Experimental evidence for chemical mate guarding in a moth

Abstract

In polyandrous species, males seek to maximize their reproductive output by monopolizing their mate. Often the male transfers substances to the female that suppress her sexual receptivity or antagonize the behavior of competing males; both are usually transferred in seminal fluids and represent forms of chemical mate guarding. In moths, more long-range female sex pheromones have been identified than in any other animal group, and males often display with close-range sex pheromones, yet odor-based post-copulatory mate guarding has not been described in moths so far. We tested the hypothesis that the male sex pheromone in the noctuid moth Heliothis virescens perfumes the female and functions as an anti-aphrodisiac. Indeed, virgin females perfumed with male pheromone extract, or with its main component, mated significantly less than control virgin females, and this effect persisted for two successive nights. This chemical mate guarding strategy was disadvantageous for H. virescens females, because the reproductive output of twice-mated females was significantly higher than that of once-mated females. Since the female and male sex pheromones are biosynthetically related in this and other moth species, chemical mate guarding may also impose selection pressure on the long-range female sex pheromone channel and consequently affect the evolution of sexual communication.

Figure 1. Average amount of 16:OAc (±SEM) extracted from one female thorax and abdomen.

Females were extracted immediately after mating (night one, n = 13), 24–25 h after mating (night two, n = 15), or as virgins (n = 18). Insert pictures: During mating the male (on the right) envelops the terminal end of the female’s abdomen with his hairpencils.

Figure 2

Male mate choice (±SEM) for virgin females perfumed with male hairpencil extract (A and D), the main male pheromone compound (16:OAc, (B and E)), or a compound found in the female pheromone gland (16:Ald, (C)). Numbers in bars are number of matings. Since we did not find differences between control females and females treated with 16:Ald, we did not test these females the second night. **P ≤ 0.0001, ns: not significant.

Figure 3. Average start and end time of all matings and the average mating duration (±SEM) of the differently treated females, showing that there were no significant differences among the groups (see text for details).