The list of invasive insects in the United States is a long one, but one entomologist offers his list of the four “most wanted” (clockwise from top left):  the spotted lanternfly (Lycorma delicatula), the brown marmorated stink bug (Halyomorpha halys), spotted wing drosophila (Drosophila suzukii), and the khapra beetle (Trogoderma granarium). (Photo credits, : top left, Lawrence Barringer, Pennsylvania Department of Agriculture, Bugwood.org; top right and bottom left, Rob Morrison, Ph.D.; bottom right, Hannah Burrack, North Carolina State University, Bugwood.org)

By Rob Morrison, Ph.D.

Rob Morrison, Ph.D.

Admittedly, it’s hard to narrow the worst invasive insect species to just four (I was aiming for three actually), because there are so many in the U.S., and each decade seems to bring increasingly damaging species from exotic locales. It is also true that there are more than just invasive insects out there; for example, northern climes battle every year with garlic mustard that has taken over the forest understory, and waterways have to deal with zebra mussels and Asian carp that dramatically change ecosystems.

In total, though, the economic impact of invasive species is estimated to be more than $30 billion annually as a result of crop losses and mitigation measures. The U.S. Department of Agriculture has appropriated $17.5 million for the eradication of the spotted lanternfly (Lycorma delicatula, see below), while an additional $14 million was appropriated for research of all other invasive species. I present to you (in my personal, taxonomically biased view) the four most wanted invasive insects in the U.S. today—and one opportunity for you to become involved and help out.

1. Brown Marmorated Stink Bug: The Plague That Won’t Stop

While populations have subsided in the eastern United States, the brown marmorated stink bug (Halyomorpha halys) is making inroads into the Midwestern and the southern U.S., where it is causing as much damage as it did when it first became a problem in the mid-Atlantic U.S. The species has now spread to 44 states. (Photo credit: Rob Morrison, Ph.D.)

The brown marmorated stink bug (Halyomorpha halys, or BMSB) was accidentally introduced to the United States in the mid-1990s, but it went undetected until the early aughts. In 2010, the species reached outbreak proportions, inflicting severe economic injury in Mid-Atlantic U.S. tree fruit production to the tune of $37 million dollars.

Insecticide use increased sometimes four-fold in specialty crop production, and many growers were on the verge of closing up shop. One stakeholder had more than 20,000 stink bugs make it into his home in a very short period; nuisance pest issues have become a fact of life for many folks on the East Coast dealing with BMSB.

Through the vigorous efforts of researchers, growers were brought back from the ledge, and BMSB has become a manageable issue. In fact, the last several years have been quieter in the Mid-Atlantic region in terms of BMSB damage, potentially from the expanding adventive range of its most effective parasitoid, the samaurai wasp (Trissolcus japonicus). However, while populations have subsided in the east, the species is making inroads into the Midwestern and the southern U.S., where it is causing as much damage as it did when it first became a problem in the Mid-Atlantic U.S. The species has now spread to 44 states, and a wave of stink bugs seems to be pushing westward and southward with no end yet in sight.

2. Spotted Wing Drosophila: Small Fruit Cannot Escape the Scourge

Spotted wing drosophila (Drosophila suzukii) is fairly unusual among fruit flies because it is attracted to not-quite-ripe or ripe fruit, and it is able to tear the fruit open with serrated hindquarters, which allows it to deposit eggs in ripening fruit. (Photo credit: Hannah Burrack, North Carolina State University, Bugwood.org)

While most Drosophila (fruit fly) species are considered nuisance pests of overripe, fermenting, or spoiled fruits, spotted wing drosophila (Drosophila suzukii, or SWD) is fairly unusual. This is because the species is attracted to not-quite-ripe or ripe fruit, and it is able to tear the fruit open with serrated hindquarters, which allows it to deposit eggs in ripening fruit. By the time the fruit are harvested, they are crawling with fly maggots—an understandably unappetizing situation, especially for fresh market.

SWD was first recorded on berries in 2008 in coastal regions of California. By the end of 2009, it had spread from southern California to British Columbia, Canada. Without adequate control, SWD-related injury in the western U.S. can result in up to $500 million in damage. Now, SWD can be found in most temperate regions of the U.S.

The species can undergo 13 generations in a season, leading to enormous pressure on late-maturing varieties of berries. There has been an ongoing search for effective lures and monitoring devices, which is an active area of research. There are also no clear-cut biological control candidates for SWD, as parasitism is very variable from different hosts and regions. There is a clear overreliance on insecticides in most areas affected by SWD, but a large number of researchers are trying to develop sustainable solutions for growers.

3. Spotted Lanternfly: A Threat Poised to Broadly Impact the U.S.

The spotted lanternfly (Lycorma delicatula) can deposit up to almost 200 egg masses on a single host, but the host need not be a plant: lanternflies are happy to place egg masses on stones, fences, and other construction material, which makes them a great hitchhiking species. (Photo credit: Lawrence Barringer, Pennsylvania Department of Agriculture, Bugwood.org)

Spotted lanternfly (Lycorma delicatula, or SLF) is another stowaway from Asia on commercial products. This species is native to northern China and was first detected in Pennsylvania in 2014. It was immediately quarantined by the Pennsylvania Department of Agriculture, and vigorous eradication efforts were deployed. However, it has since spread to neighboring states in the Mid-Atlantic region, which elicits a feeling of déjà vu with BMSB, which was first detected in Allentown, Pennsylvania, but quickly spread to neighboring states.

In the quarantine zone in Pennsylvania, SLF has been reported to be so numerous that a literal rain of honeydew (a sugary secretion produced by true bugs) falls on observers and nearby vegetation wherever aggregations are present. Preferred SLF host plants are tree of heaven (abundant in the eastern U.S.), grapes, and tree fruit.

So far, SLF has a host range that incorporates over 70 host plant species. SLF can deposit up to almost 200 egg masses on a single host, but it need not be a plant: the lanternflies are happy to place egg masses on stones, fences, and other construction material, which makes them a great hitchhiking species.

The sheer density of SLF on hosts can be overwhelming, and, with its recent expansion into neighboring states, this may be the beginning of another disruption to integrated pest management programs for specialty crop producers in the U.S.

4. Khapra Beetle: Constant Vigilance to Protect Post-Harvest Commodities

Within the last several decades, there have been an increasing number of interceptions of the khapra beetle (Trogoderma granarium) at ports of entry by the USDA Animal Plant and Health Inspection Service. Here, an adult male (left) and female (right) are shown. (Photo credit: Rob Morrison, Ph.D.)

The khapra beetle (Trogoderma granarium, or KB) was ranked as one of the top 100 worst invasive species of all time by the Invasive Species Specialist Group. KB is originally from India and the Middle East, and it is the only U.S.-designated quarantine pest that attacks stored grain and finished products. It is also listed on the European and Mediterranean Plant Protection Organization’s Schedule A2 quarantine list.

Infestation of products by KB can result in up to 70 percent weight loss and requires costly fumigations to disinfest material. In the 1950s, a large KB infestation at more than 150 sites in California, Arizona, and New Mexico was discovered. In today’s dollars, the U.S. government spent over $90 million to eradicate the pest from the country. Within the last several decades, there have been an increasing number of interceptions of KB at ports of entry by the USDA Animal Plant and Health Inspection Service (APHIS).

There is ongoing research into the most effective lure and trap combinations to successfully develop refined tools for surveillance of KB in areas of commerce. So far, there have been no further incursions, but this is a case where one must be constantly vigilant in order to avoid KB wreaking havoc on the post-harvest food system in the U.S.

How Can You Get Involved?

Good question! The latest initiative from the Plant-Insect Ecosystems (P-IE) and Systematics, Evolution, and Biodiversity (SysEB) Sections of the Entomological Society of America (ESA) is the “Science Policy Field Tour – Invasive Species Security: Protecting Our National Health, Food Supply, and Environment.” This tour will bring together experts in invasive species from ESA as well as stakeholders, policymakers, and personnel from industry in a networking session in an area of the Mid-Atlantic significantly hit by invasive species.

During the event, participants will tour the quarantine zone for spotted lanternfly, visit the Philadelphia Port of Entry and hear talks by APHIS personnel, tour the historic insect collection at Drexel Academy of Natural Sciences, and hear about research on BMSB, SWD, and others. The field tour registration cost is $645 and includes a hotel reservation for two nights, welcome reception, all meals, shuttle to and from the airport, bus transportation, and all fees and admissions. Registration is still open, but available seats on the tour are filling fast. Learn more and register.

What Else are Entomologists Doing About the Challenge of Invasive Species?

ESA has designated invasive species as one of the three priorities to improve the human condition via its Grand Challenges Agenda for Entomology. On November 9-10, immediately prior to the 2018 Joint Annual Meeting of the Entomological Societies of America, Canada, and British Columbia, in Vancouver, the Societies will host an Invasive Species Summit, which will gather experts from entomological societies, research institutions, related federal agencies, and corporate interests in North America and the Pacific Rim. Learn more about the Invasive Species Summit.

Rob Morrison, Ph.D., is a Research Entomologist at the USDA-Agricultural Research Service, Center for Grain and Animal Health Research, in the Stored Product Insects and Engineering Research Unit, in Manhattan, Kansas, and the 2017-2018 chair of the ESA Early Career Professionals Committee. Twitter: @morrisonlabUSDA. Email: william.morrison@ars.usda.gov. Website: www.ars.usda.gov/pa/cgahr/spieru/morrison.