Effect of body size and sex ratio on male alternative mating tactics of the West Indian sweetpotato weevil, Euscepes postfasciatus

Male body size is considered to be one of the major determinants of mating success among many insect species. Because the effectiveness of the sterile insect technique (SIT) depends on the ability of released sterile males to mate with and inseminate wild females, it is indispensable to understand the effect of male body size on the mating behavior of both sexes for the progress of the SIT program. We investigated how male body size and the presence of other rival males affect the guarding and copulatory durations of the West Indian sweetpotato weevil, Euscepes postfasciatus (Fairmaire) (Coleoptera: Curculionidae). In this species, males guard females before and after copulation. By observing the mating behavior under two sex-ratio conditions (male-to-female ratios of 1:1 and 2:1), we found that small males hastened to court females when rival males were present, but the females rejected these small males as mates. Therefore, we consider that female weevils adopt a counter-adaptation for mate preference in response to this male mating strategy. Body size did not affect the durations of copulation and post-copulatory guarding. Although we found a conditional mating strategy for body size in E. postfasciatus, it is unlikely to have a large influence on the weevil-eradication program using SIT.