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
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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