The Polydrusus weevils (Coleoptera: Curculionidae) of the United States of America and Canada: identification and insights into the ecology of two nonnative species in hazel (Corylus spp.)

Abstract

Seven species of Polydrusus Germar weevils (Coleoptera: Curculionidae) occur in the United States of America and Canada, three of which are introduced from Europe, are polyphagous, and may be displacing native weevil fauna in select areas of North America. We review host plant information for these species and provide distributional maps for each. We also present results on the seasonal phenology and sex ratios of two nonnative species, Polydrusus impressifrons (Gyllenhal) and Polydrusus formosus (Mayer), recorded in 2020 and 2021 in two orchards of hybrid hazelnuts (Betulaceae) in Minnesota, United States of America. These two species may present an episodic threat to the burgeoning hybrid hazelnut industry due to their ability to damage buds, foliage, and roots of hardwoods. We found that adults of these two species began emerging in late May of each year and remained present until mid-July. We found higher numbers of P. formosus than of P. impressifrons on hazel plants. Sex ratios of both species were generally between 50–60% male. We supply a compendium of species descriptions that (1) distinguishes between native and nonnative species and (2) identifies the sex of nonnative species. This research contributes to work on the ecology of Polydrusus, conservation of native species, and the management of tree crops.