Disruption of male spruce budworm orientation to calling females in a wind tunnel by synthetic pheromone.

Male spruce budworm [Chorisloneura fumiferana (Clem.)] moths were held for 3 hr in a wind tunnel and subjected to various concentrations of background synthetic pheromone. They were then exposed to calling females and their response was recorded. The background pheromone was presented either as discrete turbulent plumes or as a uniform permeation throughout the tunnel. The numbers of males wing-fanning and flying in response to the calling females decreased as the concentration of background pheromone increased. Of the males which flew, a higher proportion progressed upwind in the discrete plumes than in the uniform permeation, an indication that structure in the pheromone cloud is necessary for upwind progression. In both discrete plumes and uniform permeation fewer males were able to locate the females (i.e., disruption was greater) as the concentration of synthetic pheromone increased, but for the same total release rates, disruption was greater when the synthetic pheromone was released in discrete plumes rather than in a uniform permeation. This implies that disruption which involves luring males to sources of synthetic pheromone is more effective than masking female plumes by uniform permeation and suggests that it is more efficient to release pheromone from a few potent sources than from numerous low-potency sources.