Category: forest pest insects

Resistance Breeding – a Useful Strategy

Port-Orford cedar resistance trials at Dorena Center; photo courtesy of Richard Sniezko, USFS

I have written several times about the importance of the United States adopting a comprehensive program to address all aspects of introduced forest pests including breeding of trees resistant to the introduced pests. See Fading Forests III from seven years ago; an earlier blog; and Bonello et al. 2020 (full citation at end of blog), in which we proposed the creation of a federal Center for Forest Pest Control and Prevention to implement end-to-end integrated responses to forest pest invasions. A similar view is being voiced internationally; see, e.g., Buggs et al. 2020.

I have seen efforts to restore pest-decimated tree species to the forest lagging. I complained in a recent blog link that the recent USDA Forest Service report on invasive species (Poland et al. 2021) gave a misleading impression that significant effort was being made on resistance breeding to address several pests.

The USFS does support breeding trees resistant to pests, but in my view this support has been inadequate – including in the USFS report. Others think so, too — see Sniezko and Koch 2017. This insufficiency only grows, despite USDA claims to recognize that promoting resistance to introduced forest pests is an essential component of achieving its strategic goals of maintaining or enhancing productivity while ensuring responsible stewardship of resilient natural resources (Federman and Zankowski 2019).

Work at the Dorena Genetic Research Center

The principal and most notable and successful resistance breeding effort has been the Dorena Genetic Resource Center. The Center was established by, and is funded through the USFS Region 6 Genetic Resource (part of the National Forest System) and Forest Health Management programs. The Center has a solid foundation in the expertise and facilities needed to carry out breeding efforts. Also, it has a 50-plus-year track record.

Dorena has supported breeding of white (five-needle) pines and Port-Orford cedar. Dorena also now provides expertise and some facilities to partners exploring a) breeding Oregon ash to resist the emerald ash borer and b) two Hawaiian trees (koa and ‘ōhi‘a) to resist introduced pathogens (see below). Dorena staff is assisting low-budget, shoe-leather efforts to explore breeding of other trees at risk to non-native pests. These programs are described briefly in Box 8 of Poland et al. 2021. Despite this valuable effort with proven success funding to continue Dorena’s work is tenuous.

White Pine Blister Rust — Efforts to develop resistance to white pine blister rust (WPBR) DMF in five-needle pine species (nine grow across the country) began more than 50 years ago. Currently Dorena focuses on whitebark pine (Pinus albicaulis), denizen of high elevations in the West, along with western white pine (P. monticola), sugar pine (P. lambertiana) , limber pine (P. flexilis), southwestern white pine (P. strobiformis), and foxtail pine (P. balfouriana). Testing whitebark for resistance to WPBR began in 2002. Seedling families from >1,300 parent trees are in various stages of testing. The discovery that some whitebark populations have much higher levels and frequency of partial resistance has allowed rapid distribution of seed. The first restoration plantings in the Pacific Northwest were in 2009.

3-year old seedlings of whitebark pine at Crater Lake National Park; photo by Richard Sniezko, USFS

There are many collaborators – especially the National Park Service, Washington State’s Department of Natural Resources, several Tribes, the Whitebark Pine Ecosystem Foundation, and American Forests. However, planting has been hampered by the high cost of restoration in these high elevation ecosystems, lack of frequent good seed crops on the resistant parent trees, and lack of approval to plant in designated wilderness areas. In the areas with the highest levels of resistant parents, management activities that encourage natural regeneration might be successful. In late 2020 the U.S. Fish and Wildlife Service proposed to list whitebark pine as a Threatened species

Oregon ash (F. latifolia) has not yet been attacked by the emerald ash borer, but all expect EAB to spread to the West coast. Dorena and cooperators have already collected seed from ash trees in Oregon and obtained funding for additional collections, to include Washington and California. The seeds are being stored at both Dorena and the USDA Agriculture Research Service facility at Ft. Collins, Colorado. Seedlings from two dozen families have also been planted at Dorena and a center operated by Washington State University, plus at a USFS Northern Research Station research center in Ohio, where EAB is established and they can be tested for resistance to the insect’s attack.

Koa and ‘ōhi‘a in Hawaii — Regeneration of the koa tree (Acacia koa) has been undercut by the koa wilt pathogen, Fusarium oxysporum f. sp. koae. Dorena initiated efforts with the Hawaii Agricultural Research Center (HARC) to respond in 2003. There has been rapid progress screening seedlings to identify resistant parent trees establishing seed orchards, delineating seed zones, and releasing seed with confirmed levels of resistance for reforestation and restoration (Sniezko and Koch 2017; see also Dudley et al. 2020).

‘ōhi‘a trees killed by rapid ‘ōhi‘a death; photo courtesy of J.R. Friday

When the threat to Hawaii`s most widespread tree ‘ōhi‘a (Metrosideros polymorpha) from rapid ‘ōhi‘a death (ROD) pathogens became apparent, the Dorena staff provided advice on breeding strategies. Its Center Geneticist is part of an ad hoc resistance team. Scientists have identified surviving trees in stands affected by ROD on the Big Island using a variety of methods. These include aerial surveys by drones and fixed-wing aircraft. They then began collecting seeds and cuttings. As of spring 2021, they have collected cuttings or seeds from more than 300 ‘ōhi‘a trees belonging to five varieties. The effort is low-cost, using Americorps volunteers coordinated by a single full-time person, a USFS employee. The program is still in its infancy. It will have to find funding to expand its scope to an operational resistance program once more information on resistance is has been obtained.

Other Efforts

Most other breeding programs are small and poorly funded. In fact, they have been described by one USFS scientist as “hobby projects” of a few scientists determined to try this strategy. Not only are efforts minimal; but also retirement of those few scientists can bring an end to the individual project.

There were greater efforts in the past. I have a document (of unknown origin) from 2011 that describes breeding efforts funded by both the National Forest System and USFS Research and Development. Table 1 listed 16 projects for western conifers; Table 2 listed 32 projects funded by R&D. During this period, the USFS provided start-up funds for the Healthy Forests Initiative, a consortium that sought to prove the concept that genetic engineering could quickly produce an American chestnut able to live and reproduce in its native range. This support was in addition to support for The American Chestnut Foundation backcross hybridization program link.

Part of the problem is the longstanding decline in funding and staffing of USFS research program. A graph in Chapter 6 of FFIII shows the decline in numbers of forest entomologists and pathologists over the 20-year period 1985–2007. Wheeler et al. 2015 discuss the parallel decline in tree breeders and geneticists (citation at end of this blog).

Cuts continue. Funding for research conducted by the USFS Research stations on ten non-native pests decreased from $10 million in Fiscal Year 2010 to just $2.5 million in Fiscal Year 2020 – a cut of more than 70%. I have lobbied for increased appropriations for decades.

The need for new approaches and increased effort is more widely asserted. One example is the group I am working with that promotes a new Center for Forest Pest Control and Prevention. Link A second example is the University of Florida’s recent conference of forest health researchers, representatives of the forest products industry, non-governmental organizations, and leaders of universities with forest-resource programs. This group suggested forming a united organization to increase capacity to improve forest health research. An article outlining the proposal is available here.

The Role of Biotechnology in Breeding Resistant Trees

what happened? same tree a few years apart — a TACF hybrid chestnut

Part of the discussion on forest research explores the proper role of biotechnology in tree species’ restoration. Purdue University hosted a related workshop in April 2021, in which I took part. (“Society and Policy Influences on Biotechnology Risk Assessment for Restoration of Threatened Forest Tree Species”). I hope participants will soon publish a paper based on our discussions.

Meanwhile, Revive & Restore, a wildlife conservation organization promoting the incorporation of biotechnologies into standard conservation practice, sponsored a workshop in June 2020. The 57 conservationists, wildlife biologists, restoration specialists, conservation geneticists, ethicists, and social scientists who participated agreed on an appropriate structure for using biotechnology. These included:

  • A broader definition of risk and application of new risk assessment tools;
  • Consideration of the risks of not taking action, as well as going ahead with a proposal;
  • Transparency about social and cultural values and engaging stakeholders
  • Monitoring results to ensure actions have been successful, manage uncertainty, and codify lessons learned.

In the literature I read, the workshops I participate in (e.g., National Academy of Sciences 2019; Purdue’s), biotechnology is seen as a potentially helpful set of tools that must be integrated into broader programs, all having research, tree improvement, restoration, and reforestation components. Such programs must have sustained management and resources stemming from public support. (For more complete descriptions of components of a resistance breeding program, see Sniezko and Koch 2017 (full reference below); or Chapter 6 of FFIII). Activities that must be incorporated include:

  • Germplasm collection and storage (applying the varied strategies that are appropriate);
  • Research to detect and test potential resistance or tolerance;
  • Research to identify techniques for producing propagules;
  • Planting sites that will be secure for decades;
  • Site preparation & planting;
  • Post-planting maintenance; and
  • Monitoring to determine success or problems

During the Purdue workshop, and in my writing, I have emphasized the principal hindrance to progress is the lack of resources being allocated to resistance breeding. USFS and academic scientists determined to pursue breeding approach must scrounge for funds. I describe some of their efforts below.

Collaborations on Breeding for Specific Species

(still) healthy hemlocks in Cook Forest State Park, Pennsylania; photo by F.T. Campbell

USFS Hemlock Woolly Adelgid (HWA) Initiative [apparently no website]

This initiative was developed under the leadership and direction of FHP staff. The list of cooperators includes dozens of state, federal, university and private organizations. The annual budget has averaged between $2.5 and $3.5 million. Most resources are apparently allocated to biocontrol, but some funding has been provided for breeding activities, including:

  • Seed collection and storage for both Carolina and eastern hemlocks. Two seed orchards have been established in western North Carolina. I believe they are protected from the hemlock woolly adelgid (HWA) by application of pesticides.
  • Research on these tree species’ silviculture and ecology, including manipulation of sunlight levels to protect seedlings from the adelgid and promote growth

The 2021-2025 Program – currently under review – foresees more integrated pest management applying biocontrol, chemical control, and silviculture. It aims to maintain the health of hemlocks being used in breeding programs and “explore” hemlock replacement options, such as hybrids or HWA-tolerant hemlocks (Mayfield et al. 2021). This effort is encouraging, but I have heard complaints from academics that they can’t get funding to pursue what they regard as promising breeding strategies.

Other small programs to breed resistant hemlocks are under way. The Forest Restoration Alliance (formerly the Alliance to Save Threatened Forests) asks citizens to identify surviving hemlocks and balsam firs. The Alliance has collected and propagated both cuttings and seeds and is testing their resistance.

Ash and Other Trees of the Upper Midwest

To date, few resources have been allocated to resistance breeding of ash. Between 2003 and 2017, only about 7% of research funds allocated to ash and emerald ash borer DMF have been devoted to host resistance. Of the host resistance research, 61% applied to identifying mechanisms, 14% to use of transgenics to develop resistance, only 7% (0.5% of the total research) has supported actual breeding for resistance (Sniezko and Koch 2017).

In May 2021 the USFS announced it was seeking funds from the water-focused Great Lakes Restoration Initiative. The USFS expects to receive up to $5.4 million for reforestation, ecosystem restoration. and forest health improvements on non-federal lands in the Great Lakes basin. (This includes parts of the states of Illinois, Indiana, Michigan, Minnesota, New York, Ohio, Pennsylvania and Wisconsin). The announcement doesn’t mention resistance breeding for ash, beech, hemlock, or other trees in the region. I hope some of the new funds will be allocated to this strategy.

“lingering” ash; photos courtesy of Jennifer Koch, USFS

In an encouraging show of entrepreneurship, USFS scientists and others have formed the Great Lakes Basin Forest Health Collaborative – a partnership with Holden Forests and Gardens, American Forests, and USFS (Kappler et al. 2021). The purpose of the Collaborative is to advance resistance breeding for these important tree species. The initial focus is on the five ash species in the region, especially black ash (Fraxinus nigra) link to blog The Collaborative is recruiting a network of partners, and will provide training and technology transfer. The partners will provide volunteers and other resources. Partners do not have to be within the region if their work helps the Great Lakes Basin, but plantings have to be there.

Partners will help identify survivor trees with potential resistance (e.g., “lingering” ash); establish clone banks and/or seed orchards; and manage seed collections. Each partner will operate independently, but in collaboration with the others. The initial focus is on obtaining representative seed collections of ash and hemlock. Then cloning, testing resistance, and crosses can begin. Eventually select lines will be chosen for bulking up and reintroduction.

In future the Collaboration hopes to engage in breeding hemlocks and identifying beech trees that remain healthy in areas heavily impacted by beech leaf disease (BLD).

Other efforts under way include the Monitoring and Managing Ash (MaMA) Program, based in the Ecological Research Institute in New York State.

Beech trees with resistance to beech bark disease (BBD) were identified as early as the 1980s, but a breeding program was begun only in 2002. A collaborative, multi-agency effort has resulted in the establishment of five regional American beech seed orchards with four others in progress as of 2017. Partners provide a cost-effective process for identifying resistant parent trees. State and National Forest personnel surveyed natural forests for candidate trees and then tested each tree and identified markers associated with resistance (Sniezko and Koch 2017).

Challenges Beyond Breeding

Large-scale restoration of tree species across much of their ranges will require significant inputs of funds, over long time periods, as well as resolving daunting logistical issues.

Some think the most likely scenario will be to plant focal areas, or islands, that can aid future natural regeneration (Sniezko and Koch 2017). The American Chestnut Foundation (TACF) anticipates it will take 1,000 years to re-establish American chestnut DMF across its range through a process of three phases: long-term research and demonstration plantings; a relatively small-scale public horticultural program using trees and/or pollen made available by TACF; and a larger-scale public restoration program using progeny from years of outcrossing and production. (This assumes APHIS approves release of the transgenic “Darling 58” tree, plus – I believe – progress in developing resistance to root disease caused by Phytophthora cinnamomi). Already good progress using focal areas has started with several white pine species, and a national plan is in the works for whitebark pine.

Such efforts will require access to land that can be protected from other uses, e.g., development for decades or centuries. Also it will require management of sites to protect propagules from browsing wildlife (deer, rabbits!), provide adequate water and light, and probably give plantings a competitive advantage in relation to other plants growing there …

non-resistant elms will grow anywhere! photo by F.T. Campbell

And there is the issue of how a relatively small number of resistant propagules will succeed in spreading their improved genetics in areas where non-improved elm, ash, beech and hemlock are reproducing naturally. Is reproduction of unimproved trees likely to continue in the face of new and old pests’ spread? If biocontrol agents succeed in reducing a pest’s impact on a host tree species, will that enhance the competitive ability of unimproved trees to the disadvantage of genetically improved conspecifics? What are realistic expectation for programs, and for their success?

Criteria for Success

Woodcock, Marzano, and Quine (2019) analyzed five breeding programs to identify aspects that contribute to success. Four of the programs were in North America; they targetted chestnut, western white pines, and Sitka spruce & white pine weevil. They concluded that 

  • Success is influenced by the level of resistance present in individual trees, the frequency of resistance in the population, and the heritability of resistance.
  • It is important to consider current and potential future risks to the species in addition to the target pest or pathogen— the benefits of trees resistant to a specific threat are negated if it is susceptible to other threats.
  •  Demand [for a resistant tree to plant] should be evaluated, and the priorities of potential supporters and end users should inform the methods used to produce resistant trees.
  •  Operational deployment should balance the urgency of the threat with the consequences if resistant material does not perform as hoped. Urgency might differ for an emerging pest or pathogen.
  • Deployment strategies should be informed by the risks of imposing a strong selection pressure on the pest or pathogen to evolve to overcome host resistance, and by potential impacts on partially resistant trees.
  • Continued monitoring of field performance is important for evaluation, and can help to identify and mitigate emerging threats (e.g. new pathogen strains).

SOURCES

Bonello, P., F.T. Campbell, D. Cipollini, A.O. Conrad, C. Farinas, K.J.K. Gandhi, F.P. Hain, D. Parry, D.N. Showalter, C. Villari, and K.F. Wallin. 2020. Invasive tree pests devastate ecosystems – A proposed new response framework. Frontiers in Forests and Global Change. January 2020. Volume 3, Article 2 

Buggs, R.J.A. 2020 Changing perceptions of tree resistance research. Plants, People, Planet. 2020; 2: 2– 4. https://doi.org/10.1002/ppp3.10089

Dudley, N.; Jones, T.; Gerber, K.; Ross-Davis, A.L.; Sniezko, R.A.; Cannon, P.; Dobbs, J. 2020. Establishment of a Genetically Diverse, Disease-Resistant Acacia koa A. Gray Seed Orchard in Kokee, Kauai: Early Growth, Form, and Survival. Forests 2020, 11, 1276

Federman, S. and P. Zankowski. 2019. Strategic science planning for responsible stewardship and plant protection at the U.S. Department of Agriculture. Plants, People, Planet © New Phytologist Trust 2019;00:1–4. https://doi.org/10.1002/ ppp3.10075

Kappler, R., C. Blashka, D. burke, E. Hall, C. Pike, J. Koch. 2021. Great Lakes Basin Forest Health Collaborative: What it’s all about. North American Forest Insect Work Conference 28 May 2021

Mayfield, A.E. III, Salom, S., Jetton, R., Havill, N., Rhea, R., and Mausel, D. 2021. North American Forest Insect Work Conference 28 May 2021. Spread, impact and management of HWA in eastern North America

National Academies of Sciences, Engineering, and Medicine. 2019. Forest Health and Biotechnology: Possibilities and Considerations. Washington, DC: The National Academies Press. https://doi.org/10.17226/25221.

Poland, T.M., P. Patel-Weynand, D.M Finch, C.F. Miniat, D.C. Hayes, V.M Lopez, editors. 2021. Invasive Species in Forests and Rangelands of the United States. A Comprehensive Science Synthesis for the US Forest Sector. Springer

Sniezko, R.A. and J. Koch. 2017. Breeding trees resistant to insects & diseases: putting theory into application. Biol Invasions. 2017. 19:3377-3400. DOI 10.1007/s10530-017-1482-5

Wheeler, N.C., K.C. Steiner, S.E. Schlarbaum, D.B. Neale. 2015. The Evolution of Forest Genetics and Tree Improvement Research in the United States, Journal of Forestry, Volume 113, Issue 5, September 2015, Pages 500–510, https://doi.org/10.5849/jof.14-120

Woodcock, P., M. Marzano, C.P. Quine. 2019. Key lessons from resistant tree breeding programmes in the Northern Hemisphere. Annals of Forest Science (2019)76:51 https://doi.org/10.1007/s13595-019-0826-y

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

On the Rise: US Imports & the Risks of Tree-killing Pests

containers at Port of Long Beach; photo courtesy of Bob Kanter, Port of Long Beach

Here I update information on two of the major pathways by which tree-killing pests enter the United States: wood packaging and living plants (plant for planting).

Wood Packaging

Looking at wood packaging material, we find rising volumes for both shipping containers – and their accompanying crates and pallets; and dunnage.

Crates and pallets – Angell (2021; full citation at the end of the blog) provides data on North American maritime imports in 2020. The total number of TEUs [a standardized measure for containerized shipment; defined as the equivalent of a 20-foot long container] entering North America was 30,778,446.U.S. ports received 79.6% of these incoming containers, or 24,510,990 TEUs. Four Canadian ports handled 11.4% of the total volume (3,517,464 TEUs; four Mexican ports 8.9% (2,749, 992 TEU). Angell provides data for each of the top 25 ports, including those in Canada and Mexico.

To evaluate the pest risk associated with the containerized cargo, I rely on a pair of two decade-old studies.  Haack et al. (2014) determined that approximately 0.1% (one out of a thousand) shipments with wood packaging probably harbor a tree-killing pest. Meissner et al. (2009) found that about 75% of maritime shipments contain wood packaging. Applying these calculations, we estimate that 21,000 of the containers arriving at U.S. and Canadian ports in 2020 might have harbored tree-killing pests.

While the opportunity for pests to arrive is obviously greatest at the ports receiving the highest volumes of containers with wood packaging, the ranking (below) does not tell the full story. The type of import is significant. For example, while Houston ranks sixth for containerized imports, it ranks first for imports of break-bulk (non-containerized) cargo that is often braced by wooden dunnage (see below). Consequently, Houston poses a higher risk than its ranking by containerized shipment might indicate.

Also, Halifax Nova Scotia ranks 22nd for the number of incoming containerized shipments (258,185 containers arriving). However, three tree-killing pests are known to have been introduced there: beech bark disease (in the 1890s), brown spruce longhorned beetle (in the 1990s), and European leaf-mining weevil (before 2012) [Sweeney, Annapolis 2018]

The top ten ports receiving containerized cargo in 2020 were

Port                                         2020 market share                2020 TEU volume

Los Angeles                           15.6%                                      4,652,549

Long Beach                            13%                                         3,986,991

New York/New Jersey         12.8%                                      3,925,469

Savannah                             7.5%                                        2,294,392

Vancouver BC                        5.8%                                        1,797,582

Houston                                   4.2%                                        1,288,128

Manzanillo, MX                      4.1%                                        1,275,409

Seattle/Tacoma    4.1%                                        1,266,839

Virginia ports                        4.1%                                        1,246,609

Charleston                             3.3%                                        1,024,059

Import volumes continue to increase since these imports were recorded. U.S. imports rose substantially in the first half of 2021, especially from Asia. Imports from that content reached 9,523,959 TEUs, up 24.5% from the 7,649,095 TEUs imported in the first half of 2019. The number of containers imported in June was the highest number ever (Mongelluzzo July 12, 2021).

Applying the calculations from Haack et al. (2014) and Meissner et al. (2009) to the 2021 import data, we find that approximately 7,100 containers from Asia probably harbored tree-killing pests in the first six months of the year. (The article unfortunately reports data only for Asia.) Industry representatives quoted by Mongelluzzo expect high import volumes to continue through the summer. This figure also does not consider shipments from other source regions.

Dunnage on the pier at Port of Houston; photo by Port of Houston

Infested dunnage – Looking at dunnage, imports of break-bulk (non-containerized) cargo to Houston – the U.S. port which receives the most – are also on the upswing. Imports in April were up 21% above the pandemic-repressed 2020 levels.

Importers at the port complain that too often the wooden dunnage is infested by pests, despite having been stamped as in compliance with ISPM#15. CBP spokesman John Sagle confirms that CBP inspectors at Houston and other ports are finding higher numbers of infested shipments. CBP does not release those data, so we cannot provide exact numbers (Nodar, July 19, 2021).

The Houston importers’ suspicion has been confirmed by data previously provided by CBP to the Continental Dialogue on Non-Native Insects and Diseases. From Fiscal Year 2010 through Fiscal Year 2015, on average 97% of the wood packaging (all types) found to be infested bore the stamp. CBP no longer provides data that touch on this issue.

Detection of pests in the dunnage leads to severe problems. Importers can face fines up to the full value of the associated cargo. Often, the cargo is re-exported, causing disruption of supply chains and additional financial losses (Nodar, July 19, 2021).

In 2019 importers and shippers from the Houston area formed an informal coalition with the Cary Institute of Ecosystem Studies to try to find a solution to this problem. The chosen approach is for company employees to be trained in CBP’s inspection techniques, then apply those methods at the source of shipments to identify – and reject – suspect dunnage before the shipment is loaded.  In addition, the coalition hopes that international inspection companies, which already inspect cargo for other reasons at the loading port will also be trained to inspect for pests.  Steps to set up such a training program were interrupted by the COVID-19 pandemic, but are expected to resume soon (Nodar, July 19, 2021).

Meanwhile, the persistence of pests in “treated” wood demands answers to the question of “why”. Is the cause fraud – deliberate misrepresentations that the wood has been treated when it has not? Or is the cause a failure of the treatments – either because they were applied incorrectly or they are inadequate per se?

ISPM#15 is not working adequately. I have said so.  Gary Lovett of the Cary Institute has said so (Nodar July 19, 2021). Neither importers nor regulators can rely on the mark to separate pest-free wood packaging from packaging that is infested.

APHIS is the agency responsible for determining U.S. phytosanitary policies. APHIS has so far not accepted its responsibility for determining the cause of this continuing issue and acting to resolve it. Preferably, such detection efforts should be carried out in cooperation with other countries and such international entities as the International Plant Protection Convention (IPPC) and International Union of Forest Research Organizations (IUFRO). However, APHIS should undertake such studies alone, if necessary.

In the meantime, APHIS and CBP should assist importers who are trying to comply by facilitating access to information about which suppliers often supply wood packaging infested by pests. The marks on the wood packaging includes a code identifying the facility that carried out the treatment, so this information is readily available to U.S. authorities.

Plants for Planting

A second major pathway of pest introduction is imports of plants for planting. Data on this pathway are too poor to assess the risk – although a decade ago it was found that the percentage of incoming shipments of plants infested by a pest was 12% – more than ten times higher than the proportion for wood packaging (Liebhold et al. 2012).

According to APHIS’ annual report, in 2020 APHIS and its foreign collaborators inspected 1.05 billion plants in the 23 countries where APHIS has a pre-clearance program. In other words, these plants were inspected before they were shipped to the U.S.  At U.S. borders, APHIS inspected and cleared another 1.8 billion “plant units” (cuttings, rooted plants, tissue culture, etc.) and nearly 723,000 kilograms of seeds. Obviously, the various plant types carry very different risks of pest introduction, so lumping them together obscures the pathway’s risk. The report does not indicate whether the total volume of plant imports rose or fell in 2020 compared to earlier years.

SOURCES

Angell, M. 2021. JOC Rankings: Largest North American ports gained marke share in 2020. June 18, 2021. https://www.joc.com/port-news/us-ports/joc-rankings-largest-north-american-ports-gained-market-share-2020_20210618.html?utm_campaign=CL_JOC%20Port%206%2F23%2F21%20%20_PC00000_e-production_E-103506_TF_0623_0900&utm_medium=email&utm_source=Eloqua

Haack R.A., Britton K.O., Brockerhoff, E.G., Cavey, J.F., Garrett, L.J., et al. (2014) Effectiveness of the International Phytosanitary Standard ISPM No. 15 on Reducing Wood Borer Infestation Rates in Wood Packaging Material Entering the United States. PLoS ONE 9(5): e96611. doi:10.1371/journal.pone.0096611

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

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

Mogelluzzo, B. July 12, 2021. Strong US imports from Asia in June point to a larger summer surge.

Nodar, J. July 19, 2021. https:www.joc.com/breakbulk/project-cargo/breakbult-volume-recovery-triggers-cbp-invasive-pest-violations_20210719.htm 

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

USFS report: treatment of introduced forest pests

still-healthy hemlocks in Cook Forest State Park, PA; photo by F.T. Campbell

In February the USFS published a lengthy analysis of invasive species: Invasive Species in Forests and Rangelands of the United States. A Comprehensive Science Synthesis for the US Forest Sector (Poland et al. 2021; full citation at the end of the blog). The book is available for download at no cost here.

In a separate blog, I evaluated several aspects of the report as they apply to invasive species generally. Here I focus on invasive insects and pathogens that attack North American tree species (that is, forest pests).

As I said in the separate blog, I doubt that the book will stimulate policy-makers to increase Forest Service resources allocated to invasive species research, much less management. Sections 14.5 and 16.5 of the report state that the continued absence of a comprehensive investigation of the impacts of invasive species, especially the full value of ecosystem services lost, is a barrier to policymakers seeking to develop priorities and realistic management strategies.

I think the book’s editors tried to provide as much information about impacts as possible given existing knowledge. But the book’s length, comprehensive inclusion of all bioinvaders, organizational structure, and the detailed discussions of theories and models reduce the contribution the book might make to management decisions. I did not find “lessons learned” that could be applied in the policy realm. 

Chapters address impacts in terrestrial and aquatic systems; impacts on ecosystem processes; impacts on various sectors of the economy and cultural resources; interactions with climate change and other disturbances; management strategies for species and landscapes; tools for inventory and management. Each chapter evaluates the current status of knowledge about the topic and suggests research needs. There are also summaries of the invasive species situation in eight regions.

The choice to organize the book around the chapters listed above means that some information one might expect to find in a book about invasive species is scattered or even absent. This is not a good resource for concise descriptions of individual invasive species and their impacts. That information is scattered among the chapters depending on whether some aspect of the species was chosen to illustrate a scientific challenge or success. The regional summaries partially remedy this problem – but they do not provide perspective on organisms that have invaded more than one region, e.g., emerald ash borer or white pine blister rust. To some extent, information about individual species is provided in the several subchapters on forest insects and pathogens. Or the reader of the PDF version can use the word search function!

Of course, information on several individual high-profile bioinvaders can be found in other publications; see the species write-ups and references posted at www.dontmovefirewood.org. Under these circumstances, a description of invasive species impacts from the ecosystem perspective is a welcome addition. I have long wished for a “crown to root zone” description of invasive species’ impacts.

HWA-killed hemlocks in Linville Gorge, NC; photo by Steven Norman, USFS

In this blog, I will focus on issues that the report raises that I found most interesting.

Information in the Report on Invasive Insects & Pathogens that Attack North American Trees

At several places the report states that non-native pests that have the potential to threaten the survival of an entire tree genus should be a high priority (p. 136) (what actions should be prioritized are not specified). They name the emerald ash borer (EAB) and Dutch elm disease. Elsewhere, EAB and hemlock woolly adelgid (HWA) are described as among the most significant threats to forests in the Eastern U.S. While EAB and HWA have certainly received considerable attention from the Forest Service, threats to elm have not. (I regret that the timing of the report precluded reference to Kevin Potter’s priority-setting publication. Potter is not listed as a co-author of the book.)

Hemlock woolly adelgid, emerald ash borer, chestnut blight, white pine blister rust (WPBR), and laurel wilt are cited as examples of highly virulent, host-specific agents that kill dominant, abundant, and ecologically unique hosts (p.18), resulting in exceptionally severe long-term impacts. WPBR and HWA specifically can have profound and far-reaching negative effects on ecosystem structure and function. These can rise to the level of an irreversible change of ecological state (p. 97). Of this list, no federal agency has allocated many resources to efforts to slow the spread of laurel wilt. The Forest Service is certainly tracking its spread and impacts.

Exaggerations or Errors

I think the report exaggerates the level of resources allocated to host resistance breeding. The report mentions programs targetting Dutch elm disease, beech bark disease, EAB, HWA and laurel wilt. It describes programs for white pines and Port-Orford cedar as examples of success. However, I would say that all the programs, except American chestnut, are starved for funds and other resources. The report’s authors concede this on p. 195.

TACF American chestnut in field trial; photo by F.T. Campbell

I think the report is too optimistic about the efficacy – so far – of biocontrol agents targeting HWA & EAB. On the other hand, I appreciate the report’s recognition that application of augmentative biocontrol of the Sirex woodwasp is more complicated in North America than in Southern Hemisphere countries (p. 162).

I am concerned about the statement that many plant pathogens are transported, but few have major impact. Examples in the U.S. are said to be WPBR, chestnut blight, and Phytophthora ramorum (p. 97). However, the report does not mention laurel wilt – which has a broad host range; nor rapid ‘ōhi‘a death — which threatens the most widespread tree species on the Hawaiian Islands. Nor does it mention several pathogens attacking single tree species, including beech bark disease, Port-Orford cedar root disease, and butternut canker. The report was written before recognition of beech leaf disease. The report notes that the three diseases it did mention have huge impacts. I am greatly disappointed that the report does not address how scientists and managers should deal with this “black swan” problem other than long discussions of data gaps, and ways to improve models of introduction and spread.

In addition, I am concerned that the discussion of economic factors that influence trade flows and accompanying invasive species (p. 308) focusses too narrowly on inspection alone, rather than other strategies for curtailing introduction. This section also shortens a description of the point made in Lovett et al. (2016). The report notes that Lovett et al. (2016) say that rates of introduction of wood-boring species decreased after ISPM#15 was implemented. However, the report leaves out the major caveat in that paper and the studies by Haack et al. (2014) and Leung et al. (2014) on which it is based: the reduction was insufficient to protect America from damaging introductions! [A further error has crept in: the Haack study explicitly excluded imports from China from their calculations. The Lovett paraphrase is not really clear on this matter.]

Curiosities/Concerns Re: Regional Write-Ups

I wish the sections on the Northwest and Southwest region discussed why areas with so many characteristics favoring introduction of plant pests – major ports, extensive transportation networks, major horticultural industry, extensive agriculture, and abundant urban and native forests – have so few damaging forest pests. (Admittedly, those present are highly damaging: white pine blister rust, sudden oak death, Port-Orford cedar root disease, pitch canker, balsam woolly adelgid, larch casebearer, polyphagous shot hole borer (I add Kuroshio shot hole borer), and banded elm bark beetle). The report does mention the constant threat of introduction of the European and Asian gypsy moths. (The Entomological Society of America has decided to coin a new common name for these insects; they currently to be called by the Latin binomial Lymatria dispar). The report notes that 22 species of non-native bark and ambrosia beetles have recently been introduced in the Southwest.

The report cites a decade-old estimate by Aukema et al. (2010) in saying that a small proportion of introduced pest species has killed millions of trees or pushed ecologically foundational species toward functional extinction. The figure was 14% of the more than 450 non-native forest insect species. I greatly regret that overlapping preparation and publication periods precluded inclusion of data from studies by Potter, Guo, and Fei.  http://nivemnic.us/what-fia-data-tell-us-about-non-native-pests-of-americas-forests/

Section 7.3 of the report discusses frameworks for setting priorities. It identifies five factors: 1) pest species having the greatest negative impacts; 2) uniqueness of the affected ecosystem or community; 3) state of the invasion in space and time; 4) management goals; 5) availability of effective tools. Examples of species meeting these criteria include EAB and Dutch elm disease (pest threatens entire host genus); white pine blister rust on whitebark pine (key species in a system with low arboreal diversity).

The report notes increasing understanding of critical aspects of several important pests’ biology and host interactions – but it does not sufficiently acknowledge the decades of effort required to achieve this knowledge. The time required for additional scientific advances will probably be equal or greater, given falling number of “ologists” in government and academia.

I appreciate inclusion of a discussion (Sections 8.3.1 and 8.3.2) on breeding trees resistant to introduced pests

dead Port-Orford cedar in Redwoods National Park; photo by Richard Sniezko, USFS

This section states that host resistance, forest genetics, and tree improvement might be the most effective approaches to managing many established pests. The section says such breeding does not require the use of genetically modified organisms, although transgenic or gene editing technologies can provide useful tools. I appreciate the report conceding that necessary infrastructure and expertise has been declining for two decades (p. 195).

In discussing international cooperation to reduce transport of invasive species, the report refers to increasing availability of data allowing identification of potentially damaging species in their regions of origin. Again, since this chapter was written, the Forest Service has increased its engagement on this approach: the USFS International Program is supporting sentinel plantings managed by the International Plant Sentinel Network (http://www.plantsentinel.org) … see my recent blog here.

SOURCE

Poland, T.M., P. Patel-Weynand, D.M Finch, C.F. Miniat, D.C. Hayes, V.M Lopez, editors. 2021. Invasive Species in Forests and Rangelands of the United States. A Comprehensive Science Synthesis for the US Forest Sector. Springer

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

USFS invasive species report: Herculean effort that could have had greater impact

In February the USFS published a lengthy analysis of invasive species: Invasive Species in Forests and Rangelands of the United States. A Comprehensive Science Synthesis for the US Forest Sector (Poland et al. 2021; full citation at the end of the blog). More than 100 people contributed to the book; I helped write the chapters on legislation and regulations and international cooperation. The book is available for download at no cost here.

Chapters address impacts in terrestrial and aquatic systems; impacts on ecosystem processes; impacts on various sectors of the economy and cultural resources; interactions with climate change and other disturbances; management strategies for species and landscapes; tools for inventory and management. Each chapter evaluates the current status of knowledge about the topic and suggests research needs. There are also summaries of the invasive species situation in eight regions.

Miconia – one of many invasive plants damaging ecosystems in Hawai`i

I greatly appreciate the effort. Authors first met in 2015, and most chapters were essentially written in 2016. The long delay in its appearance came largely from negotiations with the publisher. The delay means some of the information is out of date. I am particularly aware that several experts – e.g., Potter, Guo, and Fei – have published about forest pests since the Aukema source cited. I wonder whether inclusion of their findings might change some of the conclusions about the proportion of introduced pests that cause noticeable impacts.

Since the report’s publication in February I have struggled with how to describe and evaluate this book. What is its purpose? Who is its audience? The Executive Summary says the report is a sector-wide scientific assessment of the current state of invasive species science and research in the U.S.

However, the Introduction states a somewhat different purpose. It says the report documents invasive species impacts that affect ecosystem processes and a wide range of economic sectors. This would imply an intention to enhance efforts to counter such effects– not just to shape research but also to change management. Indeed, the Conclusion of the Executive Summary (pp. xvi-xvii) is titled “An Imperative for Action”.

Tom Vilsack, Secretary of Agriculture

I am not the author to evaluate how effectively the book sets out research agendas. Regarding its usefulness in prompting policy-makers to do more, I regretfully conclude that it falls short.

Getting the balance right between an issue’s status and what needs to be done is difficult, perhaps impossible. I appreciate that the report makes clear how complex bioinvasion and ecosystem management and restoration are. Its length and density highlight the difficulty of making progress. This daunting complexity might well discourage agency leadership from prioritizing invasive species management.

On the other hand, summary sections sometimes oversimplify or bury important subtleties and caveats. The question of whether some key questions can ever be resolved by science is hinted at – but in detailed sections that few will read. The same is true regarding the restrictions imposed by funding shortfalls.

The Report Would Have Benefitted from Another Round of Editing

Editing this tome was a Herculean task. I feel like a curmudgeon suggesting that the editors do more! Nevertheless, I think the report would have been improved by the effort. One more round of editing – perhaps involving a wider range of authors – could have pulled together the most vital points to make them more accessible to policymakers. It could also have tightened the ecosystem-based descriptions of impacts, which are currently overwhelmed by too much information.

A precis for policymakers

A precis focused on information pertinent to policymakers (which the current Executive Summary does not) should contain the statement that the continued absence of a comprehensive investigation of invasive species’ impacts hampers research, management, and policy (mentioned only in §16.5, on p. 332). It should note situations in which insufficient funding is blocking recommended action. I note three examples: programs aimed at breeding trees resistant to non-native pests (resource issues discussed only in §§8.3.1 and 8.3.2, p. 195); sustaining “rapid response” programs (§6.4.3, p. 125); costs of ecosystem restoration, especially for landscape-level restoration (§16.4). I am sure there are additional under-funded activities that should be included!

cross-bred ash seedlings being tested for vulnerability to EAB; photo courtesy of Jennifer Koch

 Other important information that should be highlighted in such a precis includes the statement that many ecosystems have already reached a point where healthy functions are in a more tenuous balance due to invasive species (p. 51). Effective carbon storage and maintaining sustainable nutrient and water balance are at risk. Second, costs and losses caused by invasive forest pests generally fall disproportionately on a few economic sectors and households. They cannot be equated to governmental expenditures alone (p. 305).  Third, even a brief estimate of overall numbers of invasive species appears only in §7.4. Information about individual species is scattered because it is used as example of particular topic (e.g., impacts on forest or grassland ecosystems, or on ecosystem services, or on cultural values).

Ecosystem Impacts Overwhelmed

As noted above, the report laments the absence of a comprehensive investigation of invasive species’ impacts. Perhaps the editors intended this report to partially fill this gap. To be fair, I have long wished for a “crown to root zone” description of invasive species’ impacts at a site or in a biome. Concise descriptions of individual invasive species and their impacts are not provided by this report, but they can be found elsewhere. (The regional summaries partially address the problem of too much information – but they do not provide perspective on organisms that have invaded more than one region, e.g., emerald ash borer or white pine blister rust.) Another round of editing might have resulted in a more focused presentation that would be more easily applied by policymakers.

Welcome Straightforward Discussion of Conceptual Difficulties

I applaud the report’s openness about some important overarching concepts that science cannot yet formulate.  If supportable theories could be conceived, they would assist in the development of policies:

  • Despite decades of effort, scientists have not established a clear paradigm to explain an ecosystem’s susceptibility to invasion (p. 85). Invasibility is complex: it results from a dynamic interplay between ecosystem condition and ecological properties of the potential invader, especially local propagule pressure.
  • Scientists cannot predict how climate warming will change distributions of invasive species [see Chapter 4] and alter pathways. This inability hampers efforts to develop effective prevention, control, and restoration strategies (p. xi). Climate change and invasive species need to be studied together as interactive drivers of global environmental change with evolutionary consequences.

The Report’s Recommendations

Policy-oriented recommendations are scattered throughout the report. I note here some I find particularly important:

  • Measures of progress should be based on the degree to which people, cultures, and natural resources are protected from the harmful effects of invasive species.
  • Managers should assess the efficacy of all prevention, control, and management activities and their effect upon the environment. Such an evaluation should be based on a clear statement of the goals of the policy or action. [I wish the report explicitly recognized that both setting goals and measuring efficacy are difficult when contemplating action against a new invader that is new to science or when the impacts are poorly understood. Early detection / rapid response efforts are already undermined by an insistence on gathering information on possible impacts before acting; that delay can doom prospects for success.]
    • Risk assessment should both better incorporate uncertainty and evaluate the interactions among multiple taxa. Risk assessment tools should be used to evaluate and prioritize management efforts and strategies beyond prevention and early detection/rapid response.
    • Economic analyses aimed at exploring tradeoffs need better tools for measuring returns on invasive species management investments (§16.5).
  • Actions that might be understood as “restoration” aim at a range of goals along the gradient between being restored to a known historic state and being rehabilitated to a defined desired state. The report stresses building ecosystem resilience to create resistance to future invasions, but I am skeptical that this will work re: forest insects and disease pathogens.
  • Propagule pressure is a key determinant of invasion success. Devising methods to reduce propagule pressure is the most promising to approach to prevent future invasions (p. 115). This includes investing in quarantine capacity building in other countries can contribute significantly to preventing new invasions to the US.
  • Resource managers need additional studies of how invasive species spread through domestic trade, and how policies may differ between foreign and domestic sources of risk.

I appreciate the report’s attention to such often-ignored aspects as non-native earthworms and soil chemistry. I also praise the report’s emphasis on social aspects of bioinvasion and the essential role of engaging the public. However, I think the authors could have made greater use of surveys conducted by the Wisconsin Department of Natural Resources and The Nature Conservancy’s Don’t Move Firewood program.

Lost Opportunities

I am glad that the report makes reference to the “rule of 25” rather than “rule of 10s”. I would have appreciated a discussion of this topic, which is a current issue in bioinvasion theory. As noted at the beginning of this blog, the long time between when the report was written and when it was published might have hampered such a discussion

Also, I wish the report had explored how scientists and managers should deal with the “black swan” problem of infrequent introductions that have extremely high impacts. The report addresses this issue only through long discussions of data gaps, and ways to improve models of introduction and spread.

I wish the section on the Northwest Region included a discussion of why an area with so many characteristics favoring bioinvasion has so few damaging forest pests. Admittedly, those present are highly damaging: white pine blister rust, sudden oak death, Port-Orford cedar root disease, balsam woolly adelgid, and larch casebearer. The report also notes the constant threat that Asian and European gypsy moths will be introduced. (The Entomological Society of America has decided to coin a new common name for these insects; they currently to be called by the Latin binomial Lymatria dispar).

And I wish the section on the Southeast and Caribbean discussed introduced forest pests on the Caribbean islands. I suspect this reflects a dearth of research effort rather than the biological situation. I indulge my disagreement with the conclusion that introduced tree species have “enriched” the islands’ flora.

SOURCE

Poland, T.M., P. Patel-Weynand, D.M Finch, C.F. Miniat, D.C. Hayes, V.M Lopez, editors. 2021. Invasive species in Forests and Rangelands of the United States. A Comprehensive Science Synthesis for the US Forest Sector. Springer

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

“Rule of Tens” – Time to Refine It

are wood-borers examples of species more likely to “proceed through the steps of invasion” than the theory suggests?

Much of the literature about biological invasion has relied on the “tens rule”. First enunciated in the mid-1990s by Williamson and Fitter (1996), it was actually conceived a decade earlier by Williamson and Brown (1986).

The “tens rule” hypothesizes that about 10% of all species transported to a new environment will be released or escape and become introduced species. Subsequently, 10% of those introduced species establish viable populations in the wild. Finally, about 10% of the established species become highly damaging. That is, 1% of the number originally transported to the new environment is a highly damaging invader.

Is the “tens rule” supported by evidence?

Empirical support for the hypothesis has been mixed; the number of studies questioning it has increased over the decades (Jeschke and Pyšek 2018). So Jeschke and Pyšek (2018) decided to evaluate the basis for the hypothesis. First, they divided the hypothesis into two sub-hypotheses so they could separate the concept of impact from the process of introduction, establishment, and spread. They justified this separation by noting that novel species can have an impact at any stage. The two sub-hypotheses:

1st sub-hypothesis: At each of the three transitions between the invasion stages listed here the number of species completing the transition is reduced by 90% (invasion tens rule).

  • transport to exotic range

transition

  • introduction (release or escape into the environment)

transition

  • establishment of a least one self-sustaining population

transition

  • spread

2nd sub-hypothesis: about 10% of established non-indigenous species cause a significant detrimental impact. This sub-hypothesis applies to the transition from establishment (iii, above) to significant impact (iv). Stepping back to the earlier introduction, so as to consider the situation overall, about 1% of all introduced non-native species cause a significant detrimental impact; this sub-hypothesis thus relates to the transition from introduction (ii) to significant impact (iv).

Jeschke and Pyšek carried out a quantitative meta-analysis of 102 empirical tests of the tens rule drawn from 65 publications. They found no support for the “invasion tens rule”. Indeed, their analysis found that about 24% of non-native plant and 23% of non-native invertebrate species are successful in taking consecutive steps of the invasion process. Among non-native vertebrates, about 51% are successful in taking consecutive steps of the invasion process.

The “impact tens rule” is also not supported by currently available evidence. However, Jeschke and Pyšek decided that more data are needed before a reasonable alternative hypothesis can be formulated.

Findings

Jeschke and Pyšek state that the “tens rule” is not based on a model or other defensible concept. It is also hampered by confusion of terms. Thus, different authors define the invasion process differently. Particularly confounding is the mixing of “impact” with steps in the invasion process. At the same time, there have been few studies of the “impact tens rule” hypothesis.

Finally, the “tens rule’s” predictions are not adjusted to consider changes in temporal and spatial scales. That is, it does not recognize that more invaders will be detected in any given place during more recent times than in the past. Furthermore, more invaders will find suitable niches in large areas than small.

The note that analysis is hampered by the paucity of reliable data about establishment success – especially for taxa other than mammals and birds. They do not discuss how this lack might affect efforts to analyze proportions of entering species that succeed in becoming invasive, especially among the small and inconspicuous taxa such as insects and fungal organisms that concern thus of us that focus on threats to forests. This same data gap has limited other studies as well; see, for example, Aukema et al. (2010) – who restricted their discussion of pathogens to “high impact” species.

Although Jeschke and Pyšek (2018) do not specify which studies they relied on to determine the proportion of successful invaders among species belonging to particular taxa, it seems likely that they relied principally on Vila et al. (2010) in determining that on average 25% invertebrates that are introduced (that is, proceed to the second stage in the process given above) become invasive. Vila et al. analyze introductions to Europe. They found that 24.2% of terrestrial invertebrates caused recognized economic impacts.

Jeschke and Pyšek (2018) Results and Discussion

Considering the “invasion tens rule”, two-thirds of the empirical tests in the dataset focused on the “invasion tens rule”. The majority of these focused on the transition from introduction to establishment (the transition from (ii) to (iii). The observed average percentage of species making this transition is more than 40% – or greater than four times larger than the “tens rule’s” prediction.

At the next transition, from establishment to spread (from iii to iv), the observed percentage of species making the transition is  greater than 30% – or greater than three times the predicted value under the “tens rule”.

Considering the “impact tens rule”, on average a quarter of established non-indigenous species have a significant detrimental impact, which is again significantly more than the 1 out of 10 species predicted by the rule. Specifically by taxon, 18% of established plants have shown detrimental impacts. Among invertebrates and vertebrates that estimate is greater than 30%. All these observations are higher than predicted by the rule. However, sample sizes are low so more studies are needed to test whether these values hold true.

Regarding the fullest possible extent of the invasion process, 16 out of 100 species that were introduced (stage ii) had a significant impact. This is 16 times greater than the 1% predicted by the “tens rule”. Considering specific taxa, 6% of established plants and 15% of established invertebrates had a significant impact. Data were too poor to support an evaluation for vertebrates.

I note that the alarmingly high “impact” estimates for invertebrates are probably biased by scientists’ and funding entities’ lack of interest in species that don’t cause noticeable impacts.

Poor data preclude an analysis of the transition from transport (i) to introduced (ii).

Strengthening The Estimates

Might these introduction and impact estimates be tightened by analysis of additional sources, such as the studies led Seebens, forest pest impact analyses by Potter et al. (2019) and Fei (2019) and reviews of pest introduction numbers by Haack and Rabaglia (2013)? 

Is it worth pursuing efforts to refine the Jeschke and Pyšek (2018) estimates? I think it is. An underestimation of the risk of introduction might lead decision-makers to downplay the need for a response.

Some scientists have accepted the new “rule of 25” (Schulz, Lucardi, and Marsico. 2021. Full citation at end of blog; also cited by USFS report – Poland et al. 2021). Others have not. Venette and Hutchison (2021; full reference at end of blog) continue to cite the estimate of approximately one “invasion success” for every 1,000 attempts – that is, a low-probability, high-consequence event. This challenges those responsible for managing invasive species.

Or are there other conundrums of introduction, establishment, and predicting impacts that have more direct relationship to improving programs? I note that the recent Forest Service report on invasive species (Poland et al. 2021) does not address the “rule of tens”.

Other Reasons Why Bioinvasion Damage is Underestimated

Jaric´ and G. Cvijanovic´ (2012) note that scientists lack a full understanding of ecosystem functioning, so they probably often miss more subtle – but still important – impacts.

Jeschke and Pyšek (2018) note that the percentage of introduced or established species with a quantifiable impact is not always the most important information. A single introduced species can have devastating impact by itself. They cite the amphibian disease chytrid (Batrachochytrium dendrobatidis) and such mammals as rats and cats.

SOURCES

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

Brockerhoff, E.G. and A. M. Liebhold. 2017. Ecology of forest insect invasions. Biol Invasions (2017) 19:3141–3159

Fei, S., R.S. Morin, C.M. Oswalt, and A.M. Liebhold. 2019. Biomass losses resulting from insect and disease invasions in United States forests. Proceedings of the National Academy of Sciences of the United States of America, 12 Aug 2019, 116(35):17371-17376

Haack, R.A. and R.A. Rabaglia. 2013 Exotic Bark and Ambrosia Beetles in the USA: Potential and Current Invaders. CAB International. 2013. Potential Invasive Pests of Agricultural Crops (ed. J. Pena)

Jaric´, I. and G. Cvijanovic´. 2012. The Tens Rule in Invasion Biology: Measure of a True Impact or Our Lack of Knowledge and Understanding? Environmental Management (2012) 50:979–981 DOI 10.1007/s00267-012-9951-1

Jeschke J.M. and P. Pyšek. 2018. Tens Rule. Chapter 13 of book by CABI posted at http://www.ibot.cas.cz/personal/pysek/pdf/Jeschke,%20Pysek-Tens%20rule_CABI%202018.pdf

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

Potter, K.M., M.E. Escanferla, R.M. Jetton, G. Man, and B.S. Crane. 2019. Prioritizing the conservation needs of United States tree species: Evaluating vulnerability to forest insect and disease threats. Global Ecology and Conservation. (2019)

Schulz, A.N., R.D. Lucardi, and T.D. Marsico. 2021. Strengthening the Ties That Bind: An Evaluation of Cross-disciplinary Communication Between Invasion Ecologists and Biological Control Researchers in Entomology. Annals of the Entomological Society of America · January 2021

Seebens, H., T.M. Blackburn, et al. 2018. Global rise in emerging alien species results from increased accessibility of new source pools. www.pnas.org/cgi/doi/10.1073/pnas.1719429115

Vilà, M., C. Basnou, P. Pyšek, M. Josefsson, P. Genovesi, S. Gollasch, W. Nentwig, S. Olenin, A. Roques, D. Roy, P.E. Hulme and DAISIE partners. 2010. How well do we understand the impacts of alien spp on ecosystem services? A pan-European, cross-taxa assessment. Frontiers in Ecology and the Environment, Vol. 8, No. 3 (April 2010), pp. 135-144

Venette R.C. and W.D. Hutchison. 2021. Invasive Insect Species: Global Challenges, Strategies & Opportunities. Front. Insect Sci.1:650520. doi: 10.3389/finsc.2021.650520

Williamson M.H. and K.C. Brown. 1986. The analysis and modelling of British invasions. Philosophical Transactions of the Royal Society of London Series B 314:505–522

Williamson M. and A. Fitter. 1996 The varying success of invaders. Ecology 77(6):1661–1666

South Africa & Invasive Species: Threats to High Value Biodiversity and Human Well-Being

Protea repens and fynbos vegetation near Table Mountain; photo by Mike Wingfield

South Africa is a country of immense biological diversity. It is also one that recognizes the threat invasive species pose to its natural wealth – and to the economy and livelihoods of ordinary people.

Also, South Africans are trying hard to improve the country’s invasive species program. It recently released the second national report assessing how well it is curtailing introductions and minimizing damage. As I describe in a companion blog, I find these reports to contain exceptionally thorough and honest appraisals of South Africa’s invasive species programs. I address that value in the companion blog, where I compare the South African report — and its findings — to U.S. government reports on our invasive species programs.

In South Africa, bioinvasion ranks third – after cultivation and land degradation – as a threat to the country’s impressive biodiversity. Invasive species are responsible for 25% of all biodiversity loss. Certain taxa are at particular risk: native amphibians and freshwater fishes, and some species of plants and butterflies.

Particularly disturbing is the bioinvasion threat to the Fynbos biome. The report notes that 251 non-native species have been identified in this system. This finding causes concern because the Fynbos is a unique floral biome. In fact, it constitutes the principal component of one of only six floral kingdoms found on Earth: the Cape Floral Kingdom (or region). For more information, go here.

map of South Africa showing fynbos biome

Not surprisingly, invasive bird and plant species are most numerous around major urban centers. The report concludes that this is probably because most non-native birds are commensal with humans; most birds and plants were first introduced to urban centers; and there is greater sampling effort there. Indeed, the patterns of (detected) invasive plant richness are still highly sensitive to sampling effort.

South Africa is considered a leader on invasive species management. However, its record is spotty.

Successes

Biocontrol interventions are considered a success. South Africa has approved release of 157 biocontrol agents, including seven since 2016. All the recent agents (and probably most others) target invasive plants. The South African biocontrol community conducts a comprehensive review of their effectiveness at roughly 10-year intervals. The fourth assessment is currently under way. Also, the report considers eradication of non-native fish (primarily sport species) from several wetlands and river reaches to have been successful. (However, opposition by sport fishermen has delayed listing of some trout species as invasive.)

Failures

On the other hand, strategies to combat invasive plants, other than by biocontrol, appear to be having little success. Even the extent of plant invasions in national parks is poorly documented. Also, the report highlights ballast water as an inadequately managed pathway of invasion.

The report estimates that three new non-native species arrive in South Africa accidentally or illegally every year. Interestingly, reported species arrivals have declined in the current decade compared to the preceding one. The report’s authors consider this to probably be an underestimate caused by the well-known lag in detecting and reporting introductions. The apparent decline also is contrary to global findings. Table 1 in Seebens et al. 2020 (full citation at end of blog) projected that the African continent would receive approximately 767 new alien species between 2005 and 2050.

Even the introductory pathways are poorly known: the pathway for 54% of the taxa introduced to South Africa are unknown. Of the species for which the introductory pathway is known, horticultural or ornamental introductions of plants dominate – 15% of that total. A second important pathway – for accidental introductions – is shipping (5% of all introductions). Other pathways thought to be prominent during 2017–2019 are the timber trade, contaminants on imported animals, and natural dispersal from other African countries where they had previously been introduced.

PSHB symptoms on Vachellia sieberiana; photo by Trudy Paap

Polyphagous shothole borer

The report highlights as an example of a recent introduction that of the polyphagous shothole borer (PSHB, Euwallacea fornicatus). https://www.dontmovefirewood.org/pest_pathogen/polyphagous-shot-hole-borer-html/        http://nivemnic.us/south-africas-unique-flora-put-at-risk-by-polyphagous-shot-hole-borer/ See Box 3.1 in the report. This species is expected to have huge impacts, especially in urban areas. While most of the trees affected so far are non-native (e.g., maples, planes, oaks, avocadoes), several native trees are also reproductive hosts.  https://www.fabinet.up.ac.za/pshb  In response to the introduction, the government established an interdepartmental steering committee, which has developed a consolidated strategy and action plan. However, as of October 2020 the shot hole borer had not been listed under invasive species regulations, even on an emergency basis. It had been listed as a quarantine pest of agricultural plants (e.g., avocado) per the Agricultural Pests Act 1983.

As note in my blog assessing the report, the report bravely concludes that the government’s regulatory regime is only partially successful (whereas three years ago it graded it as “substantial”). The downgrade is the result of a more thorough evaluation of the regulatory regime’s effectiveness.

SOURCES

SANBI and CIB 2020. The status of bioinvasions and their management in South Africa in 2019. pp.71. South African National BD Institute, Kirstenbosch and DSI-NRF Centre of Excellence for Invasion Biology, Stellenbosch. http://dx.doi.org/10.5281/zenodo.3947613  

Seebens, H., S. Bacher, T.M. Blackburn, C. Capinha, W. Dawson, S. Dullinger, P. Genovesi, P.E. Hulme, M. van Kleunen, I. Kühn, J.M. Jeschke, B. Lenzner, A.M. Liebhold, Z. Pattison, J. Perg, P. Pyšek, M. Winter, F. Essl. 2020. Projecting the continental accumulation of alien species through to 2050. Global Change Biology. 2020;00:1 -13 https://onlinelibrary.wiley.com/doi/10.1111/gcb.15333

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

Federal Funding for Forest Pest Programs — Act Now! to Help Congress Decide

If you have not communicated to your Representative and senators your support for adequate funding of U.S. government programs to address non-native insects and pathogens threatening our forests, please do so now!

If political leaders do not hear from us that expanding these programs is important, these programs will continue to languish. It is easiest – and most direct – to inform your representative and Senators of your support. Please do so!  If you do not agree that these programs should be expanded & strengthened, I ask that you send a comment outlining what approach you think would be more effective in curtailing introductions, minimizing impacts, and restoring affected tree species. I can then initiate a discussion to explore these suggestions. [I already have endorsed the suggestion to create a CDC-like body to oversee management of non-native forest pests.] You can find your member of Congress here. Your Senators here.

Last week the Biden Administration sent to Congress its proposed budget for the fiscal year beginning October 1, 2021. I find it falls short in key areas. Next, the House and Senate will pass a package of appropriations bills to set actual funding levels. This is the moment to press for boosted funding. In an earlier blog I explained my reasons for seeking specific funding levels.

Asian longhorned beetles – introduced in wood packaging (USDA photo)

Two USDA agencies lead efforts to protect U.S. wildland, rural, and urban forests from non-native insects and pathogens. Their funding is set by two separate – and critical — appropriations bills:

  • USDA’s Animal and Plant Health Inspection Service (APHIS) has legal responsibility for preventing introduction of tree-killing pests; detecting newly introduced pests; and initiating eradication and containment programs intended to minimize their damage.  Funding for APHIS is contained in the Agriculture Appropriations bill.
  • USDA Forest Service (USFS)
    • The Forest Health Management (FHM) program provides funding and applied science to help partners manage pests. The program has two sides: the Cooperative component helps states and private forest managers, so it can address pests where they are first found – usually near cities – and when they spread. The federal lands component helps the USFS, National Park Service, and other federal agencies counter pests that have spread to the more rural/wildland areas that they manage.
    • The Research and Development (R&D) program supports research into pest-host relationships; pathways of introduction and spread;; management strategies (including biocontrol); and host resistance breeding

Forest Service funds are appropriated through the Interior Appropriations bill.

APHIS – the Administration’s official budget proposal, and justification, is here.

The Administration proposes a small increase for three of four APHIS programs that are particularly important for preventing introductions of forest pests or eradicating or containing those that do enter. The Administration proposed significant funding for a fourth program that plays a small but important role in managing two specific forest pests.

APHIS ProgramCurrent (FY 2021)FY22 Administration proposedFY 2022 Campbell recommended
Tree & Wood Pest$60.456 million$61 million$70 million
Specialty Crops$196.553 million209 million$200 million
Pest Detection$27.733 millionNo change$30 million
Methods Development$20.844 millionNo change$25 million

Tree and Wood Pests: It will be a major challenge for APHIS to eradicate the current outbreak of Asian longhorned beetles (ALB) in the swamps of South Carolina. APHIS should also address other pests. Even after cutting spending on the emerald ash borer (EAB), I think APHIS needs significantly more money in this account.

The Specialty Crops program is supported by such traditional USDA constituencies as the nursery and orchard industries, which probably explains the proposed increase. APHIS’ program to curtail spread of the sudden oak death (SOD) pathogen through interstate nursery trade receives funding from this program – about $5 million. I believe this program also now funds the agency’s efforts to slow spread of the spotted lanternfly.

SOD-infected rhododendrons in Indiana nursery in 2019

I would like the Pest Detection program to receive a small increase so the agency and its cooperators can better deal with rising trade volumes and associated pest risk. Similarly, Methods Development should receive a boost because of the need for improved detection and management tools.

USDA Forest Service – the Administration’s official budget proposal is here.  

While the Forest Health Management (FHM) and Research and Development (R&D) programs are the principal USFS programs that address introduced forest pests, neither has non-native pests as the principle focus. Non-native forest pests constitute only a portion of the programs’ activities. In the case of Research, this is a very small portion indeed.

President Biden’s budget proposes to spend $59.2 million on the Forest Health Management program and $313.5 million for Research. Both represent significant increases over spending during the current fiscal year. However, the FHM level is still below spending in recent years, although both the number of introduced pests and the geographic areas affected have been rising for decades.

In my earlier blog I suggested the funding levels:

USFS PROGRAMCurrent (FY21) FY22 Administration FY22  my recommendation
FHP Coop Lands$30.747 million$36.747 million$51 million (to cover both program work & personnel costs)
FHP Federal lands$15.485 million22.485 million$25 million (ditto)
    
Research & Develop$258.7 million; of which about $3.6 million allocated to invasive species$313.560 million$320 million; I seek report language instructing the USFS to spend more on invasive species

Under the FHM program, a table on pp. 46-47 of the budget justification lists existing and proposed spending on 14 pest taxa (plus invasive plants and subterranean termites). Spending on these 14 species is proposed to total $30.3 million. Of this amount, less than half – $14.9 million – is allocated to such high-profile invasive species of forests as the emerald ash borer (EAB), hemlock woolly adelgid (HWA),  sudden oak death (SOD), and threats to whitebark pine (recently listed as a threatened species under the Endangered Species Act). (The USFS does not engage in efforts to eradicate Asian longhorned beetle (ALB) outbreaks; it leaves that task to APHIS.) And of the nearly $15 million allocated to invasive non-native pests, more than half – $8 million – is allocated to European gypsy moths. While I agree that the gypsy moth program has been highly successful, I decry this imbalance. Other non-native pests cause much higher levels of mortality among hosts than does the gypsy moth.

dead whitebark pine at Crater Lake National Park; photo by FT Campbell

I applaud the modest increases in the Administration’s budget for other non-native forest pests. These range from tens to a few hundred thousand dollars per pest. FHM also supports smaller programs targetting rapid ohia death, beech leaf disease, the invasive shot hole borers in southern California, Mediterranean oak beetle, etc. Budget documents don’t report on these efforts.

The imbalance of funding allocated to damaging non-native pests compared to other forest management concerns is even worse in the Research program.  Of the $313.5 million proposed in the budget for the full research program, only $9.2 million is allocated to the 14 pest taxa (plus invasive plants and subterranean termites) specified in the table on pp. 46-47. Of this amount, less than half — $4.5 million – is allocated to the high-profile invasive species, e.g., ALB, EAB, HWA, SOD, and threats to whitebark pine. The budget does provide extremely modest increases for several of these species, ranging from $12,000 for ALB to $114,000 for EAB. Again, some smaller programs managed at the USFS regional level might address other pests. Still – the budget proposes that USFS R&D allocate only 1.4% of its total budget to addressing these threats to America’s forests! This despite plenty of documentation – including by USFS scientists – that non-native species “have caused, and will continue to cause, enormous ecological and economic damage.” (Poland et al. 2021; full citation at the end of the blog). Poland et al. go on to say:

Invasive insects and plant pathogens (or complexes involving both) cause tree mortality, resulting in canopy gaps, stand thinning, or overstory removals that, in turn, alter microenvironments and hydrologic or biogeochemical cycling regimes. These changes can shift the overall species composition and structure of the plant community, with associated effects on terrestrial and aquatic fauna. In the short term, invasive insects and diseases can generally reduce productivity of desired species in forests. Tree mortality or defoliation can affect leaf-level transpiration rates, affecting watershed hydrology. Tree mortality … also leads to enormously high costs for tree removal, other management responses, and reduced property values in urban and residential landscapes.

eastern hemlock in Shenandoah National Park; photo by FT Campbell

I seek report language specifying that at least 5% of research funding should be devoted to research in pathways of invasive species’ introduction and spread; their impacts; and management and restoration strategies, including breeding of resistant trees. Several coalitions of which the Center for Invasive Species is a member have agreed to less specific language, not the 5% goal.

Two other USFS programs contribute to invasive species management. The Urban and Community Forest program provided $2.5 million for a competitive grant program to help communities address threats to urban forest health and resilience. Of 23 projects funded in FY2020, 11 are helping communities recover from the loss of ash trees to EAB. (On average, each program received $109,000.)

The Forest Service’ International Program is helping academic and other partners establish “sentinel gardens” in China and Europe. North American trees are planted and monitored so researchers can identify insects or pathogens that attack them. This provides advance notice of organisms that could be damaging pests if introduced to the United States.

REFERENCE:

Invasive Species in Forests and Rangelands of the United States. Editors T.M. Poland, T. Patel-Weynand, D.M. Finch, C.F. Miniat, D.C. Hayes, V.M. Lopez  Open access!

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

Rising risk to East Coast as Ship Capacities Expand

brown spruce longhorned beetle

They’re coming! As I have blogged frequently over the past year,  imports through ports other than Los Angeles-Long Beach are rising – and with them the risk of pest introductions.

Demonstrating this phenomenon is the fact that the largest container ship ever to call on the North American East Coast will arrive this week. The “Marco Polo” can carry 16,022-TEU (twenty-foot equivalent; a standardized measure of container capacity). It is scheduled to call at Nova Scotia today (May 17), then work its way down the coast to New York-New Jersey on May 20, Norfolk on May 23, Savannah on May 26, and Charleston on May 28.  Most of these ports have a history of receiving tree-killing pests: beech bark disease, beech leaf weevil, and brown spruce longhorned beetle at Halifax, NS; Asian longhorned beetle at New York and possibly Charleston; redbay ambrosia beetle at Savannah.

The ship’s owner CMA CGM (a French company operating around the globe), also holds the previous record for the largest ship to visit the east Coast: the 15,072-TEU “Brazil” called at New York-New Jersey in September 2020. CMA CGM North America President Ed Aldridge credited the ports’ significant increases in capacity for allowing the increased volume.

CMA CGM is focused on imports from the Indian Subcontinent and Southeast Asia. Ships headed to the North American East Coast are transitting the Suez Canal.

CMA CGM also operates the “Jules Verne” with a capacity of 16,022-TEU; and the “Ben Franklin” at 18,000-TEU. These ships serve trans-Pacific trade.  

During the first 10 months of 2020, 15% of vessel calls were by ships with capacities of 10,000-TEU or higher, up from 11% in 2019.

Source:

https://www.joc.com/maritime-news/container-lines/cma-cgm/largest-ship-call-east-coast-arrive-next-week-cma-cgm_20210514.html?utm_source=Eloqua&utm_medicum=email&utm_campaign=CL_JOC%20Daily%205/17/21%20_PC00000_e-production_E-98549_TF_0517_0617

EAB Threat to Eastern Europe

The emerald ash borer (EAB) was first detected in European Russia in 2003, in Moscow. By 2020, EAB was recorded in 16 provinces [=‘oblast’] of European Russia, especially to the West of Moscow towards the borders with Belarus and Ukraine.  

Russian scientists have documented that the emerald ash borer is spreading faster in the southwest of the country and in neighboring Ukraine than in the northwest (near St. Petersburg and the Baltic countries).

Despite an abundance of ash [both green ash (Fraxinus pennsylvanica) – native to North America – and European ash F. excelsior], EAB population density in the northwest remains low and damage is in scattered clusters.

However, in September 2020 officials detected an isolated outbreak in a St. Petersburg suburb, 520 km away from the apparent edge of the principal Russian population. The authors believe this outbreak has been present since 2015. They think it is the result of transport of EAB either by “insect-hitchhiking” on vehicles or by movement of plants for planting or other commodities.

The Petersburg population is only 130 km from Estonia and Finland – the border with the European Union.

A thousand kilometers to the south, in southwest Russian eastern Ukraine, an outbreak was reported in June 2019. By the next summer, EAB were detected more than 100 km to the West. While this outbreak is still 800 km from Ukraine’s border with eastern Europe (Poland, Slovakia, Hungary, Romania), the authors note that rapid spread is likely since F. excelsior and F. pennsylvanica have been extensively planted along roads, railways, field shelter belts, and urban greenings.

The slower spread in the North is attributed to colder temperatures, the local abundance of food, and possibly pressure by the native parasitoid Spathius polonicus Niezabitowski (note that USDA APHIS has approved two Spathius species as biocontrol agents in the U.S.). On the other hand, the climate is milder in Saint Petersburg (along the coast) than it is inland; and ash woodlands are common along the Baltic coast.

Noting that ash dieback (Hymenoscyphus fraxineus)  has devastated more than 95% of European ash populations, the authors express concern about the future of ash.

SOURCE

Musolin, D.L.; Selikhovkin, A.V.; Peregudova, E.Y.; Popovichev, B.G.; Mandelshtam, M.Y.; Baranchikov, Y.N.; Vasaitis, R. North-Westward Expansion of the Invasive Range of Emerald Ash Borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) towards the EU: From Moscow to Saint Petersburg. Forests 2021, 12, 502. https://doi.org/10.3390/f12040502

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

13 (at Least) Exotic Tussock Moths Pose High Risk to North America

Lymantria monacha 1 Novlinder, Saxafraga -Ab H Bass

The North American Plant Protection Organization (NAPPO) has released a scientific study, Risks Associated with the Introduction of Exotic Tussock Moth Species (Lepidoptera: Erebidae: Lymantriinae) of Potential Concern to the NAPPO Region.  

The report identifies 13 species of tussock moths — other than several Asian gypsy moths – that pose a serious risk to Canada, Mexico, and the United States and that should be addressed as quarantine pests. However, vital  information was missing in key areas, on one variable for more than 84% of the 79 species  screened. Thus many additional species were not fully evaluated; some of these might also pose serious risks.                                                                                                                                                                                                                                                                                                              Study findings

North American countries already regulate several species of Lymantria native to east Asia: Lymantria dispar asiatica, L. dispar japonica, L. albescens (includes L. postalba), and L. umbrosa. NAPPO’s Regional Standard for Phytosanitary Measure (RSPM) No. 33url sets up a system requiring inspection and cleaning of marine vessels travelling from China, Korea, and Russia to the NAPPO region during the specified risk periods (SRP) of moth flight and egg mass deposition by these species.

However, the U.S. and Canada have been intercepting egg masses belonging to other lymantriid species, especially Lymantria lucescens, Leucoma salicis, Lymantria mathura, and Lymantria xylina. In response, the NAPPO countries initiated this study. All life stages — egg masses, larvae, pupae, and adults — have been intercepted in the NAPPO region primarily during maritime port inspections of vessels and shipping containers originating in Asia (Russia, Japan, China, Philippines, and Korea) and Europe.

                                                                                                                                                                                                                     There are more than 2,400 species of Lymantriids found on all continents except Antarctica. The group is also missing from Pacific islands, including New Zealand and Hawai`i. The greatest diversity occurs in the tropical areas of Africa, India, and Southeast Asia.   

Lymantriid moths can have high fecundity, which can result in large population increases in a single generation. Some undergo cyclical outbreaks resulting in large-scale defoliation of their host plants.

The larvae are highly polyphagous. Some species feed on more than 150 hosts, especially trees – both deciduous and coniferous. The host plants are better known in temperate regions of the Northern Hemisphere; little is known about hosts of tropical moth species. 

The study concluded that there is a high likelihood of introduction of lymantriid species into the NAPPO region due to the high volume of trade coming from Asia, the large number of probable lymantriid host species in North America, and the apparently suitable climatic conditions. While there are several possible pathways for transporting the moths from Asia to North America, the most important is the presence of masses of resilient eggs on surfaces of ships and hard-sided cargo (containers, motor vehicles, etc.). Once in North American ports, mated female moths can disperse either by flight (some species) or by “ballooning” on wind currents.

The authors initially collected data on 189 species. The report does not indicate whether they focused on Asia, but the results seem to be limited largely to that region. The authors winnowed the initial list down to 79 species for further analysis due largely to lack of resources and information. The Risk Assessment Model and Data Sheet are available here.

The study concluded that 13 species pose a high and that the NAPPO countries should designate them as “actionable pests” and take other actions to prevent their introduction. The high-risk species are Lymantria monacha, L. mathura, L. lunata and L. xylina, Euproctis kargalika, Euproctis subflava, Euproctis chrysorrhoea, Leucoma candida, Orgyia thyellina, Euproctis lunata, Leucom wltshirei, Lymantria fumida, and Sarsina violascens.

Evaluation Process

The 79 species were evaluated based on eight questions:

1) Are adult females attracted to light? (The authors thought such behavior would make them more likely to be flying during risk periods and attracted to ports and vessels).

2) Has the species been reported as a contaminant pest of commodities in trade in its

overwintering stage? (This presence was thought to result in species that are likely to move via trade and have the highest risk of survival and introduction).

3) Is the species reported to cause economic or environmental damage in its native range?

4) Does the species have larvae capable of ballooning?

5) Does the species have adult females capable of flight?

6) Does the species’ life history include a dormant stage able to withstand harsh environmental conditions? (Such species were thought to be more likely to survive transit to the NAPPO region and to persist once introduced).

7) Is the species capable of natural dispersal farther than 1 km/year?

8) Is the species reported to have allergenic properties?

Questions 2 & 3 were given more weight because they were considered to have a greater effect on the likelihood of the species being introduced and causing unacceptable impacts.

Weaknesses

Both the apparent focus on Asia and the emphasis on question 3 result in a process that was unlikely to uncover any potential pests that are currently “unknown unknowns”.

Vitally important information was missing for many of the species. For six of the eight questions, the evaluation found no information for more than 50 percent of the species evaluated. Information was lacking for Question 2 – one of the questions assigned greater weight – on 84 percent of the species! Ability to disperse more than 1 km per year had an even higher percentage of answers as “unknown”. Regarding “ballooning” of larvae, 80 percent of the species could not be classified.

These data gaps created a high level of uncertainty regarding the risk rankings of those species ranked as “low” risk. See Figure 2 from the report.

One of the reasons cited for the information gaps was the inability to access literature in foreign languages, specifically Russian. Surely both the U.S. and Canada have access to native Russian speakers!

The authors admit that the lack of information “affected the risk scores and possibly the risk categories for certain species.” They call for additional research and periodic reviews of the report’s findings.  

They note that the report is a quick screening tool, not a rigorous pest risk assessment. They suggested additional research and sharing of interception data to address the information gaps. The research should focus on species’ flight periods and biological information relevant to regulatory actions; and detection tools (e.g., traps, lures, predictive phenology models, and molecular identification tools).

They note that the three countries currently limit surveillance and management programs to a few taxa.

I concur with the authors’ recommendation that a moth species be considered to pose a serious threat if it feeds on a host included in a tree or shrub genus that has economic value in the NAPPO region. (Under the terms of the International Plant Protection Organization, ISPM#5, environmental damage is included in the term “economic value”.)

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