Asian giant hornet – US & Canada Differ – What are the Implications? – Updated!

Asian giant hornet (AGH) (Vespa mandarinia) is the world’s largest hornet, reaching sizes of 1.5 – 2 inches long. Its native range includes much of Asia. While media attention has focused on the hornet’s frightening size, the real threat is to honey bees (Apis spp.) and – especially – to the many important crops that bees pollinate.

Over the past year or so, several detections of the Asian giant hornet have been found in the Pacific Northwest – in British Columbia and Washington State. Four of the sites are within a few miles of each other. Two others are separated by miles of open water from the mainland sites. As of mid-October, 18 hornets had been detected in Washington State.

USDA’s Animal and Plant Health Inspection Service (APHIS) has partnered with the Washington Department of Agriculture to try to eradicate the hornet – which will not be easy! However, the Canadian Food Inspection Service (CFIA) has decided not to designate the hornet as a quarantine pest. This decision seems to threaten divergent approaches to the bioinvader. Fortunately, the Province of British Columbia is trying to eradicate its populations – so perhaps the diverging federal approaches will not result in facilitating the hornet’s establishment and spread.

Where the Hornet Is Known to Be

The first detected outbreak of the Asian giant hornet was in Nanaimo, British Columbia – on Vancouver Island. A single hornet was detected in August 2019. [A Canadian commenter said in March 2021 that this turned out to be a different species, V. soror.] A nest was detected in September and destroyed by local beekeepers and BC government officials. However, another hornet was found on the mainland – in White Rock, B.C. – in November 2019 [CFIA Decision Document]. In 2020, there have been several unconfirmed sightings in the Cowichan Valley on Vancouver Island (van Westendorp, pers. comm.).

Meanwhile, beekeepers discovered two AGH outbreaks in Whatcom County, WA, on the U.S. side of the border. These discoveries were in December 2019 and May 2020. There were other, unconfirmed reports in both Washington and British Columbia. [USDA APHIS Environmental Assessment (EA)] Indeed, later in 2020, Washington reported a few more sightings — in the Birch Bay area, just south of Blaine and at a site about eight miles east of Blaine (van Westendorp, pers. comm.)

Three of the hornets found in spring 2020 were mated queens (Zhu et al. 2020), which means at least one colony successfully reproduced last year. One of the mated queens was the second detection in Whatcom County – in Custer, Washington. One article said that the locations of this spring’s queens meant either that the new queens travelled up to 35 kilometres (about 22 miles) before founding their nests or that they came from more than one colony. Either way, it probably means that giant hornets could spread faster than initially thought.

White Rock, BC and Blaine, Washington are a few miles apart on the Canada-U.S. border. Langley is 12 miles to the northeast of White Rock – in the Fraser Valley. Custer is 7 miles southeast of Blaine. Birch Bay is 5 miles south of Blaine. The most recent detection is 8 miles east of Blaine. So all these detections are in close proximity and might represent spread from a single introduction site – or maybe not!

Nanaimo and the Cowichan Valley are on Vancouver Island, which is separated from the other locations by a significant distance and open water. The two island sites are about 30 miles apart. They surely represent one or more separate introductions.

One study found that a single hornet collected from Blaine, Washington differed genetically from  a single hornet collected at Nanaimo on Vancouver Island. This suggests separate introductions. However, too little is known about the hornet’s genetic variability across Asia to allow conclusions about possibly separate origins (van Westendorp, pers. comm.; Wilson et al. 2020).

Areas at Risk

The area at risk is potentially much broader than the Pacific Northwest. APHIS’ initial analyses, based on plant hardiness zones, indicated that the hornet could thrive in virtually all the lower 48 states. APHIS’s Environmental Assessment did not address vulnerable areas in Canada or – apparently – in Hawai`i.

Zhu et al. (2020) carried out an assessment of areas most at risk and the hornet’s potential rate of spread. They found that areas with warm to cool annual mean temperature, high precipitation, and high human activity were most likely to be suitable for the hornet. Areas meeting these criteria are found across western and eastern North America, Europe, northwestern and southeastern South America, central Africa, eastern Australia, and New Zealand. Most of central North America and California are less suitable.

Spread could be rapid in the Pacific Northwest: they predicted that the hornet could reach Oregon in 10 years, eastern Washington and British Columbia within 20 years. This prediction is based in part by experience with the invasive congener V. velutina in Europe; it has expanded by 78 km/year in France, 18 km/year in Italy.

Oregon is relying on beekeepers to detect the hornet, which they expect will arrive even earlier than 10 years from now. The Oregon Department of Agriculture has suffered severe budget cuts because of the Covid-19 crash in state tax collections, so the program is trying to save money. As of the beginning of October, none of the hundreds of citizen reports has been a Vespa of any species (J. Vlach, Oregon Department of Agriculture, pers. comm).

Pathways of Introduction

It is not known how the hornet reached North America. Reports from other countries indicate that they can hitchhike in shipments of empty plant containers, or in the straw in which the containers are packed. In addition, some Asian cultures regard the hornets as delicacies, so deliberate importation is possible. Both APHIS and the Canadian Food Inspection Agency (CFIA) have intercepted such shipments (CFIA Decision document; USDA APHIS PPQ New Pest Response).

The Threat

The AGH typically feeds on a variety of terrestrial invertebrates including beetles, mantids, caterpillars, and spiders (EA). During the spring and summer, hornets attack their prey singly. However, in the Aautumn, hornet workers carry out mass attacks against other social Hymenoptera – including other species of Vespa, yellowjackets (Vespula spp.), various paper wasps (Polistes spp.), and honey bees (Apis spp.). Commercial honeybee colonies are typically lost when attacked en masse. They are especially vulnerable because they are more concentrated than wild bee colonies. [EA]

Commercial honeybee colonies pollinate a wide variety of crops, including tree fruits, cane fruits (berries), tree nuts, tomatoes, and even potatoes. Supplies of beef and milk might also be at risk because alfalfa hay is pollinated by bees. Of course, honey production would also be threatened. As USDA APHIS has stated, if the Asian giant hornet spreads it would become a new stress on top of the multiple existing causes of honeybee decline.

Also, there is a direct threat to people. The AGH has a painful sting that can result in anaphylaxis, cardiac arrest, and other complications in susceptible people. Officials emphasize that most people will not be at risk of stings. However, beekeepers are – their usual Personal Protective Equipment (PPE) is not adequate to ward off the hornet’s sting [APHIS EA & New Pest .

APHIS’ programmatic Environmental Assessment notes that the hornet might also pose a threat to vertebrates that nest in ground burrows and decayed trunks and roots near the ground. Burrows chosen by female hornets for nest construction can be surprisingly large, up to 60 cm (24 inches) in diameter. The EA notes that, in Washington State, badgers, marmots, ground squirrels, and other small mammals use dens or burrows. Among these, four pocket gophers and the American wolverine are federally listed under the Endangered Species Act in Washington State. [For a list, see the environmental assessment.] The EA does not discuss whether cavity-nesting birds might also be affected – although the hornets do prefer hollows near or at ground level. The authors of the EA expect vertebrates to abandon any burrows used by the hornet, so they would be displaced rather than harmed by pesticides applied by the program described below.  

APHIS program

APHIS and the Washington State Department of Agriculture (WSDA) have begun an eradication program. I think eradication will be challenging because it will be very difficult both to find nests and to destroy them.

• Hornets nest typically in forested areas or urban green spaces. There are lots of suitable places in the Pacific Northwest! These wooded areas are interspersed with farms, orchards, and settlements that will provide vulnerable insects as food sources.  
• Nest destruction involves excavating a hole two meters by two meters. This digging must be in woodlands, often right next to trees.

The key to successful eradication is finding and destroying the nests before they produce reproductive females and males – in autumn. Nest detection will be carried out as follows [EA]:

• Starting in April, the agencies bottle traps in trees near the 2019 detection points. The traps are baited with a solution of rice cooking wine and orange juice to attract the worker bees. (The rice wine is added to discourage honeybees from visiting the trap.)  Traps catches help define areas where nests are located.

WSDA successfully tracked radio-tagged workers to a nest in mid-October. That nest was in a tree hollow, not underground.

WSDA scientists think there were approximately 200 queens in that single nest. Two were vacuumed out during the initial extraction. Inside the nest they found 76 emergent queens and 108 capped cells with pupae that they believe were also queens. Three more queens were trapped in a bucket of water. This nest had approximately 776 cells; large nests can have up to 4,000.  WSDA believes there are other nests in the area; they continue to search.

APHIS’ original plan to use pesticides to kill hornets in the nest has been dropped. Washington plans now to use vacuum extraction followed by introduction of CO₂ and excavation of the nest.  Washington has also not decided whether to deploy traps with the pesticide fipronil (S. Spichiger, pers. comm.)

WSDA has also asked members of the public to set out homemade hornet traps, and to report any suspicious sightings.

Canada Takes Opposite Tack

The Canadian Food Inspection Agency (CFIA) announced in February 2020 (CFIA Decision Document) that it will not attempt to regulate the Asian giant hornet as a quarantine pest for Canada. Therefore, CFIA will place no restrictions on the import or movement of any commodities that may harbor the Asian giant hornet. CFIA will, however, require permits for deliberate importation of the hornets.

CFIA’s reasoning appears to focus on two factors:

• The hornet is an indirect threat to plant health (since AGH attacks pollinators. CFIA has traditionally regulated quarantine pests based primarily on significant direct threats to plant health.
• Under the international phytosanitary system, countries that designate an organism to be a quarantine pest must put in place the necessary measures to prevent its entry into the country, as well as officially control the pest when present. CFIA states that “High uncertainties about the pathways of entry puts into question the ability to manage this risk, and ultimately the ability and feasibility of regulating V. mandarinia as a quarantine pest.”

Neither APHIS nor CFIA has authority to regulate threats to human health.

Detection and Eradication Efforts in British Columbia  (information from van Westendorp, British Columbia Ministry of Agriculture)

In 2020, British Columbia has focused on detection surveillance. Target areas include vicinity of Nanaimo on Vancouver Island; Fraser Valley from White Rock in the West to Langley/Aldergrove in the East (along the US border); and after several credible (but non-verified) sightings, the Cowichan Valley on Vancouver Island. Because of resource limits, the surveillance effort has sought to engage local governments, border agencies, First Nations, forestry & mining companies, farmers, and beekeepers.  The ministry also placed numerous bottle traps and encouraged 170 beekeepers in the Fraser Valley to install and monitor traps in their apiaries. 

So far, only one AGH specimen has been sighted or collected in the three British Columbia survey areas during 2020 – the single specimen at Langley detected in May. However, the several detections along the U.S. side of the border (see above on recent detections) has spurred BC officials to intensify survey efforts in the Fraser Valley (van Westendorp). A specimen was collected adjacent to the US border in mid-October just north of the multiple detections in the US, and South of the Langley detection last spring (S. Spicher, pers. comm.).

British Columbia will continue to monitor well into the fall season and resume our surveillance in 2021 and 2022 (van Westendorp).

Hornets are clearly able to be transported and introduced. Vespa ducalis was detected in Vancouver, BC in 2019 and in Texas in 2020. Vespa velutina has become established in Europe (J. Vlach, Oregon Department of Agriculture, pers. comm).

SOURCES

CFIA Decision document: Vespa mandarinia (Asian giant hornet) February 2020. https://www.inspection.gc.ca/plant-health/plant-pests-invasive-species/insects/asian-giant-hornet/decision-document/eng/1593718645505/1593718645899

USDA APHIS Asian Giant Hornet Control Program in Washington State Final Environmental Assessment—July 2020

USDA AHIS PPQ New Pest Response

van Westendorp, Paul. British Columbia Ministry of Agriculture, pers. comm.

Wilson, T.M., J. Takahashi, S-Erik Spichiger, I. Kim, and P. van Westendorp. 2020. First Reports of Vespa mandarinia (Hymenoptera: Vespidae) in North America Represent Two Separate Maternal Lineages in WA State, US, and BC, Canada. Annals of the Entomological Society of America · October 2020

Zhu, G., J. Gutierrez Illan, C. Looney, and D.W. Crowder. 2020. Assessing the ecological niche and invasion potential of the Asian giant hornet. PNAS Latest Articles ECOLOGY