamer, E.J. Talamas, M. Buffington, M.S. Hoddle, and T. Haye. 2020. Unintentional Biological Control Chapter for USDA Agriculture Research Service. Invasive Insect Biocontrol and Behavior Laboratory. https://www.ars.usda.gov/research/publications/publication/?seqNo115=362852

Posted by Faith Campbell

We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.

For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm

or

www.fadingforests.org

Invasive Tree Species in the U.S. Caribbean: New Attention!

African Tulip Tree (Spathodea campanulata) on Puerto Rico; photo by Joe Schlabotnik via Flickr

While it is widely accepted that tropical island ecosystems are especially vulnerable to invasions, there has been little attention to terrestrial bioinvaders in the Caribbean; there has been more attention to marine bioinvaders such as lionfish. I am glad that is starting to change. Here I review a new study by Potter et al. (full citation at end of this blog), supplemented by information from other recent studies, especially Poland et al.

Potter et al. used USFS Forest Inventory and Analysis (FIA) survey data to examine regeneration rates by non-native tree species introduced to the continental United States, Hawai`i, and Puerto Rico. I rejoice that they have included these tropical islands, often left out of studies. They are part of the United States and are centers of plant endemism!

Potter et al. sought to learn which individual non-indigenous tree species are regenerating sufficiently to raise concern that they will cause significant ecological and economic damage in the future. That is, those they consider highly invasive. They defined such species as those for which at least 75% of stems of that species detected by FIA surveys are in their small tree categories – saplings or seedlings. They concluded that these species are successfully reproducing after reaching the canopy so they might be more likely to alter forest ecosystem functions and services. They labelled species exhibiting 60 – 75% of stems in the “small” categories as moderately invasive.

The authors recognize that many factors might affect tree species’ regeneration success, especially at the stand level. They assert that successful reproduction reflects a suite of factors such as propagule pressure, time since invasion, and ability of a species to adapt to different environments.

As I reported in an earlier blog, link 17% of the total flora of the islands of the Caribbean archipelago – including but not limited to Puerto Rico – are not native (Potter et al.). In Puerto Rico, two-thirds of forests comprise novel tree assemblages. The FIA records the presence of 57 non-native tree species on Puerto Rico. Potter et al. identified 17 non-native tree species as highly invasive, 16 as potentially highly invasive, and two as moderately invasive. That is, 33 of 57 nonnative tree species, or 58% of those species tallied by FIA surveyors, are actual or potential high-impact bioinvaders. While on the continent only seven non-native tree species occurred on at least 2% of FIA plots across the ecoregions in which they were inventoried, on Puerto Rico 21 species occurred on at least 2% of the FIA plots (38%). They could not assess the invasiveness of the eight species that occurred only as small stems on a couple of survey plots. These species might be in the early stages of widespread invasion, or they might never be able to reproduce & spread.

The high invasion density probably reflects Puerto Rico’s small size (5,325 mi² / 1,379,000 ha); 500 years of exposure to colonial settlement and global trade; and wide-scale abandonment of agricultural land since the middle of the 20th Century

Naming the invaders

The most widespread and common of the highly invasive non-native tree species are river tamarind (Leucaena leucocephala), on 12.6% of 294 forested plots; algarroba (Prosopis pallida) on 10.9%; and African tuliptree (Spathodea campanulata)on 6.1%. Potter et al. attribute the prevalence of some species largely to land-use history, i.e., reforestation of formerly agricultural lands. In addition, some of the moderately to highly invasive species currently provide timber and non-timber forest products, including S. campanulata, L. leucocephala, Syzgium jambos (rose apple) and Mangifera indica (mango).

Potter et al. contrast the threat posed by Spathodea campanulata with that posed by Syzgium jambo. The latteris shade tolerant and can form dense, monotypic stands under closed canopies. Because it can reproduce under its own canopy, it might be able to remain indefinitely in forests unless it is managed. In contrast S. campanulata commonly colonizes abandoned pastures. Since it is shade intolerant, it might decline in the future as other species overtop it. Meanwhile, they suggest, S. campanulata might provide habitat appropriate for the colonization of native tree species.

Second-growth forest in Caribbean National Forest “El Yunque”

Poland et al. say the threat from Syzgium jambos might be reduced by the accidentally introduced rust fungus Puccinia psidii (= Austropuccinia psidii), which has been killing rose apple in Puerto Rico. In Hawai`i, the same fungus has devastated rose apple in wetter areas.

Potter et al. note that stands dominated by L. leucocephala and Prosopis pallida in the island’s dry forests are sometimes arrested by chronic disturbance – presumably fire. However, they do not report whether other species – native or introduced – tend to replace these two after disturbance. The authors also say that areas with highly eroded soils might persist in a degraded state without trees. The prospect of longlasting bare soil or trashy scrub is certainly is alarming.

Potter et al. warn that the FIA’s sampling protocol is not designed to detect species that are early in the invasion process. However, they do advise targetting eradication or control efforts on the eight species that occurred only as small stems on a couple of survey plots. While their invasiveness cannot yet be determined, these species might be more easily managed because presumably few trees have yet reached reproductive age. They single out Schinus terebinthifolius (Brazilian pepper), since it is already recognized as moderately invasive in Hawai`i. I add that this species is seriously invasive in nearby peninsular Florida and here! APHIS recently approved release of a biocontrol insect in Florida targetting Brazilian pepper. It might easily reach nearby Puerto Rico or other islands in the Caribbean. I am not aware of native plant species in the Caribbean region that might be damaged by the biocontrol agent. However, two native Hawaiian shrubs might be harmed if/when this thrips reaches the Hawaiian Islands. Contact me for specifics, or read the accompanying blog about Potter et al. findings in Hawai`i.

Poland et al. looked at the full taxonomic range of possible bioinvaders in forest and grassland ecosystems. The Caribbean islands receive very brief coverage in the chapter on the Southeast (see Regional Summary Appendices). This chapter contains a statement that I consider unfortunate: “Introduction of species has enriched the flora and fauna of Puerto Rico and the Virgin Islands.” The chapter’s authors assert that many of the naturalized species are restoring forest conditions on formerly agricultural lands. They say that these islands’ experience demonstrates that introduced and native species can cohabitate and complement one another. I ask – but in what kind of forest? These forests, are novel communities that bear little relationship to pre-colonial biodiversity of the islands. Was not this chapter the right place to note that loss? Forests are more than CO2 sinks.

I also regret that the chapter does not mention that the Continental United States can be the source of potentially invasive species (see several examples below).

Mealybug-infested cactus at Cabo Rojo National Wildlife Refuge, Puerto Rico. Photo by Yorelyz Rodríguez-Reyes

The chapter does concede that some introduced species are causing ecological damage now. See Table A8.1. Some of these troublesome introduced species are insects:

  • the South American Harrisia cactus mealybug (Hypogeococcus pungens) is killing columnar cacti in the islands’ dry forests. The chapter discusses impacts on several cactus species and control efforts, especially the search for biocontrol agents.
  • the agave snout weevil (Scyphophorus acupunctatus), native to the U.S. Southwest and Mexico , is threatening the endemic and endangered century plant (Agave eggersiana) in St. Croix & Puerto Rico.
  • Tabebuia thrips (Holopothrips tabebuia) is of unknown origin. It is widespread around mainland Puerto Rico. Its impacts so far are primarily esthetic, but it does apparently feed on both native and introduced tree species in the Tabebuia and Crescentia genera.

The Caribbean discussion also devotes welcome attention to belowground invaders, i.e., earthworms. At least one species has been found in relatively undisturbed cloud forests, so it is apparently widespread. Little is known about its impact; more generally, introduced earthworms can increase soil carbon dioxide (CO2) emissions as through speeded-up litter decomposition and soil respiration.

A factsheet issued by the British forestry research arm DEFRA reports that the pine tortoise scale Toumeyella parvicornis has caused the death of 95% of the native Caicos pine (Pinus caribaea var. bahamensis) forests in the Turks and Caicos Islands (a UK Overseas Territory). The scale is native to North America. It has recently been introduced to Italy as well as to Puerto Rico, and the Turks and Caicos Islands.

SOURCES

Lugo, A.E., J.E. Smith, K.M. Potter, H. Marcano Vega, C.M. Kurtz. 2022. The Contribution of Non-native Tree Species to the Structure & Composition of Forests in the Conterminous United States in Comparison with Tropical Islands in the Pacific & Caribbean. USFS International Institute of Tropical Forestry General Technical Report IITF-54.

Poland, T.M., Patel-Weynand, T., Finch, D., Miniat, C. F., and Lopez, V. (Eds) (2019), Invasive Species in Forests and Grasslands of the United States: A Comprehensive Science Synthesis for the United States Forest Sector. Especially the Appendix on the Southeast and Caribbean. Springer Verlag. Available gratis at https://link.springer.com/book/10.1007/978-3-030-45367-1

Potter K.M., Riitters, K.H. & Guo. Q. 2022. Non-nativetree regeneration indicates regional & national risks from current invasions. Frontiers in Forests & Global Change Front. For. Glob. Change 5:966407. doi: 10.3389/ffgc.2022.966407

Posted by Faith Campbell

We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.

For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm

or

www.fadingforests.org

FY 23 Funding of Tree Pest Projects

Phytophthora ramorum-infected rhododendron plant; photo by Jennifer Parke, Oregon State University

APHIS has released the list of projects funded under §7721 of the Plant Protection Act in Fiscal Year 2023.  Projects funded under the Plant Pest and Disease Management and Disaster Prevention Program (PPDMDPP) are intend to strengthen the nation’s infrastructure for pest detection and surveillance, identification, threat mitigation, and safeguard the nursery production system.

APHIS has allocated $62.975 M to fund 322 projects in 48 states, Guam, & Puerto Rico. ~ $13.5 M has been reserved for responding to pest and plant health emergencies throughout the year. USDA is funding ~70% of the more than 460 PPDMDPP proposals submitted.

Funding by Goal Area

  • 1A – Enhance Plant Pest/Disease Analysis                               $2,057,174
  • 1S – Enhance Plant Pest/Disease Survey                                 $14,375,000
  • 2 – Target Domestic Inspection Activities at Vulnerable Points              $6,356,964
  • 3 – Pest Identification and Detection Technology Enhancement            $5,295,125
  • 4 – Safeguard Nursery Production                                                                 $2,079,119
  • 5 – Outreach and Education                                                                            $4,131,333
  • 6 – Enhance Mitigation Capabilities                                                             $13,875,775

By my calculation (subject to error!), the total for projects on forest pests is ~$6.5 M – or a little over 10% of the total. The top recipient was survey and management of sudden oak death: ~$700,000 for research at NORS-DUC and NCSU plus detection efforts in nurseries of 14 states. Other well-funded efforts were surveys for bark beetles and forest pests (projects in 14 states); surveys for Asian defoliators (projects in 14 states); and outreach programs targetting the spotted lanternfly (10 states, plus surveys in California).

Three states (Iowa, Kentucky and Maryland) received funding for surveys targetting thousand cankers disease of walnut; two states (Kentucky and Maine) obtained funding for outreach about the risk associated with firewood. Funding for the Nature Conservancy’s “Don’t Move Firewood” campaign appears under the home state of its leader, Montana.

Massachusetts obtained funding for outreach re: Asian longhorned beetle. Ohio State received funding for developing a risk map for beech leaf disease.

Ten states received funding for no forest pest projects; I don’t know whether they sought funding for this purpose. These states are Arizona, Colorado, Florida, Hawai`i, Idaho, Minnesota, Nebraska, New Mexico, North Dakota, and Puerto Rico. The “National” funding category also contained no forest pest projects.

Looking at the overall funding level might give a somewhat skewed impression because several of the projects with total funding of ~ $500,000 are actually carried out by USDA agencies. These awards are listed under the state in which the USDA facility happens to be located. Nearly half this money ($213,000) goes to a project by an Agriculture Research Service unit in Delaware to study the efficacy of the biocontrol targetting emerald ash borer.  Another $105,588 is allocated to detection of the SOD pathogen (Phytophthora ramorum) in irrigation water, undertaken – I think – at the ARS quarantine facility in Frederick, Maryland. A smaller project at a USFS research facility in Connecticut is studying egg diapause in the spotted lanternfly. The Delaware ARS unit is also pursuing biological control of the red-necked longhorn beetle (RNB) Aromia bungi, which attacks primarily stone fruits. Native to China and other countries in Asia, RNB has been intercepted in wood packaging by the U.S. and Europe; it has become established in Italy and Japan [Kim Alan Hoelmer, ARS, pers. comm.] The APHIS lab in Massachusetts is developing a light trap for detection of the Asian spongy moths Lymantria dispar.

I am intrigued that two states (Mississippi and Nevada) are conducting “palm commodity” surveys. Palms are important components of the environment in some states – although I am not certain these are the two most important!

As you might remember, I am also interested in some invaders other than forest pests. Washington has obtained $998,000 to support two projects integral to its efforts to find and eradicate the Asian (or Northern) Giant hornet. Oregon has obtained funding to carry out a survey for these hornets.  

Cactus moth larvae feeding on prickly pear cactus; photo by Doug Beckers, via Flickr

I rejoice to see that the Florida Department of Agriculture continues efforts to deploy biocontrol agents targetting the cactus moth. The Agriculture Research Service is evaluating the establishment of biocontrol agents released to counter two highly invasive plants. Re: Brazilian peppertree, I don’t question the damage it has caused in southern Florida but I have grave concerns should the psyllid and thrips reach Hawai`i. I am most distressed to see that Hawaiian Division of Forestry and Wildlife and Department of Agriculture are actively pursuing deliberate introduction of the thrips. ARS is also searching for potential biocontrol agents targetting the invasive cogongrass (Imperata cylindrica). Penn State is working on registering a soil fungus native to North America, Verticillium nonalfalfae, as a biocontrol targetting the highly invasive tree of heaven (Ailanthus).  

Phragmites invading Merkle Wildlife Sanctuary, Upper Marlboro, Maryland; photo by Alicia Pimental, (c) Chesapeake Bay Foundation

APHIS is pursuing biocontrol for “Roseau” cane scale. This situation presents a conflict of geographic regions because the plant to be controlled is Phragmites australis. Phragmites is highly invasive in the Mid-Atlantic, Northeast, and Great Lakes states . On the Mississippi delta it is considered important in maintaining wetlands crucial to protecting the Louisiana coast from rising seas.

Finally, USDA is pursuing management tools to contain the Box Tree Moth – a threat to the most widely planted ornamental shrub.  

Posted by Faith Campbell

We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.

For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm

or

www.fadingforests.org

Comment to APHIS on its Strategic Plan

APHIS is seeking stakeholder input to its new strategic plan to guide the agency’s work over the next 5 years.

The strategic plan framework is a summary of the draft plan; it provides highlights including the mission and vision statements, core values, strategic goals and objectives, and trends or signals of change we expect to influence the agency’s work in the future. APHIS is seeking input on the following questions:

  • Are your interests represented in the plan?
  • Are there opportunities for APHIS to partner with others to achieve the goals and objectives?
  • Are there other trends for which the agency should be preparing?
  • Are there additional items APHIS should consider for the plan?

range of American beech – should APHIS be doing more to protect it from 3 non-native pests?

The strategic plan framework is available at https://www.regulations.gov/document/APHIS-2022-0035-0001

To comment, please visit: https://www.regulations.gov/docket/APHIS-2022-0035

Comments must be received by July 1, 2022, 11:59pm (EST).

Posted by Faith Campbell

We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.

For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm

or www.fadingforests.org

Forest Pests: What’s Improved, What’s Still to Do

sassafras – vulnerable to the rapidly spreading laurel wilt disease; photo by F.T. Campbell

In summer 2019 I posted several blogs summarizing my analysis of forest pest issues after 30 years’ engagement. I reported the continuing introductions of tree-killing insects and pathogens; their relentless spread and exacerbated impacts. I noted the continued low priority given these issues in agencies tasked with preventing and solving these problems. Also, Congress provides not only insufficiently protective policies but also way too little funding. I decried the impediments created by several Administrations; anti-regulatory ideology and USDA’s emphasis on “collaborating” with “clients” rather than imposing requirements.

In my blogs, I called for renewed effort to find more effective strategies – as I had earlier advocated in my “Fading Forests” reports (link provided at the end of this blog), previous blogs, and Lovett et al. 2016

Areas of Progress

Now two years have passed. I see five areas of progress – which give me some hope.

1) Important Activities Are Better Funded than I had realized

a) The US Forest Service is putting significant effort into breeding trees resistant to the relevant pests, more than I had realized. Examples include elms and several conifer species in the West – here and here.

b) USDA has provided at least $110 million since FY2009 to fund forest pest research, control, and outreach under the auspices of the Plant Pest and Disease Disaster Prevention Program (§10201 of the Farm Bill). This total does not include additional funding for the spotted lanternfly. Funded projects, inter alia: explored biocontrol agents for Asian longhorned beetle and emerald ash borer; supported research at NORS-DUC on sudden oak death; monitored and managed red palm weevil and coconut rhinoceros beetle; and detected Asian defoliators. Clearly, many of these projects have increased scientific understanding and promoted public compliance and assistance in pest detection and management.  

This section of the Farm Bill also provided $3.9 million to counter cactus pests – $2.7 million over 10 years targetting the Cactoblastis moth & here and $1.2 million over four years targetting the Harissia cactus mealybug and here.

flat-padded Opuntia cactus – vulnerable to the Cactoblastis moth; National Park Service photo

2) Additional publications have documented pests’ impacts – although I remain doubtful that they have increased decision-makers’ willingness to prioritize forest pests. Among these publications are the huge overview of invasive species published last spring (Poland et al.) and the regional overview of pests and invasive plants in the West (Barrett et al.).

3) There have been new efforts to improve prediction of various pests’ probable virulence (see recent blogs and here.

4) Attention is growing to the importance of protecting forest health as a vital tool in combatting climate change — see Fei et al., Quirion et al., and IUCN. We will have to wait to see whether this approach will succeed in raising the priority given to non-native pests by decision-makers and influential stakeholders.

Rep. Peter Welch

5) Some politicians are responding to forest pest crises – In the US House, Peter Welch (D-VT) is the lead sponsor of H.R. 1389.  He has been joined – so far – by eight cosponsors — Rep. Kuster (D-NH), Pappas (D-NH), Stefanik (R-NY), Fitzpatrick (R-PA), Thompson (D-CA), Ross (D-NC), Pingree (D-ME), and Delgado (D-NY). This bill would fund research into, and application of, host resistance! Also, it would make APHIS’ access to emergency funds easier. Furthermore, it calls for a study of ways to raise forest pests’ priority – thus partially responding to the proposal by me and others (Bonello et al. 2020; full reference at end of blog) to create federal Centers for Forest Pest Control and Prevention.

This year the Congress will begin work on the next Farm Bill – might these ideas be incorporated into that legislation?

What Else Must Be Done

My work is guided by three premises:

1) Robust federal leadership is crucial:

  1. The Constitution gives primacy to federal agencies in managing imports and interstate trade.
  2. Only a consistent approach can protect trees (and other plants) from non-native pests that spread  across state lines.
  3. Federal agencies have more resources than state agencies individually or in likely collective efforts – even after decades of budget and staffing cuts.

2) Success depends on a continuing, long-term effort founded on institutional and financial commitments commensurate with the scale of the threat. This requires stable funding; guidance by research and expert staff; and engagement by non-governmental players and stakeholders. Unfortunately, as I discuss below, funding has been neither adequate nor stable.

3) Programs’ effectiveness needs to be measured. Measurement must focus on outcomes, not just effort (see National Environmental Coalition on Invasive Species’ vision document).

Preventing New Introductions – Challenges and Solutions

We cannot prevent damaging new introductions without addressing two specific challenges.

1) Wood packaging continues to pose a threat despite past international and national efforts. As documented in my recent blogs, the numbers of shipping containers – presumably with wood packaging – are rising. Since 2010, CBP has detected nearly 33,000 shipments in violation of ISPM#15. The numbers of violations are down in the most recent years. However, a high proportion of pest-infested wood continues to bear the ISPM#15 mark. So, ISPM#15 is not as effective as it needs to be.

We at CISP hope that by mid-2022, a new analysis of the current proportion of wood packaging harboring pests will be available. Plus there are at least two collaborative efforts aimed at increasing industry efforts to find solutions – The Nature Conservancy with the National Wooden Pallet and Container Association; and the Cary Institute with an informal consortium of importers using wooden dunnage.

2) Imports of living plants (“plants for planting”) are less well studied so the situation is difficult to assess. However, we know this is a pathway that has often spread pests into and within the US. There have been significant declines in overall numbers of incoming shipments, but available information doesn’t tell us which types of plants – woody vs. herbaceous, plant vs. tissue culture, etc. – have decreased.

APHIS said, in a report to Congress (reference at end of blog), that introductions have been curbed – but neither that report nor other data shows me that is true.

Scientists are making efforts to improve risk assessments by reducing the number of organisms for which no information is available on their probable impacts (the “unknown unknowns”).

Solving Issues of Prevention   

While I have repeatedly proposed radical revisions to the international phytosanitary agreements (WTO SPS & IPPC) that preclude prevention of unknown unknowns (see Fading Forests II and blog), I have also endorsed measures aimed at achieving incremental improvements in preventing introductions, curtailing spread, and promoting recovery of the affected host species.

citrus longhorned beetle exit hole in bonsai tree; USDA APHIS photo

The more radical suggestions focus on: 1) revising the US Plant Protection Act to give higher priority to preventing pests introductions than to facilitating free trade (FF II Chapter 3); 2) APHIS explicitly stating that its goal is to achieve a specific, high level of protection (FF II Chapter 3); 3) APHIS using its authority under the NAPPRA program to prohibit imports of all plants belonging to the 150 genera of “woody” plants that North America shares with Europe or Asia; 4) APHIS prohibiting use of packaging made from solid wood by countries and exporters that have a record of frequent violations of ISPM#15 in the 16 years since its implementation.

Another action leading to stronger programs would be for APHIS to facilitate outside analysis of its programs and policies to ensure the agency is applying the most effective strategies (Lovett et al. 2016). The pending Haack report is an encouraging example.

I have also suggested that APHIS broaden its risk assessments so that they cover wider categories of risk, such as all pests that might be associated with bare-root woody plants from a particular region. Such an approach could speed up analyses of the many pathways of introduction and prompt their regulation.

Also, APHIS could use certain existing programs more aggressively. I have in mind pre-clearance partnerships and Critical Control Point integrated pest management programs. APHIS should also clarify the extent to which these programs are being applied to the shipments most likely to transport pests that threaten our mainland forests, i.e. imports of woody plants belonging to genera from temperate climates. APHIS should promote more sentinel plant programs. Regarding wood packaging, APHIS could follow the lead of CBP by penalizing importers for each shipment containing noncompliant SWPM.

Getting APHIS to prioritize pest prevention over free trade in general, or in current trade agreements, is a heavy lift. At the very least, the agency should ensure that the U.S. prioritize invasive species prevention in negotiations with trading partners and in developing international trade-related agreements. I borrow here from the recent report on Canadian invasive species efforts. (I complained about APHIS’ failure to even raise invasive species issues during negotiation of a recent agricultural trade agreement with China.)

Solving Issues of Spreading Pests

The absence of an effective system to prevent a pest’s spread within the U.S. is the most glaring gap in the so-called federal “safeguarding system”. Yet this gap is rarely discussed by anyone – officials or stakeholders. APHIS quarantines are the best answer – although they are not always as efficacious as needed – witness the spread of EAB and persistence of nursery outbreaks of the SOD pathogen.

areas at risk to goldspotted oak borer

APHIS and the states continue to avoid establishing official programs targetting bioinvaders expected to be difficult to control or that don’t affect agricultural interests. Example include laurel wilt, and two boring beetles in southern California – goldspotted oak borer, Kuroshio shot hole borer and polyphagous shot hole borer and their associated fungi.

One step toward limiting pests’ spread would come from strengthening APHIS’ mandate in legislation, as suggested above. A second, complementary action would be for states to adopt quarantines and regulations more aggressively. For this to happen, APHIS would need to revise its policies on the “special needs exemption” [7 U.S.C. 7756]. Then states could adopt more stringent regulations to prevent introduction of APHIS-designated quarantine pests (Fading Forests III Chapt 3).

Finally, APHIS should not drop regulating difficult-to-control species – e.g., EAB. There are repercussions. 

APHIS’ dropping EAB has not only reduced efforts to prevent the beetle’s spread to vulnerable parts of the West. It has also left states to come up with a coherent approach to regulating firewood; they are struggling to do so.

Considering interstate movement of pests via the nursery trade, the Systems Approach to Nursery Certification (SANC) program) is voluntary and was never intended to include all nurseries. Twenty-five nurseries were listed on the program’s website as of March 2020. It is not clear how many nurseries are participating now. The program ended its “pilot” phase and “went live” in January 2021. Furthermore, the program has been more than 20 years in development, so it cannot be considered a rapid response to a pressing problem.

Solving Issues of Recovery and Restoration via Resistance Breeding

I endorse the findings of two USFS scientists, Sniezko and Koch citations. They have documented the success of breeding programs when they are supported by expert staff and reliable funding, and have access to appropriate facilities. The principle example of such a facility is the Dorena Genetic Resource Center in Oregon. Regional consortia, e.g., Great Lakes Basin Forest Health Collaborative and Whitebark Pine Ecosystem Foundation are trying to overcome gaps in the system. I applaud the growing engagement of stakeholders, academic experts, and consortia. Questions remain, though, about how to ensure that these programs’ approaches and results are integrated into government programs.

resistant and vulnerable ash seedlings; photo courtesy of Jennifer Koch, USFS

In Bonello et al., I and others call for initiating resistance breeding programs early in an invasion. Often other management approaches, e.g., targetting the damaging pest or manipulating the environment, will not succeed. Therefore the most promising point of intervention is often with by breeding new or better resistance in the host. This proposal differs slightly from my suggestion in the “30 years – solutions” blog, when I suggested that USFS convene a workshop to develop consensus on breeding program’s priorities and structure early after a pest’s introduction.

Funding Shortfalls

I have complained regularly in my publications (Fading Forests reports) and blogs about inadequate funding for APHIS Plant Protection program and USFS Forest Health Protection and Research programs. Clearly the USDA Plant Pest and Disease Management and Disaster Program has supported much useful work. However, its short-term grants cannot substitute for stable, long-term funding. In recent years, APHIS has held back $14 – $15 million each year from this program to respond to plant health emergencies. (See APHIS program reports for FYs 20 and 21.) This decision might be the best solution we are likely to get to resolve APHIS’ need for emergency funds. If we think it is, we might drop §2 of H.R. 1389.

Expanding Engagement of Stakeholders 

Americans expect a broad set of actors to protect our forests. However, these groups have not pressed decision-makers to fix the widely acknowledged problems: inadequate resources – especially for long-term solutions — and weak and tardy phytosanitary measures. Employees of federal and state agencies understand these issues but are restricted from outright advocacy. Where are the professional and scientific associations, representatives of the wood products industry, forest landowners, environmental NGOs and their funders, plus urban tree advocates – who could each play an important role? The Entomological Society’s new  “Challenge” is a welcome development and one that others could copy.

SOURCES

Bonello, P., Campbell, F.T., Cipollini, D., Conrad, A.O., Farinas, C., Gandhi, K.J.K., Hain, F.P., Parry, D., Showalter, D.N, Villari, C. and Wallin, K.F. (2020) Invasive Tree Pests Devastate Ecosystems—A Proposed New Response Framework. Front. For. Glob. Change 3:2. doi: 10.3389/ffgc.2020.00002

Green, S., D.E.L. Cooke, M. Dunn, L. Barwell, B. Purse, D.S. Chapman, G. Valatin, A. Schlenzig, J. Barbrook, T. Pettitt, C. Price, A. Pérez-Sierra, D. Frederickson-Matika, L. Pritchard, P. Thorpe, P.J.A. Cock, E. Randall, B. Keillor and M. Marzano. 2021. PHYTO-THREATS: Addressing Threats to UK Forests and Woodlands from Phytophthora; Identifying Risks of Spread in Trade and Methods for Mitigation. Forests 2021, 12, 1617 https://doi.org/10.3390/f12121617ý

Krishnankutty, S., H. Nadel, A.M. Taylor, M.C. Wiemann, Y. Wu, S.W. Lingafelter, S.W. Myers, and A.M. Ray. 2020. Identification of Tree Genera Used in the Construction of Solid Wood-Packaging Materials That Arrived at U.S. Ports Infested With Live Wood-Boring Insects. Journal of Economic Entomology 2020, 1 – 12

Liebhold, A.M., E.G. Brockerhoff, L.J. Garrett, J.L. Parke, and K.O. Britton. 2012. Live plant imports: the major pathway for forest insect and pathogen invasions of the US. Front. Ecol. Environ. 2012; 10(3):135-143

Lovett, G.M., M. Weiss, A.M. Liebhold, T.P. Holmes,  B. Leung, K.F. Lambert, D.A. Orwig, F.T. Campbell, J. Rosenthal, D.G. McCullough, R. Wildova, M.P. Ayres, C.D. Canham, D.R. Foster, SL. Ladeau, and T. Weldy. 2016. NIS forest insects and pathogens in the US: Impacts and policy options. Ecological Applications, 26(5), 2016, pp. 1437–1455

Mech,  A.M., K.A. Thomas, T.D. Marsico, D.A. Herms, C.R. Allen, M.P. Ayres, K.J. K. Gandhi, J. Gurevitch, N.P. Havill, R.A. Hufbauer, A.M. Liebhold, K.F. Raffa, A.N. Schulz, D.R. Uden, & P.C. Tobin. 2019.  Evolutionary history predicts high-impact invasions by herbivorous insects. Ecol Evol. 2019 Nov; 9(21): 12216–12230.

Poland, T.M., Patel-Weynand, T., Finch, D., Miniat, C. F., and Lopez, V. (Eds) (2019), Invasive Spp in Forests and Grasslands of the US: A Comprehensive Science Synthesis for the US Forest Sector.  Springer Verlag. (in press).

Roy, B.A., H.M Alexander, J. Davidson, F.T Campbell, J.J Burdon, R. Sniezko, and C. Brasier. 2014. Increasing forest loss worldwide from invasive pests requires new trade regulations. Front Ecol Environ 2014; 12(8): 457–465

Schulz, A.N.,  A.M. Mech, M.P. Ayres, K. J. K. Gandhi, N.P. Havill, D.A. Herms, A.M. Hoover, R.A. Hufbauer, A.M. Liebhold, T.D. Marsico, K.F. Raffa, P.C. Tobin, D.R. Uden, K.A. Thomas. 2021. Predicting non-native insect impact: focusing on the trees to see the forest. Biological Invasions.

United States Department of Agriculture Animal and Plant Health Inspection Service. Report on the Arrival in the US of Forest Pests Through Restrictions on the Importation of Certain Plants for Planting. https://www.caryinstitute.org/sites/default/files/public/downloads/usda_forest_pest_report_2021.pdf

Posted by Faith Campbell

We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.

For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm

Interior’s Invasive Species Plan: Let’s Implement It!

Posted by Scott J. Cameron, former Acting Assistant Secretary for Policy Management and Budget , US Department of the Interior

locations in Hawaii Volcanoes National Park where ohia trees were infected by rapid ohia death pathogen in 2017

In 2019 Congress passed the John D. Dingell, Jr. Conservation, Management, and Recreation Act. Among other things, it directed the Department of the Interior to “develop a strategic plan that will achieve, to the maximum extent practicable, a substantive annual net reduction of invasive species population or infested acreage on land or water managed by the Secretary.”  This provision triggered a year-long process of public involvement and inter-bureau coordination. The result was a plan published in January 2021.  It represents the first attempt by Interior at a Department-wide multi-taxa, multi-year approach to invasive species.  It has the potential to spur integration of invasive species work across the Department’s many bureaus and to focus each bureau’s efforts on a set of common goals, strategies, and performance metrics.

While Congress’ language is open-ended, any planning exercise is constrained by the most recent President’s budget and existing law.  It is up to those of us who are not, or at least no longer, executive branch employees to advocate for plans unbound by those constraints. 

In that spirit, I offer eight recommendations to improve invasive species management. Four are within existing authorities; four more are outside the current budgetary and statutory framework.  Many more ideas are without a doubt worth pursuing.

Opuntia (prickly pear) cactus – common plant in western National parks and on Bureau of Land Management lands; under threat by cactus moth

First, within existing funding and legal authorities, the Department has unfinished business that it can act on now.

  1. Secure approval of the package of categorical exclusions under the National Environmental Policy Act (NEPA) — now awaiting approval by the President’s Council on Environmental Quality (CEQ). Over many years agencies have documented how invasive species control improves, rather than harms, the environment.  Absent an applicable NEPA categorical exclusion approved by CEQ, though, each such action needs to run the time- and money-consuming gauntlet of NEPA compliance. In the meantime, the invasive plants germinate, the invasive animals reproduce, and what might have been a localized and inexpensive problem has expanded geographically and in terms of cost and complexity.  In the Fall of 2020 Interior submitted hundreds of pages of documentation on numerous practices proven to control invasive species without harming the environment.  Due to time and staffing constraints at CEQ, these categorical exclusions still await action.  Interior and CEQ should take prompt steps to finish them.
  • Allocate to the US Geological Survey at least $10 million of the roughly $90 million remaining available to the Secretary in CARES Act appropriations for research on invasive zoonotic diseases. These are diseases like COVID-19 and West Nile virus that can move from one species to another.  Many zoonotic diseases fit the definition of invasive species, since they are not native to the United States and endanger human health.  In the case of COVID-19 funding is available to the Secretary of the Interior, without need for further Congressional action, from funds appropriated by the CARES Act. The availability of these funds will expire at the end of September 2021, so Interior should provide this research funding to USGS as soon as possible. 
  • Join the existing Memorandum of Understanding between the Western Governors Association (WGA) and the US Department of Agriculture’s Forest Service. These groups have established “a framework to allow the U.S. Forest Service (USFS) and WGA to work collaboratively to accomplish mutual goals, further common interests, and effectively respond to the increasing suite of challenges facing western landscapes.”  This provides a forum to improve coordination between the States and the federal government on the management of invasive species, and Interior needs to be part of that team.
  • Interior should work with USDA to accelerate and intensify efforts to systematically improve coordination between the interagency Wildland Fire Leadership Council and the interagency National Invasive Species Council.  Both Councils have member agencies that practice vegetation management using similar tools and techniques, although for different purposes. The two Councils should identify a select number of initiatives in FY21 where their efforts would benefit both wildland fire management and invasive plant management .
swamp bay trees in Everglades National Park killed by laurel wilt; photo by Tony Pernas

Four steps to implement the strategic plan outside the scope of current law and the President’s Fiscal Year 2021 budget. I offer the following:

  1. Improve implementation of the Lacey Act program to list injurious species.  There are both legislative and administrative elements to this proposal.  

In a federal District Court decision on May 19, 2015, on a lawsuit filed by the Association of Reptile Keepers, the Court undid the longstanding Fish and Wildlife Service policy that the Lacey Act allowed FWS to ban interstate transport of injurious species. On April 7, 2017, the D.C. Circuit Court of Appeals upheld the District Court’s view. These rulings mean that FWS authority only applies to international commerce.  Unfortunately, the court’s interpretation of the law and legislative history are reasonable, so Congress needs to amend the law to make it clear that FWS is explicitly authorized to regulate interstate commerce in injurious species. The Department of the Interior should work with the Department of Justice and the Office of Management and Budget to develop the necessary bill language and submit it to Congress.

At the same time, the FWS injurious species listing process is notoriously slow, even causing Congress to occasionally list species legislatively.  The fact that these legislative initiatives have sometimes been promoted by Members of Congress who normally  are opposed to more federal regulation signals just how awkward the current FWS process is. Thus there might well be strong bipartisan support to amend the Lacey Act on the interstate commerce matter. Acting on its own authority, FWS should procure an independent third party review of the injurious species listing process and ask the contractor to make suggestions for “business process reengineering” to improve and streamline current practices, along with evaluating whether higher funding or new technology is needed.

  • The Bureau of Reclamation, Department of the Interior, and the Office of Management and Budget should develop legislative language to submit to Congress for the 2022 Water Resources Development Act, that explicitly authorizes an aquatic nuisance species program in the Bureau of Reclamation.  It could parallel the relatively new authority enjoyed by the Army Corps of Engineers and mandate increased coordination between the two water agencies.
  • Any climate change legislation pursued by Congress and the Administration should include provisions for addressing invasive species.  Climate change will make some North American habitats more suitable for foreign organisms, as cold-intolerant species might be able to survive in more northern latitudes in the U.S. than previously was the case. Second, the disruptive effect of climate change on North American ecosystem structure and trophic relationships at any latitude will make those ecosystems more vulnerable to invasion. Finally, the spread of invasive species may in and of itself exacerbate climate change, such as through the increased carbon dioxide emissions from rangeland wildfires aggravated by the dominance of invasive cheatgrass.
  • The Senate Committee on Environment and Public Works and the House Natural Resources Committee should each hold oversight hearings on how best to help state and local governments detect and respond to new invasive species that are not within the statutory purview of USDA/APHIS.  This is a complex topic, important for both ecological and financial reasons. Over the years several attempts to address it have failed.  A thoughtful review by Congress and the Administration, which perhaps would lead to passage of new statutory authority and funding, is worth exploring.

The Author:

Scott Cameron recently left the federal government, where he had served as Acting Assistant Secretary for Policy, Management and Budget at the U.S. Department of the Interior. In that capacity he oversaw Department-wide budget, invasive species, natural resource damage assessment and restoration, environmental compliance and numerous administrative functions of this $14 billion agency with 65,000 employees. Previously, Scott held other civil service job (e.g., at the White House Office of Management and Budget) & political appointments in the federal government, on the staff of the Governor of California, and on Congressional staffs. While not in government, Scott led formation of the Reduce Risk from Invasive Species Coalition.

CISP welcomes comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.

Further information on the plant pests mentioned in the photo captions can be obtained at www.dontmovefirewood.org; click the “invasive species” button.