8 - Alkaloid-Derived Pheromones and Sexual Selection in Lepidoptera

Abstract

This chapter discusses alkaloid-derived pheromones and sexual selection in Lepidoptera. In certain insects, foreplay is basically a sexually selective process, involving assessment by the female of certain male traits that are a measure of an eventual benefit to the offspring. The foreplay is in the nature of a pheromone-mediated dialogue, and the insects are certain butterflies and moths. What kindled the interest in this area of research was the seminal paper by Brower et al. on the courtship of the queen butterfly, Danaus gilippus, and the motion picture that these investigators made of this behavior. Their data showed clearly that the two brushlike structures, or hairpencils, that the males ordinarily keep tucked away in their abdomen are in fact everted and splayed during courtship, and are brushed against the female prior to copulation. The hairpencils of Danaus gilippus turned out to be chemically similar to those of Lycorea. While they lacked the esters, and had instead the viscous terpenoid alcohol, they too were laden with danaidone. It became clear that danaidone and closely related pyrrolizidines are very generally present in the hairpencils of these insects, having been found in a number of genera beside Danaus and Lycorea. Accompanying compounds are also present, but these are variable and have been identified in only a few species.