Effects of ejaculate size on remating, attractiveness, and oviposition in females of the sweetpotato weevil, Cylas formicarius

Abstract

AbstractIn many insect species, female remating is triggered by the reduction in male ejaculates stored by females, including sperm and/or seminal fluids transferred during mating. Although females of the sweetpotato weevil, Cylas formicarius (Fabricius) (Coleoptera: Brentidae) are not monogamous, they are slow to remate. We investigated whether male age and mating history, which affect ejaculate size, influence female reproduction in this weevil. We prepared two female groups with different ejaculate sizes (small or large). Females that mated with young (10‐day‐old) virgin males with small ejaculates remated earlier than those that mated with older (30‐ or 50‐day‐old) virgin males with large ejaculates. The 6‐day fecundity did not differ between females that attracted males and those that did not, suggesting that most females with less ejaculate can lay eggs. Given that the number of sperm in the spermathecae of females that attracted males was smaller than that in females that did not attract males, we hypothesize that less ejaculate might enhance a female's attractiveness to males. Interestingly, 20% of females that laid no eggs on the last day observed (day 6) contained >1000 sperm in the spermatheca suggesting that sperm depletion alone did not suppress oviposition behavior. In conclusion, females of this weevil that had received small ejaculates were likely to be attractive to males, resulting in female remating, but cessation of oviposition is not due to sperm depletion alone; instead, it is likely a response to a decrease in the level of seminal fluids.