Yellowjacket (Vespula pensylvanica): biology and abatement in the National Parks of Hawaii

Abstract

The western yellowjacket Vespula pensylvanica (Saussure) has become widely established in the Hawaiian Islands, where it exhibits a high degree of reproductive plasticity. Although most colonies in Hawaii Volcanoes and Haleakala National Park adhere to the basic annual cycle dominant throughout this wasp's native range in western North America, overwintered colonies were detected in some years. Polygyny, achieved by adding queens to an established colony, is a likely prerequisite for successful overwintering. The large size of overwintered colonies and some annual colonies (with more than 300 worker sorties per minute from the nest) results in very heavy predation on local arthropod biota. Workers of Vespula pensylvanica take a wide variety of prey at or near plant and soil surfaces. Populations of highly precinctive endemic arthropods may in some instances be unable to recover from such intense predation pressure. Although even local eradication of Y. pensylvanica is not feasible, toxic baiting trials using Knoxout 2FM in canned chicken bait, with enhancement of bait acceptance with heptyl butyrate, were in many instances effective in drastically reducing yellowjacket forager populations. Toxic baiting was most consistently effective in high elevation shrubland and least effective in forest situations. A protocol is presented for use by resource managers in dealing with yellowjacket threats to native biota and to visitors.