A team of researchers at Montana State University analyzed environmental and habitat conditions across four states in the Pacific Northwest to create a county-by-county risk rating for establishment of the invasive giant hornet Vespa mandarinia. (Image originally published in Norderud et al 2021, Journal of Insect Science)

By Reagan Colyer

A team of researchers from Montana State University’s College of Agriculture published a study this month in the Journal of Insect Science outlining the risk of the invasive giant hornet Vespa mandarinia establishing populations in the Pacific Northwest, including Montana.

Bob Peterson, Ph.D.

Scott Powell, Ph.D.

Erik Norderud

Recent graduate Erik Norderud, associate professor Scott Powell, Ph.D., and professor Bob Peterson, Ph.D., of the Department of Land Resources and Environmental Sciences (LRES) examined factors that may lead to higher risk for the insect’s establishment. The invasive hornets have earned wide attention and concern due to their status as a primary predator to honey bees. The team conducted risk assessments for every county in Idaho, Montana, Oregon, and Washington—a total of 175 counties.

Vespa mandarinia, sometimes known as the Asian giant hornet, is the largest hornet species in the world. It was first detected in North America in Vancouver, British Columbia, and later in Whatcom County, Washington, in late 2019. The first sighting of the insect in 2021 occurred in early August, also in Whatcom County in northwestern Washington, and its nest was located nearby last week. There have not yet been any confirmed sightings of the hornets in Montana.

“Asian giant hornets typically feed on insects, sap, and soft fruits, but they are known to attack and kill bee hives in the late summer and early fall when developing males and future queens need protein,” says Norderud, who graduated from the LRES professional master’s program in fall 2020 and is the lead author on the paper. “This behavior can affect beekeeping and pollination, and, if the hornets become established, they could also displace native wasp species.”

Norderud now works with the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS), in Washington state. He said factors that make a county high-risk for hornet establishment are ideal temperature and suitable habitat. Vespa mandarinia queens need an environment warm enough to survive the winter, but they also seem to be sensitive to very hot climates. The queens also prefer green spaces for nest colonization, Norderud says, such as parks or forests.

Vespa mandarinia is the largest hornet species in the world. It was first detected in North America in Vancouver, British Columbia, and later in Whatcom County, Washington, in late 2019. The first sighting of the insect in 2021 occurred in early August, also in Whatcom County in northwestern Washington, and its nest was located nearby last week shortly after. In 2021, a team of researchers at Montana State University analyzed environmental and habitat conditions across four states in the Pacific Northwest to create a county-by-county risk rating for establishment of V. mandarinia. (Photo by Karla Salp, Washington State Department of Agriculture, Bugwood.org)

The risk assessment for the study included factors such as forest cover, apiary locations, and locations of ports and freight hubs in all 175 counties across those four states. Because the hornets are native to Asia, port locations were key as potential places where the insects could be introduced through trade coming from Asian countries.

The data was turned into maps of risk factors. Compiling the data allowed the team to see where the risk factors overlapped most, assigning each county an overall risk rating score, or ORS, classified as low, medium, or high risk.

In total, the team identified 32 counties across the four states as “low risk,” 120 as “medium risk,” and 23 as “high risk,” including Montana’s Lewis & Clark County, which received an ORS of 9 due to its large numbers of apiaries and high density of forest cover. Lewis & Clark was the only Montana county deemed “high risk,” along with one county in Idaho, nine in Washington and 12 in Oregon.

“This risk assessment is important because it helps professionals who are monitoring for this invasive species to prioritize areas where the hornet is more likely to establish,” says Peterson.

The best way to protect native pollinators and manage beehives, says Norderud, is to prevent the hornets from establishing in larger numbers in the western U.S. He noted that some native hornets look similar to the invasive species and that public involvement in monitoring the pollinators they see around their homes and towns is critical to identifying any V. mandarinia hornets in their communities.

“When the hornet was first found in the U.S. and reported in the media, there were reports from people all around the country claiming that they were finding them,” he says. “The interest and enthusiasm is great, but there are many native lookalikes which are important to the local ecosystem. Most importantly, I hope this publication will increase awareness of the threat [these] hornets can pose to essential pollinators in the U.S.”

Reagan Colyer is a communications specialist at Montana State University. Email: reagan.colyer@montana.edu.

This article was originally published by the Montana State University News Service. Adapted and republished with permission.