Costs and benefits of alternative overwintering strategies by the alder bark beetle (Coleoptera: Curculionidae: Scolytinae)

Abstract

Diverse strategies for overwintering are found among bark beetle (Coleoptera: Curculionidae: Scolytinae) species, yet costs and benefits of these strategies are seldom considered. The lifecycle of the alder bark beetle, Alniphagus aspericollis (LeConte), in red alder, Alnus rubra Bongard (Betulaceae), is univoltine and comprises two cohorts; the first overwinters as adults, often inside branch nodes, and the second overwinters as mature larvae in the main stems ( i.e., boles) of trees. We investigated prevalence of the entomopathogen Beauveria Vuillemin (Ascomycota: Cordycipitaceae) and adult body size in both beetle cohorts to determine whether fitness trade-offs may exist for these alternative overwintering strategies. Adult beetles were collected from sites across southwestern British Columbia and evaluated for presence of Beauveria on the exoskeleton ( via culturing) and body size. Bole-overwintering beetles were eight times more likely than branch-overwintering beetles to be associated with Beauveria . Branch-overwintering beetles, however, were approximately 11% smaller than bole-overwintering beetles, and dissections revealed that these beetles may use maturation feeding to offset some costs of dispersal and reduced body size associated with overwintering. We speculate that potential fitness costs associated with dispersal and reduced body size in the branch-overwintering cohort may be outweighed by benefits of reduced exposure to Beauveria .