Antiaphrodisiacs in pierid butterflies: a theme with variation!

Male Pieris napi butterflies previously have been shown to synthesize and transfer an antiaphrodisiac, methyl salicylate (MeS), to females at mating. This substance curtails courtship and decreases the likelihood of female remating. Here, we show that similar systems occur in Pieris rapae and Pieris brassicae. In P. rapae, 13C-labeling studies showed that males utilize the amino acids phenylalanine and tryptophan as precursors to MeS and indole, respectively. These volatiles are transferred to females at mating and function as antiaphrodisiacs, as demonstrated by field tests entailing painting MeS, indole, or a mixture on the abdomens of virgin females and assessing their attractiveness to wild males. With P. brassicae, 13C-labeling studies showed that males use phenylalanine as a precursor to synthesize benzyl cyanide, which was demonstrated to function as an antiaphrodisiac by field tests similar to those for P. rapae. This communication system exhibits both similarities and differences among the three species; in P. napi and P. rapae, males are fragrant but transfer a volatile antiaphrodisiac to females that is completely different from the male odor, whereas in P. brassicae the antiaphrodisiac transferred by male to female is identical with male odor.