Male pheromone blend preference function measured in choice and no-choice wind tunnel trials with almond moths, Cadra cautella

An almost universal component of moth reproduction is the long-range attraction of males by female-produced sex pheromones. Males are hypothesized to discriminate against incomplete and aberrant blend ratios. Male moth preference functions would then be unimodal with a single optimum coincident with the mean female sex pheromone blend. The resulting variation in female mating success would impose stabilizing selection on the ratio of components in the female sex pheromone. Stabilizing male preference functions would tend to constrain pheromone evolution, reduce phenotypic variation, and eliminate heritable variation. Despite the fact that these predictions are implicit to some models of pheromone evolution, there are few studies that have examined the shape of male moth preference functions over the range of pheromone blends produced by female moths. The shape of the male almond moth preference function was estimated using choice and no-choice wind tunnel trials to a range of naturally occurring ratios of pheromone components. Choice trials documented the predicted unimodal (stabilizing selection) preference function, whereas in the no-choice trials a flat (no selection) male preference function was documented. The no-choice trials are likely to be more representative of mating opportunities under natural conditions than the choice trials, as the opportunity to choose among equally receptive and available females may be rare in the field. If choice does not occur, this may reflect historical stabilizing selection, and male mating preferences may not be stabilizing over the range of currently produced female blend ratios.