Laboratory investigation of secondary attraction in Gnathotrichus sulcatus (Coleoptera: Scolytidae)

Abstract

Gnathotrichus sulcatus of both sexes responded by moving upwind in a laboratory bioassay to benzene extracts of guts from males boring in logs of western hemlock. It was concluded that the response was to an aggregating pheromone which forms the major constituent of the secondary attraction in this species. Although there was a primary attraction to host sawdust, boring dust produced by males elicited a greater response from both sexes. Male guts became attractive between 6 and 12 h after attack of a new host, and attraction persisted at least 8 days. Extracts of female guts were unattractive, either before or after attack, indicating that females do not produce an independently active pheromone. Guts from males which were paired with females were only marginally attractive after 48 h in host logs. An unexplained response occurred to a mixture of male and female gut extracts from paired beetles, but the response was much lower than to the gut extract from single males allowed to bore for 48 h. Wood surrounding up to 15-day-old galleries of single males was significantly more attractive than wood from fresh host logs.