Local, Geographical, and Contextual Variation in the Aggregation Pheromone Blend of the Spruce Beetle, Dendroctonus rufipennis (Coleoptera: Curculionidae).

Prior research from trapping experiments using synthetic pheromone components suggested the existence of local and geographical variation in the pheromone system of the spruce beetle, Dendroctonus rufipennis (Kirby). To test hypotheses concerning variation in the spruce beetle's aggregation pheromone blend, we extracted volatiles from the hindguts of individual spruce beetles sampled from sites in eastern Canada (Nova Scotia and Newfoundland) and western Canada (British Columbia and Alberta) and quantified the amounts of four known aggregation pheromone components within each sample. Chiral analyses were performed on a subset of samples. Frontalin (1,5-dimethyl-6,8-dioxabicyclo[3.2.1]octane) was more dominant in western Canada, whereas MCOL (1-methyl-2-cyclohexen-1-ol) and seudenol (3-methyl-2-cyclohexen-1-ol) were more dominant in the east. Verbenene (4-methylene-6,6-dimethylbicyclo[3.1.1]hept-2-ene) was prevalent only in one of our six sites (Rocky Mountain House, AB). Female beetles in Rocky Mountain House (AB) also produced a higher proportion of (+)-frontalin than females from the other sites, and a comparison to previously published data suggests additional geographic variation that was not captured among our sites. When paired with a male in a gallery, female spruce beetles produced pheromone blends with more frontalin and less MCOL compared to solitary female beetles. Our results show that variation in the spruce beetle's pheromone blend exists at both large and small spatial scales, possibly a consequence of local selective pressures and assortative mating.

The Effect of Feeding and Mate Presence on the Pheromone Production of the Spruce Beetle (Coleoptera: Curculionidae).

Dendroctonus rufipennis (Kirby, Coleoptera: Curculionidae) uses pheromone blends containing aggregative components (frontalin, verbenene, 1-methyl-2-cyclohexen-1-ol [MCOL], and seudenol) and an anti-aggregative component (3-methyl-2-cyclohexen-1-one [MCH]) to coordinate attacks against host trees, but little is known about the influence of external stimuli on pheromone production. We conducted feeding experiments followed by pheromone extractions to determine if feeding duration and mate presence affected pheromone production in D. rufipennis. Unfed beetles of both sexes produced very little of any pheromone component. Females fed for 48 h produced significantly more MCH and MCOL compared to those which fed for 24 h. Males fed for 48 h produced significantly less seudenol than those which fed for 24 h. Male presence did not significantly affect female pheromone production. We propose that the pheromone blend produced by beetles transitions from aggregative to anti-aggregative shortly after colonizing a host, regardless of mate presence.