Why Taxonomic Preparedness is Critical for Invasive Species Response

By Matthew L. Buffington, Ph.D.; Elijah J. Talamas, Ph.D.; and Kim A. Hoelmer, Ph.D.

Responding to invasive insects is a three-fold endeavor, involving detection or interception, accurate and fast identification (i.e., taxonomy), and thorough ecological investigations. In the latest issue of American Entomologist, we recount the taxonomic work that sprang into action to investigate natural enemies of the brown marmorated stink bug (Halyomorpha halys) after its arrival in North America in the late 1990s, as an example of how taxonomic preparedness is critical to the success of biological control efforts to respond to invasive species.

Here we share a short summary of that story, and we hope you’ll dig into the full story as well: “Team Trissolcus: Integrating Taxonomy and Biological Control to Combat the Brown Marmorated Stink Bug.”

A Stinky Situation

The brown marmorated stink bug is native to China, Japan, and South Korea. Beginning in 2005, foreign exploration expeditions were organized to locate and collect specialized natural enemies of the pest in these countries.

The results of initial surveys in Asia suggested that egg parasitoids in the wasp genus Trissolcus were among the most important natural enemies of H. halys. Collections over the next several years established a number of geographically distinct colonies of several species of Trissolcus, maintained in the USDA–ARS quarantine lab in Newark, Delaware.

However, a critical question remained unanswered regarding these parasitoids: What species were they? The existing literature on parasitoids of stink bugs from Asia, and on H. halys in particular, was sparse, and the taxonomy of these parasitoids was complicated by a number of issues:

• The genus has nearly 200 described species worldwide.
• Specimens are small, 1–2 mm long.
• The last major genus-wide taxonomic study of Trissolcus in Asia was completed in the 1970s.
• Many of the original specimens (i.e., vouchers of the named species) were not readily available to study.
• The descriptions of most species were insufficient and lacked quality illustration.

The USDA Animal Plant Health Inspection Service (APHIS), which regulates the release of non-native biological control agents, requires that the identity of an agent be well known to consider its release. Misidentification of the natural enemy may lead to imprecise or erroneous conclusions, which could have unintended consequences should releases be approved. Thus, the taxonomic problems regarding Trissolcus needed immediate attention, and the solution came in the form of a concerted effort among taxonomists, biological control researchers, and agency administrators to bring taxonomic preparedness to the forefront of the classical biocontrol program targeting H. halys in the U.S.

The parasitoid samurai wasp (Trissolcus japonicus) is a natural enemy of the brown marmorated stink bug (Halyomorpha halys). Taxonomic work in the years after the H. halys invasion in North America identified T. japonicus in Asia as a promising candidate for biological control against the stink bug. As Trissolcus was an understudied genus, taxonomic experts within the entomological community worked quickly to deepen the discipline’s understanding of Trissolcus to prepare for potential deployment of biological control efforts in the United States. (Image originally published in Buffington et al 2018, American Entomologist)

In 2012, the first of what would become a series of workshops on parasitoid natural enemies of the brown marmorated stink bug (Halyomorpha halys) was hosted at the USDA Beneficial Insects Research Laboratory in Newark, Delaware. (Image originally published in Buffington et al 2018, American Entomologist)

The brown marmorated stink bug (Halyomorpha halys) was accidentally imported from Asia to North America in the mid- to late 1990s. Today, this invasive species is present in nearly all of the contiguous United States and has is widely recognized for its ability to feed destructively on a wide variety of different host plants of economic and landscape value and to invade homes and other buildings in large numbers. (Photo credit: Susan Ellis, Bugwood.org)

The Formation of Team Trissolcus

After an initial natural enemy workshop hosted at the University of Delaware in 2012, a project was planned to mobilize USDA resources to clarify and modernize the taxonomy of Trissolcus. To achieve this goal, entomological collections from around the would be examined carefully for relevant material to study. In addition, and perhaps most critically, a systematist would be hired to lead the research to revise the taxonomy of Trissolcus.

Given the enormity of the brown marmorated stink bug invasion, this work had to be completed in a relatively short time. One of us (Elijah) trained with Norman Johnson, the last major revisor of Trissolcus. Within a few months, we had solved part of the Trissolcus problem: A species known as Trissolcus halyomorphae, frequently reared from parasitized egg masses in Asia, was, in fact, another species, Trissolcus japonicus, which had been described more than 100 years earlier! We have since discovered that four more species named in existing literature were also in fact T. japonicus; all of these are now formally treated as junior synonyms to T. japonicus.

Concurrently, samples of Asian Trissolcus species from the Newark quarantine laboratory cultures, as well as additional specimens collected in China, Korea and Japan, were analyzed to distinguish different geographic populations of T. japonicus from one another.

The Samurai Wasp in North America

The next major step was to update the knowledge of Trissolcus species native to North America. When poorly known exotic species are released into a poorly known native fauna, biological control scientists have difficulty documenting what has happened and which released natural enemy species have succeeded or failed. We avoided this potential problem by developing an updated identification key to North American species of Trissolcus.

The critical timing of these events became apparent when a series of non-native T. japonicus was collected in 2014 from a H. halys egg mass in Maryland. At the time, populations of T. japonicus (now dubbed the “samurai wasp”) were known to be present in North America only in quarantine. Collaborative efforts were initiated immediately to determine whether these parasitoids had escaped from quarantine or had arrived independently by other means; results indicated that the Maryland populations were adventive and did not match any of the populations maintained in quarantine.

This is where taxonomic preparedness was invaluable. Without the combined efforts of our ongoing research on the behavior and taxonomy of native and exotic Trissolcus parasitoids, we could easily have missed the fact that the very species being considered for release as an exotic biological control agent had arrived in the United States on its own. Furthermore, the biological control project could have been wrongly implicated as the source of these populations.

The Future is Bright

So, where do we go from here? Using the tools already published, we are in a position to track the spread and the impact of this self-introduced natural enemy.

More broadly, as we continue to discover and identify effective natural enemies of new invasive pests, accurate taxonomic identifications will be particularly critical. Consider this: How can anyone know what species are going to be important to the human condition in the future, especially invasive pests and their associated natural enemies? We cannot know ahead of time what species are going to become problematic; the most cost-effective and responsible position to take in understanding invasive species is to document all species. And so, the “brush fire” mentality toward solving pest problems must shift toward a fire prevention policy, where taxonomic preparedness provides the necessary framework for species to be identified, and biological control projects are, as a result, efficacious.

Matthew L. Buffington, Ph.D., is a research entomologist at the USDA–ARS Systematic Entomology Laboratory in Washington, DC. Email: matt.buffington@ars.usda.gov. Elijah J. Talamas, Ph.D., is curator of Hymenoptera, Mollusca and Neuroptera, at the Florida Department of Agriculture and Consumer Services, Division of Plant Industry, in Gainesville, Florida. Email: elijah.talamas@freshfromflorida.com. Kim A. Hoelmer, Ph.D., is research leader at the USDA–ARS Beneficial Insects Introduction Research Unit in Newark, Delaware. Email: kim.hoelmer@ars.usda.gov.