Category: international trade

Australia Builds Capacity to Address Forest Pests

Australian Eucalypts; photo by John Turnbull via Flickr

I congratulate Australian scientists for bringing about substantial improvements of their country’s biosecurity program for forest pests. While it is too early to know how effective the changes will be in preventing new introductions, they are promising. What can we Americans learn from the Australian efforts? [I have previously praised South Africa’s efforts – there is much to learn there, too.]

Australia has a reputation of being very active in managing the invasive species threat. However, until recently biosecurity programs targetting forest pests were minimal and ad hoc. Scientists spent 30 years trying to close those gaps (Carnegie et al. 2022). Their efforts included publishing several reports or publications (listed at the end of the blog) and an international webinar on myrtle rust. Scientists are hopeful that the new early detection program (described below) will greatly enhance forest protection. However, thorough pest risk assessments are still not routinely conducted for forest pests. (Nahrung and Carnegie 2022).

The native flora of Australia is unique. That uniqueness has provided protection because fewer of the non-native insects and pathogens familiar to us in the Northern Hemisphere have found suitable hosts (Nahrung and Carnegie 2020). Also – I would argue – the uniqueness of this flora imposes a special responsibility to protect it from threats that do arise.

Only 17% of Australia’s landmass is covered by forests. Australia is large, however; consequently, these forests cover 134 million hectares (Nahrung and Carnegie 2020). This is the 7th largest forest estate in the world (Carnegie et al. 2022).

Australia’s forests are dominated by eucalypts (Eucalyptus, Corymbia and Angophora). These cover 101 million ha; or 75% of the forest). Acacia (11 million ha; 8%); and Melaleuca (6 million ha) are also significant. The forest also includes one million ha of plantations dominated by Pinus species native to North America (Carnegie et al. 2022). A wide range of native and exotic genera have been planted as amenity trees in urban and peri-urban areas, including pines, sycamores, poplars, oaks, and elms (Carnegie et al. 2022). These urban trees are highly valued for their ecosystem services as well as social, cultural, and property values (Nahrung and Carnegie 2020). Of course, these exotic trees can support establishment and spread of the forest pest species familiar to us in the Northern Hemisphere. On the positive side, they can also be used as sentinel plantings for early detection of non-native species (Carnegie et al. 2022 and Nahrung and Carnegie 2020).

Despite Australia’s geographic isolation, its unique native flora, and what is widely considered to be one of the world’s most robust biosecurity system, at least 260 non-native arthropods and pathogens of forests have established in Australia since 1885 (Nahrung and Carnegie 2020). [(This number is about half the number of non-native forest insects and pathogens that have established in the United States over a period just 25 years longer (Aukema et al. 2010).] As I noted, forest scientists have cited these introductions as a reason to strengthen Australia’s biosecurity system specifically as it applies to forest pests.

What steps have been taken to address this onslaught? For which pests? With what impacts? What gaps have been identified?

Which Pests?

Nahrung and Carnegie (2020) compiled the first comprehensive database of tree and forest pests established in Australia. The 260 species of non-native forest insect pests and pathogens comprise 143 arthropods, 117 pathogens. Nineteen of them (17 insects and 2 fungal species) had been detected before 1900. These species have accumulated at an overall rate of 1.9 species per year; the rate of accumulation after 1955 is slightly higher than during the earlier period, but it has not grown at the exponential rate of import volumes.

While over the entire period insects and pathogens were detected at an almost equal rate (insects at 1.1/year; pathogens at 0.9/year), this disguises an interesting disparity: half of the arthropods were detected before 1940; half of the pathogens after 1960 (Nahrung and Carnegie (2020). By 2022, Nahrung and Carnegie (2022) said that, on average, one new forest insect is introduced each year. Some of these recently detected organisms have probably been established for years. More robust surveillance has  just detected them recently. I have blogged often about an apparent explosion of pathogens being transported globally in recent decades.

In a more recent article (Nahrung and Carnegie, 2022), gave 135 as the number of non-native forest insect pests. The authors don’t explain why this differs from the 143 arthropods listed before.

damage to pine plantations caused by Sirex noctilio; photo courtesy of Helen Nahrung

Eighty-seven percent of the established alien arthropods are associated with non-native hosts (e.g., Pinus, Platanus, Populus, Quercus, Ulmus) (Carnegie et al. 2022). Some of these have escaped eradication attempts and caused financial impact to commercial plantations (e.g., sirex wood wasp, Sirex noctilio) and amenity forests (e.g., elm leaf beetle, Xanthogaleruca luteola) (Carnegie and Nahrung 2019).

About 40% of the alien arthropods were largely cosmopolitan at the time of their introduction in Australia (Carnegie et al. 2022). Only six insects and six fungal species are not recorded as invasive elsewhere (Nahrung and Carnegie 2020). Of the species not yet established, 91% of interceptions from 2003 to- 2016 were known to be invasive elsewhere. There is strong evidence of the bridgehead effect: 95% of interceptions of three species were from their invaded range (Nahrung and Carnegie 2022). These included most of the insects detected in shipments from North America, Europe and New Zealand. These ubiquitous “superinvaders” have been circulating in trade for decades and continue to be intercepted at Australia’s borders. This situation suggests that higher interception rates of these species reflect their invasion success rather than predict it (Nahrung and Carnegie 2021).  

I find it alarming that most species detected in shipments from Africa, South America, and New Zealand were of species not even recorded as established in those regions (Nahrung and Carnegie 2021; Nahrung and Carnegie 2022).

Arhopalus ferus, a Eurasian pine insect often detected in wood from New Zealand; photo by Jon Sullivan – in New Zealand; via Flickr

Half of the alien forest pests established in Australia are highly polyphagous. This includes 73% of Asian-origin pests but only 15% of those from Europe (Nahrung and Carnegie 2021). Nahrung and Carnegie (2022) confirm that polyphagous species are more likely to be detected during border inspections.

PATHWAYS

As in North America and Europe, introductions of Hemiptera are overwhelmingly (98%) associated with fresh plant material (e.g. nursery stock, fruit, foliage). Coleoptera introductions are predominantly (64%) associated with wood (e.g. packaging, timber, furniture, and artefacts). Both pathways are subject to strict regulations by Australia (Nahrung and Carnegie 2021).

Eradication of High-Priority Pests

Eight-five percent of all new detections were not considered high-priority risks. Of the four that were, two had not previously been recognized as threats (Carnegie and Nahrung 2019). One high-priority pest – expected to pose a severe threat to at least some of Australia’s endemic plant species – is myrtle rust, Austropuccinia psidii. Despite this designation, when the rust appeared in Australia in 2010, the response was confused and ended in an early decision that eradication was impossible.  Myrtle rust has now spread along the continent’s east coast, with localized distribution in Victoria, Tasmania, the Northern Territory, and – in 2022, Western Australia.   `

Melaleuca quinquenervia forest; photo by Doug Beckers via Wikimedia

There have been significant impacts to native plant communities. Several reviews of the emergency response criticized the haste with which the initial decision was made to end eradication (Carnegie and Nahrung 2019). (A review of these impacts is here; unfortunately, it is behind a paywall.)

A second newly introduced species has been recognized as a significant threat, but only after its introduction to offshore islands. This is Erythina gall wasp Quadrastichus erythrinae (Carnegie and Nahrung 2019). DMF Although Australia is home to at least one native species in the Erythrina genus, E. vespertilio,, the gall wasp is not included on the environmental pest watch list.

Four of the recently detected species were considered to be high impact. Therefore eradication was attempted. Unfortunately, these attempts failed in three cases. The single success involved a pinewood nematode, Bursaphelenchus hunanesis. See Nahrung and Carnegie (2021) for a discussion of the reasons. This means three species recognized as high-impact pests have established in Australia over 15 years (Nahrung and Carnegie (2021). In fact, Australia’s record of successful forest pest eradications is only half the global average (Carnegie and Nahrung (2019).

Carnegie and Nahrung (2019) conclude that improving early detection strategies is key to increasing the likelihood of eradication. They discuss the strengths and weaknesses of various strategies. Non-officials (citizen scientists) reported 59% of the 260 forest pests detected (Carnegie and Nahrung 2019). Few alien pests have been detected by official surveillance (Carnegie et al 2022). However, managing citizen scientists’ reports involves a significant workload. Futhermore, surveillance by industry, while appreciated, is likely to detect only established species (Carnegie and Nahrung 2019).

Interception Frequency Is Not an Indicator of Likelihood of Establishment

Nahrung & Carnegie (2021) document that taxonomic groups already established in Australia are rarely detected at the border. Furthermore, only two species were intercepted before they were discovered to be established in Australia.

Indeed, 76% of species established in Australia were either never or rarely intercepted at the border. While more Hemiptera species are established in Australia, significantly more species of Coleoptera are intercepted at the border. Among beetles, the most-intercepted family is Bostrichid borers (powderpost beetles). Over the period 2003 – 2016, Bostrichid beetles made up 82% of interceptions in wood packaging and 44% in wood products (Nahrung and Carnegie 2022). This beetle family is not considered a quarantine concern by either Australian or American phytosanitary officials. I believe USDA APHIS does not even bother recording detections of powderpost beetles. Nahrung and Carnegie (2021) think the high proportion of Bostrichids might be partially explained by intense inspection of baggage, mail, and personal effects. While Australia actively instructs travelers not to bring in fruits and vegetables because of the pest risk, there are fewer warnings about risks associated with wood products. 

Nahrung & Carnegie (2021) concluded that interception frequencies did not provide a good overall indicator of likelihood of risk of contemporaneous establishment.

Do Programs Focus on the Right Species?

Although Hemiptera comprise about a third of recent detections and establishments, and four of eight established species are causing medium-to-high impact, no Hemiptera are currently listed as high priority forestry pests by Australian phytosanitary agencies (Nahrung & Carnegie (2021). On the other hand, Lepidoptera make up about a third of the high-priority species, yet only two have established in Australia over 130 years. Similarly, Cerambycidae are the most frequently intercepted forest pests and several are listed as high risk. But only three forest-related species have established (Nahrung and Carnegie 2020). (Note discussion of Bostrichidae above.).

Unlike the transcontinental exchanges under way in the Northern Hemisphere, none of the established beetles is from Asia; all are native to Europe. This is especially striking since interceptions from Asia-Pacific areas account for more than half of all interceptions Nahrung and Carnegie (2021).

Interestingly, 32 Australian Lepidopteran and eight Cerambycid species are considered pests in New Zealand. However, no forest pests native to New Zealand have established in Australia despite high levels of trade, geographic proximity, and the high number of shared exotic tree forest species (Nahrung and Carnegie 2020).

STRUCTURE OF PROGRAM

The structure of Australia’s plant biosecurity system is described in detail in Carnegie et al. (2022). These authors call the program “comprehensive” but to me it looks highly fragmented. The federal Department of Agriculture and Water Resources (DAWR,[recently renamed the Department of Agriculture, Fisheries, and Forestry, or DAFF) is responsible for pre-border (e.g., off-shore compliance) and border (e.g., import inspection) activities. The seven state governments, along with DAFF, are responsible for surveillance within the country, management of pest incursions, and regulation of pests. Once an alien pest has become established, its management becomes the responsibility of the land manager. In Australia, then, biosecurity is considered to be a responsibility shared between governments, industry and individuals.

Even this fragmented approach was developed more recently than one might expect given Australia’s reputation for having a stringent biosecurity system. Perhaps this reflects the earlier worldwide neglect of the Plant Kingdom? Carnegie and Nahrung (2019) describe recent improvements. Until the year 2000, Australia’s response to the detection of exotic plant pests was primarily case-by-case. In that year Plant Health Australia (PHA) was incorporated. Its purpose was to facilitate preparedness and response arrangements between governments and industry for plant pests. In 2005, the Emergency Plant Pest Response Deed (EPPRD) was created. It is a legally-binding agreement between the federal, state, and territorial governments and plant industry bodies. 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. A national response plan (PLANTPLAN) provides management guidelines and outlines procedures, roles and responsibilities for all parties. A national committee (Consultative Committee on Emergency Plant Pests (CCEPP) works with surveys to determine invaded areas (delimitation surveys) and other data to determine whether eradicating the pest is technically feasible and has higher economic benefits than costs..

Austropuccinia psidii on Melaleuca quinquenervia; photo by John Tann via Flickr

Even after creation of EPPRD in 2005, studies revealed significant gaps in Australia’s post-border forest biosecurity systems regarding forest pests (Carnegie et al. 2022; Carnegie and Nahrung 2019). These studies – and the disappointing response to the arrival of myrtle rust – led to development of the National Forest Biosecurity Surveillance Strategy (NFBSS) – published in 2018; accompanied by an Implementation Plan. A National Forest Biosecurity Coordinator was appointed.

The forest sector is funding a significant proportion of the proposed activities for the next five years; extension is probable. Drs. Carnegie and Nahrung are pleased that the national surveillance program has been established. It includes specific surveillance at high-risk sites and training of stakeholders who can be additional eyes on the ground. The Australian Forest Products Association has appointed a biosecurity manager (pers. comm.)

This mechanism is expected to ensure that current and future needs of the plant biosecurity system can be mutually agreed on, issues identified, and solutions found. Plant Health Australia’s independence and impartiality allow the company to put the interests of the plant biosecurity system first. It also supports a longer-term perspective (Carnegie et al. (2022). Leading natural resource management organizations are also engaged (Carnegie, pers. comm.).

Presumably the forest surveillance strategy (NFBSS) structure is intended to address the following problems (Carnegie and Nahrung 2019):

  • Alien forest pests are monitored offshore and at the border, but post-border surveillance is less structured and poorly resourced. Australia still lacks a surveillance strategy for environmental pests.
  • Several plant industries have developed their own biosecurity programs, co-funded by the government. These include the National Forest Biosecurity Surveillance Strategy (NFBSS).

Some pilot projects targetting high risk sites were initiated in the early 2000s. By 2019, only one surveillance program remained — trapping for Asian spongy (gypsy) moth.

  • The states of Victoria and New South Wales have set up sentinel site programs. Victoria’s uses local council tree databases. It is apparently focused on urban trees and is primarily pest-specific – e.g., Dutch elm disease. The New South Wales program monitors more than 1,500 sentinel trees and traps insects near ports. This program is funded by a single forest grower through 2022.  

Dr. Carnegie states: “With the start of the national forest biosecurity surveillance program in December 2022, the issues and gaps identified by Carnegie et al. 2022 are starting to be addressed. The program will conduct biosecurity surveillance specifically for forest pests and pathogens and be integrated with national and state biosecurity activities. While biosecurity in Australia is still agri-centric, a concerted and sustained effort from technical experts from the forest industry is changing this. And finally, the new Biosecurity Levy should ensure sustained funding for biosecurity surveillance.”

There is a separate National Environmental Biosecurity Response Agreement (NEBRA), adopted in 2012. It is intended to provide guidelines for responding, cost-sharing arrangements, etc. when the alien pest threatens predominantly the environment or public amenity assets (Carnegie et al. (2022). However, when the polyphagous shot hole borer was detected, the system didn’t work as might have been expected. While PSHB had previously been identified as an environmental priority pest, specifically to Acacia, the decision whether to engage was made under auspices of the the Emergency Plant Pest Response Deed (EPPRD) rather than the environmental agreement (NEBRA). As a result, stakeholders focused on environmental, amenity and indigenous concerns had no formal representation in decision-making processes; instead, industries that had assessed the species as a low priority (e.g., avocado and plantation forestry) did (Nahrung, pers.comm.).

Additional Issues Needing Attention

Some needs are not addressed by the National Forest Pest Strategic Plan (Carnegie et al. 2022) (Nahrung, pers. comm.):

1) The long-term strategic investment from the commercial forestry sector and government needed to maintain surveillance and diagnostic expertise;

2) Studies to assess social acceptance of response and eradication activities such as tree removal; 

3) Studies to improve pest risk prioritization and assessment methods; and

4) Resolving the biosecurity responsibilities for pests of timber that has been cut and used in construction.

In 2019, 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 note that surveillance and management programs must be prepared to expect and respond to the unexpected since 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. See Nahrung and Carnegie 2022 for a thorough discussion of the usefulness and weaknesses of predictive pest listing.

SOURCES

Aukema, J.E., D.G. McCullough, B. Von Holle, A.M. Liebhold, K. Britton, & S.J. Frankel. 2010. Historical Accumulation of Nonindigenous Forest Pests in the Continental United States. Bioscience. December 2010 / Vol. 60 No. 11

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

Carnegie A.J., F. Tovar, S. Collins, S.A. Lawson, and H.F. Nahrung. 2022. A Coordinated, Risk-Based, National Forest Biosecurity Surveillance Program for AU Forests. Front. For. Glob. Change 4:756885. doi: 10.3389/ffgc.2021.756885

Nahrung H.F. and A.J. Carnegie. 2020. NIS Forest Insects and Pathogens in Australia: Establishmebt, Spread, and Impact. Frontiers in Forests and Global Change 3:37. doi: 10.3389/ffgc.2020.00037 March 2020 | Volume 3 | Article 37

Nahrung, H.F. and A.J. Carnegie. 2021. Border interceps of forest insects estab in AU: intercepted invaders travel early and often. NeoBiota 64: 69–86. https://doi.org/10.3897/neobiota.64.60424

Nahrung, H.F. & A.J. Carnegie. 2022. Predicting Forest Pest Threats in Australia: Are Risk Lists Worth the Paper they’re Written on? Global Biosecurity, 2022; 4(1).

Posted by Faith Campbell

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

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

or

www.fadingforests.org

We Need Analyses of Pest Approach Rates, but Detection Data Are Not Adequate Basis

plants for sale in UK; Evelyn Grimak via Geograph what pests could be here?

There has recently been a series of studies trying to use port detection data to determine which types of insects are most likely to arrive and possibly establish in the country. These studies – and related sources – are listed at the end of this blog. Some of the studies focus on the U.S. experience, but not all. Their – and my – conclusions are meant to be relevant around the globe.

I agree with Nahrung et al. (2022) as a correct definition of the problem:

“… despite decades of research on and implementation of [biosecurity] measures, insect invasions continue to occur with no evidence of saturation, and are even predicted to accelerate.” 

I also think the issue they raise applies more broadly. As these experts point out, forest pests have received considerable attention, are the subject of a specific international regulation (ISPM#15), and the pest risks to a range of forests is relatively well understood and appreciated. So what does failing to control this group of pests – as I say the international phytosanitary system is – imply for other pests and pathways?

I appreciate these experts’ efforts to improve the many elements of excluding pests: prediction, pest risk analysis, targeted phytosanitary measures, enforcement actions, and early detection. However, we have a long way to go before we can confidently apply port data to determine pest approach rates as well as the efficacy of phytosanitary measures.

Problems with the Quality of the Port Detection Data

inspection by APHIS

There is general agreement that detection data are not a reliable indicator of the true pest approach / arrival rate. Even Turner et al. (2022) – who titled their article “Worldwide border interceptions provide a window …” — concede this, although they try to find ways to apply the detection data anyway. According to pages 2 and 15 of Turner et al., true arrival rates of potentially invading species are usually difficult to estimate and probably exceed the number reported in the article. Allison et al. (2021) agree.

Turner et al. and Nahrung & Carnegie both note that many insect species established in the destination country are never or rarely detected. Turner et al. cite as an example spotted lanternfly, Lycorma delicatula, which appeared only once out of almost 1.9 million interceptions recorded in the combined global data. Nahrung & Carnegie note that 76% of species established in Australia were either never or rarely intercepted at the border.

Turner et al. explain that interception frequencies are a function of both the true arrival rates and the probability of (1) being detected during inspections (which depends on how these are carried out) and (2) being recorded. They say the data are more reliable when they report detections at the family-level. . The authors call on countries to base port inspections on a statistically based sampling program that would better reflect pest approach rates than do data biased by inspection priorities.

The issue of data quality might be broader. Certain kinds of pests travelling in certain types of imports might be sufficiently cryptic as to be rarely detected by even the best border inspections. Liebhold et al. (2012) found that APHIS inspectors detected actionable pests in only 2.6% of incoming shipments of plants, whereas a statistically valid audit determined that the actual approach rate was 12%. It is probable that many pests are never or rarely reported in official port detection data.

See a thorough discussion of the issues undermining use of interception data in Nahrung and Carnegie 2022, cited at the end of this blog.

Problems Due to Narrow Taxonomic Range of Pests Studied

Protection of our forests requires preventing introductions of many taxonomic groups, e.g., nematodes, fungal and other pathogens, viruses, and arthropods other than ambrosia beetles and Hemiptera.

I recognize that it is much more difficult to study and manage organisms other than common beetles. But the impacts of some introduced organisms in other categories have been devastating. I list some of the pathogens that have been introduced to the United States in recent decades, probably on imported plants: several Phytophthoras, ohia rust (Austropuccinia psidii), rapid ohia death (Ceratocystis lukuohia and C. huliohia), beech leaf disease, and the boxwood blight fungi. See Garbelotto and Gonthier (2022) for a thorough discussion of impacts of introduced forest pathogens.

boxwood hedge at Longwood Gardens; photo by F.T. Campbell

Points of Agreement

I agree with Nahrung et al. that:

  1. Biosecurity successes are probably under-recognized because they are difficult to see whereas failures are more evident. They call this the “Biosecurity Paradox”: the more successful biosecurity is, the fewer new species establish so the less important it appears.
  2. Uncertainty regarding the costs and benefits of forest border biosecurity measures appears to have led to under-regulation and wait-and-see approaches. Some recent reviews (Cuthbert et al.) show that delay substantially increases the costs associated with bioinvasion. 297https://www.nivemnic.us/?p=3209
  3. Helping “weakest links” improve their performance is crucial. (see Geoff Williams et al.  
  4. We need to revise international and national biosecurity practices. However, my proposals differ from those cited on page 221 of Nahrung et al.; see my “Fading Forests” reports [links at end of this blog] and earlier blogs here and here. A new complication is that pathologists complain that proposed systems proposed by various invasive species experts don’t reflect realities of managing plant pathogens (Paap et al. 2022).

I wish Nahrung et al. had suggested bolder interim steps that go beyond data management and research.

I appreciate that the Canadian report on forest biosecurity (Allison et al.) notes that claiming most introduced forest pests are reported to cause no measurable impact probably reflects our ignorance. I wish others who repeat this assertion, e.g., Nahrung et al. 2022, would explore this claim’s truth more carefully.

Points of Disagreement

Customs and Border Protection officers inspecting infested pallet

I also found other statements about the efficacy of existing efforts to be too uncritical. So yes, ISPM#15 has resulted in decreased arrivals of bark- and wood-boring insects, as stated by Nahrung et al. 2022. However, the 36-52% decrease documented by Haack et al. (2014) is not sufficient to protect forests, in my view. Many publications have documented continuing introductions of damaging pests via the wood packaging pathway. For example, there have been 16 outbreaks of the Asian longhorned beetle (ALB) detected around the globe between 2012 and 2015 (Wang). Before we conclude that ISPM#15 has been a success, let’s see what the just-completed new study by Haack and colleagues shows. In addition, there has been controversy for a decade or more about what causes continuing introductions, that is, whether they result from treatment inadequacy v. sloppy application of treatments v. fraud. Why have scientists and regulators not collaborated to clarify this issue during this time?

I note – again – that many pathogens have been introduced widely over the last couple of decades. This is a global problem. My recent blogs have discussed introductions of tens of species of Phytophthora to countries around the world. Other examples include myrtle rust (Austropuccinia psidii) to 27 countries and the two causal agents of boxwood blight to at least 24 countries in Eurasia, New Zealand, and North America. Most of these species were unknown to science at the time of their introduction. Other species were known – but not believed to pose a threat because, in their native regions, their co-evolved hosts are not harmed. 

Rhodomyrtus psidioidis in Australia killed by myrtle rust; photo by Peter Entwistle

I think Helen Nahrung (Nahrung et al.) exaggerates when she says that Australia has one of the strictest biosecurity systems in world. Several publications – some coauthored by her! – cite numerous shortfalls in applying the country’s phytosanitary programs to forest pests (Carnegie et al 2022). This latter group’s efforts have determined that at least 260 non-native arthropods and pathogens of forest hosts have established in Australia since 1885 (Nahrung and Carnegie 2020). True, this number is about half the number of non-native forest insects and pathogens that have established in the United States over a period just 25 years longer (Aukema et al. 2010). However, it is enough – and they have had sufficient impact – to prod these scientists to spend 30 years pushing for improvements.

Lessons Learned

Still, we can learn from these studies. Turner et al. compared insect interception data from nine regions over a 25-year period (1995 to 2019) – at ports in New Zealand, Australia, South Korea, Japan, Canada, mainland United States, Hawai`i, United Kingdom, and the region united under European Plant Protection Organization (EPPO) – Europe and the Mediterranean region.

They found that 174 species (2% of the total) were “superinvaders.” They were intercepted more than 100 times, and constituted 81% of all interceptions across all regions. Most of the same types of insects – even the same species – are arriving at ports around the world. The three species most frequently intercepted are all sap-feeding insects commonly associated with widely traded plants. In a separate study, Australian scientists found the same: about 40% of the alien pests detected at Australian borders were already widely introduced at the time of their introduction in Australia (Carnegie et al. 2022). The Australians report strong evidence of the bridgehead effect [that is, species being spread from locations to which they have been introduced] (Nahrung and Carnegie 2021). In fact, they conclude that higher interception rates might confirm invasion success rather than predict it.

Most of the species, however, are intercepted rarely. Turner et al. found that 75% of species reported in their nine regions were intercepted in only a single region. In fact, 44% of all species were intercepted only once (= “singletons”). Such singletons made up about half of individual species in five insect orders; the exception was Thysanoptera – 29% of those species were intercepted only once.

The 75% of all species that were intercepted in only one region included both species rarely intercepted anywhere and species intercepted numerous times – but only in that one region. The authors note that several possible factors might explain these differences. Some species are less likely to be intercepted, so it is not odd that they are detected infrequently, especially if all the regions have the same blind spots. Countries also have their unique approaches to data collection and inspection prioritization that could introduce biases in the data. Finally, countries vary in the sources of goods they import. Unfortunately, some of the data sets Turner at al. analyzed said nothing about the source country, pathway, or commodity. Consequently, they were unable to evaluate the influence of these factors.

Improving Our Understanding of the Current Risk to the U.S.

Dendrobium officinale via Wikipedia; Fusarium stilboides has been detected on this orchid in China; F. stilboides is reported to attack pine trees

As I noted in a previous blog, U.S. imports of plants have increased by more than 400% since the 1960s; 35% in just the last 15 years (MacLachlan et al. 2022). In 2011, APHIS adopted an important new policy: temporary prohibition of plant taxa determined to be “Not Authorized for Importation Pending Pest Risk Assessment” (NAPPRA). Now we have a decade of experience with NAPPRA. Given that, and because the “plants for planting” pathway is among the most risky, APHIS should update the Liebhold et al. 2012 study to determine the current approach rate for all types of organisms that threaten North American tree species. Unlike the previous study, the update should include trees on Hawai`i, Guam, Puerto Rico and the other U.S possessions and territories. Finally, the study should try to evaluate the difference in risks associated with various types of plants and – possibly – also source regions.

Hawaiian native plant naio; photo by Forrest and Kim Starr

Unknown Unknowns

As I noted above, problems curtailing introduction of tree-killing pests are not limited to the U.S. For more than a decade, scientists have noted that the international phytosanitary system has failed to prevent the rapid worldwide spread of significant pathogens via the international nursery trade. Examples include Brasier 2008; Liebhold el. al. 2012; Santini et al. 2013; Roy et al. 2014; Eschen et al. 2015; Jung et al. 2015; Meurisse et al. 2019; O’Hanlon et al. 2021. One of the principal concerns is the fact that most species of microorganisms have not been named by science, much less evaluated for their potential impacts on naïve hosts. This issue was raised by Sarah Green of British Forest Research at the annual meeting of the Continental Dialogue on Non-Native Forest Insects and Pathogens. She asked the APHIS representative whether the agency’s phytosanitary procedures (described here) are working to prevent introductions. She pointed to the issues raised by numerous scientific experts: pest risk analyses address only known organisms, so they cannot protect importers from unknown organisms.

U.S. scientists are beginning to address the issue of “unknown unknowns”. Some studies have taken a stab at evaluating traits of insects that are more likely to damage conifers (Mech et al.) and hardwoods (Schultz et al.).  Jiri Hulcr – of the University of Florida — assessed the threat posed by 55 insect-vectored fungi to two species of oak and two species of pines. However, the forests of the southeastern U.S. comprise many other tree genera! He also set a very high bar for defining a threat as serious: the damage to the host must be equivalent to that caused by Dutch elm disease or laurel wilt. We urgently need APHIS, USDA/Forest Service, and academia to sponsor more similar studies to evaluate the full range of risks more thoroughly.

SOURCES

Allison J.D., M. Marcotte, M. Noseworthy and T. Ramsfield. 2021. Forest Biosecurity in Canada – An Integrated Multi-Agency Approach. Front. For. Glob. Change 4:700825. doi: 10.3389/ffgc. 2021.700825 Frontiers in Forests and Global Change July 2021 | Volume 4 | Article 700825

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

Carnegie A.J., F. Tovar, S. Collins, S.A. Lawson, and H.F. Nahrung. 2022. A Coordinated, Risk-Based, National Forest Biosecurity Surveillance Program for AU Forests. Front. For. Glob. Change 4:756885. doi: 10.3389/ffgc.2021.756885

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

Garbelotto M. and P. Gonthier. 2022.  Ecological, evolutionary, and societal impacts of invasions by emergent forest pathogens. Chapter 7, Forest Microbiology. Elsevier 2022.

Li, Y. C. Bateman, J. Skilton, B. Wang, A. Black, Y-T. Huang, A. Gonzalez, M.A. Jusino, Z.J. Nolen, S. Freemen, Z. Mendel, C-Y. Chen, H-F. Li, M. Kolarik, M. Knizek, J-H. Park, W. Sittichaya, P.H. Thai, S-I. Ito, M. Torii, L. Gao, A.J. Johnson, M. Lu, J. Sun, Z. Zhang, D.C. Adams, J. Hulcr. 2021. Pre-invasion assessment of exotic bark beetle-vectored fungi to detect tree-killing pathogens. Phytopathology. https://doi.org/10.1094/PHYTO-01-21-0041-R

Liebhold, A.M., E.G. Brockerhoff, L.J. Garrett, J.L. Parke, and K.O. Britton. 2012. Live Plant Imports: the Major Pathway for Forest Insect and Pathogen Invasions of the US. www.frontiersinecology.org

MacLachlan, M.J., A. M. Liebhold, T. Yamanaka, M. R. Springborn. 2022. Hidden patterns of insect establishment risk revealed from two centuries of alien species discoveries. Sci. Adv. 7, eabj1012 (2021).

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

Nahrung, H.F. and A.J. Carnegie. 2020. NIS Forest Insects and Pathogens in Australia: Establishment, Spread, and Impact. Front. For. Glob. Change 3:37. doi: 10.3389/ffgc.2020.00037 Frontiers in Forests and Global Change | www.frontiersin.org 2 March 2020 | Volume 3 | Article 37

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.64.604

Nahrung, H.F. & A.J. Carnegie. 2022. Predicting Forest Pest Threats in Australia: Are Risk Lists Worth the Paper they’re Written on? Global Biosecurity, 2022; 4(1).

Nahrung, H.F., A.M. Liebhold, E.G. Brockerhoff, and D. Rassati. 2022. Forest Insect Biosecurity: Processes, Patterns, Predictions, Pitfalls. Annu. Rev. Entomol. 2023.68.

Paap, T., M.J. Wingfield, T.I. Burgess, J.R.U. Wilson, D.M. Richardson, A. Santini. 2022. Invasion Frameworks: a Forest Pathogen Perspective.  FOREST PATHOLOGY https://doi.org/10.1007/s40725-021-00157-4

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

Turner, R. M., E. G. Brockerhoff, C. Bertelsmeier, R. E. Blake, B. Caton, A. James, A. MacLeod, H. F. Nahrung, S. M. Pawson, M. J. Plank, D. S. Pureswaran, H. Seebens, T. Yamanaka, and A. M. Liebhold. 2021. Worldwide border interceptions provide a window into human-mediated global insect movement. Ecological Applications 31(7):e02412. 10.1002/eap.2412

Wang, Q. (Ed.). 2017. Cerambycidae of the world: biology and pest management.  Boca Raton, FL: CRC Press

Posted by Faith Campbell

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

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

or

www.fadingforests.org

Plants for Planting – Major Pathway, Too Little Attention

Phytopthora cinnamomi on manzanita in California; photo courtesy of Ted Swiecki/Phytosphere

While I blog often about wood packaging the fact is that imports of live plant [= “plants for planting” in USDA’s terms] have historically posed a higher risk of introducing tree-killing pests. In 2012, Liebhold et al. found that nearly 70% of 455 damaging pests introduced to the continental U.S. as of 2006 had probably been introduced via plant imports. These included 95% of sap feeding and 89% of foliage feeding insects and about half of the pathogens. Imported plants not only carry a greater variety of pests than wood packaging; they also carry many more.

Introductions on imported plants for planting is not a rare event. An analysis of data in the Agriculture Quarantine Inspection Monitoring (AQIM) during 2009 found that the approach rate of pests on imported plants was apparently 12% (Liebhold et al. 2012) — more than 100 times higher than the 0.1% approach rate found by Haack et al. (2014) for wood packaging. This alarming statistic receives less attention than warranted because APHIS objected to the accuracy of other aspects of the study.

APHIS has adopted changes to its phytosanitary system for plants for planting in the decade since 2009. The question is, have these changes reduced the known risks associate with live plant imports – especially given skyrocketing imports? Are more measures necessary? Current data and analyses cannot provide a scientifically valid answer.

ohia rust on endangered Hawaiian native plant Eugenia koolauensis

First, most studies focus on insects – they even exclude pathogens. Among pathogens introduced in recent decades, probably by the plant trade, are several Phytophthoras, rapid ‘ōhi‘a death, beech leaf disease, boxwood blight. (I am assuming that the Fusarium dieback disease vectored by Euwallacea beetles was introduced via wood packaging.) There have been repeated detections of the Ralstonia solanacearum Race 3 biovar 2, a bacterium that attacks a range of herbaceous plants, despite APHIS requiring specific integrated pest management programs in producing nurseries located in Central America. Examples of recently introduced leaf feeders include the European beech leaf-mining weevil and elm zigzag sawfly.

I concede that it is difficult to study introduced pathogens. It is nearly impossible to compile a complete list of introduced fungi and related organisms since only the most damaging are typically detected and their native ranges are frequently undeterminable. However, European forest pathologists are much more active on these questions. Why? What can we do to focus Americans on the threats these organism pose?

Second, most studies analyzing the pest risk associated with plant imports use port inspection data. However, port inspection data are not reliable indicators of the pest approach rate – as explained by  Liebhold et al. 2012 and Haack et al. 2014 (as it pertains to wood packaging). Thus, most of the analyses carried out by Liebhold et al. and MachLachlan et al. (2022) are based on the pests found by APHIS inspectors: actionable pests were detected on only 2.6% of the incoming plants that they inspected.

Here I discuss two recent discussions of the risk associated with imported plant for planting. One is an analysis of establishments of one order of insects in the United States over 200 years (MacLachlan et al. 2022; full citation at the end of the blog). Again, the focus is on insects! The other is a discussion of the pathway during the recent annual meeting of the Continental Dialogue on Non-Native Forest Insects and Diseases. link to posting of presentations This discussion raised some of the key questions, although no answers were provided.

U.S. imports of plants have increased by more than 400% since the 1960s; 35% in just the last 15 years (in 2007 the U.S. imported approximately 3.7 billion plants [Liebhold et al. 2012]; in 2021 it was about 5 billion [MacLachlan et al. 2022]. Yet establishments of new non-native insects associated with this pathway have not risen commensurately. MacLachlan et al. (2022) attempt to answer why this is so. However, pests are often not detected for several years or a decade after their introduction. Furthermore, I doubt that an analysis based on inspection data, not the more reliable AQIM data, can provide an accurate assessment.

To clarify the pest risk associated with plant imports, studies of some insect types, excluding pathogens, is not sufficient. Again, APHIS should update the Liebhold et al. study to determine the approach rate for all types of organisms that threaten North American tree species. Any such study should include trees on Hawai`i, Guam, Puerto Rico, and other U.S possessions and territories. These islands are usually excluded from analyses of imported pests, including Liebhold et al. 2012. I concede that there are probably scientific and data-management challenges but these islands are immensely important from a biodiversity point of view, and they are parts of the United States!

Cycas micronesica endemic to Guam; threatened by cycad scale & cycad blue butterfly; photo courtesy A. Gawel

MacLachlan et al. (2022) focused their analysis on the insect order Hemiptera, including the so-called true bugs, including cicadas, aphids, planthoppers, and leafhoppers. This is the insect order most frequently transported with imported plants. In addition, establishments of Hemiptera can be attributed to plant imports rather than to wood or other vectors. Of the 3,500 species of non-native insects established in North America (including the contiguous U.S. states, Alaska, and Canada), about 27% are Hemiptera. Many are serious pests, e.g., hemlock woolly adelgid and balsam woolly adelgid). Complicating the analysis, however, is the fact that some Hemiptera are inconspicuous so they are difficult to detect. In fact, MacLaughlan et al. 2022 estimate the median delay between introduction and detection to be 80 years! They believe that many introduced species remain undiscovered, ranging from 21% for Eurasian regions to 38% for the Neotropics and 52% for Australasia.

eastern hemlocks killed by hemlock woolly adelgied; Linville Gorge, NC; photo by Steven Norman, USFS

MacLachlan et al. (2022) compare the relationship between plant imports and discoveries of Hemiptera from 1800 to the present in an attempt to answer the puzzle of why new Hemiptera establishments have remained relatively steady despite quadrupled plant imports. Perhaps the pool of novel insect species in the source region has been depleted. Or other factors might have changed, such as

  • the commodities imported (plant species or types; or geographic source)
  • phytosanitary measures applied by the U.S.

MacLachlan et al. (2022) tracked plant imports since 1854 from seven ecological regions: Afrotropic, Asian Palearctic, Australasia, European Palearctic, Indomalaya, Nearctic, Neotropic. In the early decades, both imported plants and introduced Hemiptera detected in the U.S., came predominantly from European and Asian Palearctic regions. Now, however, almost no new Hemiptera species are being introduced on plants imported from the European and Asian Palearctic regions. Since the 1950s, estimated establishments from the Indomalaya region have remained relatively stable. Establishments from the Neotropic and Afrotropic regions rose following World War II and have remained relatively high. After also declining in the first half of the 20th century, establishments of new species from Australasia have recently increased.

Generally, the regions associated with declining establishments of new species (Eurasia) are experiencing relatively gradual increases in their exports to the U.S. Those regions which contribute relatively steady or increasing establishments (Neotropics, Indomalaya, Australasia, and Afrotropic) have each undergone rapid increases in exports to the U.S.

Establishment Risk Among Regions

Source regions vary in the type of plants they export (e.g., rootless cuttings v. whole plants) and in the volume of exports. They also differ in the composition of their indigenous and introduced insect populations. Imports from areas with an abundance of species capable of establishing and adapted to environmental conditions in North America pose greater establishment risk, although it is challenging to determine the risk associated with individual species.

Establishment risk of shipments from a particular region also changes over time. The number of potential new species of invaders might shrink as more and more arrive in North America. (This situation has no effect on the continued introduction of insect species already established in North America. These reintroductions might arrive in new areas – so expanding the area at risk; or their increasing number contributes to propagule pressure at establishment sites.) Another factor might be phytosanitary policies. Strengthening of phytosanitary measures might suppress the number of organisms that travel with the plant shipment, enter North America, and establish. The opposite might happen if phytosanitary measures are relaxed or if the sourcing or type of imports diversifies in ways that connect additional species in source regions with trade pathways.

Considering all regional plant sources, MacLachlan et al. (2022) estimate that establishments per unit of additional imports – of Hemipterans – have shrunk because of a combination of increased imports, accumulated introductions associated with past imports, and the passage of time. These decreases are substantial – between 75.2% and 99.8% for the various regions from 1962 to 2012. For the Asian Palearctic and Neotropic regions, MacLachlan et al. (2022) determined that depletion of species pools is a contributing factor. Other factors are thought to explain the substantial decline in establishment likelihood for the other regions.  However, note the caveats above re: lag times in detecting introductions.

However, despite that significant decrease in risk per unit of imports, the number of establishments has remained relatively constant over the past century. MacLachlan et al. (2022) attribute this pattern to the decreases in marginal risk from additional imports being offset by substantial increases in overall import levels and diversification of the origins of imports across regions, which exposed the U.S. to new source species pools.

MacLachlan et al. (2022) suggest that APHIS should target biosecurity resources to the specific commodity-country pairs associated with a demonstrated higher relative risk of introducing additional insect species.

MacLachlan et al. (2022) are unable to evaluate the efficacy of APHIS’ most important policy change: creation of the “Not Authorized for Importation Pending Pest Risk Assessment” (NAPPRA) program because it was adopted in 2011 and they analyzed data only through 2012. A decade later this policy restricts imports of about 250 taxa (Regelbrugge to Continental Dialogue). It is certainly time to evaluate its efficacy through a new study of pest approach rates in the “plants for planting” trade.

I do not think that U.S. phytosanitary policy should be based on an analysis of just one of at least three types of pests that travel via the pathway. We need analysis of the risk from pathogens, nematodes, viruses … and other orders of arthropods.

The Continental Dialogue on Non-Native Forest Insets and Pathogens

The Continental Dialogue on Non-Native Forest Insects and Pathogens hosted a discussion of the risk of pest introduction via the plant trade during its recent annual meeting. Participants asked: How can the international phytosanitary system curtail introductions of unknown organisms when it is based on risk assessments that address only species that are fully known and – usually – have proven to be invasive elsewhere.

Rhodomyrtos psidioides in eastern Australia killed by myrtle rust; photo by Peter Entwistle

In recent decades, tens of species of Phytophthora have been introduced to countries around the world. Myrtle rust (Austropuccinia psidii) has been introduced to 27 countries from the U.S. to Australia and South Africa. The two causal agents of boxwood blight has been introduced to at least 24 countries in three geographic areas: Europe and western Asia; New Zealand; and North America. The ash decline fungus has been introduced across Europe. Most of these species were unknown to science at the time of their introduction. Other species were known – but not believed to pose a threat because, in their native regions, their co-evolved hosts are not harmed. 

For more than a decade, scientists have noted that the international phytosanitary system has failed to prevent this rapid worldwide spread of significant pathogens via the international nursery trade. Examples include Brasier 2008; Liebhold el. al. 2012; Santini et al. 2013; Roy et al. 2014; Eschen et al. 2015; Jung et al. 2015; Meurisse et al. 2019; O’Hanlon et al. 2021.

During the Continental Dialogue discussion, Craig Regebrugge, Vice President of AmericanHort (the principal nursery trade association) noted the economic importance of greenhouse and nursery production and the importance of offering novel plants to their customers. Also, he noted that U.S. retail nurseries import primarily unrooted plant cuttings. In so doing, they have a strong incentive to ensure that they are pest-free in order to avoid delays arising during inspections. Those delays would probably kill these highly perishable products. Most U.S. imports of “finished” plants come from Canada. There have been pest problems; one of the most recent examples is a moth that attacks boxwoods (Buxus), which is the top-selling shrub crop in the U.S. Earlier there was confusion over whether plants shipped from British Columbia had been infected by the sudden oak death pathogen.

Regelbrugge noted that the industry’s voluntary integrated pest management program – Systems Approach to Nursery Certification (SANC) – currently has about two dozen participating nurseries. Hoped-for adoption by more of the hundreds of production nurseries in the country has been delayed by COVID-related travel restrictions, but he hopes to restore momentum. The industry is looking for opportunities to strengthen the program through marketing messages.

Regelbrugge and a second speaker, Rebecca Epanchin-Niell of the University of Maryland, warned that prohibitions on imports will stimulate smuggling. Both raised concerns about direct-to-consumer sales by e-commerce vendors and sought ideas on how to change the behavior of both exporters and consumers.

Later Sarah Green of British Forest Research asked the APHIS representative whether the agency’s import procedures are working to prevent introductions. She pointed to the issues raised by the scientific sources I cited above: pest risk analyses address only known organisms, so this process cannot protect importers from unknown organisms. She noted that the United Kingdom is struggling to contain a number of introductions of previously unknown pathogens. Gary Lovett of the Cary Institute noted that this weakness of pest risk assessments also hampers U.S. attempts to prevent introductions – especially of pathogens. He called on the Dialogue to focus on the resource at risk – native and urban forests – and change our phytosanitary programs on this basis. He has advocated halting imports of plants that are congenerics of important North American tree species, in order to minimize the risk that pests that damage those genera will be introduced.

an American elm that has survived DED – at Longwood Gardens; photo by F.T. Campbell

Jiri Hulcr of the University of Florida tried to reassure Dialogue participants by stating that recent research has substantially reduced the threat from “unknown unkowns”. I applaud Dr. Hulcr’s efforts to reduce scientific uncertainty about the invasive potential of pathogens native to regions other than North America. His study might be the largest attempted by U.S.-based scientists. However, I note that his study assessed the threat posed by 55 insect-vectored fungi to two species of oak and two species of pines. The forests of the southeastern U.S. comprise many other tree genera! He also set a very high bar for defining a threat as serious: the damage to the host must be equivalent to that caused by Dutch elm disease or laurel wilt. Both have devastated their respective hosts. I believe U.S. phytosanitary policy must aim at protecting the full range of native species. Furthermore, levels of damage that affect the host’s role in the ecosystem – not just rapid mortality — should not be acceptable.

SOURCES

Epanchin-Niell, R., M. Springborn, an A. Lindsay.  2016. Resources No. 193 Fall 2016.  http://www.rff.org/files/document/file/RFF_Resources_193_Web.pdf

Li, Y. C. Bateman, J. Skelton, B. Want, A. Black, Y-T. Huang, A. Gonzalez, M.A. Jusino, Z.J. Nolen, S. Freemen, Z. Mendel, C-Y. Chen, H-F. Li, M. Kolarik, M. Knizek, J-H. Park, W. Sittichaya, P.H. Thai, S-I. Ito, M. Torii, L. Gao, A.J. Johnson, M. Lu, J. Sun, Z. Zhang, D.C. Adams, J. Hulcr. 2021. Pre-invasion assessment of exotic bark beetle-vectored fungi to detect tree-killing pathogen. Phytopathology. https://doi.org/10.1094/PHYTO-01-21-0041-R

Liebhold, A.M., E.G. Brockerhoff, L.J. Garrett, J.L. Parke, and K.O. Britton. 2012. Live Plant Imports: the Major Pathway for Forest Insect and Pathogen Invasions of the US. www.frontiersinecology.org

MacLachlan, M.J., A. M. Liebhold, T. Yamanaka, M. R. Springborn. 2022. Hidden patterns of insect establishment risk revealed from two centuries of alien species discoveries. Sci. Adv. 7, eabj1012 (2021).

Posted by Faith Campbell

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

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

or

www.fadingforests.org

Invasive shot hole borers: global threat; will international phytosanitary system prevent further spread?

ISHB-infested California sycamore; photo by Beatriz Nobua-Behrmann, University of California Cooperative Extension

Numerous ambrosia beetles have become introduced species. Their invasions are facilitated by their cryptic habits and ecologies, wide host ranges, and specialized breeding systems – all of which allow extremely low populations to start an infestation. The way they breed often results in low genetic diversity in their introduced ranges, but this has not hampered their success. [Bierman et al. 2022]

Also, ambrosia beetles carry fungi, which provide food needed by their larvae. While most of these fungi don’t harm living trees, some do. The United States has been invaded by three damaging ambrosia beetle-fungal complexes: laurel wilt in the Southeast, and Fusarium dieback disease, carried to southern California with polyphagous and Kuroshio shot hole borers.

These shot hole borers and their fungi represent an especially high risk to our forests because they can be transported in both living and dead wood. So not only massive U.S. imports of live plants but also the global movement of goods enclosed in solid wood packaging offer ready pathways for them to arrive and spread here. Neither pathway is regulated effectively enough to prevent either pest imports or interstate spread.

Invasive ambrosia beetles in California and Hawai’i

The invasive ambrosia beetles introduced to California are in the genus Euwallacea. This genus has undergone several taxonomic revisions. Now, the Euwallacea are divided into four species (Stouthammer 2017), of which three are in the U.S.:

  • Euwallacea fornicatus s.s. – common name polyphagous shot hole borer; first came to attention in southern California in 2012; formerly known as E. whitfordiodendrus.
  • E. perbrevis – common name tea shot hole borer; formerly known as E. fornicatus s.l.
  •  E. kuroshio – unchanged nomenclature since detected in California in 2013;
  • E. fornicatior — apparently has not invaded outside of its native range in Asia.

Those now in the U.S. have been introduced to naïve habitats here and elsewhere, often with dire consequences. E. perbrevis, and possibly other species in the complex, are established on the Hawaiian islands.

For an extensive discussion of their introduction history go here  

The Fungi: U.S. and Worldwide

Several fungal associates are vectored by the polyphagous shot hole borer (PSHB) and Kuroshio shot hole borer (KSHB). The most important are Fusarium euwallacea and Fusarium kuroshium, respectively. These fungi were only described after they appeared in California in the 2010s. They cause Fusarium dieback disease.

Because the two beetle species are difficult to distinguish and the associated diseases cause very similar impacts, Californians studying them and educating stakeholders now speak of the two beetle-fungus complexes as one unit, “invasive shot hole borers”.  

Both PSHB and KSHB have numerous genetic strains, or haplotypes. For PSHB, the greatest haplotype diversity is in Asia – Thailand, Vietnam and China. Remember that these same regions are also a center of diversity for the huge genus Phytophthora, blog a genus widely recognized as containing many plant pathogens. https://www.dontmovefirewood.org/pest_pathogen/sudden-oak-death-syndrome-html/ One of the PSHB haplotypes, H33, has invaded many more regions than the others, including Israel, California, and South Africa. It has also been detected in several tropical plant greenhouses in Europe (where it has been eradicated). H33apparently is native to Vietnam – near Hanoi and Ho Chi Minh City – the country’s major ports (Rugman-Jones et al 2020 and pers. comm.). Does this haplotype’s spread to three continents reflect circumstances, such as the proximity of its native range to major ports and a “bridgehead effect” from its multiple introductions (the insects can be introduced to new regions on shipments from invaded regions established earlier)? Or does it point to an unknown genetic superiority (Bierman et al. 2022). This issue seems worth exploring.

I have blogged about the rising volume of imports from Vietnam, including to ports on the Gulf Coast –a region that has climatic similarities to Vietnam and known host species, so it seems quite vulnerable to invasion by either PSHB or KSHB.

A second species in the genus, KSHB, was detected in southern California in 2012; it has now spread to Mexico. So far, only one haplotype of this species has been detected in North America; this haplotype is widespread in Taiwan.

Finally, E. perbrevis (formerly known as E. fornicatus s.l.) has been detected in Florida, Hawai`i (island of Maui), and West Australia (to which it is probably native). This species has also been detected in nurseries in the Netherlands, where authorities report that it has been eradicated (Rugman-Jones et al. 2020).

Akacia koa – native tree in Hawai“i attacked by Euwallaceae; photo by David Eckhoff, via Flickr

Some species or haplotypes have been detected in only one introduced location: E. fornicatus H35 and E. kuroshio (H20) in California; H38 in South Africa; H43 on Oahu and the Big Island of Hawai`i; and an unnamed haplotype in West Australia (Rugman-Jones et al. 2020).

This is a brief guide to worldwide invasions by one or more Euwallacea-fungus complexes (Rugman-Jones et al. 2020):

  • Southern California — two haplotypes of E. fornicatus s.s. (H33 & H35) and E. kuroshio (one  haplotype).
  • Hawai`i – a unique haplotype of E. fornicatus s.s. (H43) on Oahu, the Big Island, and possibly other islands; E. perbrevis on Maui and possibly other islands.
  • Israel — E. fornicatus s.s. haplotype H33 only.
  • South Africa — E. fornicatus s.s. haplotype H33 and a unique haplotype (H38).
  • Western Australia — a unique haplotype of E. fornicatus s.s. and E. perbrevis (which is probably native in northern Queensland).
  • Greenhouses in Europe – both E. fornicatus s.s. (haplotype not specified) and – in the Netherlands — E. perbrevis; both reported eradicated.

When a location has been invaded by two or more species or haplotypes, this is probably an indication of separate introductions. Multiple introductions thus are suspected in California (Stouthamer et al. 2017; Bierman et al. 2022); South Africa (Bierman et al. 2022); and Hawai`i (Bierman et al. 2022).

As is true of other pathogens, e.g., Phytophthoras, there appears to have been a spurt of introductions in recent decades, to, e.g., California, South Africa, and the second species in Hawai`i. Bierman et al 2022 note the constantly growing number of locations with introductions.

Indigofera jucuna – reproductive host of PSHB in South Africa; photo by Giardano de Barcelona

Impact and Spread

As is common in the case of forest pests, especially pathogens, detection occurred only years after the initial introduction. In South Africa this delay was five years – from 2012 to 2017 or 2018. In California, identification of the species as PSHB in 2012 was nine years after the organism was first detected in the state (2003).

Over the decade since 2012, PHSB, KSHB, and the pathogens they transmit have spread through large portions of southern California. KSHB has spread through “jumps” to distant locations in Orange, Los Angeles, and as far as Santa Barbara and Ventura counties. There have also been detections in even more distant San Luis Obispo and Santa Clara. These latter apparently have not become established.

A likely explanation for this pattern is the movement of firewood. (Rugman-Jones et al 2020 and pers. comm.) See the map here The two beetles and the plant pathogens they carry are expected to spread throughout much of California wherever their many host plants occur.

On Hawai`i, PSHB is attacking several endemic species including one of the largest forest trees, Acacia koa, as well as Pipturus albidus and Planchonella sandwicensis. Numerous non-native species growing on the Islandsare also attacked, including crops (Macadamia and Mangifera) and invasive species

In South Africa, PSHB has spread faster and farther. It has been present since at least 2012 (Stouthamer et al. 2017), although it was not identified until 2018. In about a decade it has spread to every province except Limpopo – PSHB’s largest geographical outbreak of this beetle [Bierman et al. 2022]

Hosts and Areas at Greatest Risk

Hundreds of plant species in at least 33 plant families support successful reproduction of both beetle and fungus. These include many species widespread in southern California, other parts of the U.S., and South Africa. Some California ecosystems are at particular risk because they are dominated by susceptible tree or shrub species. These vulnerable ecosystems are mixed evergreen forests, oak woodlands, foothill woodlands, and riparian habitats. In San Diego County alone, more than 58,000 acres of riparian woodlands are at risk (California Forest Pest Council).

Experience with the Kuroshio shot hole borer (KSHB) in the Tijuana River valley along the California-Mexico border demonstrates the importance of ecological factors in determining disease outcomes. Following introduction, the KSHB killed a high proportion of the willows near the main river channel. However, beginning in 2016, these trees have regrown to almost pre-infestation sizes. Lead researcher John Boland is not certain why these new, fast-growing trees have not been attacked by the KSHB which remains in the area. See links to the Boland studies below.

riparian forest in Tijuana River Valley after recovery from KSHB attack; photo by John Bolton

Urban forests are at particular risk. For example, in South Africa, conservative estimates were that 25% of urban trees would be lost (Bierman et al. 2022). In California, a model developed by Shannon Lynch found the cities at greatest jeopardy are San Diego, Los Angeles, the San Francisco Bay area, and Sacramento. In other areas in the state that lack data on city tree composition, Lynch applied climate models; this approach extended the list of threatened areas to the eastern half of southern California and other parts of the Central Valley. (Lynch presentation to ISHB webinar April 2022; 2nd day.) In my view, this model should also be applied to cities in Arizona and Nevada with similar climates.

Management

Symptoms of PSHB attack and fungus infection differ among tree species. For illustrations of the symptoms on various species, visit here.

Most important, prevent the beetles’ spread through movement of dead or cut wood, e.g., green waste, firewood, and even large wood chips or mulch. Websites provide information on managing these sources.

Where the beetles have already established, California scientists recommend focusing management on heavily infested “amplifier trees”. On these trees, dead limbs should be pruned; dying trees and those with beetles infesting the main trunk should be removed. The wood must be disposed of properly.

Sources

Bierman, A., F. Roets, J.S. Terblanche. 2022.  Population structure of the invasive ambrosia beetle, Euwallacea fornicatus, indicates multiple introductions into South Africa. Biol Invasions (2022) 24:2301–2312 https://doi.org/10.1007/s10530-022-02801-x

Boland, J.M. — all of Boland’s reports and articles on the KSHB are available at: The Ecology and Management of the Kuroshio Shot Hole Borer in the Tijuana River Valley — Tijuana Estuary : TRNERR]

California Forest Pest Council. 2015. 2015 California Forest Pest Conditions. http://bofdata.fire.ca.gov/hot_topics_resources/2015_california_forest_pest_conditions_report.pdf

Eskalen, A., Stouthamer, R., Lynch, S. C., Twizeyimana, M., Gonzalez, A., and Thibault, T. 2013. Host range of Fusarium dieback and its ambrosia beetle (Coleoptera: Scolytinae) vector in southern California. Plant Dis. 97:938-951.

Stouthamer, R., P. Rugman-Jones, P.Q. Thu, et al. 2017. Tracing the origin of a cryptic invader: phylogeography of the Euwallacea fornicatus (Coleoptera: Curculionidae: Scolytinae) species complex. Agric For Entomol 19:366-375. https://doi.org/10.1111/afe.12215

recordings of April 2022 webinar posted at https://youtu.be/RyqJYyLkshk  day 1; and https://youtu.be/kWmtcbjTczw day 2

Posted by Faith Campbell

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

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

or

www.fadingforests.org

More & bigger ships, deeper ports = more pests?

Port of Houston – Bayport Container Terminal; photo by Ray Luck via Flickr

The U.S. continued to import large amounts of goods from Asia in the first three months of 2022. During this period, total volume imported from Asia increased to 1.62 million TEU — 31.1% higher than in the same period in pre-pandemic 2019 (Mogelluzzo, B. April 22, 2022).

Due to congestion in West Coast ports, the proportion of Asian goods entering the country through East Coast and Gulf Coast ports also rose in the first quarter of 2022 compared to the same period in 2021: by about 33% along the Atlantic and 6% along the Gulf (Mogelluzzo, B. April 22, 2022). Increases were particularly steep in the south: 9.2% at Savannah; 12.5% at Norfolk; 26% at Charleston; and an astonishing 52.1% through Houston.

Due to Covid-19-related port and factory shutdowns in China, a rising share of imports to the U.S. in 2022 came from other countries in Asia. Imports grew especially from Vietnam but also Thailand, Malaysia, Indonesia, and South Korea (Wallis, K. May 11, 2022).

Port of Long Beach Pier G – ITS – MOL vessel; photo by port authority

Starting in May 2022, West Coast ports began to recover their dominant role – probably because East Coast and Gulf Coast ports were now suffering their own congestion-related delays. Virtually all the restored traffic entered through the Los Angeles-Long Beach port complex; these ports imported a monthly record of 851,956 TEU from Asia in May. Imports through Seattle and Tacoma actually declined from the previous month, while Oakland’s imports from Asia remained steady (Mongelluzzo, June 15, 2022).

Thus, the “baseline” for US imports from Asia each month is now 20 to 30% higher than it was before COVID-19 disrupted supply chains (Mongelluzzo, June 15, 2022).

East Coast Ports Deepening and Expanding to Accept Larger Ships

Meanwhile, East Coast ports continue efforts to deepen their channels and expand their infrastructure so that they can service the larger container ships.

In late June 2022 the US Army Corps of Engineers approved the plan by the Port of New York-New Jersey (PANYNJ) to dredge channels to accommodate more post-Panamax ships. The largest ship that has called at NY-NJ was 16,000 TEU; port officials hope to accommodate ships up to 21,000 TEU, apparently using current capacity (Angell, June 23, 2022; Angell, May 27, 2022). PANYNJ Port Director Bethann Rooney says the port expects to see annual volumes rise to 17 million TEU by 2050, almost double its throughput in 2021 (Angell, May 27, 2022).

The Corps found the PANYNJ plan to be both environmentally and economically sound. The Corps will now seek Congressional funding for the project in the 2024 Water Resources Development Act; the Port Authority will also contribute to the project (Angell, June 23, 2022).  We need to be more active in commenting on these port expansion environmental assessments!

The Port of NY-NJ is also seeking to expand storage facilities for incoming shipping containers. Several sites are at various stages of consideration and development; one – part of the “Port Ivory” site on Staten Island – includes a tidal wetland.  A November 2021 application by PANYNJ a change-in-use permit is under review by New York State Department of Environmental Conservation (NYSDEC) (Angell, May 27, 2022). Can those interested in environmental protection express their opposition?

The Port of Charleston is expected to finish dredging its inner harbor and channel this year. Last year, the Port of Virginia has received initial funding for a dredging project that should be completed by 2024 (Angell, May 27, 2022).

As we know, numerous tree-killing insects have been introduced from Asia to the ecologically similar forests of eastern North America – often in wood packaging. ALB in Charleston These include Asian longhorned beetle, emerald ash borer, redbay ambrosia beetle, phytophagous and Kuroshia shot hole borers (for profiles of each visit here). Indeed, 15 of 16 non-native bark beetles in the Xyleborini (a tribe of ambrosia beetles) detected in the United States since 2000 are from Asia (Bob Rabaglia, USFS Forest Health Protection, presentation at IUFRO meeting in Prague, September 2021).

Growing numbers of containers entering Atlantic and Gulf Coast ports raises the risk of additional introductions. Insects associated with imports from semi-tropical ports in Vietnam entering the U.S. through Gulf or southern Atlantic ports might well find these regions hospitable. I worry, for example, about the polyphagous and Kuroshio shot hole borers – surely the Gulf Coast provides a more suitable environment for insects from Vietnam and Taiwan than does southern California? And known hosts are present – box elder, willows, sweetgum, mimosa, tree of heaven …

Of course, containers are then sent on from the ports to distribution centers – presenting opportunities for pest introductions in inland areas. New or expanded distribution centers include Atlanta and Appalachian Regional Port and Statesboro Airport in Georgia, Rocky Mount, North Carolina; Huntsville, Alabama; Portsmouth and Front Royal, Virginia (Ashe and Angell July 5, 2022). Front Royal is at the northern end of Shenandoah National Park!

photo by Daveylin via Flickr

European Trade

Meanwhile, U.S. imports from Europe continued at high levels – although they were not breaking records. In the first half of 2022, the U.S. imported just under 1.77 million TEU from Europe. The largest category of commodity from Northern Europe was foodstuffs — 410,930 TEU. Machinery and mechanical products imports – the type of good often associated with infested wood packaging – numbered 228,521 TEU. Vehicles, aircraft, and vessels imports were 107,526 TEU. “Miscellaneous manufactured articles” that include furniture, bedding, mattresses, and light fittings were 132,979 TEU. I expect – although the source does not so state – that this last category includes decorative stone and tile – again, a category often associated with infested wood packaging.

 While fewer damaging pests have been introduced from Europe in recent decades, the risk remains.

Updated Haack Analysis

As has been documented repeatedly (e.g., my blogs, including 248), the current approach to curtailing pest introductions associated with wood packaging is not sufficiently effective. Customs officials continue to detect live quarantine pests in wood packaging as it enters the country. However, the exact level of this threat is unclear since the only assessment was based on data from 2009 (Haack et al., 2014).  I eagerly await the results of Bob Haack’s updated analysis, which I hope will be published soon.

SOURCES

Angell, M. NY-NJ port lays groundwork for larger ships ahead of dredging. May 27, 2022.  https://www.joc.com/port-news/us-ports/port-new-york-and-new-jersey/ny-nj-port-lays-groundwork-larger-ships-ahead-dredging_20220527.html

Angell, M. NY-NJ deepening study gets US Army Corps blessing. June 23, 2022. https://www.joc.com/port-news/us-ports/port-new-york-and-new-jersey/ny-nj-deepening-study-gets-us-army-corps-blessing_20220623.html?utm_campaign=CL_JOC%20Ports%206%2F29%2F22%20%20%20REDO_PC00000_e-production_E-140850_SA_0629_0900&utm_medium=email&utm_source=Eloqua

Ashe, A. and Angell, M. Rising volumes slowing port flow on East, Gulf coasts. July 5, 2022. https://www.joc.com/port-news/us-ports/rising-volumes-slowing-port-flow-east-gulf-coasts_20220705.html?utm_source=Eloqua&utm_medium=email&utm_campaign=CL_JOC%20Daily%207%2F6%2F22%20NONSUBSCRIBER_PC015255_e-production_E-141183_KB_0706_0617

Knowler, G. Rising US imports keep pressure on trans-Atlantic. July 18, 2022.  https://www.joc.com/port-news/international-ports/rising-us-imports-keep-pressure-trans-atlantic_20220718.html?utm_source=Eloqua&utm_medium=email&utm_campaign=CL_JOC%20Daily%207%2F19%2F22%20NONSUBSCRIBER_PC015255_e-production_E-141796_KB_0719_0617

Mongelluzzo, B. Q1 US imports from Asia show no slowing in consumer demand. Apr 22, 2022. https://www.joc.com/maritime-news/container-lines/q1-us-imports-asia-show-no-slowing-consumer-demand_20220422.html

Mongelluzzo, B. U.S. imports from Asia surge to unexpected record in May. June 15, 2022. https://www.joc.com/port-news/us-ports/us-imports-asia-surge-unexpected-record-may_20220615.html?utm_source=Eloqua&utm_medium=email&utm_campaign=CL_JOC%20Daily%206%2F16%2F22%20NONSUBSCRIBER_PC015255_e-production_E-140076_KB_0616_0617

Wallis, K. Asia shippers plug trans-Pacific export gap from China COVID-19 disruption. May 11, 2022.

https://www.joc.com/maritime-news/trade-lanes/asia-shippers-plug-trans-pacific-export-gap-china-covid-19-disruption_20220511.html?utm_source=Eloqua&utm_medium=email&utm_campaign=CL_JOC%20Daily%205%2F12%2F22%20NONSUBSCRIBER_PC015255_e-production_E-137446_KB_0512_0617

Posted by Faith Campbell

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

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

or

www.fadingforests.org

Search for Asian giant hornet

Asian giant hornet (Vespa mandarinia); photo by University of Florida Dept. of Entomology

Washington State’s “Giant Hornet – Hornet Herald” for June asks people to help with detecting this pest by monitoring paper wasp nests (hornets attack them). Hornet visits last 5 – 10 minutes while the hornet removes paper wasp larvae.  How to help:

  • Locate paper wasp nests that you have access to and can monitor through October. Then log the nest locations using the form here
  • Visit the nests each week, observe them, and then log your nest activity on a different form – here. Please monitor the nests for at least 5 minutes during the day once per week, but you can check the nests for as long and as often as you would like.

If you would like guidance on how to become a citizen-science monitor or trapper of Asian giant hornets – or presumably other bioinvaders – go here

Meanwhile, Washington State Department of Agriculture entomologists are in South Korea testing several hornet attractants and studying hornet foraging behavior. The goal  is to improve Washington’s trapping and tracking techniques.

Of course, 2022 is only half over, but so far neither Washington nor British Columbia has confirmed any detections.

Posted by Faith Campbell

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

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

or

www.fadingforests.org

Boxwood Blight – Another Failure of the Global Phytosanitary System

boxwood garden at Gunston Hall – home of founding father George Mason; Virginia; photo by Roger 4336 via Wikimedia

Boxwood blight is a disease caused by a group of fungal pathogens. While boxwoods are horticultural plants in the U.S. – important ones! – they are keystone forest species in several regions of the tropics and subtropics.

The situation with boxwood blight is yet another example of a too-frequent pattern for plant pathogens. This pattern applies even to plant taxa that are important to the ornamental horticulture industry – not only plants that are important in natural ecosystems. [See other blogs posted here under the category “plants as pest vectors”, e.g., here. The boxwood blight pathogens:  

  • are of unknown origin;
  • have a wide range of known hosts; additional hosts probable;
  • have been introduced to many new sites over about 30 years;
  • have caused considerable economic, aesthetic, and ecological harm;
  • are a threat to centers of endemism;
  • have no known methods to treat plants in forests;
  • are spread by international plant trade;
  • complicate detection by having hosts that sometimes are asymptomatic; or symptoms can be suppressed by fungicides;
  • apparently few efforts to apply phytosanitary measures to prevent further spread.

Also typical: concerned scientists are trying to promote adoption of phytosanitary measures. This takes the form of a study by Barke, Coop and Hong (full citation at the end of the blog; unless otherwise stated, information in this blog is from this source). They use several models based largely on climatic factors to predict additional geographic areas where else boxwood blight might establish.

I think it is most unfortunate that the U.S. horticultural industry prefers to avoid federal regulation despite the significant costs to its members. Instead, it has advocated for a primarily voluntary response (see below). This undermines efforts to restructure regulatory programs to improve phytosanitary agencies’ management of pathogens. Since the U.S. is such a powerful player on this issue, reducing pressure on APHIS to find more effective measures has global implications. I recognize that preventing transmission of unknown and cryptic pathogens is an intrinsically difficult task. However, tackling this problem should be a top priority for people concerned about retaining healthy floral communities.

Specifics About Boxwood Blight

Boxwood blight is caused by two ascomycete fungi, Calonectria pseudonaviculata [synonym Cylindrocladium buxicola] and Calonectria henricotiae. Both can infect and blight boxwood foliage, resulting in rapid plant death. C. henricotiae is known from only five countries in Europe; C. pseudonaviculata is currently established in 24 countries in three geographic areas: Europe and western Asia; New Zealand; and North America (30 US states and British Columbia). The disease caused by C. pseudonaviculata could spread well beyond its currently invaded range in these regions.

range of Buxus sempervirens; via Wikimedia

Native plants in the family Buxaceae grow in tropical or subtropical areas around the world. Plants in the genera Buxus, Didymeles, Haptanthus, Pachysandra, Sarcococca, and Styloceras are found in some areas of western and southern Europe; Turkey and the Caucuses into Iran; several countries in southeast and east Asia (China, Japan, South Korea, Vietnam, Indonesia); coastal Australia; high elevation areas of Africa, including Madagascar; parts of South America (southern Brazil, Uruguay, northern Argentina, and southern Chile, and foothills of the Andes); parts of Central America and the Caribbean. Asia is home to about 40 species of Buxus, four species of Pachysandra, and 11 species of Sarcococca.  In the Andes region, all five species of Styloceras are endemic. Central America and the Caribbean are home to about 50 species of Buxus; there are 37 species endemic to Cuba! Madagascar has nine endemic Buxus species.

Many Buxus species occur in small and isolated distributions resulting from both natural causes (e.g., island endemism) and anthropogenic disturbances (including deforestation and invasions of by other non-native pests, such as the box tree moth Cydalima perspectalis in Europe and western Asia).

In native stands of Buxus sempervirens in Georgia and northern Iran, where C. pseudonaviculata was detected in 2010, the disease has caused rapid and intensive defoliation of boxwood plants of different ages. [See also Lehtijarvi, Dogmus-Lehtijarvi and Oskay. Boxwood Blight in Turkey: Impact on Natural Boxwood Populations and Management Challenges. Baltic Forestry 2017, vol. 23(1)] Infected plants are also vulnerable to attacks by secondary opportunistic pathogens that can lead to eventual death. Damage to these forests could lead to reductions in soil stability and subsequent declines in water quality and flood protection, changes in forest structure and composition, and declines in Buxus-associated biodiversity (at least 63 species of lichens, fungi, chromista and invertebrates might be obligate).

Barke, Coop and Hong expect excessive heat and seasonal dryness at one extreme and excessive cold at the other to limit areas in North America and Europe/central Asia where the disease can establish. Areas with oceanic rather than continental climates are probably more vulnerable. However, heat and aridity barriers could be overcome by artificial irrigation of horticultural plantings.

Indeed, the conditions favoring C. pseudonaviculata establishment – warm temperatures and high humidity or water on the leaves – are commonly found in production nurseries. Overhead irrigation exacerbates the risk. Production nurseries also have large numbers of host plants in close proximity – so it is easy for disease to spread (Douglas). 

I am reminded that the causal agent of sudden oak death, Phytophthora ramorum,  has been spread from production nurseries located in hot, dry areas that were considered unsuitable to the pathogen – because conditions inside the nursery were suitable.

wild Buxus on island of Corsica; photo by Sten Porse via Wikimedia

As I noted, the origin of C. pseudonaviculata is unknown. Barke, Coop and Hong think it is most likely in eastern Asia, which is thought to be the likely native region of box tree moth. However, they cannot rule out some other center of diversity for Buxaceae species e.g., the Caribbean or Madagascar.

Barke, Coop and Hong call for additional studies to

  1. Explore potential effects of climate change on establishment risk, especially higher latitude areas expected to see increasing humidity, precipitation, and rising temperatures.
  2. Determine ability of C. pseudonaviculata microsclerotia to survive higher temperatures, e.g. in parts of the U.S. Deep South that may have ideal growing conditions during cool seasons.
  3. Modify the CLIMEX model developed for this study to predict the potential distribution of C. henricotiae, a closely related but genetically distinct species with greater tolerance of higher temperatures.

They call for a strict phytosanitary protocol for risk mitigation of accidental intro, with effective surveillance for early detection, and development of a recovery plan.

Regulatory (non) Response

Boxwood blight was first detected in the United Kingdom in mid-1990s; then in New Zealand in 2002. Only then was the causal agent determined. It was first detected in the U.S. in October 2011 (in Connecticut). It was quickly determined to be established in the mid-Atlantic region. Apparently the British, other European countries, and APHIS all decided the pathogen was too widespread to regulate (Douglas).

The U.S. is relying on a voluntary program. The nursery industry, through its Horticultural Research Institute (HRI), and the National Plant Board developed guidance for best management practices – updated as recently as 2020. 

boxwood blight symptoms; Oregon State University; via Flickr

In contrast, APHIS has acted to regulate the boxwood tree moth, Cydalima perspectalis. The moth was first detected in North America near Toronto in 2018. U.S. nurseries in six states received infected plants in spring 2021. On May 26, 2021, APHIS prohibited importation of host plants from Canada, including boxwood (Buxus spp), Euonymus (Euonymus spp), and holly (Ilex spp).

In July 2021, the moth was detected in Niagara County, New York. It was thought that the moths had flown or been blown into the area from Canada.  New York adopted an intrastate quarantine of three counties (Erie, Niagara, and Orleans) in December 10, 2021. APHIS followed with an interstate quarantine on March 23, 2022.

SOURCES

Barke, B.S., L. Coop and C. Hong. 2022.  Potential Distribution of Invasive Boxwood Blight Pathogen (Calonectria pseudonaviculata) as Predicted by Process-Based and Correlative Models. Biology 2022, 11, 849. https://doi.org/10.3390/biology11060849 www.mdpi.com/journal/biology

Douglas, S.M. Fact sheet; Connecticut Agricultural Experiment Station https://portal.ct.gov/-/media/CAES/DOCUMENTS/Publications/Fact_Sheets/Plant_Pathology_and_Ecology/2020/Boxwood-Blight-(1).pdf?la=en&hash=A4C6AF39765F27FDDEB5B4DC3FD3B6F3

Posted by Faith Campbell

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

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

or

www.fadingforests.org

Invasions cost protected areas more than $22 billion in 35 years

Burmese python in Everglades National Park; photo by Bob Reed, US FWS

Scientists continue to apply data collected in an international database (InvaCost; see “methods” section of Cuthbert et al.; full citation at end of this blog) to estimate the economic costs associated with invasive alien species (IAS). These sources reported $22.24 billion in economic costs of bioinvasion in protected areas over the 35-year period 1975 – 2020. Because the data has significant gaps, no doubt invasions really cost much more.

Moodley et al. 2022 (full citation at end of this blog) attempt to apply these data to analyze economic costs in protected areas. As they note, protected areas are a pillar of global biodiversity conservation. So it is important to understand the extent to which bioinvasion threatens this purpose. 

Unfortunately, the data are still too scant to support any conclusions. Such distortions are acknowledged by Moodley et al. I will discuss the data gaps below a summary of the study’s findings.

The Details

Of the estimated $22.24 billion, only 4% were observed costs; 96% were “potential” costs (= extrapolated or predicted based on models). Both had generally increased in more recent years, especially “potential” costs after 1995. As is true in other analyses of InvaCost data, the great majority (73%) of observed costs covered management efforts rather than losses due to impacts. The 24% of total costs ascribed to losses, or damage, exceeded the authors’ expectation. They had thought that the minimal presence of human infrastructure inside protected areas would result in low records of “economic” damages.

The great majority (83%) of reported management costs were reactive, that is, undertaken after the invasion had occurred. In terrestrial environments, there were significantly higher bioinvasion costs inside protected areas than outside (although this varied by continent). However, when considering predicted or modelled costs, the importance was reversed: expected management costs represented only 5% while these “potential” damages were 94%.

Higher expenditures were reported in more developed countries – which have more resources to allocate and are better able to carry out research documenting both damage and effort. 

More than 80% of management costs were shouldered by governmental services and/or official organizations (e.g. conservation agencies, forest services, or associations). The “agriculture” and “public and social welfare” sectors sustained 60% of observed “damage” and 89% of “mixed damage and management” costs respectively. The “environmental” and “public and social welfare” sectors together accounted for 94% of all the “potential” costs (predicted based on models) generated by invasive species in protected areas; 99% of damage costs. With the partial exception of the agricultural sector, the economic sectors that contribute the most to movement to invasive species are spared from carrying the resulting costs.

Lord Howe Island, Australia; threatened by myrtle rust; photo by Robert Whyte, via Flickr

Invasive plants dominated by numbers of published reports – 64% of reports of observed costs, 79% of reports of “potential”. However, both actual and “potential” costs allotted to plant invasions were much lower than for vertebrates and invertebrates. Mammals and insects dominated observed animal costs.

It is often asserted that protected areas are less vulnerable to bioinvasion because of the relative absence of human activity. Moodley et al. suggest the contrary: that protected areas might be more vulnerable to bioinvasion because they often host a larger proportion of native, endemic and threatened species less adapted to anthropogenic disturbances. Of course, no place on Earth is free of anthropogenic influences; this was true even before climate change became an overriding threat. Plenty of U.S. National parks and wilderness areas have suffered invasion by species that are causing significant change (see, for example, here, here, and here).

Despite Best Efforts, Data are Scant and Skewed

Economic data on invasive species in protected areas were available for only a tiny proportion of these sites — 55 out of 266,561 protected areas.

As Moodley et al. state, their study was hampered by several data gaps:

  1. Taxonomic bias – plants are both more frequently studied and managed in protected areas, but their reported observed costs are substantially lower than those of either mammals or insects.
  2. The data relate to economic rather than ecological effects. The costliest species economically might not cause the greatest ecological harm.
  3. Geographical bias – studies are more plentiful in the Americas and Pacific Islands. However, studies from Europe, Africa and South America more often report observed costs. The South African attention to invasive species (see blogs here, here, and here), and economic importance of tourism to the Galápagos Islands exacerbate these data biases.
  4. Methodological bias – although reporting bioinvasion costs has steadily increased, it is still erratic and dominated by “potential” costs = predictions, models or simulations.

I note that, in addition, individual examples of high-cost invasive species are not representative. The highest costs reported pertained to one agricultural pest (mango beetle) and one human health threat (mosquitoes).

Great Smokey Mountains National Park; threatened by mammals (pigs), forest pests, worms, invasive plants … Photo by Domenico Convertini via Flickr

As these weaknesses demonstrate, a significant need remains for increased attention to the economic aspects of bioinvasion – especially since political leaders pay so much greater attention to economics than to other metrics. However, the reported costs – $22.24 billion over 35 years, and growing! – are sufficient in the view of Moodley et al. to support advocating investment of more resources in invasive species management in protected areas, including – or especially – it is not quite clear — preventative measures.

SOURCES

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

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

Posted by Faith Campbell

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

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

or www.fadingforests.org

Comment to APHIS on its Strategic Plan

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

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

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

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

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

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

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

Posted by Faith Campbell

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

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

or www.fadingforests.org

APHIS – 50 years + plant pest detection month

beech leaf disease – Not one of the plant pests that APHIS is regulating! Photo by Jennifer Koch, USFS

APHIS has reminded us that 2022 is the agency’s 50th year. In its press release, APHIS claims several accomplishments over this period:

  • Eradicating plant pests like European grapevine moth and plum pox from the country, while reducing the impact of others plant diseases, including boll weevil and Mediterranean and Mexican fruit flies;
  • Eradicating serious animal diseases, including highly pathogenic avian influenza, virulent Newcastle disease, and pseudorabies, from the country’s herds and flocks, while reducing the prevalence of other animal diseases like bovine tuberculosis and brucellosis;
  • Improving care for laboratory animals, exhibited animals and other animals;
  • Ensuring genetically engineered plants do not pose a risk to plant health, while keeping up with the ever-changing technology in this field;
  • Reducing the impact of wildlife damage on agriculture and natural resources; and
  • Ensuring safe trade of agriculture commodities across the globe

APHIS also launched a new page on its website to share a series of visual timelines of its history and important milestones.

APHIS also states that USDA) has declared April 2022 to be Invasive Plant Pest and Disease Awareness Month (IPPDAM). The link Invasive Plant Pest and Disease Awareness Month connects you to APHIS’ webpage. Secretary Vilsack asks people to be alert. He noted particularly the risk that pests will hitch a ride on untreated firewood, outdoor gear and vehicles, and soil, seeds, homegrown produce, and plants.

The notice urges people to:

  • Familiarize yourself with the invasive pests that are in your area, and their symptoms. [Faith says – also look for pests not “here” yet – early detection!]
  • Look for signs of new invasive plant pests and diseases and report them to your local Extension office, State department of agriculture or your USDA State Plant Health Director’s office.
  • When returning from travel overseas, declare all agricultural items to U.S. Customs and Border Protection so they can ensure your items won’t harm U.S. agriculture or the environment.
  • Don’t move untreated firewood. Buy local or use certified heat-treated firewood, or responsibly gather it on site where permitted.
  • Source your plants and seeds responsibly. When ordering online, don’t assume items available from foreign retailers are legal to import into the United States. Learn how to safely and legally order plants and seeds online.
  • Don’t mail homegrown plants, fruits and vegetables. You may live in an area under quarantine for a harmful invasive plant pest. You could inadvertently mail a pest.
  • When in doubt, contact your local USDA State Plant Health Director’s office to find out what you need to do before buying seeds or plants online from an international vendor or before mailing your homegrown agricultural goods.