Category: invasive species policy

Analysis of Methods to Predict a New Pest’s Invasiveness: Which Work Best Under What Conditions?

spotted lanternfly – could we have predicted its arrival? Its Impacts? Photo by Holly Ragusa, Pennsylvania Department of Agriculture

As readers of my blogs know, I wish to prevent introduction and spread of tree-killing insects and pathogens and advocate tighter and more pro-active regulation as the most promising approach. I cannot claim to have had great success.

Of course, international trade agreements have powerful defenders and the benefit of inertia. And in any case, prevention will be enhanced by improving the accuracy of predictions as to which specific pests are likely to cause significant damage, which are likely to have little impact in a naïve ecosystem. This knowledge would allow countries to can then focus their prevention, containment, and eradication efforts on this smaller number of organisms.

I applaud a group of eminent forest entomologists and pathologists’ recent analysis of widely-used predictive methods’ efficacy [see Raffa et al.; full citation at the end of this blog]. I am particularly glad that they have included pathogens, not just insects. See earlier blogs here, here, here, and here.

I review their findings in some detail in order to demonstrate their importance. National and international phytosanitary agencies need to incorporate this information and adopt new strategies to carry out their duty to protect Earth’s forests from devastation by introduced pests.

Raffa et al. note the usual challenges to plant health officials:

  • the high volumes of international trade that can transport tree-killing pests;
  • the high diversity of possible pest taxa, exacerbated by the lack of knowledge about many of them, especially pathogens;
  • the restrictions on precautionary approaches imposed by the World Trade Organization’s Sanitary and Phytosanitary Agreement (the international phytosanitary system) – here, here, and here.   
  • the high cost and frequent failure of  control efforts.
ash trees killed by emerald ash borer; Mattawoman Creek, Maryland; photo by Leslie A. Brice

The Four Approaches to Predicting Damaging Invaders

At present, four approaches are widely used to predict behavior of a species introduced to a naïve environment:

(1) pest status of the organism in its native or previously invaded regions;

(2) statistical patterns of traits and gene sequences associated with high-impact pests;

(3) sentinel plantings to expose trees to novel pests; and

(4) laboratory tests of detached plant parts or seedlings under controlled conditions.

Raffa et al. first identify each method’s underlying assumptions, then discuss the strengths and weaknesses of each approach for addressing three categories of biological factors that they believe explain why some organisms that are relatively benign, sparse, or unknown in their native region become highly damaging in naïve regions:

(1) the lack of effective natural enemies in the new region compared with the community of predators, parasites, pathogens, and competitors in the historical region (i.e., the loss of top-down control);

(2) the lack of evolutionary adaptation by naïve trees in the new region compared with long-term native interactions that select for effective defenses or tolerance (i.e., the loss of bottom-up control); and

(3) novel insect–microbe associations formed in invaded regions in which one or both members of the complex are non-native, resulting in increased vectoring of or infection courts for disease-causing pathogens (i.e., novel symbioses). I summarize these findings in some detail later in this blog.

Most important, Raffa et al. say none of these four predictive approaches can, by itself, provide a sufficiently high level of combined precision and generality to be useful in predictions. Therefore, Raffa et al. outline a framework for applying the strengths of the several approaches (see Figure 4). The framework can also be updated to address the challenges posed by global climate change.

Raffa et al. repeatedly note that lack of information about pests undercuts evaluation efforts. This is especially true for pathogens and the processes determine which microbes that are innocuous symbionts in co-evolved hosts become damaging pathogens when introduced to naïve hosts in new ecosystems.

Findings in Brief

Raffa et al. found that:

  1. Previous pest history in invaded environments provides greater predictive power than population dynamics in the organism’s native regions.
  2. Models comparing pest–host interactions across taxa are more predictive when they incorporate phylogenies of both pest and host. Traits better predict a pest’s likelihood of transport and establishment than its impact.
  3. Sentinel plantings are most applicable for pests that are not primarily limited to older trees. Ex patria sentinel plantations are more likely to detect pest species liberated by loss of bottom-up controls than top-down controls, i.e., most fungi and woodborers but not insect defoliators.
  4. Laboratory tests are most promising for pest species whose performance on seedlings and detached parts (e.g., leaves) accurately reflects their performance on live mature trees. They are thus better at predicting impacts of insect folivores and sap feeders than woodborers or vascular wilt pathogens.

Raffa et al. also ask some fundamental questions:

  • How realistic is it to expect reliable predictions, given the uniqueness of each biotic system?
  • When should negative data – lack of data showing a species is invasive – justify decisions not to act? Especially when there are so many data gaps?  
  • Who should make decisions about whether to act? How should the varying values of different social sectors be incorporated into decisions?

Raffa et al. identify critical areas for improved understanding:

1) Statistical tools and estimates of sample size needed for reliable forecasts by the various approaches.

2) Reliability, breadth, and efficiency of bioassays.

3) Processes by which some microorganisms transition from saprophytic to pathogenic lifestyles.

4) Procedures for scaling up results from bioassays and plantings to ecosystem- and landscape-level dynamics.

5) Targetting and synergizing predictive approaches and methods for more rapid and complete information transfer across jurisdictional boundaries.

I am struck by two generalizations:

  1. While most introduced forest insects are first detected in urban areas, introduced pathogens are more commonly detected in forests. I suggest that more intensive surveys of urban trees and “sentinel gardens” might result in detection of pathogens before they reach the forest.
  2. Enemy release is rarely documented as the primary basis for pathogens that cause little or no impact in their native region but become damaging in an introduced region. Enemy release appears generally more important with folivores and sap feeders than with woodborers.

Detailed Evaluation of Predictive Methodologies

white pine blister rust-killed whitebark pine at Crater Lake National Park; photo by F.T. Campbell
  1. Empirical assessment of pest status in previously occupied habitats

This is the most commonly applied method now, partly because it seems to follow logically from the World Trade Organization’s requirement that national governments provide scientific evidence of risk to justify adopting phytosanitary measures. The underlying assumption is that species that have caused damage in either their native or previously invaded ranges are those most likely to cause damage if introduced elsewhere. The corollary is that species that have not previously caused damage are unlikely to cause significant harm in a new ecosystem.

As noted above, Raffa et al. found that a species’ damaging activity in a previously invaded area can help indicate likely pest status in other regions. However, its status — pest or not — in its native range is not predictive. See Table 1 for numerous examples of both pests and non-pests. For example, Lymantria dispar has proved damaging in both native and introduced ranges. Ips typographus has not invaded new territories despite being damaging in its nature range and frequently being transported in wood. White pine blister rust is not an important mortality source on native species in its native range but is extremely damaging in North America.

Raffa et al. also note the importance of whether effective detection and management strategies exist in determining a pest’s impact ranking. Insects are more easily detected than pathogens; some respond to long distance attractants such as pheromones or plant volatiles. These methods can include insect vectors of damaging pathogens.

Re: the difficulty of assessing insect–microbe associations, they name several examples of symbionts which have caused widespread damage to naïve hosts: laurel wilt in North America; Sirex noctilio and Amylosterum areolatum around the Southern Hemisphere; Monochamus spp. and Bursaphelenchus xylophilus in Asian and European pines. Dutch elm disease illustrates a widespread epidemic caused by replacement of a nonaggressive native microorganism in an existing association with a non-native pathogen. Beech bark disease resulted from independent co-occurrence of an otherwise harmless fungus and harmless insect.

In sum, “watch” lists are disappointingly poor at identifying species that are largely benign in their native region but become pests when transported to naive ecosystems. Many of our most damaging pests are in this group. Raffa et al. note that this is not surprising because naïve systems lack the very powerful top-down, bottom-up, and lateral forces that suppress pests’ populations in co-adapted system. Countries often try to overcome this uncertainty by shifting to pathway mitigation and other “horizontal measures” – as I have often advocated. Raffa et al. emphasize that such approaches are costly to implement and constrain free trade.

  • Predictive models based on traits of pests and hosts

Predictive models provide the most all-encompassing and logistically adaptable of the forecasting approaches. Typically, models consider various components of risk, e.g. probability of transport, probability of establishment, anticipated level of damage.

The overriding assumption is that patterns emerging from either previous invasions or basic biological relationships can provide reliable predictions of impacts that might result from future invasions. However, Raffa et al. note that the models’ reliability and specificity are hampered by small sample sizes and data gaps.

They found that specific life history traits have proved to be more predictive of insect — and to a lesser extent fungal – establishment than of impact. Earlier studies [Mech et al. (2019) and Schulz et al. (2021)] found no association between life history traits and impacts for either conifer-feeding or angiosperm-feeding insects.   

Some traits of pathogens have been linked to invasion success, e.g., dispersal distance, type of reproduction, spore characteristics, and some temperature characteristics for growth and parasitic specialization. Raffa et al. say that root-infecting oomycete pathogens have a broader host range and invasive range than those that attack aboveground parts. Oomycetes that grow faster and produce thick-walled resting structures have broader host ranges. Phenotypic plasticity is also important. Raffa et al. say that those organisms that require alternate hosts can be limited in their ability to establish. However, they don’t mention that – once introduced — they can have huge impacts, as the example of white pine blister rust illustrates.

Raffa et al. say that phylogenetic distance of native and introduced hosts is more predictive for foliar ascomycetes than for basidiomycete and oomycete pathogens with broad host ranges. They suggest predictive ability can be improved by incorporating other factors, e.g., feeding guild. They note that the findings of Mech et al. and Schulz et al. (see links above) show the importance of both host associations with pests and phylogenetic relationships between native and naïve hosts for predicting impacts.

Geography is important: while there is a greater chance of Northern Hemisphere pests invading in the same hemisphere, this is not universal, as shown by Sirex (of course, the woodwasp is attacking hosts native to the Northern Hemisphere – pines).

Genomic analyses have been used more often with pathogens. There are two general approaches:

trees killed by chestnut blight; USDA Forest Service photo

1) Comparing the genomes of different species to identify the determinants associated with certain traits or lifestyles. For example, a post hoc analysis of the genus Cryphonectria could distinguish nonpathogenic species from the chestnut blight fungus C. parasitica.

2) Using genomic variation within a single species to identify markers associated with traits. Genome sequencing of a worldwide collection of the pathogens that cause Dutch elm disease revealed that some genome regions that originated from hybridization between fungal species contained genes involved in host–pathogen interactions and reproduction, such as enhanced pathogenicity and growth rate.

Raffa et al. point out that the growth of databases will facilitate genomic approaches to identify important invasiveness and impact traits, such as sporulation, sexual reproduction, and host specificity.

At present, Raffa et al. believe that models based on traits, phylogeny, and genomics offer potential for a rapid first pass to predicting levels of pest damage. However, assessors must first have a list of candidate pest species and detailed information about each. Plus there is still too much uncertainty to rely exclusively on the models.

  • Sentinel trees

Raffa et al. say that sentinel trees can potentially provide the most direct tests of tree susceptibility and the putative impact of introduced pests. Three types of plantations offer different types of information:

  1. In patria sentinels [= sentinel nurseries] = native trees strategically located in an exporting country and exposed to native pests. The intention is to detect problematic hitchhikers before they are transported to a new region. These plantings are useful for commodity risk assessment.  However, all the taxa associated with the sentinel trees must be identified to ascertain whether they can become a threat to plants in the new ecosystem.
  • Ex patria plantings [= sentinel plantations] = trees from an importing country are planted in an exporting country with the aim of assessing new pest–host associations. These plantings are most useful for identifying threats that arise primarily from lack of coevolved host tree resistance (i.e., loss of bottom-up control). They cannot predict the effects of lack of co-adapted natural enemies in the importing region (i.e., loss of top-down control). Plantings are thus more helpful in predicting impacts by pathogens and woodborers than folivores and sap feeders. However, ex patria plantings cannot predict pest problems that arise from novel microbial associations, or increased susceptibility to native pests.
  • Trees in botanic gardens, arboreta, large-scale plantations, and urban parks and yards can provide information on both existing native-to-native associations and new pest–host associations. Analyzing these plantings can be useful for studying host-shift events and novel pest–host associations. Again, all the taxa associated with the sentinel trees must be identified to ascertain whether they can become a threat to plants in the new ecosystem. Monitoring these planting have detected previously unknown plant–host associations (such as polyphagous shot hole borer and tree species in California and South Africa), and entirely unknown taxa. Pest surveillance in urban areas can also facilitate early detection, thereby strengthening the possibility of eradication.
PSHB attack on Erythrina caffri; photo by Paap

Sentinel tree programs are limited by 1) small sample sizes; 2) immature trees; and 3) the fact that trees planted outside their native range might not be accurate surrogates for the same species in native conditions. Some of these issues can be reduced by establishing reciprocal international agreements among trading partners; the International Plant Sentinel Network helps to coordinate these collaborations.

Botanic gardens and arboreta have the advantage of containing adult trees; this is important because pest impacts can vary between sapling to mature trees. However, they probably contain only a few individuals per plant species, usually composed of narrow genetic base.

Large-scale plantations of exotic tree species, e.g., exotic commercial plantations, comprise large numbers of trees planted over large areas with varied environmental conditions, and they stand for longer times. Still, they commonly have a narrow genetic base that might not be representative of wild native plants. Also, only a few species are represented in commercial plantations.

Raffa et al. report that experience in commercial Eucalyptus plantations in Brazil alerted Australia to the threat from myrtle rust (Austropuccinia psidii). However, in an earlier blog I showed that Australia did not act quickly based on this knowledge.

  • Laboratory assays using plant parts or seedlings

Laboratory tests artificially challenge seedlings, plant parts (e.g., leaves, branches, logs), or other forms of germplasm of potential hosts to determine their vulnerability. These tests are potentially powerful because they are amenable to experimental control, standardized challenge, and replication. They also avoid many of the logistical constraints of sentinel plantings. Finally, they can be performed relatively rapidly.

The key underlying assumption is that results can be extrapolated to predict injury to live, mature trees under natural conditions. The validity of this assumption depends on the degree to which exogenous biotic and abiotic stressors affect the outcomes. Raffa et al. report that environmental stressors tend to more strongly influence tree interactions with woodborers than folivores.

These assumption are more likely to be met by pathogens that infect shoots or young tissues, such as the myrtle rust pathogen Austropuccinia psidii, ash dieback pathogen Hymenoscyphus fraxineus, and the sudden oak death pathogen Phytophthora ramorum. 

The host range of and relative susceptibilities to insects is usually tested on twigs bearing foliage for defoliators and sap suckers; bark disks, logs, or branches for bark beetles, ambrosia beetles, and wood borers. These methods do not work as well for bark beetle species that attack mature trees in which active induced responses and transport of resins through established ducts are critically important.

The major advantages of laboratory tests is that they readily incorporate both positive (known hosts) and negative (known nonhosts) controls, can provide a range of environmental conditions, can be performed relatively rapidly, are statistically replicable at relatively low costs, and can test multiple host species and genotypes simultaneously. The ability to statistically replicate a multiplicity of environmental combinations and species is particularly valuable for evaluating relationships under anticipated future climatic conditions.

However, there are several important limitations. In testing pathogens, environmental conditions required for infection are often unknown. Choice of non-conducive conditions might result in false negatives; choice of too-conducive conditions might result in exaggerating the likelihood of infection. Results of tests of insect pests can vary depending on whether the insects are allowed to choose among potential host plants. Other complications arise when the pest being evaluated requires alternate hosts. In addition, seedlings are not always good surrogates for mature trees – especially as regards pathogens and bark, wood-boring and root collar insects. Folivores are less affected by conditions. Plus, the costs can be significant since they involve maintaining a relatively large number of viable and virulent pathogen cultures, insects, and candidate trees in quarantine.

Finally, although lab assays are well suited for identifying new host associations, results might not be amenable to scaling up to predict a pest’s population-level performance in a new ecosystem. Scaling up is especially problematic for those insect species whose dynamics are strongly affected by trophic interactions.

SOURCE

Raffa, K.F., E.G. Brockerhoff, J-C Gregoire, R.C. Hamelin, A.M. Liebhold, A. Santini, R.C. Venette, and M.J. Wingfield. 2023. Approaches to Forecasting Damage by Invasive Forest P&P: A Cross-Assessment.  BioScience Vol. 73 No. 2: 85–111    https://doi.org/10.1093/biosci/biac108  

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

Eradicating Invasive Species: You need “social license” to succeed

spread of non-native conifers in mountains of New Zealand; photos by Richard Bowman; New Zealand government website

As those of us who want to “do something” to counter bioinvasions struggle to mobilize both the  resources and the political will necessary, I rejoice that more studies are examining what factors affect “social license” [= public approva] for such programs. One such study was recently published in New Zealand — Mason et al. (full citation at the end of the blog). New Zealand enjoys a greater appreciation of the uniqueness of its biology and awareness of invasive species’ impacts than the United States. However, their findings might provide useful guidance in the US and elsewhere.

Mason et al. sought to understand motivations of, and constraints on, those local groups responsible for controlling the spread of non-native conifers into New Zealand’s remnant native ecosystems. Non-forest ecosystems across much of the country are at risk of rapidly transforming into exotic conifer forests. For these reasons, authorities are pressing for timely removal of existing seed sources, that is, mature non-native conifer trees of several species. The blog I posted earlier apparently describes effects of conifer invasions in lowland ecosystems, whereas the Programme described here is focused on high-elevation systems.

The eradication effort in the study is the National Wilding Conifer Control Programme, establishedin 2016. A large increase in funding provided during the COVID-19 lockdown made it practical to try to eradicate seed sources from large swathes of vulnerable land. The Programme coordinates control efforts across the country, working across property and land-tenure boundaries. Landowners are expected to cover 20% of the cost of removing conifers from their land. Since removing all seed sources of high-risk conifer species from the landscape is key to achieving long-term goals, success is unlikely if significant seed sources are allowed to persist.

Mason et al. combined workshops, questionnaires, and site visits to gather data on particular aspects of this Programme. They found that social resistance, rather than lack of scientific knowledge, was often the main barrier to success in managing widespread invasive species. The authors do not address whether the fact that only 30 people provided information for their study might undermine the reliability of their findings.

map of conifer wilding sites; adapted from Wilding conifers – New Zealand history and research background, a presentation by Nick Ledgard at the “Managing wilding conifers in New Zealand – present and future” workshop (2003)

The authors suggest that the main benefit of scientific information might be to increase stakeholders’ support for management interventions — rather than to guide manager’ decisions about which strategies to pursue.  To support social license, invasive species research programs might need to focus not only on cost-effective control technologies and strategies, but – perhaps especially — the benefits (both tangible and intangible) of invasive species control for society.

Mason et al. found that people were motivated to combat conifer invasions by impacts with direct influence on humans or human activities (e.g., reduced water yield, damage to infrastructure from wildfires, reduced tourist activities due to landscape transformation) and also by impacts affect ecosystems (e.g.,  impacts on biodiversity, aquatic ecosystems and landscapes).  

People objected to control or eradication programs primarily because of social concerns. These included the unwillingness of landowners to participate and regulatory frameworks that had perverse incentives.

Mason et al. called for greater efforts by scientists to persuade stakeholders[p1]  to allow removal of “wilding” conifers from private land and development of more appropriate regulations. They found that forecasting models were particularly effective in persuading people to support these efforts. It seems to me that outreach teams might need “translators” to convert scientists’ findings to information that would be more useful by stakeholders.

The authors concede that the “wilding conifer” situation has unique attributes. First, invading conifers present a stark, easily seen difference between native and invaded ecosystems. Second, some – but not all—stakeholders appreciate the uniqueness of New Zealand’s biomes. Third, the impacts of conifer invasion are sufficiently well known that they can be described succinctly and accurately.

Do these unique attributes undercut the relevance of this study to North America? It is still true that ongoing support from local stakeholders (including landowners and community groups) influences the effectiveness or profitability of managing invasive species. .It is also true that groups’ varying values affect willingness to support the activities.

Mason et al. think through the issue of stakeholders’ conflicting perspectives on the value of particular invasive species and the values threatened by that invader. These can include ethical or safety concerns around management methods, particularly regarding toxins and genetic modification. Economoic costs are also a factor – especially if the landowner must pay all or some of them.

I find it interesting that the government simultaneously funded a 5-year research program to study various issues regarding the spread, ecosystem impacts, and control of wilding conifers. The result is the Mason et al. study discussed here. I wish the U.S. funded independent analyses of its invasive species programs!

Pinus contorta – the most rapidly growing Pinus introduced to New Zealand; photo by Walter Siegmund / Wikimedia

More Details, Policy Suggestions

Workshop attendees unanimously identified landscape impacts as a reason for controlling wilding conifers. This primarily concerned the loss of New Zealand’s visual heritage or cultural identity rather than loss of native species’ habitats. When the landowner was raised in Europe, these cultural or heritage values sometimes had the opposite effect, since they see conifer forests as important components of “natural” landscapes.

Currently, landowner funding and permission is required for conifer removal. Some individual landowners want to establish new forestry plantings. Some resist removal of existing forestry plantations (which provide income) and shelter belts (which provide shelter for livestock in high country landscapes). Some landowners were unwilling to pay their 20% of removal costs. Or they objected to certain conifer control methods—particularly helicopter spraying of herbicides. New Zealand’s regulatory process also requires years of negotiating to remove standing trees – further delaying any action. In theory, landowners who resist removal could be prosecuted under the Biosecurity Act. However, this approach has never been tried for removing wilding conifers.

Mason et al. suggested several changes in policy to overcome some of these barriers.

First, forestry consultants can “game” the wilding conifer “risk calculator” to obtain government approval to establish conifer plantations in high-risk environments. The authors suggest that authorities create a “liability calculator.” Under this system, landowners wishing to retain conifers on their land for whatever reason would be liable for any subsequent containment costs. However, developing such a tool requires more finely-scaled models of conifer spread.

Second, given the high costs of combatting invading conifers if seed sources are allowed to persist, they suggested that it might be more cost-effective for the control program to pay for plantation removal under New Zealand’s Emissions Trading Scheme.

Given the overwhelmingly social and regulatory nature of barriers to success, the primary role for scientific information is providing assessments of outcomes in the absence of wilding conifer control. Preferred messages were return-on-investment estimates and forecasts of ecosystem impacts, particularly relating to biodiversity loss, water yield reduction, and wildfire hazard. Forecasts were key to demonstrating that management interventions reduced future control costs and avoided environmental impacts which large sections of the community value (i.e. biodiversity loss, reduction in water yield and agricultural productivity, increased wildfire risks). Practitioners felt that forecasting models might also channel research toward areas of high uncertainty. Mason et al. recognize the difficulties presented by inherent complexity of ecological systems. However, they think “good practice” guidelines on forecasting are emerging.

The authors find that information content and presentation need to be tailored to the various audiences – most of whom lack experience in interpreting data from environmental forecasting models. They suggest that outreach materials focus on clear illustration of the tangible and intangible benefits of wilding conifer management rather than detailed explorations of scenarios. Participants suggested ways to improve the web tool to make it more accessible to a non-expert audience. 

Mason et al. mention aspects that require balancing, but don’t suggest criteria for making these choices. They say it is important to include all relevant stakeholders in invasive species management governance bodies. The absence of stakeholders with positive attitudes to wilding conifer invasions led to unanticipated external social resistance to the Programme. They recognize that including stakeholders with conflicting interests might obstruct the decision-making process.  Also, in areas where there has been success in containing conifers’ spread, people can’t see invading trees, so they don’t recognize the problem. They also note that existing data do not adequately recognize risks of spread from deliberately planted seed sources such as shelter-belts, plantations and amenity plantings. The authors do not discuss how to integrate these data into analyses and public outreach.

Finally, Mason et al. recognize that many other factors strongly influence stakeholders’ willingness to support invasive species control programs, especially the level of trust and strength of relationships between bioinvasion program staff and stakeholders.

Also, they suggest topics for future research: assessing how well forecasting models are integrated with  communications with stakeholders; how qualitative and quantitative research methods in different fields might support one another; and empirical tests to measure the relative effects on social license of a) involving stakeholders in developing models, b) using forecasts to assess the consequences of different management decisions and, c) the usefulness of different methods for incorporating scientific information in stakeholder engagement.

SOURCE

Mason, N.W.H., Kirk, N.A., Price, R.J. et al. Science for social license to arrest an ecosystem-transforming invasion. Biol Invasions 25, 873–888 (2023). https://doi.org/10.1007/s10530-022-02953-w

see also https://www.doc.govt.nz/nature/pests-and-threats/weeds/common-weeds/wilding-conifers/

Posted by Faith Campbell

What do YOU think about the role “social license” plays in US invasive species programs? 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

 

Help Fight for $$ to Protect Forests

Help Fight for Money to Protect Forests

This blog asks YOU!!! to support funding for some of the key USDA programs. This blog focuses on USDA’s Animal and Plant Health Inspection Service (APHIS). APHIS is responsible for preventing introduction of pests that harm agriculture, including forests; and for immediate efforts to eradicate or contain those pests that do enter. While most port inspections are carried out by the Department of Homeland Security Bureau of Customs and Border Protection, APHIS sets the policy guidance. APHIS also inspects imports of living plants.

Please help by contacting your members of the House and Senate Appropriations Committees. I provide a list of members – by state – at the end of this blog. APHIS is funded by the House and Senate Appropriations Subcommittees on Agriculture and Related Agencies. These Subcommittees have scheduled hearings on the topic and I’ve drafted written testimony for them. I expect CISP will be joined by additional members of the Sustainable Urban Forest Coalition in signing the testimony. You can add the crucial voice of constituent’s support.

I will blog soon about funding for USDA’s Forest Service (USFS) – I don’t yet have necessary information to suggest specific funding levels.

Your letter or email need be no more than a couple paragraphs. To make the case for greater funding, feel free to pick-and-choose from the information that follows. Your greatest impact comes from speaking specifically about what you know and where you live.

These are the specific dollar amounts we’d like you to ask for. The rationale for each is below.

Appropriations for APHIS programs (in $ millions)

ProgramFY 2022 (millions)FY 2023FY 2024 Pres.’ request Our ask
Tree & Wood Pest$61$63$64$65 M
Specialty Crops$210$216$222$222 M
Pest Detection$28$29$30$30 M
Methods Development$21$23$23$25 M

The Costs of Introduced Pests

Introduced pests threaten many forest products and services benefitting all Americans, including wood products, wildlife habitat, carbon sequestration, clean water and air, storm water management, lower energy costs, improved health, aesthetic enjoyment, and related jobs. Already, the 15 most damaging non-native pests threaten at least 41% of forest biomass in the “lower 48” states. In total, these 15 species have caused an additional annual conversion of live biomass to dead wood at a rate similar in magnitude to that attributed to fire (5.53 TgC per year for pests versus 5.4 to 14.2 TgC per year for fire) [Fei et al.; full citation at end of blog; see also earlier].

tanoaks killed by SOD; Oregon Department of Forestry photo

These pests also impose significant costs that are borne principally by municipal governments and homeowners. As more pests have been accidentally introduced over time, these costs have risen. A study published last year [Hudgins et al.] projected that by 2050 1.4 million street trees in urban areas and communities will be killed by introduced insect pests. Municipalities on the forefront include Milwaukee and Madison Wisconsin; the Chicago area; Cleveland; and Baltimore, Towson, and Salisbury, Maryland. Removing and replacing these trees is projected to cost cities $30 million per year. Additional urban trees – in parks, on homeowners’ properties, and in urban woodlands – are also expected to die and require removal and replacement.

Pathways of Introduction

Tree-killing pests are linked to the international supply chain. Many pests—especially the highly damaging wood-borers like emerald ash borer, Asian longhorned beetle, polyphagous and Kuroshio shot hole borers, and redbay ambrosia beetle—arrive in inadequately treated crates, pallets, and other forms of packaging made of wood. Other pests—especially plant diseases like sudden oak death and sap sucking insects like hemlock woolly adelgid—come on imported plants. Some pests take shelter, or lay their eggs, in or on virtually any exposed hard surface, such as steel, decorative stone, or shipping containers.

infested wood from a crate; Oregon Department of Agriculture photo

Wood Packaging

Imports from Asia have historically transported the most damaging pests, e.g., Asian longhorned beetle, emerald ash borer, redbay ambrosia beetle, and the invasive shot hole borers. For decades goods from Asia have dominated imports. As of February 2022, U.S. imports from Asia were running at a rate of 20 million shipping containers per year. A recent analysis [Haack et al.; see also here] indicates that at least 33,000 of these shipping containers, perhaps twice that number, are carrying a tree-killing pest. These facts have led scientists to project [Leung et al.] that by 2050, the number of non-native wood-boring insects established in the US could triple. Hudgins et al. say the greatest damage would occur if an Asian wood-boring insect that attacks maples or oaks were introduced. Such a pest could kill 6.1 million trees and cost American cities $4.9 billion over 30 years. The risk would be highest if this pest were introduced to the South – and U.S. southern ports are receiving more direct shipments from Asia after the expansion of the Panama Canal in 2016. https://www.nivemnic.us/?m=202207

After introduction of the ALB, APHIS acted to curtail further introductions in wood packaging from China. First – in 1998 – APHIS required China to treat its wood packaging. Second, it worked with foreign governments to develop the International Standard for Phytosanitary Measures (ISPM) #15. The U.S. and Canada began phasing in ISPM#15 in 2005 with full implementation in 2006. Under ISPM#15, all countries shipping goods to North America must treat their wood packaging according to specified protocols with the goal of “significantly reducing” the risk that pests will be present.

However, as I have often blogged [see blogs under “wood packaging” category on this site] ISPM#15 has fallen short. Haack et al. found that as recently as 2020, 0.22% [1/5th of 1 percent] of the shipping containers entering the U.S. were infested by a tree-killing insect. This equates to tens of thousands of containers harboring tree-killing insects.

Worse, the data indicate that our trade partners’ compliance with the rules has deteriorated; the “approach rate” of pest-infested wood packaging fell in 2005-2006, but has since gone back up.

The most troubling offender is China. Although required since 1998 to treat its wood packaging, China consistently has one of the highest pest approach rates: it was 0.73% [or ¾ of 1%] during the 2010- 2020 period. This is three times the global average for the period. Since China supplied 40.7% of U.S. imports in 2022 [Szakonyi], or 5,655,000 containers. Thus China alone might be sending to the U.S. 30,000 containers infested with tree-killing insects. These pests threaten our urban, rural, and wildland forests and reduce forest productivity, carbon sequestration, the rural job base, water supplies and quality, and many other ecosystem services. 

ISPM#15 falls short at the global level. The fact that a pallet or crate bears the mark indicating that it complies with ISPM#15 has not proved to be reliable.

You might ask your Member of Congress or Senators to ask APHIS what steps it will take to correct the problem of Chinese non-compliance. (Remind him or her that that the Asian longhorned beetle, emerald ash borer, and many other insects of so-far lesser impact were introduced in wood packaging from China.

Asian longhorned beetle

Remind them also that the Department of Homeland Security’s Bureau of Customs and Border Protection has twice enhanced its enforcement of wood packaging rules. In 2017 it began penalizing importers of non-compliant wood packaging under Title 19 United States Code (USC) §1595a(b) or under 19 USC §1592. In 2021, it incorporated the wood packaging requirements into its voluntary C-TPAC program.)  

You might also urge them to ask APHIS what steps it is taking at the global level to improve the efficacy of ISPM#15 – or to replace it if necessary to ensure that pests are not being introduced.

spread of beech leaf disease

Imported Plants (“Plants for Planting”)

Some pest types—especially plant diseases like sudden oak death and sap-sucking insects like hemlock woolly adelgid—come on imported plants. The U.S. imported about 5 billion plants in 2021 [MacLachlan]. Recent introductions probably via this pathway include several pathogens — Phytophthoras, rapid ʻōhiʻa death in Hawai`i, beech leaf disease (established from Ohio to Maine), and boxwood blight. Insects have also been introduced on imported plants recently; one example is the elm zigzag sawfly (present in North Carolina, Virginia, and New York and Ontario). https://www.nivemnic.us/?p=4115

An analysis of data from 2009 [Liebhold et al.] found that approximately 12% of plant shipments were infested by a pest. This pest approach rate is more than 50 times higher than the 0.22% approach rate for wood packaging. APHIS has adopted several changes to its phytosanitary system for imported plants in the decade since 2009. A few studies have been published, but they have focussed on insects and excluded pathogens. We have noted that pathogens continue to be introduced via the plant trade. Therefore, please ask your Member or Senators to ask APHIS to facilitate an independent analysis of the efficacy of the agency’s current phytosanitary programs to prevent introductions of pests on important plants, with an emphasis on introductions of plant pathogens.

APHIS is responsible for preventing spread of the SOD pathogen, Phytophthora ramorum, through trade in nursery plants. In recent years California has had few detections in nurseries and little expansion in forests – but the situation suggests that this good news is probably more the result of the drought than of program efficacy. In cooler, wetter conditions in Oregon and Washington, detections in nurseries and alarming detections in the forest or plantings continue.

In 2022, the APHIS SOD Program supported detection and regulatory activities in 25 states. P. ramorum was detected at 18 establishment, 12 of which were first-time detections. The California nursery regulatory program – which is funded by APHIS – saw reduced funding in 2022. We think these cuts are unwise since this year’s very wet winter will probably lead to a new disease outbreaks. Programs in Oregon and Washington continue to detect infestations in additional retailers brought in by plants bought from other nurseries. Washington responded to four separate “trace forward” incidents, one involving more than 160 residential sites. Clearly, the federal-state program is not succeeding in eradicating P. ramorum from nurseries. Please suggest that your Congressperson and Senators ask APHIS what steps it is taking to improve the efficacy of the SOD program.

SOD-infected rhodoendron on plants in Indiana; photo by Indiana Department of Natural Resources

In the East, P. ramorum was found in three of 65 streams sampled in 10 states in 2022 (reaching across the Southeast from Mississippi through North Carolina, plus Texas, Maryland, Pennsylvania, and Illinois). One stream is troubling: a first-time detection in South Carolina, with no obvious nursery source. Since stream sampling began, P. ramorum has been detected from eight streams in four states, Alabama, Mississippi, North Carolina, and now South Carolina. The pathogen has been present in some of these streams for more than 10 years.

Oregon faces particularly high risks. Three of the four known strains of P. ramorum are established in Oregon forests. One of them, the EU1 lineage, is more aggressive than the NA1 clonal lineage already present in forests. In addition, the EU1 strain might facilitate sexual reproduction of the pathogen, thus exacerbating Oregon’s struggle to contain the disease.

As we know, introduced pests do not stay in the cities where they first arrived — they spread! Often that spread is facilitated by our movement of firewood, plants, or outdoor household goods such as patio furniture.

The beech trees so important to wildlife conservation in the Northeast are under attack by two pathogens and at risk to an insect. Most alarming is the spread – in a dozen years! — of beech leaf disease DMF from Ohio to Maine. A leaf-feeding weevil is spreading south in eastern Canada. Please suggest that your Member or Senators to ask APHIS what steps it is taking to prevent the weevil’s introduction to the U.S.

‘Ōhi‘a trees make up 80% of the biomass of forests in both wet and dry areas of the Hawaiian archipelago. It is under attack by two diseases caused by introduced pathogens first detected in 2010. ‘Ōhi‘a forests support more threatened and endangered species than any other forest system in the U.S. They also play a uniquely important role in providing other ecosystem services, including water supplies.

Asking for the Money Pest Problems Deserve


To respond effectively to these pests and to the others that will be introduced in coming years, the key APHIS programs identified above must have adequate funds. The funding levels I request – and hope you will support – are lower than I would wish, but everyone expects the Congress to refuse significant increases in funding (see table at beginning of this blog).

The Tree and Wood Pests account supports eradication and control efforts targeting principally the ALB and spongy (= gypsy) moth. Eradicating the ALB normally receives about two-thirds of the funds. The programs in Massachusetts, New York, Ohio, and South Carolina must continue until eradication succeeds.

Oregon detected the EAB in 2022. Although the state and Portland have been preparing for a decade for this eventuality, there will still be significant impacts. Four percent of Portland’s street trees are ash – more than 9,000 trees. Young ash constitute three percent of young trees in parks. Loss of Oregon’s ash will also have severe ecosystem impacts. In Willamette Valley wetlands, ash constitutes up to 100% of the forest trees. Washington and California are also concerned. Indeed, the Hudgins study identified Seattle and Takoma as likely to lose thousands of ash trees. The numerous ash in riparian forests, windbreaks, and towns of North Dakota are also at risk since the EAB is established in South Dakota, Minnesota, and Manitoba.

APHIS manages damaging pests introduced on imported plants or other items through its Specialty Crops program. The principal example is its efforts to prevent spread of the SOD pathogen through the interstate trade in nursery plants. We noted above that this program is not as successful as it should be. We support the Administration’s request for $222 million; however, you might suggest that your Member or Senator urge APHIS to allot adequate funding under this budget line to management of SOD, rapid ʻōhiʻa death pathogens in Hawai`i, and beech leaf disease and elm zig-zag sawfly in the East.

The Pest Detection program is key to the prompt detection of newly introduced pests that is critical to successful pest eradication or containment. The “Methods Development” program enables APHIS to improve development of essential detection and eradication tools.

The Administration’s request include a $1 million emergency fund. This is far below the level needed to respond when a new pest is discovered. Funding constraints have hampered APHIS’ response to past pest incursions.

Please note that many of the members of the Agriculture Appropriations Subcommittee are from states where non-native pests are probably not top of mind. It is important that everyone that knows about these threats communicate with your Member/Senators!!

Members of House or Senate Subcommittees that Fund APHIS

(Names of Senators are italicized)

STATEMEMBERAPHIS APPROPHOUSESENATE
AKLisa Murkowski  X
ALJerry Carl Katie BrittXX  X
CalifBarbara Lee David Valadao Josh Harder Diane FeinsteinX X   XX X X        X
FLDebbie Wasserman Scultz Scott FranklinX XX X 
GASanford BishopXX 
IDMike Simpson X 
ILLauren UnderwoodXX 
KSJerry MoranX X
KYMitch McConnellX X
LAJulia Letlow Ashley HinsonX XX X 
MDAndy Harris Chris Van HollenXX    X
MEChellie Pingree Susan CollinsX XX  X
MIJohn Moolenaar Gary PetersX Xx  X
MNBetty McCollumXX 
MSCindy Hyde-SmithX X
MTJon Tester Ryan ZinkeX    XX
NBDeb Fischer  X
NDJohn HoevenX X
NMMartin HeinrichX X
NVMark Amodei X 
OHMarcy KapturXX 
ORJeff MerkleyXXX
PAGuy ReschenthalerXX 
RIJack Reed  X
TXMichael Cloud Jake EllzeyXX X 
UTChris Stewart X 
VABen ClineXX 
WADan Newhouse Derek KilmerXX X 
WVShelly Moore Capito Joe Manchin  X X X
WIMark Pocan Tammy BaldwinX XX  X

SOURCES

Fei, S., R.S. Morin, C.M. Oswalt, and A.M. 2019. Biomass losses resulting from insect and disease invasions in United States forests. PNAS August 27, 2019. Vol. 116 No. 35  17371–17376

Haack R.A., J.A. Hardin, B.P. Caton and T.R. Petrice .2022. Wood borer detection rates on wood packaging materials entering the United States during different phases of ISPM#15 implementation and regulatory changes. Front. For. Glob. Change 5:1069117. doi: 10.3389/ffgc.2022.1069117

Hudgins, E.J., F.H. Koch, M.J. Ambrose, and B. Leung. 2022.  Hotspots of pest-induced US urban tree death, 2020–2050. Journal of Applied Ecology

Leung, B., M.R. Springborn, J.A. Turner, and E.G. Brockerhoff. 2014. Pathway-level risk analysis: the net present value of an invasive species policy in the US. Front Ecol Environ 2014; doi:10.1890/130311

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. Frontiers in Ecology.

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).

Szakonyi, M. 2023. Sourcing shift from China pulls US import share to more than a decade low.

One State’s Program Illustrates Importance of Federal Funding

Dead ash along Mattawoman Creek in 2019; Mattawoman Creek is a Maryland tributary of the Potomac River, hence of the Chesapeake Bay. Photo courtesy of Leslie A. Brice

In this blog I describe one state’s forest health efforts – Virginia. The pertinent lesson is the importance of external funding, especially that provided by USFS Forest Health Protection program, in supporting states’ efforts. Is your state’s forest health program as dependent upon federal funding as Virginia’s is? If so, there is a role for everyone: lobby your Congressional representative and senators to increase funding for this program!

I have based most of this blog on the Virginia Department of Forestry’s annual report for 2022.

Forests grow on more than 16 million acres in Virginia, or 62% of the Commonwealth’s land area. Eighty percent of these forests are hardwood or hardwood-pine. They break down as follows: 61% oak-hickory; 11% oak-pine; 5% bottomland hardwood; and 2% maple-beech-birch. A fifth of the forest is pine, composed of pine plantation (14%) and natural pine (7%). The long term trend is growth, especially among hardwoods.

The report devotes much of its attention to the agency’s programs to advise private landowners (individuals own 80% of the Commonwealth’s forestland); fire management (including prescribed burns); and state and federal conservation programs (e.g., easements). A major program shares reforestation costs on harvested pine lands. In 2022, this program assisted reforestation practices on 74,702 acres. Virginia has an impressive tree-raising program. VDOF grows more than 40 species, including longleaf and shortleaf pine, several spruce species, and dozens of hardwoods. The aim is to provide stock suited for the Commonwealth’s soils and climate. Many of the hardwood species are grown from acorns and seeds collected and donated by volunteers.

VDOF also helps to protect and improve the Commonwealth’s water quality through tree planting and sound forest management. VDOF has an unusual responsibility: enforcing the Virginia Silvicultural Water Quality Law.

The report also summarizes several urban and community forestry programs focused on education, community engagement, tree selection, and grants for tree planting to ensure canopy retention & management.

Forest Health – Importance of Federal Funding

Spongy Moth

Slightly over 1 million acres was mapped by aerial surveys in FY22. I believe the funding for these surveys came largely from the USFS. The surveys detected heavy to moderate defoliation by the spongy moth on 24,493 acres (almost twice the area detected in FY21). The spongy moth infestation is primarily in counties on the western side of the state, in the mountainous region, which has the highest densities of oaks and other hardwoods.

Spotted Lanternfly

The spotted lanternfly (SLF) was detected in Virginia early – in 2018 in Winchester at the northern end of the Shenandoah Valley. Winchester is connected to central Pennsylvania by Interstate 81, so rapid movement of SLF to Virginia from outbreaks slightly to the east of I-81 in Pennsylvania doesn’t surprise me. SLF has been spreading south along the mountains and over the Blue Ridge to Loudoun and Fairfax counties (in 2022). Fairfax County has announced a four-year, $200,000 effort to try to slow SLF spread by eradicating high densities of its preferred host, Ailanthus, from two county parks in the far south and north ends of the county. Ailanthus removal requires not just cutting the trees, but applying herbicide to prevent sprouting from the roots. This work is funded by the county, the local park authority and a $20,000 grant from the regional energy company, Dominion Energy Charitable Foundation.

Emerald Ash Borer

Virginia has six species of ash: white and green (both common), and smaller populations of black, blue, pumpkin and Carolina. EAB is now confirmed in 84 counties – most of the Commonwealth except the far southeast. The Department of Forestry treats 130 – 150 trees per year – half or more on state lands. At least in FY21, the funding came from federal sources. The report also notes outreach efforts at two minor league baseball games. Virginia recently adopted a priority of protecting the Chesapeake Bay watershed by promoting tree planting in riparian forest buffers. The EAB threatens this goal; see the photo (at top) of ash mortality along a Maryland tributary of the Bay. In 2021, EAB was detected in Gloucester County – a peninsula east of the York River that has Bay shoreline on the eastern side, tributary on the west (see photo).

Gloucester Point – Virginia Institute of Marine Sciences “living shoreline”; EAB was detected in Gloucester County in 2021, threatening riparian areas. Photo courtesy of the Chesapeake Bay Program

Threats to Beech

Beech bark disease is present in the western mountainous parts of the Commonwealth. One new county – Augusta – was detected in 2022. Three other counties are infested with the scale, but the fungal pathogen has not yet been detected. The alarming new threat, beech leaf disease, was detected in Prince William County in 2021. In 2022, it was confirmed in neighboring Fairfax County. The source of funding is not specified.

beech in a typical northern Virginia second-growth forest; photo by F.T. Campbell

Laurel Wilt Disease

Sassafras; photo by David Moynihan

I am pleased that the Commonwealth is paying attention to laurel wilt disease, which has been spreading north on sassafras. The closest outbreaks are in Tennessee, to the southwest of Virginia. The Commonwealth hosted a detection training program attend by 26 participants from six agencies from three states. The report does not specify the source of the funding.

Southern Pine Beetle

Virginia has also utilized funding from the USFS FHP program to manage the southern pine beetle. Since the program’s inception in 2004, Virginia has thinned pines on more than 70,000 acres, including 4,240 acres in FY22.

Invasive Plants

USFS FHP invasive species grants funded control treatments of invasive plants on somewhat less than 1,300 acres of state lands. Different figures on different pages of the report cause confusion. However, it is clear that nearly all the funds came from the USFS FHP program. Ailanthus was the main target; other species mentioned are privet, mimosa, autumn olive and Miscanthus.

State Funding of Conservation Initiatives; Will They Continue?

While the state’s government was controlled by Democrats, the governor and state legislature launched new programs with broader conservation goals. It is unclear whether they will continue now that Republicans have won the governorship and control of the House of Delegates.

Among the programs enjoying increased funding from the state budget during the current two-year cycle are

  • Efforts to restore depleted populations of two groups of tree taxa, shortleaf and longleaf pines. The emphasis has shifted to longleaf pine: the number of projects and acreages rose from 220 acres in FY21 to 1,212 acres in FY22. Restoration of shortleaf pine forests was limited to slightly over 600 acres in both years.
  • Programs to improve management of hardwood stands. These projects included crop tree release, control of “invasive species” (I think probably targetting invasive plants), prescribed burning and commercial thinning. There were also several demonstration projects on state-owned lands, a small land-owner planning assistance program, and training of state foresters and private consulting foresters in hardwood management. Apparently these aspects had been largely ignored in the past.
  • Creation of a dedicated Watershed program focused on increasing riparian forest buffers. This section of the report does not mention the threat posed by loss of ash to the emerald ash borer (EAB) [see EAB section above]
  • Urban forestry projects, many linked to protecting surface and ground water (including Chesapeake Bay watershed).

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

see also the article about beech leaf disease in the mid-Atlantic region written by Gabe Popkin; posted here

Imports from China down slightly, but high pest risk continues

I have blogged often about the pest risk of wood packaging associated with imports from Asia – especially China – and the shift in that risk arising from import volumes and ports at which they are arriving (increasing volumes entering country at ports along Atlantic and Gulf coasts). [See blogs posted on this site, under the “wood packaging” category (listed below the archives by date).] As noted, U.S. imports from Asia are at all-time highs: in the first three months of 2022, they reached 1.62 million TEU (shipping containers measured as twenty-foot equivalents). This was 31.1% higher than in the same period in pre-pandemic 2019 (Mogelluzzo, B. April 22, 2022).

The most recent information (Szakonyi, M. 2023) confirms that U.S. importers are shifting suppliers to countries other than China, primarily because of lengthy shutdowns in Chinese factories linked to the “0 COVID” policy and some U.S. restrictions and tariffs. Over 2022 (full year), China – including Hong Kong – supplied 40.7% of U.S. imports. This is still a huge proportion, but lower than in 2021, when it was 42.4%. The Journal of Commerce calculates that the number of containers coming from China fell by 435,000. At the current rate of infestation in wood packaging from China calculated by Haack et al. 2022, that might mean about 1,200 fewer containers from China with infested wood packaging entering the U.S.

[Explanation of calculations: I divided 435,000 by 2 to convert 20-ft TEU into 40-ft containers that CBP encounters at the ports; multiplied the result by 0.75 – based on the decade-old Meissner estimate of % of containers that have SWPM; then multiplied the result by .0073 because that is infestation rate for China during 2010-2020 period]

This might be progress. China continues to have a terrible record of non-compliant wood packaging 23 years after U.S. and Canada instituted phytosanitary requirements. According to Haack et al. (2022), packaging from China made up 4.6% of all shipments inspected under the terms of their analysis, but 22% of the 180 consignments with infested wood packaging. Thus the proportion of Chinese consignments with infested wood is five times greater than expected based on their proportion of the dataset. The rate of wood packaging from China that is infested has remained relatively steady = 1.26% during 2003–2004, 0.73% during 2010 – 2020. And the insects present belong to the group that causes the greatest damage: longhorned beetles (Cerambycids). Indeed, 78% of beetles in this family that were detected were from China.

There is some good news: some types of goods likely to be enclosed in crates have decreased notably. The proportion of furniture and other home items imported from China has declined from 71.6% of all U.S. imports in 2010 to 52.6% in 2022. As Haack et al. (2022) found, crates are the type of wood packaging where wood pests are most commonly found. While crates constituted only 7.5% of the wood packaging inspected, they made up 29.4% of the infested packaging – or four times greater than their proportion of the dataset.

The pest risk might not be changing significantly, however, because some of the new suppliers are also in Asia. Vietnam’s share of U.S. imports rose from 8.2% to 8.7%. The types of goods most often imported from Vietnam included electronics, shoes, and apparel. The U.S. has already been invaded by insect-pathogen complexes native to Vietnam, Taiwan, and other parts of southeast Asia – e.g., redbay ambrosia beetle and laurel wilt; invasive shot hole borers and Fusarium disease.

U.S. imports from South Korea, mostly electronics and autoparts, climbed from 3.8% to 4.1%. Imports from India also saw a tiny increase – from 3.8% to 3.9%. These shipments were primarily apparel and iron and steel components. These goods prompt concern because wood packaging associated with heavy materials are often infested by insects (Eyre et al. 2018). The Haack et al. (2022) analysis found two interceptions of wood packaging from Vietnam, one from Korea, and three from India.

Besides, the Journal of Commerce notes that shifts in suppliers cannot go far. These countries’ manufacturing capacity and transportation infrastructure are far below those of China (Szakonyi, M. 2023).

In February 2023, U.S. imports from Asia continued to decline from record levels in 2021 and 2022 to 1.09 million TEU. This level still exceeds by 25% the 869,091 TEU recorded in March 2020, at the beginning of the COVID-19 shutdown (Mongelluzzo, March 17, 2023).

[Reminder: higher shares of imports from Asia are going to ports along the Atlantic and Gulf coasts – spreading the risk. See earlier blogs. In early March the Port of Savannah posted an advertisement to the on-line Journal of Commerce, crowing that by July it will complete straightening the river at the Garden City Terminal (the container terminal). This fix will enable Savannah to raise its annual container processing capacity by 1.5 million TEU, to 7.5 million.]

The most hopeful finding is that imports from Mexico jumped 19.2% in the first 11 months of 2022 compared to the same period in 2021. Importers have their reasons: a desire to buy from producers closer to the U.S. market. These motivations have nothing to do with the risk of forest pest introductions. However, we can rejoice because Mexico has greatly improved the pest-infestation rates of its exports since 2009. The rate fell from 0.29% in 2003-2004 to 0.04% in 2010-2020 (Haack et al. (2022).  

larval Asian longhorned beetle; Thomas Denholm, NJ Department of Agriculture; Bugwood

I remain outraged that U.S. agencies have not taken effective steps to deal with the nearly 25-year-long problem of Chinese noncompliance with our phytosanitary requirements. As I noted in my previous blog, link to blog 303 Customs and Border Protection officials are disappointed that their enhanced enforcement in 2017 and 2021 has not yet resulted in improved compliance.

I suggested that the U.S. and Canadian government agencies should penalize trade partners with high records of not complying with ISPM#15. Among steps they should consider are

  • U.S. and Canada should refuse to accept wood packaging from foreign suppliers that have a record of repeated violations – whatever the apparent cause of the non-compliance. Institute severe penalties to deter foreign suppliers from taking devious steps to escape being associated with their violation record.
  • APHIS and CBP and their Canadian counterparts should provide guidance to importers on which foreign treatment facilities have a record of poor compliance or suspected fraud – so they can avoid purchasing SWPM from them. I greatly regret that the death of Gary Lovett might put an end to the voluntary industry program he had been developing, described here.
  • Encourage a rapid switch to materials that don’t transport wood-borers. Plastic is one such material. While no one wants to encourage production of more plastic, the Earth is drowning under discarded plastic. Some firms are recycling plastic waste into pallets.

Haack et al. 2022 fully describes the methodology used, the structure of USDA’s Agriculture Quarantine Inspection Monitoring (AQIM) program, detailed requirements of ISPM#15, the phases of U.S. implementation, etc.  Also see the supplemental data sheet in Haack et al. (2022) that compares the methods used in each analysis.

SOURCES

Eyre, D., Macarthur, R., Haack, R.A., Lu, Y. and Krehan, H., 2018. Variation in inspection efficacy by member states of wood packaging material entering the European Union. Journal of Economic Entomology, 111(2), pp.707-715.

Haack RA, Hardin JA, Caton BP and Petrice TR (2022) Wood borer detection rates on wood packaging materials entering the United States during different phases of ISPM#15 implementation and regulatory changes. Frontiers in Forests and Global Change 5:1069117. doi: 10.3389/ffgc.2022.1069117

Meissner, H., A. Lemay, C. Bertone, K. Schwartzburg, L. Ferguson, L. Newton. 2009. Evaluation of Pathways for Exotic Plant Pest Movement into and within the Greater Caribbean Region. A slightly different version of this report is posted at 45th Annual Meeting of the Caribbean Food Crops Society https://econpapers.repec.org/paper/agscfcs09/256354.htm

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. US imports from Asia hit three-year low in February: data. https://www.joc.com/article/us-imports-asia-hit-three-year-low-february-data_20230317.html

Szakonyi, M. 2023. Sourcing shift from China pulls US import share to more than a decade low. https://www.joc.com/article/sourcing-shift-china-pulls-us-import-share-more-decade-low_20230201.html

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

Protecting ash & hemlock – latest information

nearly dead ash in Shenandoah National Park; photo by F.T. Campbell

I participated in the annual USDA Interagency Invasive Species Research Forum in Annapolis in January 2023; as usual, I learned interesting developments. I focus here on updates re: efforts to protect ash and hemlock

Hopeful Developments re: countering EAB to protect ash

There are hopeful results in both the biocontrol and resistance breeding programs. The overall goal is to maintain ash as a viable part of the North American landscape.

Biocontrol

Juli Gould (APHIS) reminded us that the agency began a classical biocontrol program targetting emerald ash borer (EAB) in 2003 – only a year after EAB had been detected and much earlier than is the usual practice. [Thank you, former APHIS PPQ Deputy Administrator Ric Dunkle!] By 2007 scientists had identified, tested, and approved three agents; a fourth was approved in 2015.

Nicole Quinn (University of Florida) stressed that the egg prarasitoid, Oobius — if it is effective — could prevent EAB from damaging trees. However, it is so small that it is very difficult to sample. One small study demonstrated that Oobius will parasitize EAB eggs laid in white fringe trees (Chionanthus virginicus) as well as in ash. This is important because it means this secondary host is not likely to be a reservoir of EAB.

The numbers

According to Ben Slager (APHIS), more than 8 million parasitoids have been released at 950 sites since the program began in 2007. These releases have been in 418 counties in 31 states, DC, and four Canadian provinces. Still, these represent just 28% of infested counties. Parasitoids have been recovered in 21 states and two provinces.

Rafael de Andrade (University of Maryland) specified that these releases included more than 5 million Tetrastichus in 787 sites; ~2.5 million Oobius in 828 sites in 30 states; ~500,000 Spathius agrili – lately only north of the 40th parallel. Releases of Spathius galinae began in 2015; so far ~ 470,000 in 395 sites.

 Impact

Several presenters addressed questions of whether the agents are establishing, dispersing, and – most important – improving ash survival. Also, can classical biocontrol be integrated with other management techniques, especially use of the pesticide emamectin benzoate.

Dispersal

Several studies have shown that the four biocontrol agents disperse well (with the caveat that Oobius is very difficult to detect so its status is much less certain).

Implementation considerations

De Andrade found that the longer the delay between the date when EAB was detected and release of Oobius, the less likely Oobius will be recovered. Tetrastichus surprised because the higher the numbers released, the fewer were recovered. He could determine no association between recovery of S. agrili and variations in release regime [numbers released; delay in releasing biocontrol agents; or frequency of releases]. He said it is too early to assess Sp. galinae since releases began only in 2015, but he did see expected relationship to propagule pressure – the more wasps released, the higher the number that were recovered. Sp. galinae did surprise in one way: it seemed to perform better at lower latitudes. De Andrade noted he was working data from less than half of release sites. He asked collaborators to submit data!!!!

Initial signs of ash persistence and recovery 

Claire Rutledge (Connecticut Agriculture Experiment Station) determined that

  • More large trees were surviving in plots where the biocontrol agents were released
  • EAB density was lower at long-invaded sites
  • Parasitism rates were similar across release age treatments and release/control plots

Gould focused on protecting saplings so they can grow into mature trees which could be sources of seeds to establish future generations. She noted that there are many “aftermath” forests across the northern United States – those dominated by ash saplings.

In Michigan, at a site of green ash, as of 2015 – 2021, EAB populations are still low, parasitism rate by Tetrastichus and S. galinae high. The percentage of saplings that remained healthy was greater than 80%. There were similar findings in white ash in New York: very low EAB larval density; and more than 70% of ash saplings had no fresh galleries. Gould reported that Tetrastrichus impcts could be detected within three years of release.

So, EAB are being killed by the biocontrol agents combined with woodpecker predation; but in their fourth instar, after considerable damage to the trees.

downy woodpecker in Central Park, NYC. photo by Steven Bellovin, Columbia University

Jian Duan reported on two long-term studies in green & white ash in Michigan and New England. His team used the most labor-intensive but best approach to determine EAB larval mortality and the cause – debarking trees – to determine whether the EAB larva were parasitized, were preyed on by woodpeckers, or were killed by undetermined cause, such as tree resistance, disease, or competition. In Michigan, he linked a crash of EAB population in 2010 was caused by Tetrastichus; EAB tried to recover, but crashed again, due to S. galinae. EAB larval densities had been reduced to 10 / m2. Predation by abundant woodpeckers and the native parasitoid Atanycolus was also important.

In New England, EAB has also declined from 20-30 larvae /m2 to ~ 10 m2.

In Michigan, healthy ash with dbh of larger than 5 inches were much more plentiful in sites where parasitoids had been released. Their survival/healthy rate also was much higher in release sites but the difference declined as years passed. In New England there were growing numbers of healthy trees in 2021-22; (almost none in 2017). Duan conceded that he could not prove a direct link but the data points to recovery.

Tim Morris (SUNY-Syracuse) found that white ash saplings continued to die in large numbers, but the mortality rate was significantly below the rate in 2017. Canopy conditions varied; some trees that were declining in 2013 were recovering in 2017. Forty percent of “healthy” ash in 2013 continued recovering in 2021. Few living trees were declining; trees were either healthy or dead. He thinks probably a combination of genetics and presence of parasitoids explains which trees recover. Morris also reported some signs of regeneration.

beaver feeding on ash saplings, Fairfax County, Va;
photo by F.T. Campbell

At this point, I noted that in parts of northern Virginia, beavers have killed ash saplings. Morris reported finding the same in some sites in New York. Perhaps others have, also; my comment was greeted by laughter.

Theresa Murphy (APHIS) looked at integration of biocontrol and insecticide treatment in urban and natural sites. A study of black and green ash in Syracuse, NY Naperville, IL, and Boulder, CO found continued high parasitism by Tetrasticus and S. galinae and woodpecker attacks in trees treated with emamectin benzoate. Researchers could not detect Oobius. By 2020, most of the untreated trees had died but treated trees remained healthy.

Murphy has begun studying integration of biocontrol and pesticides in green and black ash forests. The goal is to protect large trees to ensure reproduction; the biocontrol agents do not yet protect the large trees. This is especially important for black ash because it declines very quickly after EAB invades. Sites have been established in New York, through collaboration with New York parks, Department of Environmental Conservation, and the Mohawk tribe. She is still looking for sites in Wisconsin – where EAB is spreading more slowly than expected.

1 of the infested ash in Oregon; photo by Wyatt Williams, ODF

Max Ragozzino of the Oregon Department of Agriculture reported on imminent release of biocontrol agents targetting the recently detected outbreak there. I am encouraged by the rapid response by both the state and APHIS.

EAB resistance in ash

Jennifer Koch (USFS) said the goal is not to produce populations where every seedling is fully EAB-resistant, but to develop populations of ash trees with enough resistance to allow continued improvement through natural selection while retaining sufficient genetic diversity to adapt to future stressors (changing climate, pests, diseases). The program has developed methods to quantify resistance in individuals.. Initial field selections of “lingering ash” were shown to be able to kill as many as 45 % of EAB larvae. Already green ash seedling families have been produced by breeding lingering ash parents.  This first generation of progeny had higher levels of resistance, on average, than the parent trees.  Each generation of breeding can increase the proportion of resistance. Although the bioassays to test for EAB-resistance are destructive (e.g., cutting and peeling to count numbers of surviving larvae), the potted ash seedling stumps can resprout. Once the new sprouts are big enough they are planted in field trials to correlate bioassay results with field performers.  Poor performers are culled; those with higher levels of resistance remain and become sources of improved seed.

To ensure preservation of local adaptive traits, this process must be repeated with new genotypes to develop many seed orchards from across the species’ wide range. To support this work, concerned scientists are building multi-partner collaborative breeding networks. These organizations provide ways for citizens and a variety of partners to engage through monitoring and reporting lingering ash, making land available for test planting, and helping with the work of propagation.

See Great Lakes Basin Forest Health Collaborative » Holden Forests & Gardens (holdenfg.org), Monitoring and Managing Ash (MaMA) – A citizen-science-driven program for conservation and mitigation (monitoringash.org), and TreeSnap – Help Our Nation’s Trees! for more information.

Resistance levels in some of the first generation progeny were high enough for use in horticulture, where it is important that trees can remain healthy in challenging environments (street trees, city parks, landscaping, etc.). Koch hopes to develop about a dozen cultivars comprising the best-performing trees, appropriate for planting in parts of Ohio, Michigan, Indiana, and Pennsylvania.   Local NGO partners are planting some of these promising genotypes in Detroit to see how they withstand EAB attack.

a black ash swamp; photo via Flickr

The threat to black ash is especially severe, and this species presents unique difficulties. While scientists found several seedlings from unselected seedlots had killed high levels of larvae, those deaths did not always result in better tree survival. Koch thinks the tree’s defense response becomes detrimental to tree by blocking transport of water and nutrients. She is working with experts in genomics and others, such as Kew Royal Botanic Gardens, to try to identify candidate trees for breeding programs.  The genomics work has been supported by APHIS and the UK forest research agency, DEFRA. Michigan and Pennsylvania have supported the breeding work. USFS Forest Health Protection has supported work with black and Oregon ash (see below) (J. Koch, USFS, pers. comm.).

Koch has also begun working with Oregon ash, in collaboration with the USFS Dorena Genetic Resource Center (located in Cottage Grove, Oregon) and other partners.

dead hemlock in Massachusetts; photo by Ian Kinahan,
University of Rhode Island

Hemlock woolly adelgid

Scientists are still trying to find the right combination of biocontrol, chemical treatments, and silvicultural manipulation.

For several years, hope has focused on two has been on two predatory beetles, Laricobius nigrinus and L. osakiensis. Scott Salom (Virginia Tech) reports that release of these beetles over the past 20 years has had a significant impact on HWA density and tree photosynthetic rate and growth. However, Laricobius aredifficult to rear and they attack only the sistens generation of the adelgid. Ryan Crandall (University of Massachusetts) reports it has been difficult to establish these beetles in the Northeast. He links this difficulty is caused by temporary drops in HWA populations after cold snaps.

Scientists now agree that need to find predators that attack HWA during other parts of its lifecycle. Hope now focuses on silverflies — Leucotaraxis argenticollis and Le. piniperda.  While both species are established in eastern North America, the clades in the east feed almost exclusively on pine bark adelgid, and have not begun attacking HWA. Biocontrol practitioners therefore collect flies in the Pacific Northwest for release in the east. Salom is increasing his lab’s capacity to rear silverflies and exploring release strategies.

Preliminary evidence indicates that the western clades of Leucotaraxis are establishing, although data are not yet definitive (Havill, USFS).

Detecting the presence of biocontrol agents presents several challenges. Tonya Bittner (Cornell) described efforts to use eDNA analysis for this. Some puzzles have persisted; e.g., at some sites, she detected eDNA but caught no silverflies. This raised the question of long eDNA associated with the original release might persist. Another problem is that the assay cannot separate the introduced western L. nigrinus from the native congener, L. rubus (which also does not feed on HWA). She continues efforts to improve this technique.

Others explored interactions of the biocontrol agents with insecticides. Salom is studying the impact of soil-applied insecticides on Laricobius populations, which aestivate in the soil. Preliminary results showed significant reduction in the beetle’s population under soil drench application but not under soil injection. He has not yet analyzed all the data.

Michigan is trying to prevent spread of HWA from five counties along the eastern shore of Lake Michigan (where HWA was introduced on nursery stock) to widespread hemlock forests in northern part of the state. Phil Lewis (APHIS) is studying persistence of systemic insecticides in hemlock tissues, particularly twigs and needles. The pesticides involved are imidacloprid, dinotefuran, and Olefin. He has found that pesticide levels are highest 18 – 22 months after treatment, then decline. They are significantly higher after trunk injection compared to bark spray or soil treatments. Imidacloprid had higher residues in twigs; dinotefuran in needles. This difference affects the likelihood of adelgids actually ingesting the toxin.

healthy hemlock in experimental gap; Jefferson National Forest, VA; photo by Bud Mayfield, USFS

Bud Mayfield (USFS) reported on his study of silvicultural strategies to support healthier hemlocks. While hemlocks normally thrive in shade, it has been determined that sunlight assists small trees  reducing HWA sufficiently to counter the tree’s leaf-level stress. Small sapling hemlocks grown in sunlight fix more carbon and convert it to growth in shoots and trunk diameter.

Mayfield found promising immediate suppression of HWA in large gaps in Georgia and Tennessee. By the third year the saplings were still growing, although their faster growth had attracted more HWA. These findings were less clear farther north in central Virginia and western Maryland – Mayfield thinks because HWA pressure there is lower. However, managers must maintain the gaps by cutting rapidly-growing competing woody species. He plans to test this strategy farther north in Pennsylvania. He is still trying to determine the optimal size of the gap.

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

Plant Diversity & Invading Insects: Key Relationship has Policy Applications

spotted lanternfly; photo by Stephen Ausmus, USDA; establishment facilitated by extent of invasion by its preferred host, Ailanthus

Seven coauthors (full citation at end of blog) compared various factors associated with numbers of invasive insect species in 44 land areas.These ranged from small oceanic islands to entire continents in different world regions, Liebhold et al. determined that the numbers of established non-native insect species are primarily driven by diversity of plants, including both native and non-indigenous. Other factors, e.g., land area, latitude, climate, and insularity, strongly affect plant diversity. Through this mechanism these factors affect insect diversity as a secondary impact.

Seven coauthors (full citation at end of blog) compared various factors associated with numbers of invasive insect species in 44 land areas.These ranged from small oceanic islands to entire continents in different world regions, Liebhold et al. determined that the numbers of established non-native insect species are primarily driven by diversity of plants, including both native and non-indigenous. Other factors, e.g., land area, latitude, climate, and insularity, strongly affect plant diversity. Through this mechanism these factors affect insect diversity as a secondary impact.

At large spatial scales [greater than 10 km2], regions supporting more diverse plant communities offer greater opportunities for herbivore colonization. Thus, plant diversity promotes invasion through the “facilitation effect”. Since most insects – including most of those introduced to naïve ecosystems – are herbivores, a greater number of possible foods is a clear advantage. Those insects that prey on herbivores benefit by plant diversity indirectly.

Non-native coral tree, Erythrina, in Hawai`i; photo by Forrest and Kim Starr; did wide planting of exotic Erythrina facilitate invasion by Erythrina gall wasp?

At smaller spatial scales, plant diversity might impair the ability of insects to locate hosts because of the “dilution effect”. I have been asking for decades why so few of the Eurasian insects established in eastern North America have not also established along the Pacific coast from Oregon into British Columbia. The region has a plant-friendly climate and almost every plant species from temperate climates is grown there in cultivation. Perhaps the non-native plants – while numerous enough to become invaders themselves – are still sufficiently scarce or dispersed to impair introduced insects’ locating an familiar host?

According to the Smithsonian Institution, Hawai`i has approximately 2,499 taxa of flowering plants and 222 taxa of ferns and related groups. The native flora of the United States includes about 17,000 species of vascular plants; at least 3,800 non-native species of vascular plants are recorded as established outside cultivation. I don’t know how many non-native plant species are in cultivation.

horticultural viburnum invading riparian forest in Fairfax County, VA. photo by F.T. Campbell; did the widespread presence of many non-native viburnum species facilitate establishment of the viburnum leaf beetle?

I note that this article appeared more than four years ago. However, its important findings do not appear to have been integrated into either policy formulation governing plant introductions or pest risk analysis applied to insects or pathogens that might be introduced. (Indeed, we probably need a separate analysis of whether fungi, oomycetes, nematodes, and other pathogens show the same association with plant diversity in the receiving environment.)

How do we – government agencies, academics, conservation organizations, plant industry representatives — use this information to help curtail introductions of plant pests? Can it be integrated into APHIS’ NAPPRA process?

SOURCE

Liebhold, A.M., T. Yamanaka, A. Roques, S. August, S.L. Chown, E.G. Brockerhoff & P. Pyšek. 2018. Plant diversity drives global patterns of insect invasion. www.nature.com/scientificreports/

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

Can we work together to curtail introductions of new diseases?

Phytopthora ramorum-infected potted plants; photo by Washington State University

At this year’s USDA Invasive Species Forum I will be seeking to promote a discussion of what American and other stakeholders can do to suppress spread of forest pathogens. I have raised this issue many times before.  To see my blogs about the P4P pathway, scroll down below the archives to the “categories”.  See especially here  and here. 

I note that:

  • Non-native invasive pathogens and pests are decimating forests worldwide, threatening biodiversity & limiting efforts to rely on forests to alleviate impacts of climate change.
  • Many of the most damaging non-native organisms are pathogens that are especially difficult to detect at borders or to contain or eradicate once introduced.
  • A principal pathway by which pathogens are introduced is the international trade in living plants, or “plants for planting” (P4P).
  • Forest pathologists have long advocated a more pro-active approach – but national and international plant health officials have not taken up the challenge. [think Clive Brasier, Bitty Roy, Thomas Jung, Michael Winfield …]
Austropuccinia psidii on Melalecua in Australia; John Tann via Flickr

At the global level I suggest that we need:

  1. National agricultural agencies, stakeholders, FAO & International Plant Protection Convention (IPPC) to consider amending IPPC requirement that scientists identify a disease’s causal agents before regulating it. I think experience shows that this policy virtually guarantees that pathogens will continue to enter, establish, & damage natural and agricultural environments.
  2. National governments & FAO / IPPC to fund greatly expanded research to identify microbes resident in regions that are important sources of origin for traded plants, vulnerability of hosts in importing countries, and new technologies for detecting pathogens (e.g., molecular tools, volatile organic compounds [VOCs]).
  3. Researchers & agencies to expand international “sentinel plants” networks; incorporate data from forestry plantations, urban plantings, etc. of non-native trees.
  4. Application of ISPM#36 to promote use of HACCP programs for plants in trade. (See also my discussion in Fading Forests III – link at end of this blog.)
‘ohi‘a trees killed by rapid ‘ohi‘a death; photo by Richard Sniezko, USFS

We Americans need to

  1. Evaluate efficacy of current regulations – incorporating NAPPRA & Q-37 revision.  Rely on AQIM data. Include arthropods, fungal pathogens, oomycetes, bacteria, viruses, nematodes. Include threats to U.S. tropical islands (Hawai`i,  Puerto Rico, Guam, etc.) which are centers of plant endemism.
  2. Apply existing programs (e.g., NAPPRA, Clean Stock Network, post-entry quarantine) to strictly regulate trade in plant taxa most likely to transport pests that threaten our native plants; e.g., plants belonging to genera shared between North American trees & plants on other continents.
  3. Recognize that plant nurseries are incubators for microbial growth, hybridization, and evolution; require nurseries to adopt sanitary operation procedures regardless of whether they sell in inter-state or intra-state commerce

I will explain my sense of urgency by noting the many recent introductions of pathogens – most probably via P4P or cut vegetation:

  • 13 outbreaks of Phytophthora-caused disease in forests and natural ecosystems of Europe, Australia and the Americas. Three of four known strains of P. ramorum are established in U.S. forests.
  • Myrtle rust (Austropuccinia psidii) has been introduced to 27 countries, including the U.S., Australia, and South Africa.
  • Two new species of Ceratocystis (C. lukohia & C. huliohia)—causal agents of rapid ‘ohi‘a death (ROD) – spreading on the Hawaiian Islands. The former species appears to have originated in the Caribbean; the latter in Asia.
  • Since 2012, beech leaf disease has spread from northeastern Ohio to Maine.   
  • Boxwood blight (caused by 2 ascomycete fungi, Calonectria pseudonaviculata & C. henricotiae) introduced to at least 24 countries in 3 geographic areas: Europe / western Asia; New Zealand, North America.
  • ash dieback fungus (Hymenoscyphus fraxineus) has spread across Europe after introduction from Asia.

What do you think? Can we find more effective methods to curtail introductions?

beech leaf disease

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

America & Russia – Sharing the Pests

Platanus orientalis in Turkey; photo by Zeynek Zebeci

A current issue of the journal Forests (2022 Vol. 13) is a special issue focused on forest pests. This topic was chosen because of increased pest incursions. Choi and Park (full citations at the end of the blog) link this to climate change and increased international trade, as well as difficulties of predicting which pests will cause damage where.

The journal issue contains 15 papers. Several patterns appear throughout. First is the important role of international trade in living plants – “plants for planting” – in introductions. This is hardly news! A second pattern is that at least two North American species were introduced to Europe during the 1940s, probably in wood packaging used to transport military supplies during World War II.

This compilation provides the opportunity to review which organisms of North American origin have become damaging invaders in Eurasia — and sometimes other continents. For example, the journal carries four articles discussing pine wilt disease (PWD). It is caused by the North American nematode Bursaphelenchus xylophilus, and is vectored by wood-boring insects in the genus Monochamus. Beetles introduced from North America and those native to the invaded area are both involved. This disease is considered a severe threat to forest health globally. No apparent association with WWII exists for PWD.

Two fungal pathogens from North America cause serious damage in urban and natural forests of Europe and central Asia. Neither is discussed in the special issue:

  • Ceratocystis platani has devastated urban trees in the Platanus genus, especially the “London plane” hybrid, and the native European tree, Platanus orientalis. This fungus was accidentally introduced to southern Europe during WWII – as were the two insects described by Musolin et al. It was first reported in northern Italy and Mediterranean France in the early 1970s, but disease symptoms had been observed years earlier. C. platani is established across the northern rim of the Mediterranean and to the east in Armenia and Iran. The worst damage has been in Greece, especially in natural forest stands in riparian areas. Spread of the pathogen there is facilitated by root grafts and by tree wounds caused by floating wooden debris during floods (Tsopelas et al. 2017.)
Platanus orientalis along Voidomatis River in Greece; photo by Onno Zweers, via Wikimedia
  • Heterobasidion irregulare infects conifers. It has spread and killed large numbers of Italian stone pine (Pinus pinea). The disease was inadvertently introduced to central Italy in the 1940s. H. irregulare has greater sporulation potential and decays wood more quickly than the native congener H. annosum. H. irregulare appears to be replacing the European species; scientists fear it will exacerbate tree infection and mortality rates (Garbelotto, Leone, and Martiniuc. date?)

A third North American pathogen, sooty bark disease (Cryptostroma corticale) has been introduced to Europe. This disease, found on sugar maple in eastern North America, was detected in Great Britain in 1945; it is now throughout Europe (Tanney 2022). EPPO reports that it is widespread in western Europe and in some Balkan countries. The website provides no information on its impact in Europe.

Pests in Russia

A paper authored by Musolin, et al. discusses 14 species of invasive or emerging tree pests found in Russian forest and urban ecosystems. Of these, two are native to North America. Another eight pose a threat to North America if they are introduced here.

As Musolin et al. point out, Russia covers a huge territory across Europe and Asia – stretching 10,500 km, or 6,500 miles. These encompass a great variety of ecological zones. Russia is also actively involved in international trade. It is not surprising, then, numerous non-native organisms have been introduced.

As of 2011, 192 species of phytophagous non-native insects from 48 families and eight orders were documented in the European part of Russia. This number does not include the vast areas in Asian Russia. Additional introductions have probably occurred in the most recent decade. Some of these introduced species have cause significant economic losses. Still, Russia appears to rarely mount a serious control effort.

Of course, the opposite is also true: pests native to some part of Russia can be transported to new regions of Russia or beyond its borders. We North Americans have focused on various species of tussock moths (Lymantria spp., etc.). There are many others. Musolin et al. describe eight in detail. All the information in this blog are from that article unless otherwise indicated.

Two North American Species’ Damage in Eurasia

Both these introductions were detected around the year 2000. Was there some event – other than simply expanding trade – that might explain these introductions?

Leptoglossus occidentalis; photo by nutmeg66 via Flickr
  • Western Coniferous Seed Bug, Leptoglossus occidentalis

This insect from western North America has invaded Eurasia, North Africa, and Central America. The first detection in Europe was in 1999 in Italy. It spread quickly and is present now from Morocco to Japan, as well as in South Africa and South America. The seed bug is spreading northward in European Russia, including into the forest-steppe zone. Its ability to spread to the East is uncertain.

L. occidentalis attacks a wide range of Pinaceae and Cupressaceae. In the Mediterranean region it has had serious impacts on the pine nut supply (Ana Farinha, IUFRO, Prague, September 2021). In southern parts of Russia it has caused “significant damage”. L. occidentalis also vectors a pathogenic fungus Sphaeropsis sapinea (=Diplodia pinea), which causes diplodia tip blight. The cumulative damage of insect and pathogen to pines can be significant.

The introduction pathway to Russia is unknown. It might have flown from established populations in Europe, or it might have been transported on plants for planting or Christmas decorations.

  • Oak Lace Bug, Corythucha arcuata  

This insect is widespread in the United States and southern Canada. It was first detected in Europe – again, Italy – in 2000. Twenty years later it has spread to almost 20 countries.

Russia was invaded relatively recently; the first outbreak was detected in 2015 in the subtropical zone along the Black Sea coast and Caucasus. Musolin et al. expect the lace bug to spread to natural forests of Central Asia and other countries of the Caucasus. Its spread will be assisted by air currents and movement of plants for planting. The insect is causing considerable aesthetic damage, but other impacts have not been estimated.

Hosts include many species of oak (Quercus spp.), European and American chestnuts (Castanea spp.) plus trees from other botanical families: willows and maples (Salicaceae), redbay (Fagaceae), and alder (Betulaceae).  

Pests in Russia that Could Damage North America if Introduced Here

Malus sierversii; photo by Lukacz Szczurowski via Wikimedia

Threat to Apples — Apple Buprestid, Agrilus mali

This Asian beetle has caused extensive mortality of wild apple (Malus sieversii) forests in Xinjiang, China. Wild apple trees are important components of deciduous forests in the Central Asian mountains. The species is also an ancestor of the domestic apple tree. Consequently, the borer is considered a potential threat to cultivated apple trees – presumably everywhere. A. mali might also attack other fruit trees in the Rose family, i.e., Prunus (plums, cherries, peaches, apricots, almonds) and Pyrus (pears).

Unlike most of the other species described here, A. mali is a quarantine pest in Russia and across Europe and the Mediterranean regions – the region where phytosanitary policies are coordinated by the European and Mediterranean Plant Protection Organization (EPPO). Russia bans imports of apple seedlings from infested areas.

China is reported to be experimenting with a possible biocontrol agent, Sclerodermus pupariae (a parasitoid of emerald ash borer).

Threat to Pines and Firs, Already Under Invasive Species Threats

  • Small Spruce Bark Beetle, Ips amitinus

This European beetle has been considered a secondary pest of dying conifers. Over the last 100 years, it has moved farther North. The first Russian record was 100 years ago, in the region where Russia, Belarus, and Ukraine meet. (Did military action during World War I play a role? This is not discussed by the authors.) By 2022, the beetle occupies 31 million ha. It is probably spread through transport of logs by rail.

In Western Siberia, the spruce beetle has attacked a new host, Siberian pine (Pinus sibirica).

The danger to North America arises from this beetle’s preference for five-needle pines (genus Pinus section Quinquefoliae). North America’s five-needle pines are already under severe pressure from the introduced pathogen white pine blister rust (Cornartium ribicola) and the native mountain pine beetle (Dendroctonus ponderosae). 

  • Four-Eyed Fir Bark Beetle, Polygraphus proximus

This East Asian beetle feeds on firs (Abies spp.). Less commonly, it feeds on other genera in the Pinaceae: spruce (Picea ), pines (Pinus), larch (Larix), hemlock (Tsuga).

This beetle has been spreading west; the first substantiated record in European Russia was 2006 in Moscow. The beetle was probably present in western Siberia in the 1960s, although it was not detected until 2008. Again, the probable pathway of spread is movement of lumber by railroad.

P. proximus vectors an obligate symbiotic fungus, which can rapidly weaken the host. Musolin et al. comment on the beetle’s impacts – which they rarely do in this article. (Does this signify more damaging impacts, or availability of past studies?) They note significant changes in the forests’ ecosystem structure and microclimate, vegetation cover, and local insect fauna.

The danger to North America arises from this beetle’s preference for firs from the sections Balsamea and Grandis. Many North American firs are in these sections, including Fraser fir (Abies fraseri), balsam fir (A. balsamea), subalpine fir (A. lasiocarpa), grand fir (A. grandis), white fir (A. concolor), and others. Several of these firs already are challenged by the introduced balsam woolly adelgid. Firs in central and western Europe are less vulnerable since they are in the section Abies, which the beetle prefers less.

Threats to Poplars

  • Spotted Poplar Borer, Agrilus fleischeri

This boring beetle is native to northern Asia. It has caused significant mortality in native and exotic Populus plantations in China. Although there have been no reports of this beetle moving beyond its native range, many other Agrilus species have. Canada has twice intercepted adult spotted poplar borers on wood packaging. Musolin et al. fear that the adoption of non-native hosts might trigger an outbreak that would facilitate spread.

  • Poplar Leafminer, Phyllonorycter populifoliella
balsam poplar; photo by Matt Lavin via Flickr

This micromoth is widely distributed across the Palearctic. It was recently detected on introduced poplars growing in India.  

The danger to North America arises from the beetle’s preference for black and balsam poplars. Several species in these taxonomic groups are common in North America, including Populus balsamifera, P. trichocarpa, P. deltoides, and Populus × Canadensis.

Threat to Oaks — Leaf Blotch Miner Moth, Acrocercops brongniardella

This micromoth is widely distributed in Europe and expanding to the north. The pest mines the leaves of several oak species (Quercus spp.), especially English oak, Q. robur; and sometimes European chestnut (Castanea sativa). Leaf blotch miner is considered one of the most important folivore insect pests of oaks in Russia. Damage has been greater in Omsk Oblast (Siberia), where both English oak and the micromoth are introduced species, than in St. Petersburg, which is on the northern limit of their natural range. Musolin et al. fear that the warming climate will lead to the pest causing greater damage in the northern portions of its range.

Threat to Basswood — Lime Leaf Miner, Phyllonorycter issikii

This Asian moth has been moving west since the mid-1980s. It now occupies most of European Russia with some outbreaks in Siberia. In Europe, it is a conspicuous pest of Tilia species.

In these invaded regions, the leaf miner has shifted to novel hosts, including American basswood (T. americana). Basswood is a common plant in the eastern deciduous forest of North America.

Threat to Horse Chestnuts & Urban Trees — Horse-Chestnut Leaf Miner, Cameraria ohridella

This tiny moth was unknown to science before the first recorded outbreak in the late 1980s. Over the next three decades it spread to most of Europe, where horse chestnut (Aesculus hippocastanum)has been widely planted for three centuries. It has caused significant damage.

The first Russian detection was in Kaliningrad, on the shores of the Baltic Sea, in 2003. The leaf miner now occupies 69% of administrative units of European Russia. It is considered one of the Top 100 most dangerous invasive species in Russia.

In North America, the moth might attack native horse chestnuts, Ae. octandra (=flava) and Ae. glabra. Urban plantings are at particular risk because the leaf miner might attack both European horse chestnuts and two non-native maples that have been planted widely, sycamore maple (Acer pseudoplatanus) and Norway maple (A. platanoides). Data cited by Musolin et al. are contradictory regarding larval development on the maples. Once introduced, the leaf miner is difficult to contain because it spreads through natural flight of adults, wind-blown leaves, hitchhiking on vehicles, and movement of infected plants. 

Shared Pests

Russia has been invaded by two species that have been introduced in many countries (beyond pine wilt nematode). These two entered the country on plants for planting being imported to landscape venues for the XXII Winter Olympic Games – held in Sochi in 2014.

First to arrive was the Box Tree Moth, Cydalima perspectalis. This East Asian species was first detected outside its native range in Germany in 2006. By 2011 it was widespread in European and Mediterranean countries. In 2021, the boxwood moth was found in North America (first Canada, then the United States).  [I discuss the boxwood moth briefly here.]

boxtree moth; photographer unknown

In Russia, box tree moth larvae were first recorded in 2012 on the planting stock of its principal host, Buxus sempervirens. The moth quickly spread around the Black Sea region and to the North Caucasus. It spread farther, too: it reached the Kaliningrad Oblast (southeast coast of the Baltic Sea) in 2020. The main pathway of C. perspectalis invasion was the introduction of infested box-wood planting material.

Further spread of C. perspectalis is likely from Russia into the natural forests across the Caucasus (Transcaucasia) and to countries located further south. This is most distressing because the region has extensive natural forests of Buxus sempervirens. In 2015–2017, C. perspectalis almost completely destroyed the natural boxwood populationsin these regions of Russia and further eastwards in Abkhazia. Boxwood stands in Georgia and northern Iran are already suffering intensive defoliation as the result of infection by two non-native pathogens, Calonectria pseudonaviculata [synonym Cylindrocladium buxicola] and Calonectria henricotiae. 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). (In December 2022, Iryna Matsiakh presented a compelling overview of threats to these forests in a webinar sponsored by the Horticulture Research Initiative; apparently no recording is available.)

The second global invader to appear was the Brown Marmorated Stink Bug, Halyomorpha halys.

This insect from southeast and east Asia invaded the United States in 1996. The first detection in Europe was in Liechtenstein in 2004. In both cases, it spread quickly across these continents.

Russia’s first detection of stinkbug was in 2014 in parks in Sochi and elsewhere along the Black Sea coast. The spread in Russia appears to have been limited to the Black Sea – Caucasus area.

The brown marmorated stinkbug is highly polyphagous, feeding on more than 300 species of plants.  In southern Russia, 107 species have been documented as hosts. At times, stinkbug feeding has caused severe losses in yields of fruit and vegetable crops.

Patterns

Musolin et al. stress the importance of the pest shifting to new hosts–usually from the same or a closely related genus. They cite several examples of these shifts occurring in the pest’s native range, including Agrilus planipennis (from local Asian ash species to introduced North American ash species); Phyllonorycter populifoliella and Agrilus fleischeri (from local poplars to widely cultivated introduced North American poplars and hybrids); Agrilus mali (from cultivated to wild apples).

As I noted above, the introduction and spread pathways are the usual ones: plants for planting (three species) and shipments of logs. There is one indication of wood packaging – Spotted Poplar Borer, Agrilus fleischeri at the Canadian border.

SOURCES

Choi, W.I.; Park, Y.-S. Management of Forest Pests and Diseases. Forests 2022, 13, 1765. https://doi.org/10.3390/f13111765

Garbelotto, M., G. Lione, and A.V. Martiniuc. date?  The alien invasive forest pathogen Heterobasidion irregulare is replacing the native Heterobasidion annosum. Biological Invasions https://doi.org/10.1007/s10530-022-02775-w

Musolin, D.L.; Kirichenko, N.I.; Karpun, N.N.; Aksenenko, E.V.; Golub, V.B.; Kerchev, I.A.; Mandelshtam, M.Y.; Vasaitis, R.; Volkovitsh, M.G.; Zhuravleva, E.N.; et al. Invasive insect pests of forests and urban trees in Russia: Origin, pathways, damage, and management. Forests 2022, 13, 521.

Tanney, J. Forest Health Challenges Exacerbated by a Changing Climate: Swiss Needle Cast and Sooty Bark Disease in B.C. 65th ANNUAL FOREST PEST MANAGEMENT FORUM (Canada). December 7, 2022.

Tsopelas, P., A. Santini, M.J. Wingfield, and Z.W. de Beer. Canker Stain: A Lethal Disease Destroying Iconic Plane Trees. Plant Disease 2017. 101-645-658 American Phytopathological Society

Climate Change + CO2 Levels – Can Scientists Include the Complexity in their Analyses?

Spruce budworm (Choristoneura fumiferana); photo by Jerald E. Dewey, USFS; via Bugwood; populations of several forest birds, including Cape May, Tennessee and Bay-Breasted warblers, become more numerous during budworm outbreaks

Now that Drs. Ziska and Aucott have educated us about the strong impact atmospheric CO2 can have on both plants and phytopagous insects, I have asked the experts whether these interactions have been incorporated in the models scientists are using to forecast pest activity in American forests as the climate changes.

The answer is no.

bay-breasted warbler; photograph by Dave Inman at Presque Isle State Park, PA; via Flickr

Dr. Bethany A. Bradley, Co-Director, Northeast Climate Adaptation Science Center at the University of Massachusetts, says empirical models of species range shifts typically only use climate and sometimes other environmental factors (like soils or topography) as predictors of potential geography. Inclusion of demographic processes like how plant growth is affected by more or less water, CO2, competition with other plants etc. would require a lot of data. It is currently impossible since there are tens of thousands of plant species interacting in the forests of eastern North America – and perhaps these factors have been analysed for only a hundred of them.

Mike Aucott points to the same difficulty: inclusion of CO2 in models of the future populations of specific plants would be difficult since the impacts vary from species to species and are compounded by other factors such as soil nitrogen levels, moisture levels, temperature, presence of competing plants, etc.  

Regarding insects, Dr. Aucott thinks it is clear that some orders, such as Lepidoptera, don’t fare as well when feeding on plants grown under elevated CO2.  He is not aware of efforts to model impacts of high CO2 on specific insects or even orders or feeding guilds. 

juniper geometer (inchworm); Dr. Tallamy says inchworms are hairless & good tasting – so sought by birds

Dr. Ziska concurs about the difficulties. Dr. Ziska asks why there is so little funding to study these issues, especially given their probable impact on human food supplies and health – as described in his blog and an opinion piece published in Scientific American two years ago.

I hope that scientists, decision-makers, readers of this blog … maybe even the media! – take into consideration these complexities, even if they cannot be defined.

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 – [but do not address climate or CO2 aspects] review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm

or

www.fadingforests.org