DISRUPTION OF SECONDARY ATTRACTION OF THE SPRUCE BEETLE, DENDROCTONUS-RUFIPENNIS, BY PHEROMONES OF 2 SYMPATRIC SPECIES

Capture of spruce beetles, Dendroctonus rufipennis, in multiple funnel traps baited with frontalin and alpha-pinene was reduced by up to 42% in the presence of synthetic (+)-exo-and (+)-endo-brevicomin, aggrega tion pheromones of the sympatric species Dryocoetes affaber. (+/-)-end o-Brevicomin was inhibitory to spruce beetles in two experiments and ( +/-)-exo-brevicomin was inhibitory in one experiment, reducing spruce beetle trap catches by up to 87% and 75%, respectively. Spruce beetle trap catches were also reduced by 85% by (+/-)-or (+)-ipsdienol, but n ot by (-)-ipsdienol. Ips tridens, a second sympatric species, produces both enantiomers of ipsdienol in its pheromone blend. Responses by D. affaber to its own pheromone were significantly enhanced by addition of the spruce beetle lure. Enantiospecific pheromones of secondary com peting species, or less costly racemic substitutes, may be useful for managing spruce beetles using competitive displacement or exclusion. B aiting susceptible hosts with pheromones of secondary species may enha nce attack by secondary species, while partially repelling spruce beet les.