Mate selection in the moth Neoleucinodes elegantalis: evidence for a supernormal chemical stimulus in sexual attraction

We studied mate selection mechanisms in the tomato fruit borer moth Neoleucinodes elegantalis, and we found that males and females tended to mate monogamously. Males chose a female according to the blend of her sex pheromone, and they preferred heavier females for mating. Females that produced the preferred blend of the sex pheromone were heavier and had larger wings. Heavier males were more likely to initiate flight sooner and to be the first to copulate with the female. These results suggest that females compete for faster-responding males by producing an attractive blend of sex pheromone, and that males compete for females that synthesize the more attractive sex pheromone blend by responding to the calling female faster. We propose that the pheromone blend preferred by males constitutes a signal reflecting the genetic and physiological quality of the female that is difficult to achieve for biosynthetic reasons. We found that a synthetic ‘supernormal’ pheromone blend was more effective in attracting males than was the pheromone produced by calling females, thus providing a useful means of mass trapping of males (e.g. to control infestations in tomato plantations). The results support theoretical predictions that mate selection behaviour in both sexes regulates most sexual encounters, even those modulated by sex pheromones.