Cibotium glaucum in Hawaii Volcanoes National Park; F.T. Campbell
A year ago I blogged about the status of Hawaiian species in the face of high levels of bioinvasions. I now update that discussion as it pertains to one of the invaders, the Australian tree fern Sphaeropteris cooperi.
S. cooperi has successfully invaded multiple regions, including the southern coast of South Africa, the Azores and Mascarene Archipelagos, and Hawai`i. The invasion’s impacts have been assessed only in Hawai`i. Studies found that the non-native tree ferns have outcompeted the dominant native tree fern Cibotium glaucum (Cibotiaceae), and altered leaf litter composition hence soil nutrient cycling. This in turn affects species assemblages (van den Berg et al. 2025).
Chau, Walker and Mehltreter (2013) documented the litter and soil chemistry in Hawaiian rainforests. They found that S. cooperi produces more leaves that grow faster, contain more nitrogen and phosphsorus, and decompose faster than the leaves of the dominant native tree fern C. glaucum. They compared the effect of leaf litter from the native and tree ferns on the growth and nutrient content of four native angiosperm species when they were grown in N-rich forest soil and P-rich landslide soil. The results suggested that nitrogen availability is the strongest driver of growth. The introduced tree fern, S. cooperi, can thus prompt more rapid growth of some native HI plants. They point out, however, that under natural conditions, native plants must compete for these additional nutrients with various non-native plants, including S. cooperi. The ultimate impact, then, remains unclear.
van den Berg et al. (2025) report that other invaded sites are at great risk Both the Garden Route region of South Africa and La Reunion Island in the Mascarene Archipelago in the eastern Indian Ocean have high bioidiversity. Both contain large, globally-recognized protected areas established to protect the native biodiversity: UNESCO Garden Route Biosphere Reserve and Reunion National Park. Despite their biological importance, both are among the top10 most invaded countries/territories globally (Tuberlin et al. 2017).
Sphaeropteris cooperi; photo via Easyscape
While climate change is expected to reduce the extent of suitable habitat for the Australian tree fern in both South Africa and La Reunion, the current situation is troubling. At present the tree fern occupies a narrower range of climatic conditions in both the Garden Route and especially on La Reunion than in Australia. (On La Reunion, 13.74 % of the fern’s apparent niche remains unoccupied.) van den Berg et al. (2025) are not sure what factors might be limiting the tree fern’s spread. They do urge educational campaigns to persuade people living near the Biodiversity Reserve to avoid planting the non-native tree fern.
The tree fern’s actual niche is somewhat uncertain because predation by deer (non-native to Australia) might have reduced its reproduction. The authors mention this but do not speculate further on the possible response of the fern to the absence of such stresses on La Reunion.
SOURCES
Chau, M.M., Walker, L.R. and Mehltreter, K. An invasive tree fern alters soil and plant nutrient dynamics in Hawaii. Biol Invasions15, 355–370 (2013). https://doi.org/10.1007/s10530-012-0291-0
Turbelin,A.J., Malamud,B.D., Francis,R.A. 2017. Mapping the global state of invasive alien species: patterns of invasion and policy responses. Glob. Ecol. Biogeogr. 26,78–92. https://doi.org/10.1111/geb.12517.
van den Berg, M.L., G. Singh, E.J. McCulloch-Jones, M. Rouget, D.M. Richardson, T.B. Robinson. 2025. The invaded range of the tree fern Sphaeropteris cooperi is predicted to shrink in two southern hemisphere biodiversity hotspots. African Journal of Botany 178 (2025) 390-399
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
We are beginning to get more information about invasive species on the African continent.
a flyer naming principal invasive ornamental plants in Kruger National Park
In several countries, the focus has been on threats to agriculture. Previous blog about horizon-scanning in Ghana. In Zimbabwe, N. Mudada and colleagues (2026; full citation and the end of this blog) found alarming, if not surprising, levels of risk to food production from introduced invasive plants. They investigated 1,668 human-aided transboundary plant introductions at 14 ports of entry and non-official crossing points over the course of four years.
They estimate that the 20,000 trucks that transported maize into the country over the four years carried over 20,700 metric tons of weed seeds and rubbish! They recorded detections of 11 species in eight orders. The pathways are familiar. As noted, several weeds were contaminants of grain shipments; Convolvulus arvensis in wheat for human consumption, Helianthus annus and Datura stramonium in maize for animal feed. Adenium obesum and Vitex agnus-castus were being smuggled for planting as flowers and ornamentals. (Vitex agnus-castus was also smuggled in passenger baggage for its medicinal properties). Several Lemna species (an aquatic plant) were also smuggled for planting as animal feeds.
In some cases, the focus is the threat to native ecosystems. I posted a blog the about threat of an introduced pathogen to trees in the remnant rain forests of Madagascar.
South Africa still has the lead in addressing invasive species. Regarding invasive plants specifically, the country has the benefit of more than 150 years of botanizing. The richness of the region’s flora is globally recognized. South Africa also has a long history of studying and managing invasive species, especially plants.
South African scientists and colleagues in Botswana, Eswatini, Lesotho, and Namibia have published four editions of the Flora of the Southern Africa region since 1984. In 2006, the PRECIS database of the South African National Biological Diversity Institute (SANBI) was combined with the Tropical African Plant Checklist published by the Conservatory and Botanical Garden of Geneva to create the African Plant Checklist and Database Project. It is continually updated. This is the first continental flora checklist for Africa; it fulfils countries’ obligations under the Convention on Biological Diversity’s Global Strategy for Plant Conservation.
The 2025 Checklist reports that 21,539 plant species are extant outside cultivation in the country; these comprise 20,204 indigenous species and 1,329 naturalized species. Thus, 6% of the total flora is non-indigenous. Of these, 649 (48.8% of the non-indigenous species, 3% of all plants) of them are invasive.
[Naturalized species are defined as species whose documented natural range does not include South Africa, but have overcome a biogeographic barrier and now sustain self-replacing populations for two or more life cycles or over a given period of time in the country. These populations are maintained without direct intervention by people, or despite human intervention. Invasive species meet the above definition plus produce reproductive offspring, often in large #s at considerable distances from the parent and/or site of introduction, and have the potential to spread over long distances.]
Since the previous checklist was published in 2006, botanists have identified 1,048 additional species – a 4.9% increase. Eighty-two percent of the newly identified species (865 species) are “naturalized”. Specifically, 414 new species are categorized as naturalized (a 31.1% increase), and 451 new species are classified as invasive (a whopping 69.5% increase). Le Roux and Klopper attribute these steep increases to active botanizing by SANBI’s Invasive Species Programme (begun in 2008), and the Southern African Plant Invaders Atlas Project (begun in 2010).
Of the 384 plant families present in South Africa, 350 contain at least some indigenous species. Thirty-four families contain only naturalized species. Among the 2,189 plant genera present, 459 (21%) contain only species that are non-indigenous.
Three families stand out because of the particularly high numbers of naturalized species: Fabaceae (143 species; 11% of all naturalized species), Asteraceae (140 species; 10%), Poaceae (123 species; 9%). Two of these families — Asteraceae and Fabaceae — are also the largest families among native South African plants. The third, grasses (Poaceae), ranks seventh in the list of most specious families indigenous to South Africa. The next group of families with high numbers of naturalized species has less than half as many invasive species: Myrtacae (55), Amaranthacea (52), Solanaceae (48). None of these families ranked within the top 20 families of indigenous plant species.
The genera with the most naturalized species were Solanum,Euphorbia and Acacia (all 24 or 23 species).
Acacia cyclops; photo by David M. Richardson
South African scientists are also exploring how to balance conflicting goals and perspectives when an invasive plant species has economic or social value. The example chosen by Mbobo et al. (2025) is guava (Psidium guajava) – a nutritious and popular tropical fruit grown commercially in South Africa, but also invasive along roadsides, watercourses and forest margins. Invasions are especially common in eastern parts of country; large monocultures are found in KwaZulu-Natal. Outbreaks have also been detected at five sites in Western Cape in riparian zones and at a hot spring. Mbobo et al. (2025) note that the microclimatic conditions at this last location differ from the broader conditions in the region – which are what most models would measure.
The scientists used models to predict where guava might invade – especially in large monocultures – and compared those areas to where the tree can be grown in cultivation with human inputs, e.g., irrigation. They then assessed whether six regulatory approaches would avoid restricting guava farming in areas at minimal or low risk while still protecting vulnerable locations. They also considered the amount of information required to implement the approach and costs of acquiring the information; and level of likely public acceptance. Mbobo et al. (2025) laid out the trade-offs between continuing to regulate planting of the species at the provincial level vs. at the municipal level. Prohibiting planting of guava in provinces where it is recorded as invasive allows some plantings near natural forests and riparian areas that are highly susceptible to guava invasions. On the other hand, nearly half of the prohibited area is outside the known or likely at-risk area. The provinces do allow exceptions through a permit process. Adopting more geographically limited rules by regulating at the municipal level would enable a tighter link to geographic areas at highest risk. However, this approach does not address long-distance seed dispersal by animals. Furthermore, the very detailed regulations might confuse stakeholders and complicate enforcement. Also, the models lack sufficiently fine spatial resolutions to predict invasible areas so accurately. Finally, the reduction in regulated area is minimal (~ 14%), so the economic benefits are unlikely to outweigh the significantly higher administrative costs and risk of allowing guava invasions in new sites.
Guava fruit on tree; Roenashy via Wikimedia
Gildenhuys et al. (2026) analyzed the factors that drive which non-native plants establish where. They assessed the roles of temperature, precipitation, urbanization intensity, urban area, travel time, year of city’s establishment, and human population density in determining which plant species are present in 54 urban centers in Western Cape Province. The cities have significant differences in climate: Mediterranean in the far southwest, warm temperate in the southeast, and semi-arid towards the interior. The expectation was that these drivers and assembly processes are influential at more advanced invasion stages when the species have already overcome some barriers to dispersal, so are now found in reasonably suitable habitats.
Gildenhuys et al. (2026) found temperature and precipitation were most important in determining plant species’ presence. This was especially true at the boundary between arid and mesic climates. These strong environmental gradients are the same ones which have driven high differences in native species presence across the province. [See pamphlet describing invasive plants in Cape Town.] This finding supports the “Goldilocks hypothesis”: that non-native plant species assemblages are driven by the same abiotic variables as native species assemblages. While did not directly study the “Biome decides hypothesis” (the composition of non-native flora is mediated by the biotic effects of native flora and fauna), Gildenhuys et al. (2026) doubt its applicability here because native species’ presence has probably been greatly reduced by the effects of urbanization.
Urbanisation intensity itself ranked third as a factor. Its effect was strongest at low to medium urbanization intensities. Because urbanization creates novel habitats, such as, “hardscapes” of paved surfaces that resemble deserts, their non-native plant assemblages are dominated by similar, urban specialist, species. At lower urbanization intensities a greater variety of habitats is available. Gildenhuys et al. (2026) conclude that urbanization acts primarily as a driver of opportunistic habitats for species at later invasion stages rather than as a filter of species introduction.
An earlier study found a similar effect from road density (often associated w/ urbanization) as an explanation for where specific woody non-native species establish. They do concede that larger urban areas might experience greater propagule pressure.
Gildenhuys et al. (2026) note that recent globalization of the plant trade has probably changed the specis planted in urban centers. For example, cities in the Western Cape are increasingly replacing English oak (Quercus robur) with more disease-resistant oaks. The change might reflect greater environmental awareness and regulations issued under the National Environmental Management: Biodiversity Act 10 of 2004. In newly established urban centers, fewer invasive species are being planted — at least among trees.
SOURCES
Gildenhuys, C.P., L.J. Potgieter, C. Hui, D.M. Richardson. 2026. Drivers of compositional turnover of the NIS urban flora in the W Cape, South Africa. Urban Ecosystems (2026) 29:51 https://doi.org/10.1007/s11252-026-01919-3
Le Roux, M.M., R.R. Klopper. 2025. Taking stock of South Africa’s flora. South African Journal of Botany 184 (2025) 571-579
Mbobo, T., D.M. Richardson, A. Datta, K.T. Faulkner, J.R.U. 2025. Wilson. Spatially-Differentiated Reg of NIS Can Be Improved Using Spp Distribution Models: Psidium guajava in South Africa as a Case Study. Diversity and Distributions. 2025 31:e70102 https://doi.org/10.1111/ddi.70102
Mudada, N., J. Chitamba, E. Nyangani, C. Chapano, N. Mapope,and W. Ngezimana. 2026. Weeds associated with cross border traffic, their approach and infestation rates in Zimbabwe. ISABB Journal of Food and Agricultural Sciences. Vol. 12(1) January-June 2026. DOI: 10.5897/ISABB-JFAS2025.0192
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
Cape Coast lily (Crinum macowanii); photo by Jaqui Geux
South Africa is rich in plant diversity. That diversity is strongly shaped by the country’s varied topography, soils, & climate. Nine biomes & 465 vegetation types are recognized in a country of just 1.2 million km2(471,445 square miles).
There is a long history of botanizing in southern Africa – with impressive results that include a Flora of the Southern Africa region (it covers Botswana, Eswatini, Lesotho, Namibia, as well as South Africa) and the African Plant Checklist & Database Project, which is the first continental checklist for Africa. This publication – which is being maintained continuously – contributes to goals of the Convention on Biological Diversity’s Global Strategy for Plant Conservation.
South Africans have also produced a national plant checklist that is updated every year. The most recent Checklist dates from 2025.The checklist includes bryophytes (mosses, hornworts, & liverworts), lycophytes & pteridophytes, gymnosperms, & angiosperms. Compilers plan to include marine macro-algae in future.
The 2025 checklist names 21,539 species in South Africa – 20,204 indigenous species, 1,329 naturalised species. Based on the, South Africa’s national flora comprises 5.3 % of the estimated ~ 380,000 plant species on Earth.
Geissoloma marginatum; photo by Tony Rebelo via Wikimedia
South Africa is home to 384 plant families, of which all but 34 contain only indigenous species. All the species in seven families are endemic to South Africa. These families are Bruniaceae, Geissolomataceae, Grubbiaceae, Lanariaceae, Penaeaceae (excl. Oliniaceae), Rhynchocalycaceae, & Roridulaceae. Of the 2,654 genera, 2,189 are indigenous. Three hundred (12%) of these genera are endemic. Sixty percent of the 20,204 indigenous species are endemic. All the endemic families other than Bruniaceae are composed of a single genus – demonstrating the phylogenetic uniqueness of this flora.
The 2025 Checklist contains 1,048 species that did not appear in the previous checklist (published in 2006). This is an increase of 4.9%. Numbers of indigenous taxa increased by less than 5%: additional 623 indigenous species (3.1%); 520 endemic species (4.3%). Numbers of non-indigenous species increased by considerably higher proportions: naturalized species increased by 414 species (31.1%), & invasive species by 451 (69.5%). These 865 species constitute 82.5% of all 1,048 newly recorded species. (I report the findings on non-indigenous species in a separate blog.)
The detection of previously unidentified species and infraspecific taxa – both native and non-indigenous – is the result of systemic botanizing campaigns focused on particular families. Thus, a study of the family Iridaceae in southern Africa led to description of 169 species in 20 genera. More than two decades of work on the Pelargonium (Geraniaceae) resulted in recognition of 34 new taxa. Thirty-three new species have been described in the genus Indigofera (Fabaceae).
The most specious plant family indigenous to South Africa is Asteraceae, with 2,124 species. Aizoaceae & Fabaceae follow with 1,603 & 1,566 species, respectively. The newly expanded Iridaceae is fourth; it encompasses 1,189 species. The world-famous Proteaceae rank 13th, with only 355 species. Considering genera, the largest by far is Erica (heath) at 734 species; no other genus houses more than 300 species. [The famous orchid genus Disa ranks 18th. There are ~182 species on the continent, primarily in East & Southern Africa.]
Disa uniflora on Table Mountain; F.T. Campbell
When considering phylogenies with high levels of endemism, the leading families are – again — Aizoaceae (1,426) and Asteraceae (1,352). Ranked third is Iridaceae (983). Fabaceae is ranked 4th (961). Nearly half (49%) of species in 1,071 genera are endemic. Again Erica ranks highest: 581 species – 78% of the species in the genus – are endemic. This is double the number in the genus ranked second — Aspalanthus (261species; all but 34 species are endemic). Pelargonium is 3rd : 204 of 261 species are endemic.
Flora of the provinces
Of South Africa’s nine provinces, KwaZulu-Natal (94,361 km2) is home to the greatest diversity in terms of plant families (331 families) and genera (1,718 genera). Neighboring Eastern Cape Province (168,966 km2) ranks second with 305 families and 1,576 genera. Western Cape has somewhat fewer plant families (294) and genera (1,475), but by far the most species (11,379). Western Cape also leads in the proportion of its plant taxa that are endemic to the province: 58%. (This reflects the presence of a globally recognized distinct flora, the Cape Floral Kingdom.) KwaZulu-Natal and Eastern Cape (16% endemic) share most of their plant taxa with neighboring provinces or countries – Mozambique. Therefore, their levels of endemism are only 8% and 16%, respectively.
The clustering plant diversity and endemism in the south & east reflects the topographic variation provided by the Escarpment of South Africa.
The largest province is Northern Cape Province at 372,889 km2. It is home to 5,058 species but its fairly uniform terrain means there is not very high species diversity (25 % – half the proportion in Western Cape). However, the flora is unique because adapted to the harsh environment (I concede these statements seem contradictory).
Pachypodium namaquanam; F.T. Campbell
SOURCE
Le Roux, M.M., R.R. Klopper. 2025. Taking stock of South Africa’s flora. South African Journal of Botany 184 (2025) 571-579
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
Hernández‐Gutiérrez, Nichols, and Kelly (2026) (full citation at the end of the blog) analyzed interactions between this genus of beetles and oaks (Quercus species). In this context, they report that 32 Agrilus species from Africa, Asia, Europe, and North and South America use 51 Quercus species as hosts in their native range. Eighteen (56.25%) use only Quercus hosts.
Oaks that host Agrilus species cluster in several clades, i.e., the entire Section Cerris and one clade of Section Ilex and two clades of section Lobatae. Clades where Agrilus hosts are underrepresented are Sections Cyclobalanopsis and Quercus &, surprisingly, two clades in Section Lobatae.
Their analysis indicated that beetle-oak interactions involving all the 32 Agrilus species and 105 Quercus species in their study had a significant likelihood of being damaging. For example, northern red oak (Q. rubra) is already known to host six Agrilus species. Hernández‐Gutiérrez, Nichols, and Kelly (2026)’s analysis indicated that this tree species might be utilized by all 32 Agrilus species assessed. The tree’s wide distribution (both native and introduced) places it close to other known or probable hosts, which exacerbates the risk of an interaction. Another 26 Quercus species are predicted to host ten or more Agrilus species.
The model was not successful in predicting hosts of A. auroguttatus (goldspotted oakborer) in its introduced range in California.
black oak (Quercus kelloggii) in Cleveland National Forest killed by GSOB; photo by F.T. Campbell
It also predicted that few of China’s oak species might host Agrilus beetles. However, as Dr. Robert Haack notes (pers. comm. June 2026), larval hosts have been identified for only 13% of the nearly 1,200 Asian Agrilus.
Some Agrilus species have a very large number of predicted novel interactions. A. graminis and A. angustulus are predicted to have more than 40 novel oak hosts. Both have numerous known oak hosts; so their “polyphagous” nature is already documented.
Since two-thirds of 666 Agrilus species with known larval hosts exploit only one plant genus as a host in their native range, Hernández‐Gutiérrez, Nichols, and Kelly (2026) assert that they might spread faster if introduced to homogeneous rather than species-rich habitats. Dr. Haack believes that this statement is too broad (pers. comm. June 2026).
A. bilineatus; photo by Christina Butler via Wikimedia
Twolined chestnut borer
Haack and Blank (2024) document that the twolined chestnut borer, Agrilus bilineatus has preferentially infested apparently healthy English oak (Quercus robur) trees over healthy native oak trees in Michigan. In North America, A. bilineatus is a major pest of oaks and American chestnut (Castanea dentata)when they are stressed by drought or other factors. Infestation typically begins in the upper crown and proceeds downward; tree death often occurs within three years.
At several sites in southern Michigan, where English oaks were intermixed with native white oaks (Quercus alba) and close to northern red oaks (Quercus rubra), A. bilineatus preferentially infested Q. robur trees that initially appeared healthy. Further study revealed that many of the English oaks attacked had low or depleted root starch levels.
Although these findings are cause for alarm, English oak is already used by 11 species of Agrilus in Europe. Perhaps the tree and ecosystem might have sufficient defenses in Europe. Meanwhile, A. bilineatus has been reported in Turkey as of 2018; I have found no recent information about the damage whether it is causing any damage there.
Data from Britain and Worldwide
Peyton et al. (2026) reviewed the effectiveness of a “horizon scanning” exercise conducted for Great Britain (England, Scotland and Wales). They report that 3,248 recognized non-native species have been detected in Great Britain, of which 2,016 have established self-sustaining populations. Some 194 (~10%) are considered invasive, that is, have negative impacts on biodiversity and wider ecosystem viability. These consist of 108 terrestrial species, 47 freshwater species, and 39 marine species. These bioinvaders cost the British economy an estimated ~£3.9 billion per year (the bulk of the damage is attributed to ash dieback, caused by the fungus Hymenoscyphus fraxineus).
In the decade between completion of the “horizon scan” and the present, 143 species were recorded as being introduced. The horizon scan predicted 31 of these species, 22%. Peyton et al. (2026) consider this to be success.
Peyton et al. (2026) report that globally, ~ 6% of non-native plant species are ranked as invasive. Among invertebrates, this proportion rises to 22%. Considering vertebrates introduced to Europe or North America, the figure is more than 50%!! I welcome global data that support my call for rethinking the “rule of tens” long relied on for estimating the proportion of non-native species that are invasive.
Discussing bioinvaders’ role in causing extinctions, Peyton et al. (2026) report that 30 predators have been linked to declines and extinctions of 738 vertebrate species.
Peyton et al. (2026) also discuss the difficulty in predicting an introduced species’ impacts when in some cases the time lag between introduction and presence in the wild or between establishment and spread w/in the region can last decades or even a century. They cite as an example Senecio squalidus, which escaped the Oxford Botanic Gardens in the 1700s but started to spread only during mid-1900s.
Australia
More than 300 non-native insect pests, pathogens and nematodes have established on tree or shrub hosts in Australia; 20% have caused moderate to high impacts to commercial plantations, urban forests, or trees in natural ecosystems (Carnegie et al. 2026).The rate at which non-native forest pests and pathogens have been detected in Australia has doubled since 2018 compared to earlier decades: from ~ 1.5 to ~ 3 per year. Carnegie et al. (2026) attribute this rise to greatly expanded official surveillance efforts. Still, three-quarters of the most recent detections came too late for eradication to be attempted.
The Forestwatch program (inaugurated – under a different name – in 2022) includes pathogens. I rejoice!!! Still, the target species threaten primarily tree species not native to Australia but important to commercial forestry or urban forests: Asian longhorned beetle, burnt pine longicorn (Arhopalus ferus), pine pitch canker, pine wilt disease, red turpentine beetle (Dendroctonus valens), Asian spongy moth, red needle cast, and sudden oak death. The exceptions are strains of Austropuccinia psidiinot yet intro to Australia, and eucalypt leaf blight (caused by Teratosphaeria destructans) (Carnegie et al. 2026).
Austropuccinia psidii infection on Melaleuca in Australia; photo by John Tann via Flickr
Among the introduced pests causing the greatest damage to native species are
Phytophthora cinnamomi: this soil fungus can kill 40% of the plant species in the southern portion of Western Australia – which is one of 36 “Biodiversity Hotspots” recognized by the Critical Ecosystem Partnership Fund.
Austropuccinia psidii (cause of myrtle rust) in natural ecosystems; Members of the host family Myrtaceae occur in 11 of 13 major vegetation formations on Australia. Various authorities have identified 76 species as at risk to the rust.
I hope the Australians are developing strategies for landowners to counter damage by the polyphagous shot hole borer (Euwallacea fornicatus) and its associated fungus (Fusarium euwallaceae). DMF Outbreak detected near Perth, Western Australia, in 2021 – apparently three years after the actual introduction. By June 2025 authorities had determined that it was too widespread to be eradicated, so landowners will be responsible for any management. (Carnegie et al. 2026) Impact is predicted to be greatest in urban landscapes, and cost up to AU$9.7 M per annum to manage.
Phytophthora pluvivora was first detected in Australia on an English oak, Quercus robur. However, it has since been recorded on native species in the Blue Mountains, including the critically endangered dwarf mountain pine (Pherosphaera fitzgeraldii) in a National Park.
SOURCES
Carnegie. A.J., B.A. Summerell, C. Trollip, F. Tovar, D.I. Smith, and J. McDonald. 2026. Sentinel trees for early detection of non-native forest pests and pathogens in Australia. Front. For. Glob. Change 9:1801183. doi: 10.3389/ffgc.2026.1801183
Haack, R.A. and R.B. Blank. 2025. Susceptibility of English Oak (Quercus robur) to the Twolined Chestnut Borer, Agrilus bilineatus (Coleoptera: Buprestidae): Observations from Michigan. The Great Lakes Entomologist. 57: 113-125. https://doi.org/10.22543/0090-0222.2492
Hernández‐Gutiérrez, E., R.A. Nichols, and L.J. Kelly. 2026. Combined phylogenetic and geographic data can predict plant–pest interactions with high accuracy. New Phytologist (2026) doi: 10.1111/nph.71306
Peyton, J.M., S. Rorke, D.C. Aldridge, O.L. Pescott, K. Dehnen- Schmutz, D.G. Noble, J. Sewell, A.J.A. Stewart, T. Adriaens, B.C. Beckmann, J. R. Britton, J. Brodie1, P.M.J. Brown, I.C.N. Cavadino, P.F. Clark, A.M. Dunn, J.Foster, C. Harrower, M.C. Harvey, M.C. Jackson, T. Jones, C.A. Maggs, G. Martin, F. Mathews, A.C. Mill, D. Murphy, E. Paganini, R. Payne, W. Rabitsch, T. Renals, K. Schönrogge, R.H. Shaw, G.C. Smith, P.D. Stebbing, P.A. Stroh, H. Tidbury, E. Tricarico, J. Vallet, K.J. Walker, L.E. Wood, C.A. Wood, B. Woodcock, H.E. Roy. 2026. Assessing the success of a horizon scanning approach in predicting invasive non- native species arrival. J Appl Ecol. 2026;63: https://doi.org/10.1111/1365-2664.70217
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
Prostanthera cuneata – member of a genus endemic to Australia. Photo by Leonora (Ellie) Enking via Flickr
In 2023 a global meeting of plant conservation experts convened by The Royal Botanic Gardens, Kew (U.K.) released the 5th edition of a report on the State of the World’s Plants and Fungi.
Associate Professor of Plant Ecology and Conservation Science Rachael Gallagher from Western Sydney University had led the global evaluation of conservation assessments for unique flora species. She is also the lead author of an article (2023; full citation at the end of this blog) evaluating how well countries around the world met their treaty obligation to assess the conservation status of endemic plant species native to their territories. The analysis identified 221,399 endemic plant species in a total of 173 countries. The treasure is not distributed evenly. Five countries harbor a third of the endemic plant species: in descending order, Brazil, Australia, China, Mexico, and South Africa. (The United States, including its islands, ranks 8th.)
On average, countries completed assessments of just 34% of their endemic species. New Zealand and here and South Africa shone: they assessed 87% of their unique species. China assessed 71%. One of the world’s poorest countries, Madagascar, evaluated 42% of its ~10,000 endemic plant species. Reminder: tiny Madagascar ranks 6th in the number of endemic plants. Australia – one of the richest countries– carried out the process for 39% — slightly more than the global average. Other countries that are stewards of numerous endemic plants were below the average: Brazil reviewed 29%, Mexico assessed only 24%.
Rachael Gallagher and her colleagues in the Australian Biodiversity Council were quite critical of Australia’s low level of performance. They called on their countrymen to do much more to prevent the decline and extinction of the country’s unique plant species. Australia, as party to the Convention on the Conservation of Biological Diversity, has a treaty obligation to prevent extinction of species which occur nowhere else. Remember, Australia’s flora and fauna rank extremely high on a scale of phylogenetic distinctness as an heir of the isolated continent of Gondwanaland.
Gallagher and colleagues concede that many endemic plant taxa in Australia have huge ranges — averaging 235,829 km2. But these vast expanses do not prevent sudden population crashes caused by calamities. They mention the megafires of 2019–2020 and – over the longer term – climate change. I think of the invasion by the rust fungus Austropuccinia psidii.
When we think about Australia, we wonder at the kangaroos and koalas. I assume Australians consider their unusual fauna to be iconic symbols of their country. Why are they not equally committed to their flora – 88% of their plant species are endemic. Do they suffer from the same “plant blindness” I have encountered in the United States? South Africa undertook an assessment of her endemic flora that concluded that a quarter of these species are threatened. Sixty percent of the country’s 20,000 plant species are endemic.
a protea in South Africa’s fynbos; photo by Michael Wingfield
[I have found no parallel analysis of America’s endemic plant species. Our nation’s rank of 8th in number of endemic species is explained by the highly unique floras of the islands, especially the Hawaiian archipelago. More than 95% of native species on the Islands are endemic. This includes 67% of the large trees still present in the forests (Potter et al. 2023).]
This study reflects the findings of the International Union for the Conservation of nature (IUCN)’s 2024 Red List of Threatened Species. A decade-long global project had found that at least 16,425 of the 47,282 tree species (38%) assessed are at risk of extinction. Trees accounted for over one quarter of species on the IUCN Red List. Tree species are at risk of extinction in 192 countries around the world.
Sources
Gallagher, R.V., S. P. Allen, R. Govaerts, M.C. Rivers, A.P. Allen, D.A. Keith, C. Merow, B. Maitner, N. Butt, T.D. Auld, B.J. Enquist, W.L. Eiserhardt, I.J. Wright, J.C.O. Mifsud, S. Espinosa-Ruiz, H. Possingham, V.M. Adams. 2023. Global shortfalls in threat assessments for endemic flora by country. Plants, People, Planet. DOI: 10.1002/ppp3.1036
Potter, K.M., C. Giardina, R.F. Hughes, S. Cordell, O. Kuegler, A. Koch, E. Yuen. 2023. How invaded are Hawaiian forests? Non-native understory tree dominance signals potential canopy replacement. Landsc Ecol 2023 https://doi.org/10.1007/s10980-023-01662-6
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
an aye-aye – one of the highly endangered lemurs dependent on moist tropical forests of Madagascar; photo by Andrew Ciscel via Wikimedia
A forthcoming study examines two important issues: interactions of pathogens’ spread and changing climate, and invasive species threats to tropical islands’ forests.
Underwood et al. (in press) analyzed how an introduced vascular wilt pathogen — Leptographium calophylli – is likely to affect a tree endemic to Madagascar’s already threatened mid-level elevation humid & subhumid forests, Calophyllum paniculatum (sorry; I can find no photographs of the tree species).
Climate change is expected to cause substantial shifts in temperature and precipitation patterns on the island. These temperature and moisture regimes in turn govern pathogen sporulation, infection efficiency, and survival. They also affect the host’s levels of stress and defenses. The direction of change is not certain, however. In some cases, warming and other changes to the climate might facilitate a pathogen’s spread, allowing it to track shifts in the host’s range and expand into previously unoccupied refugia. In other cases, these changes might erect environmental thresholds that limit the pathogen’s survival and spread, thereby creating spatial refugia for the host.
diademed lemur, courtesy of Animalia
Environmental change increases the area of suitable landscape, that is, it weakens climatic barriers to establishment. Continued anthropogenic movement of some vector (biological or not) generates multiple introductory events over time. As a result, the likelihood of a successful establishment also increases, even if the probability per individual introduction is unchanged. Underwood et al. say that invasion outcomes thus become increasingly dependent on propagule pressure.
On many other tropical islands the threat from climate change is exacerbated by deforestation. On Madagascar, clearing driven by slash-and-burn agriculture and fuelwood harvesting has already reduced natural forest cover to less than 10% of its original extent. [For more on this topic, see e.g., Mittermeier et al. (2011).] Underwood et al. cite a determination by the ForestAtRisk model that humid forest in Madagascar could be almost entirely lost by 2100.
Loss of Madagascar’s forest has global implications. The island is one of 36 global biodiversity hotspots for both flora and fauna (e.g., lemurs). Its flora exceeds 12,000 plant species, of which 83% are endemic. In this case, the host tree species — Calophyllum paniculatum — is already considered vulnerable by the International Union for the Conservation of Nature (IUCN). Thus it is of global importance to understand the relative importance of several threats so that conservations can adopt the most effective countermeasures.
While they do not say so explicitly, it appears that Underwood et al. worry that too few of the conservationists active on Madagascar are paying attention to the possible impact of introduced pathogens. They note that pathogen-driven mortality of dominant or functionally unique trees can rapidly alter community structure and ecosystem function, potentially triggering local extinctions and cascading ecological consequences. For example, if an infection removes mature trees, their loss reduces fruit and nectar availability and so depresses populations of dependent wildlife. The trees’ death also diminishes above-ground carbon stocks and litter inputs. In combination, these impacts can shift community composition toward disturbance-tolerant states and heighten susceptibility at forest margins. These changes difficult to reverse once thresholds crossed.
red-bellied lemur in Ranomafana National Park – site of the first detection of Leptographium calphylli; via Flickr
This threat is not hypothetical. Since 2016 mature C. paniculatum at one site – a National Park – have been dying from a vascular wilt disease caused by a species in the Leptographium genus, probably Leptographium (formerly Verticillium) calophylli. While the species hasnot yet officially been recorded in Madagascar, it is established on neighboring Indian Ocean islands and across much of mainland Africa. Various species in the fungal genus are known to cause disease in other woody hosts. Underwood et al. suggest it was probably transported to Madagascar on infected wood, although they present no data.
Inside forests, Leptographium spp. are vectored by bark beetles in the Cryphalus genus. At least 25 Cryphalus species occur on the African Continent; some are vectoring disease on Seychelles and Mauritius.
The analysis by Underwood et al. indicates that future climatic conditions are likely to worsen the Leptographium calophylli infection over coming decades. The causal agent is likely to retain two-thirds of its current probable distribution and expand into previously uninhabited regions. The suitable habitat is expected to stretch across the entire north-south humid belt – the entire distribution of the host tree. Underwood et al. (in press) say it is even possible that the pathogen might remain in the forest, subsisting on other hosts, after C. paniculatum becomes functionally extinct across its range.
Meanwhile, that host – Calophyllum paniculatum – is projected to experience severe range shifts, with an overall net contraction across all climate change scenarios. It is forecast up to 67% of its current area by 2100. This range contraction will be compounded by fragmentation and dispersal limitation resulting from from deforestation. The refugia will be few and geographically isolated by late in the 21st century.
red-veined swallowtail; photographed in Ranomafana National Park by Frank Vassen, via Wikimedia
Are conservationists considering the implications of Leptographium calophylli’s probable persistence? Underwood et al. imply they are not; they say the impact of this and related pathogens on Madagascar & nearby islands is “still an unknown to the conservation community”. They urge their colleagues to conduct a set of research actions to identify, monitor, & limit the fungus’ spread – – and thereby improve the effectiveness of conservation efforts.
Host range & other targets: determine whether L. calophylli infects other taxa in Madagascar – especially the endemic species and genera. They suggest systematic field sampling of multiple species across sites within the core probable range of L. calophylli. A trained pathologists should be consulted to officially identify the pathogen.
Determine the spread phase of the pathogen. They suggest random sampling of species & sites within & outside of the fungus’ probable distribution, mapping the possible start point & dispersal patterns, including both anthropogenic & natural spread routes.
Assess applicability of IPBES tools & suggestions for invasive species management to the case of a fatal pathogen in the context of tropical islands’ characteristics. How might Madagascar implement prevention, early detection & rapid response systems?
I applaud Underwood et al. for trying to alert the conservation community active on tropical islands to the simultaneous impacts of multiple global & regional change drivers on vulnerable species. Probably other host-pathogen systems are experiencing the same diverging trajectories that might intensify their biodiversity loss, particularly when compounded by deforestation.
SOURCES
Mittermeier, R.A., E.E. Louis Jr., M. Richardson, C. Schwitzer, O. Langrand, A.B. Rylands. 2010. Lemurs of Madagascar. Conservation International, Arlington, USA. ISBN 9781934151235
Underwood, E.L., K.A Brown, A. Ronnfeldt, M. Mulligan, N. Walford, R. Allgayer. In press. Climate change facilitates fungal pathogen expansion while driving endemic host range contractions in a tropical biodiversity hotspot. Research Square.
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
sorting coffee beans; photo by Niels Van Iperen via Wikimedia
Many have recognized that preventing introduction of invasive species is the most efficient approach to minimizing their ecological and economic impacts. Prevention requires many capacities, including control over a country’s borders, strong border biosecurity agencies and policies, and foreknowledge of probable pathways of introduction and high-impact species that might arrive.
Horizon scanning is one tool for gathering information about non-native species likely to enter, how they might arrive, and their probable impact. Horizon scanning involves a systematic search for potential invaders, assessment of their potential to harm BD, economic activities and human health, and opportunities for impact mitigation. It thus supports choice of prevention policies, targetting of efforts, and implementation of early identification and eradication procedures (Kenis et al. 2022; Martinou et al. 2026)
I have reviewed two case studies of the application of horizon scans.
Plant Pests in Ghana
One horizon scanning exercise aimed to identify and rank potential invasive non-native plant pest species that could be harmful to agriculture, forestry, and the environment in Ghana. The ultimate objective was to enable prioritization of actions aimed at preventing their introduction. As the participants in this exercise note (Kenis et al. 2022), the resource-poor farmers of Sub-Saharan Africa are particularly vulnerable to invasive pests that attack their crops, both those grown for subsistence e.g., maize and sorghum, and those grown for the international market, e.g., cacao and tomatoes. The continent’s vulnerability is increased by porous borders, weak cross border biosecurity, and inadequate capacity to limit or stop invasions. This exposes Africa both to repeated invasions and to continued spread across the continent once they have arrived.
Marc Kenis and 21 others assessed 110 arthropod and 64 pathogenic species using a simplified pest risk assessment. This set had been winnowed from an initial list of 1486 arthropods, nematodes and pathogens. Unfortunately, assessors were unable to agree on confidence levels for the assessments.
Sixteen of the assessed species – 14 arthropods and two pathogens – were thought at the time to not be on the African continent. Another 19 arthropod and 46 pathogenic species had been reported established in the neighboring countries of Burkina Faso, Côte d’Ivoire, and Togo. Seventy-seven species [62 of them pathogens] were recognized as established elsewhere in Africa.
Ninety-five percent of the arthropods were considered likely to arrive as contaminants on commodities, i.e. on their host plants; 23% were also likely to arrive as stowaways; some good fliers already present in neighboring countries could also enter unaided.
The 64 pathogen species included 14 bacteria, 16 fungi, 14 nematode, seven water moulds (Kingdom: Chromista), and 13 viruses. Sixty-two of these species have been detected on the African continent; 46 are reported in neighboring countries. Thirty-one (48.4%) of the pathogenic organisms were considered likely to arrive both as contaminants on commodities and/or as stowaways; Twenty-six (40.6%) probably arrive only as contaminants; five could arrive exclusively as stowaways. Kenis et al. (2022) specify which of the fungi, nematodes, viruses, bacteria, and water moulds fall into which category.
The most important input in the threat scoring process was likelihood of entry. The unsurprising result was that species known to be in neighboring countries or spreading rapidly in Africa received the highest overall scores. The likelihood of establishment was less important because the assessors had already excluded species they thought would encounter an unsuitable climate or absence of host plants. The impact score played an important role in the overall score; it was based primarily through their potential economic impact. There is little information about or attention to the potential threat of non-native plant pest species to non-commercial plants. Kenis et al. (2022) cite well-known examples to remind us that invasive plant pest species have had “huge impacts” on native tree species and biodiversity in North America and Europe. On the African continent, most non-native pests attack mostly concern exotic trees. They note one exception, Euwallacea fornicatus, DMF a wood-boring beetle from Asia killing many native trees in South Africa.
Bemisia tabaci; one of the arthropod pests in a country bordering Ghana; photo courtesy of INCTELUNI
Kenis et al. (2022) state that some of the several alien arthropods and pathogens identified in neighboring countries might already be present in Ghana although not yet recorded or identified to the species level. They say it is essential to clarify these species’ status by enhanced surveillance and applying morphological and molecular methods. Some of these possibly introduced species received high scores in the assessment. They threaten cocoa, a key crop in Ghana, and vegetable crops.
I am disappointed that Kenis et al. (2022)’s main actions suggested for both arthropod and pathogenic species that scored highly are to ramp up surveys and to conduct full pest risk analyses. It is true, as thy point out, that such assessments are required by international regulations before a country may implement phytosanitary measures. [See discussion of the requirements of the International Plant Protection Convention here.]
To some extent, the horizon scan echoed the obvious: most of species ranked high are already on the African continent, including 19 arthropod and 46 pathogenic species known to be established in neighboring countries. Plus, the recommended actions are minimal. Since Kenis et al. (2022) is essentially the scan itself, it provides no information on whether Ghana has implemented the recommendations. Still, given what I assume is lagging preparation across most of Africa, the horizon scan might be useful in encouraging countries to set priorities and take some action.
Cyprus
The second case study of applying horizon scanning is more encouraging. Scientists on Cyprus tried to assess the efficacy of their own horizon scanning exercise. I applaud their decision to do so. The horizon scan itself might have been undertaken on their own initiative? Or it might have been taken on in response to European Union regulations, which oblige Member States to enact measures to prevent or manage introduction and spread of invasive species designated as of Union Concern. The Union also encourages development of national invasive species lists and provides a legal basis for emergency measures in response to a detection.
Scientists carried out two horizon scan workshops in 2017 and 2019. The two workshops evaluated 225 and 352 species, respectively, to predict which are most likely to arrive and the level of provable impact to Cyprus’ biodiversity, human health, and economy. In 2023, four to six years after the workshops, scientists evaluated the listed species to reveal the accuracy of the predictions and actions taken so far (Martinou et al. 2026).
During the period 2017 – 2023 there were 183 Martinou et al. (2026) found publications naming 183 non-native species not previously officially detected in Cyprus. (As I will discuss later, a significant number of these species had been present on the island in 2017 but knowledge of their presence did not reach the assessors.) Of the 183 newly reported species, 31 had been included on some list of invasive species (e.g., EPPO or European Union list of species “of Concern”) or predicted by the horizon scanning exercises to rank amongst the top 100 riskiest species.
Cyprus’ horizon scans highlighted the risk posed by 10 of these 26 species. Martinou et al. (2026) focused on seven of them as having been ranked as high risk to the nation’s BD, human-health or economy. They added an eighth species, a venomous marine fish.
A further 10 species that were detected in the country had received lower impact scores, so they had not been included on the high priority lists of the horizon scans.
One of the species allotted a lower impact score, Spodoptera frugiperda, is under eradication, although it is widely distributed on the island. This action might be in response to the species’ inclusion on the EPPO A2 list.
As I noted above, scientists learned that 17 of the species had been present in Cyprus before the scanning exercises were undertaken but since their presence was then unknown to the participants, they were assessed as if still had not been introduced. This points to the country’s non-native species checklists not being fully up to date at the time.
Nine plant species common in the plant trade were most certainly present on Cyprus before the horizon scans (2017), but there were no published reports of their escape from cultivation. Nevertheless, they might have already been present in the wild. It is also possible that at least some escaped since the scans. Always tricky; always depends on who looking where.
Actions upon detection of specific taxa Detection of the common myna (Acridotheres tristis) – a species widely recognized as invasive – occurred in January 2022, close to a port. Eradication measures were implemented by the wildlife agency. Martinou et al. (2026) believe the introduction was facilitated by shipping. They think there is an extremely high risk of repeated introductions of mynas.
Aedes aegypti; photo by James Gathany via Flickr
Two mosquitoes were detected in 2022. A pilot project to eradicate The yellow fever mosquito, Aedes aegypti, was begun in 2023. There is no information about its success. The Asian tiger mosquito, Aedes albopictus, has been documented by citizen scientists as spreading rapidly in the suburbs of Limassol and Nicosia. To date the proposed interventions have been unsuccessful, possibly due to focusing on public land while the mosquitoes can also breed on private properties. Detection of the little fire ant Wasmannia auropunctata (in 2022) was not surprising since it had already invaded other regions of the Mediterranean. Martinou et al. (2026) believe the introduction was probably facilitated by the plant trade. The scientists note that ant management and eradication efforts are both challenging and costly, but do not report whether any has been initiated. Detection of several marine invasive species was reported, some by citizens, e.g., divers or fishermen. Among the 17 species determined to have been present on the island since before 2017 were some fairly conspicuous vertebrates: brown rat (Rattus norvegicus), raccoon Procyon lotor, two tortoise species, house crow (Corvus splendens) ruddy duck (Oxyura jamaicensis). Also two more ant species, Solenopsis geminata and Trichomyrmex destructor. There were also several non-native plant species, including the notorious seaweed Caulerpa taxifolia.
Value of the Horizon Scan I am surprised that Martinou et al. (2026) do not explore why so many detections were published in 2022 since they assert that horizon scanning helped raise awareness amongst the authorities, scientists and the public. They do note that this awareness led, in some cases, to a rapid response by the competent authorities. Martinou et al. (2026) assert further that the exercise facilitated communication between invasive species experts, policy makers and society, encouraged active engagement and raised awareness regarding the importance of early warning, rapid response, and management of IAS. They therefore propose that the horizon scanning process for the island of Cyprus be repeated regularly – every five to 10 years – since new introductions continue. These efforts should include development pathway management plans and contingency planning that would be shared with local authorities and stakeholders.
Martinou et al. (2026) note two detections that have not, apparently, resulted in establishment. A dead specimen of brown marmorated stink bug (Halyomorpha halys) was reported in luggage in May 2022, the result of ‘Bug Alert Cyprus’ awareness campaign. The Colorado potato beetle (Leptinotarsa decemlineata) was detected in 2010 by Department of Agriculture inspectors in a consignment of potatoes. The agency ordered immediate destruction. Imports of potatoes are subject to special phytosanitary requirements for protected zones. It is not clear that this measure was implemented by Cyprus or is a European Union decree.
brown marmorated stinkbug; courtesy of Oregon Department of Agriculture
Martinou et al. (2026) are worried that no introductions have been reported at border crossings across the ‘Green Line’ [the United Nations-controlled buffer zone between Greek and Turkish portions of the island]. They call for enhanced cross-community collaboration and improved information and data sharing for border control staff and customs officers about invasive species. They suggest that border order inspections and pathway monitoring could be supported by local experts offering identification services for a variety of taxa. They suggest that the horticultural industry is a major pathway for the introduction of plants and insects such as ants.
Martinou et al. (2026) also advocate efforts to improve communication among the various institutions and authorities that discover bioinvasions and are responsible for taking action. While researchers + experts from government departments involved in the horizon scans are informed, the findings of the horizon scanning needs to be provided to e.g., customs officers, fishers, ship crews, pet shop owners, and school teachers. Much of this information might be exchanged through informal networks and through a growing body of web-based databases and other resources.
Early detection and rapid response depends increasingly on efforts by citizen scientists to report observations of IAS of concern. Martinou et al. (2026) note that six of the invasive species identified in the horizon scanning exercise were reported by citizen scientists. They express the hope that artificial intelligence and deep learning models could help identify species from photographs collected by citizen scientists on platforms such as iNaturalist. Such platforms also facilitate rapid dissemination of information to decision-makers who can take appropriate action. Martinou et al. (2026) also hope eDNA can help detect cryptic bionvaders, including freshwater or marine taxa.
As I blogged earlier, Mark Hoddle had endorsed several components of prevention programs: * Early research to identify natural enemy species that might “self-introduce” along with the invading host. * Collaborating with non-U.S. scientists to identify and mitigate invasion bridgeheads. * Sentinel plantings. These plantings can also support research on natural enemies of key pests. [A year ago, Eliana Torres Bedoya of Ohio State alerted participants in the annual USDA research forum on invasive species that fungi, including potential pathogens, were isolated from asymptomatic plants; Detection of the full range of fungal pathogens requires that samples must be collected throughout the growing season; microbes present differ. Need to expand surveillance beyond symptomatic plants – at both sentinel gardens and plant health border inspection stations. *Integrating online platforms, networks, professional meetings, and incursion monitoring programs into “horizon scans” for potential invasive species. He mentions specifically PestLens, (https://pestlens.info/); 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.
That blog also cites Weber et al.’s support for sentinel plant nurseries because accidental plant and herbivore invasions often occur at the same points of entry.
At the 2026 meeting of the annual USDA Research Forum on Invasive Species, Ashley Schulz (Mississippi State) reported findings of study analyzing establishment of insects imported deliberately as biocontrol agents as clues to bioinvasion. She found that generalist phytophagous insects might be more likely to find a suitable host and survive after introduction. The “goldilocks” standard applies: the host must be sufficiently closely related to the insect’s native host to be recognizable but sufficiently distant so that it lacks defenses. Considering impact, phytophagous insects that feed on structures not easily restored – e.g., main stem or root, cause more damage than those that feed on easily replaced leaves. Entomopagous insect, on the other hand, must be able to find hosts that can hide or defend themselves. This means that highly specialized insects might be more likely to establish.
Kenis et al. 2022. Horizon scanning for prioritizing invasive alien species with potential to threaten agriculture and biodiversity in Ghana. Neobiota 71: 129-148 (2022) doi: 10.3897
Martinou, A.F., J. Demetirou, I. Angelidou, N. Kassinis, A. Melifronidou, J.M. Peyton, H.E. Roy, A.N.G. Kirschel. 2026. Multiple introductiions of invasive alien species on a Mediterranean Island predicted by horizon scanning. Biological Invasions (2026) 28:41 https://doi.org/10.1007/s10530-025-03729-8
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/
pines in a plantation in Argentina killed by Sirex noctilio; photo by J. Villacide
A decade ago, Payn et al. (2015) compiled studies from around the globe to evaluate threats to widespread tree plantations. At that time, they said climate change posed the greatest threat to plantation forestry globally, in the forms of storm and flood damage and simultaneous warming and drying trends with extreme temperatures.
Still, the authors warned that forest health would be an increasingly important constraint to plantation productivity. They were optimistic, however, that modern breeding and other technologies could offset losses.
What is the current situation? The countries that depend on these plantations for fiber production are not demanding that leaders of the international phytosanitary structure build a more effective system to protect their investments. Instead, individual scientists struggle to better understand threats. Mostly, they propose expanded research.
Economic Importance of these Species
Eucalypts
“Eucalypts” comprises three genera in the family Myrtaceae: Angophora, Corymbia and Eucalyptus. These include more than 700 tree species native primarily to Australia. A few species are native to Indonesia, New Guinea and the Philippines (Paine et al. 2011; Crous et al. 2019). Some of these species have been extensively planted outside their native ranges for more than 100 years. These plantations have expanded rapidly in recent decades, especially in Southeast Asia and the Southern Hemisphere (Crous et al. 2019). Eucalypts are now the most widely planted hardwood timber in the world (Paine et al. 2011).
Eucalypt plantation in Brazil; photo by Jonathan Wilken via Wikimedia
Eucalypts’ popularity has been driven chiefly by their rapid growth; short rotation times including through coppicing; and adaptability to a very wide variety of sites and climatic conditions (Paine et al. 2011; Crous et al. 2019). Also, these trees are an important source of the short-fiber pulp required for production of high-quality paper used in modern office copiers and printers (Paine et al. 2011). Plantations are increasing even in Australia, where harvesting of native forests is increasingly being restricted (Paine et al. 2011).
Pines
Pines – a genus restricted naturally to the Northern Hemisphere – is second in global popularity. South America hosts 4.6 million hectares of pine plantations (Lantschner and Villacide 2025). South America is more dependent on forestry plantations for wood production than any other region. In 2012, 88% of its industrial roundwood was produced by non-native plantations. This far exceeded the global proportion of approximately 19%.
These intensively managed plantations have enabled Brazil and Chile to become “planted forest powerhouses.” Uruguay and, more slowly, Argentina are following the same path (Payn et al. 2015).
Documentation of the Damage
Euclaypts
The highly diverse eucalypts host an even greater diversity of fungi. As of 30 years ago, scientists were aware of more than 500 species of just one type, the leaf-infecting fungi. Additional fungi are associated with seeds, capsules, twigs, branches, and stems. Little is known about the vast majority of these fungi. Even species considered causal agents of important diseases have not yet been confirmed using Koch’s Postulates. Areas of origin for most is also unknown (Crous et al. 2019).
Crous et al. (2019) compiled information on 110 genera of fungi found on eucalypt foliage. Some genera include well-recognized primary pathogens. They name Austropuccinia and Calonectria, Coniella, Elsinoe, Pseudocercospora, Quambalaria and Teratosphaeria. Other genera are thought to include species that are opportunists that develop on stressed or dying tissues. Many other leaf fungi are putative pathogens, but unstudied. Additional fungi cause vascular wilts (e.g. Ceratocystidaceae), stem canker diseases (Cryphonectriaceae, Botryosphaeriaceae) and root diseases (e.g. Armillaria, Ganoderma) of eucalypts.
Crous et al. (2019) state that the rust Austropuccinia psidii is one of the most damaging of the foliage fungal pathogens. They consider it to be a greater threat to eucalypt plantations outside the trees’ native ranges. (The Myrtaceous species in Australia most damaged by A. psidii are in other genera.)
Two families of leaf fungi – Mycosphaerellaceae and Teratosphaeriaceae – include species that cause serious diseases. Pérez, et al. report a study in plantation in Uruguay that detected six new species. They also discovered new hosts for some known species. (Such initial detections of new fungal species in out-of-native-range plantations is a usual occurrence.)
Over the 100-year history of planting eucalyptus outside Australasia, dozens of leaf pathogens have been transported to novel regions. Crous et al. 2019 report the wide geographic breadth of many of these introductions. For example, Mycosphaerellaheimii is crippling plantation forestry in five global regions – South America (Brazil and Venezuela); Asia (Indonesia and Thailand); Africa (Madagascar), Europe (Portugal); and in its presumably native Australia. A second species, M. marksii, has a similarly wide introduced range: Portugal, China and Indonesia, South Africa, Ethiopia, and Uruguay. Pérez et al. calls Mycosphaerella leaf diseases one of the most important impediments to Eucalyptus plantation forestry in Uruguay.
Although Crous et al. do not provide dates of detection, it appears that many of these leaf pathogens were introduced outside Australasia before the mid-990s, when the World Trade Organization (WTO) and International Plant Protection Convention (IPPC) came into force. Together, these agreements govern what actions phytosanitary officials may take to curtail international movement of plant pests. (To see my critique of the WTO/IPPC system, visit here.) The possible exception might be Kirramyces gauchensis, a well-known pathogen of Eucalyptus grandis in South America (Argentina and Uruguay), Hawai`i, and Africa (Uganda and Ethiopia) (Pérez, et al. 2009). Crous et al. (2019) expect another genus, Quambalaria species, to become a threat to eucalypt plantation forestry globally in the future.
Phoracantha semipunctata; photo by Umo Schmidt via Flickr
Arthropod pests have also been spread to many Eucalyptus-growing regions in North and South America, Europe and Africa since the 1980s. Some species have colonized virtually all eucalypt-growing regions, e.g.,Phoracantha semipunctata. Some have – so far – appeared on only one continent.
In an effort to determine how many of these introductions have occurred after adoption of the WTO/ IPPC system, I Googled the species named by Paine et al. (2011). I used the year 2000 as the cutoff date, to allow for detection lag. Among the insect species that fit this criterion are a lerp psyllid, a leaf beetle, and two gall wasps detected in North America; a true bug, two galling insects, and a leaf beetle in South Africa; and three psyllids in Europe.
Asia stands out as having very few introduced Australian insects plaguing eucalyptus plantations. Only one insect of Australian origin is causing significant damage in this region, Leptocybe invasa. It was detected after 2000, so it might have been introduced under the WTO/IPPC regime. Many widespread species, e.g., Phoracantha semipunctata, are notably absent. Instead, large numbers of endemic insects use these trees. This contrasts with the situation in the Southern Hemisphere, where few of the numerous native insects have shifted onto eucalypts.
New Zealand has detected only two new species of Australian origin since 1999 — two psyllids. This is despite the two nations’ proximity, the large volume of trade that passes between them, and the likelihood that at least some small sap-suckers might be introduced via aerial dispersal. New Zealand is famous for its strict phytosanitary (and sanitary) policies and programs.
Eucalyptus plantation in Kwa-Zulu, South Africa
Plantations’ vulnerability has been increased by expanding reliance on clonal, artificially-induced hybridization. Developers’ goals – and initial results – are enhanced adaptation to specific environments, desired fiber characteristics, and hybrid vigor. However, these vast areas planted in genetically identical trees are sitting ducks. An insect or pathogen that overcomes the host’s defenses can spread rapidly across the entire planting.
These hybrids also can act as “bridges,” facilitating spread of fungi to formerly resistant host species. Crous et al. (2019) fear that this process will undermine resistance in Eucalyptus pellita to the pathogen Teratosphaeria destructans. Plantations in Southeast Asia and South Africa now comprise hybrids between this resistant species and the highly susceptible Eucalyptus brassiana.
Pines
As with the eucalypts, the intensively managed pine plantations are comprised of fast-growing exotic species, all at the same developmental stage, and with minimal genetic diversity, planted to maximize wood production. These practices again lead to biological homogenization and reduced resilience to pests (Villacide and Fuetealba, 2025)
In the Southern Hemisphere, Sirex noctilio has become the most significant economic pest of Pinus species. These attacks can cause up to 80% mortality. Several other Sirex species have also been introduced, all apparently in the 1980s or earlier (Wilcken et al., 2025) – before adoption of the current international phytosanitary regime. However, in 2023, a new species, Sirexobesus, was discovered causing tree mortality in pine plantations in southeastern Brazil. This species is indigenous to the United States and Mexico.
Stazione et al. (2026) discuss two other non-native pine pests that established recently in South America.
Analysis of mitochondrial DNA of Orthotomicus erosus points to a western Eurasian lineage. The low genetic diversity of the introduced population in Argentina and Uruguay suggests a single or limited introduction event followed by regional spread.
The source region of Cyrtogenius luteus is more difficult to determine but is probably somewhere in China. The higher haplotype diversity might reflect multiple introductions. Again, shared haplotypes between Argentina and Uruguay countries indicates a contiguous regional spread, possibly driven by extensive pine plantations & intra-regional trade (Stazione et al. 2026)
Policy Aspects
Some scientists express concern about the failure of international phytosanitary measures. But are their countries speaking up in regulatory bodies, especially the International Plant Protection Convention?
Studies by Crous et al. (2019) and Pérez et al. (2009) clearly show that pathogens from Australia continue to be transported to regions where eucalypt plantations are grown. This happens despite most of the movement of genetic material being in the form of seeds – which should be less likely to transport pathogens than trade in plants. Pérez et al. (2009) explicitly raise concerns about the effectiveness of current quarantine procedures. Crous et al. (2019) state that quarantinescontinue to fail in many parts of the world.
Burgess and Wingfield (2017) list pathogens that have spread widely since the beginning of the 21st Century: Austropuccinia psidii, Calonectria (= Cylindrocladium) eudonaviculata (=Cylindrocladium buxicola), Ceratocystis lukuohia and C. huliohia introduced to Hawai`i. I add that insect-vectored diseases such as Euwallacea species carryingFusarium fungi have also experienced a burst of introductions around the globe since 2000.
Crous et al. (2019) attribute this failure partially to the enormous difficulty of applying effective quarantine to the huge volumes of planting material traded globally. Another factor is undoubtedly the poor understanding of microbial species, their pathogenicity, hosts, pathways of spread, even taxonomies. Some genera cannot be grown in culture.
Furthermore, pathogens’ impacts vary, possibly due to environmental conditions of the location or differing virulence on different hosts. Finally, with so many fungi and so little knowledge, it is difficult to separate true disease agents from multiple secondary infections.
Crous et al. (2019) express the hope that increased recognition of the importance of pathogens, along with improved detection and identification tools, will clarify patterns of spread. But is that enough? Are there no policy changes needed?
Crous et al. (2019) also warn us about additional pathways for spreading pathogens. Some potential pathogens of eucalypts have been moved on plants of other, related genera. Furthermore, Botryosphaeriaceae have been detected in the skins of mangoes (Mangifera indica) and avocados (Persea americana). Both of these fruits move globally in large volumes.
mangoes; photo by Obsidian Soul via Wikimedia
Regarding insects, Paine et al. (2011) focus on a concern that species native to the plantation countries and generalist herbivores from other parts of world will invade Australia and threaten eualypts in their native ranges. See other blog They also call for research to understand international pathways, develop detection methods, improve understanding of patterns of host suitability, susceptibility, and selection.
Villacide and Fuetealba (2025) note that while the introductory pathway for that new species, Sirex obesus, has not been determined, they suspect it might have been wood packaging materials. Villacide and another colleague (Lantschner and Villacide 2025) suggest an initial step would be for Argentina and other countries in the region to negotiate with Brazil to adopt more protective protocols governing trade in wood products, including wood packaging.
I have repeatedly advocated strengthening regulation of wood packaging. Such measures could improve protection of Earth’s forests from pests that use a well-documented high-risk introductory pathway. To see my arguments and underlying data, scoll down below the “archives” to “Categories” and click on “wood packaging”.
SOURCES
Burgess, T.I. and M.J. Wingfield. 2017. Pathogens on the Move: A 100-Year Global Experiment with Planted Eucalypts. Bioscience. Volume 67, Issue 1, January 2017. https://doi.org/10.1093/biosci/biw146
Crous, P.W., M.J. Wingfield, R. Cheewangkoon, A.J. Carnegie, T.I. Burgess, B.A. Summerell, J. Edwards, P.W.J. Taylor, and J.Z. Groenewald. 2019. Folia pathogens o eucalypts. Studies in Mycology 94:125-298 (2019).
Lantschner, V. and J. Villacide. 2025. Invasion Potential of the Recently Established Woodwasp Sirex obesus. Neotropical Entomology. (2025) 54:117 https://doi.org/10.1007/s13744-025-01347-6
Paine, T.D., M.J. Steinbauer, and S.A. Lawson. 2011. Native and Exotic Pests of Eucalyptus: A Worldwide Perspective. Annu. Rev. Entomol. 2011. 56:181-201
Payn, T., J-M. Carnus, P. Freer-Smith, M. Kimberley, W. Kollert, S. Liu, C. Orazio, L. Rodriguez, L. Neves Silva, M.J. Wingfield. 2015. Changes in planted forests and future global implications. Forest Ecology and Management 352 (2015)
Pérez,, C.A., M.J. Wingfield, N.A. Altier, and R.A. Blanchette. 2009. Mycosphaerellaceae and Teratosphaeriaceae associated with Eucalyptus leaf diseases and stem cankers in Uruguay For. Path. 39 (2009) 349–360 doi: 10.1111/j.1439-0329.2009.00598.x www3.interscience.wiley.com
Stazione, L., Soliani, C., Cognato, A. et al. Reconstructing the invasion history of the bark beetles Orthotomicus erosus & Cyrtogenius luteus (Coleoptera, Curculionidae, Scolytinae) in South America. Biol Invasions28, 49 (2026). https://doi.org/10.1007/s10530-026-03779-6
Villacide, J. and A. Fuetealba. 2025. Pests in plantations: Challenging traditional productive paradigms in the Southern Cone of America. Forest Ecology and Management 597 (2025) 123127
Wilcken, C.F., T.A. da Mota, C.H. de Oliveir, V.R. de Carvalho, L.A. Benso, J.A. Gabia, S.R.S. Wilcken, E.L. Furtado, N.M. Schiff, M.B. de Camargo, M.F. Ribeiro. 2025. Sirex obesus (Hymenoptera: Siricidae) as invasive pest in pine plantations in Brazil. Scientific Reports. 2025. 15:22522 https://doi.org/10.1038/541598-025-06418-7
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
Blepharocalyx salicifolius – a tree in the Myrtaceae native to South America on which found symptoms similar to those caused by Mycosphaerellaceae or Teratosphaeriaceae; photo by Pablo di Flores via Wikimedia
Pests that have followed their hosts to plantations outside the trees’ native ranges might threaten native plants in their new, introduced ranges. That is, the countries where the plantations are located.
Eucalypts
Eucalypts are now the most widely planted hardwood timber taxon in the world (Paine et al 2011). The 700 – 800 species in the three genera considered “eucalypts” (Angophora, Corymbia, and Eucalyptus) host a highly diverse fungal community — more than 500 species have been identified of just one type, leaf-infecting fungi (Crous et al. 2019).
As I described in a related blog, link dozens of leaf pathogens have been transported to countries hosting eucalypt plantations. Among them, two families – Mycosphaerellaceae and Teratosphaeriaceae – are prominent in both numbers of introductions and potential to cause serious diseases.
Nunez Chapa
Pérez et al. (2009) reported that a relatively large number of Mycosphaerellaceae and Teratosphaeriaceae are found on Eucalyptusin Uruguay. The authors cite one troubling case of host shifting: Mycosphaerella lateralis is causing leaf disease on a Musa cultivar (banana!) which is not in the Myrtaceae.
A follow-up study by the same authors (Pérez et al. 2013) surveyed several native forests, paying special attention to those located close to Eucalyptus plantations. They found five species belonging to the Mycosphaerellaceae and Teratosphaeriaceae clades on native Myrtaceous trees; three of these had previously been reported on Eucalyptus in Uruguay. Those occurring on both Eucalyptus and native Myrtaceae included Pallidocercospora heimii, Pseudocercospora norchiensis, and Teratosphaeria aurantia. A fourth species, Mycosphaerella yunnanensis, not previously recorded in Uruguay, was found on the leaves of two native Myrtaceous hosts. Pérez et al. (2013) believe circumstances indicate that all these fungi have been introduced. They warn that these apparent jumps to new hosts have the potential to result in serious disease problems and they should be carefully monitored. This finding is more than a decade old; I have not found a more recent report.
On the global level, Pérez et al. (2013) report, at least 23 species of Mycosphaerellaceae and Teratosphaeriaceae have been found on non-Eucalyptus species in the Myrtaceae. These hosts are in several plant orders, including Myrtales, Proteales, Fabaes and Apiales. The authors express “considerable concern” about the apparent ease of movement in these fungi between hosts. I have been unable to learn more details about these introductions.
Arthropod pests have also been spread to many Eucalyptus-growing regions in North and South America, Europe, and Africa since the 1980s – but not to Asia or New Zealand (Paine et al. 2011). blog
Myrrhinium atropurpureum – another South American plant in the Myrtaceae on which symptoms found; photo by Prof. Atilio L, Botanical Garden of Uruguay
Pines
Pines – a genus restricted naturally to the Northern Hemisphere – is second in popularity for intensively managed plantations. South America has 4.6 million hectares of pine plantations (Lantschner and Villacide 2025). Most are in Brazil, Chile, Uruguay, and Argentina (Payn et al. 2015).
Cinara cupressi; photo by LBM via Wikimedia
As I reported in an earlier blog, some of the insect pests that followed pines to South America have entered native forests. The most alarming of which I am aware is the aphid Cinara cupressi. It attacks the native conifer Austrocedrus chilensis, which forms pure and mixed stands with southern hemisphere beech (Nothofagus spp.) across approximately 160,000 hectares (Villacide and Fuetealba 2025). Cordilleran cypress is also under attack by the oomycete Phytophthora austrocedri, an oomycete of unknown origin.
Some scientists express concern about phytosanitary measures … but are their countries speaking up in meetings of the International Plant Protection Convention?
Studies by Crous et al. and Pérez et al. clearly show that pathogens from Australia continue to be transported to regions where eucalypt plantations are grown – despite the fact that most of the movement of tree genetic material is in the form of seeds – which should be less likely to transport pathogens than trade in plants. Pérez et al. (2009) explicitly raise concerns about the effectiveness of current quarantine procedures. Crous et al. (2019) state that the quarantinescontinue to fail in many parts of the world.
See my critique of the international phytosanitary system under the IPPC by visiting the Fading Forest II report (see link below) and reading other blogs under the categories “invasive species policy” and “plants as vectors of pests”.
SOURCES
Crous, P.W., M.J. Wingfield, R. Cheewangkoon, A.J. Carnegie, T.I. Burgess, B.A. Summerell, J. Edwards, P.W.J. Taylor, and J.Z. Groenewald. 2019. Foliar pathogens of eucalypts. Studies in Mycology 94:125-298 (2019)
Lantschner, V. and J. Villacide. 2025. Invasion Potential of the Recently Established Woodwasp Sirex obesus. Neotropical Entomology. (2025) 54:117 https://doi.org/10.1007/s13744-025-01347-6
Paine, T.D., M.J. Steinbauer, and S.A. Lawson. 2011. Native & Exotic Pests of Eucalyptus: A Worldwide Perspective. Annu. Rev. Entomol. 2011. 56:181-201
Payn, T., J-M. Carnus, P. Freer-Smith, M. Kimberley, W. Kollert, S. Liu, C. Orazio, L. Rodriguez, L. Neves Silva, M.J. Wingfield. 2015. Changes in planted forests & future global implications. Forest Ecology and Management 352 (2015)
Pérez, C.A., M.J. Wingfield, N. Altier, and R.A. Blanchette. 2013. Species of Mycosphaerellaceae and Teratosphaeriaceae on native Myrtaceae in Uruguay: evidence of fungal host jumps. Fungal Biology Volume 117, Issue 2, February 2013.
Villacide, J. and A. Fuetealba. 2025. Pests in plantations: Challenging traditional productive paradigms in the Southern Cone of America. Forest Ecology and Management 597 (2025) 123127
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
Chilecomadia valdiviana – one of the South American moths that attack Eucalyptus; photo by Natural History Museum of London via Wikimedia
Fifteen years ago, Paine, Steinbauer, and Lawson (2011) worried that insects in South America, Africa, Asia, and Europe that adapt to attacking Eucayptus trees planted there might be introduced to Australasia and threaten the genus in its native range. Their analysis applies to species in all three genera considered to be “eucalypts” — Angophora, Corymbia and Eucalyptus.
Some insects native to those continents have made this host shift already. Paine, Steinbauer, and Lawson reported that such host switching was especially prevalent among lepidopterans. They name several from Brazil, the Chilean cossid moth, Chilecomadia valdiviana, and southern African Coryphodema tristis. In their view, Brazilian eucalypt plantations’ proximity to native vegetation facilitates host-switching. Still, at that time they thought that there were no established pathways for introduction of the South American moths to Australia.
Host-switching is exceptionally common in Asia. Paine, Steinbauer, and Lawson (2011) thought the risk was greatest from insects on native eucalypts in near-neighbors Papua New Guinea, Timor, and The Philippines. An earlier risk assessment evaluating 10 insect species from the region concluded that most are polyphagous and probably switched to eucalypts. Two woodborers – Agrilus opulentus and A. sexsignatus –seem to have coevolved with Eucalyptus deglupta in New Guinea and The Philippines.
According to the same authors, most of the insects that have switched hosts are either polyphagous or normally feed on other myrtaceous species native to these regions. Thus, the Brazilian moth Thyrinteina arnobia feeds on Psidium guajava and several other Myrtaceae. Sarsina violascens is also a pest of Psidium species, as well as species in the Asteraceae, and Oleaceae. And the foliar rust Austropuccinia psidii was first described from Psidium guajava in Brazil and boasts a wide host range in the Myrtaceae in South America. It has been introduced to many regions with plants in the Myrtaceae, notably Hawai`i, Australia, South Africa, New Caledonia, and New Zealand. At least 15 Myrtaceae species in Australia are threatened with extinction.
Still, few non-native insects were damaging eucalypts in Australia’s native forests or plantations as of 2011. Those few are highly polyphagous. Several, if not most, were introduced in the first half of the 20th Century.
Why so few? Paine, Steinbauer, and Lawson (2011) suggest three possibilities: (a) Australia’s diverse endemic insects already occupy most niches, so they exclude new, foreign competitors; (b) most introduced insects were not previously exposed to Myrtaceae in their native range; and (c) Australia has strong quarantine procedures aiming to limit introductions of non-native herbivores.
The fact that none of the introduced insects has adapted to feed significantly on mature eucalypts’ above-ground tissues seems to me to point to protection provided by the adult trees’ phytochemicals and leaf structure. Paine, Steinbauer, and Lawson (2011) discuss some aspects of leaf structure and wax coatings.
As to Australia’s quarantine procedures, as I reported before, the country has been much less proactive regarding plant pests and diseases that threaten tree species rather than agricultural crops. Significant new programs were established only after 2000, when Plant Health Australia (PHA) was incorporated. The PHA is supposed to facilitate preparedness and response arrangements between governments and industry for plant pests (once an alien pest has become established, management becomes responsibility of the land manager). In 2005, federal, state, and territorial governments and plant industry bodies signed a legally-binding agreement — the Emergency Plant Pest Response Deed (EPPRD). As of 2022, 38 were engaged. It sets up a process to implement management and funding of agreed responses to the detection of exotic plant pests – including cost-sharing and owner reimbursement.
Still, studies documented significant gaps in post-border forest biosecurity systems and the country’s response to the anticipated introduction of the foliar rust Austropuccinia psidii was disappointing. This prompted yet another initiative: development of the National Forest Biosecurity Surveillance Strategy (NFBSS) in 2018. The strategy was; accompanied by an Implementation Plan and appointment of a National Forest Biosecurity Coordinator. The forest sector fund a significant proportion of the proposed activities for the first five years. Still, Drs. Carnegie and Nahrung thought that in-country forest pest surveillance was still too fragmented.
Paine, Steinbauer, and Lawson (2011) consider the Asian spongy mothsLymantria dispar and Orgyia thyellina to pose serious threats. Five eucalypt species were assessed to be at risk of attack as are two preferred host oaks in Europe, Quercus pubescens and Q. robur. They note high volumes of imports from East Asia of containers, vehicles, and machinery, which are known to transport spongy moth egg-masses. It is not known whether the numerous natural enemies of Australia’s diverse lymantriid fauna [which includes four in the genus Lymantria] might provide some protection. These experts also worried that the highly polyphagous Asian longhorned beetle (Anoplophora glabripennis) might arrive in Australia. Eucalypts are not recognized as hosts.
Australia has adopted an enhanced surveillance program for ships arriving from Asian and European Lymantria ranges during female flight periods. Described here. Nahrung and Carnegie (2021) though that the high priority assigned to Lepidoptera exceeded the actual risk; only two non-native species had established in Australia over 130 years.
Paine, Steinbauer, and Lawson (2011) suggest several research topics aimed at reducing the risk to eucalypts in Australia. These include interactions between these insects and mechanisms by which insects adapt to new hosts; host chemistry and resistance mechanisms), chemical ecology (including host selection), population and community dynamics, including possible biocontrol agents, and pathway and risk analysis.
On the other hand, Carnegie and Nahrung (2019) called for developing more effective methods of detection, especially of Hemiptera and pathogens. They also promoted national standardization of data collection. Finally, they advocated inclusion of technical experts from state governments, research organizations and industry in developing and implementing responses to pest incursions. They noted that surveillance and management programs must expect and be prepared to respond to introductions of unanticipated species. They had found that 85% of the pests detected over the last 20 years—and 75% of subsequently mid-to high-impact species established—were not on high-priority pest list.
SOURCES
Carnegie A.J. and H.F. Nahrung. 2019. Post-Border Forest Biosecurity in AU: Response to Recent Exotic Detections, Current Surveillance and Ongoing Needs. Forests 2019, 10, 336; doi:10.3390/f10040336 www.mdpi.com/journal/forests
Nahrung, H.F. and A.J. Carnegie. 2021. Border interceptions of forest insects established in Australia: intercepted invaders travel early and often. NeoBiota 64: 69–86. https://doi.org/10.3897/neobiota.64.60424
Paine, T.D., M.J. Steinbauer, and S.A. Lawson. 2011. Native & Exotic Pests of Eucalyptus: A Worldwide Perspective. Annu. Rev. Entomol. 2011. 56:181-201
Native & Exotic Pests of Eucalyptus: A Worldwide Perspective
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
