D3407: Description of four Vespa mandarinia (Hymenoptera: Vespidae) nests collected in Washington State, USA

Vespa mandarinia Smith 1852 is the one of the two largest species of Vespa, and is a semi-specialized predator of other social Hymenoptera. Several specimens of this predatory wasp were detected in Canada and the United States in 2019, including an entire nest that was located and destroyed in Nanaimo, British Columbia. The Washington State Department of Agriculture and the United States Department of Agriculture collaborated to survey Washington State for V. mandarinia in 2020-2021, using traps staffed by agency personnel, collaborators from local governments and NGOs, and the general public. Trap data and public reports were used to select sites for live-trapping or net surveys, and live hornets were subsequently collected and fitted with radio tags in order to locate nests. The survey ultimately led to the discovery of a V. mandarinianest in October, 2020, and three nests in August and September, 2021. All of the nests were in Alnus rubra trees, with one just above the ground in a standing dead tree, and the other three in cavities 1.5 to 5 meters above the ground in living trees. The number of combs varied between four and ten, cells between and 1329, and total hornets per nest between 449 and 1474 (immature and mature stages). Together, the four nests indicate an incipient population of V. mandarinia in the Cascadia region, and ongoing action by local, state, provincial, and federal governments, and residents of both countries, is required to avoid establishment of another exotic species in the region.