Effects of mating duration on female reproductive traits of the seed bug Togo hemipterus (Heteroptera: Lygaeidae)

Abstract

During insect copulation, males typically transfer to females complex ejaculates that contain more than just sperm. These fluids can have a variety of effects on females (e.g., they can supply energy and nutrients, increase egg production and egg laying, inhibit female re-mating, and reduce female longevity). Although these effects of seminal fluid on females are often volume-dependent, and despite the several functions of seminal fluids, few studies have investigated the effects of mating duration on female reproductive traits. We therefore controlled mating duration and investigated the effects of seminal fluid on reproductive traits (lifetime fecundity, oviposition time, and oviposition rate) and longevity of females of the seed bug Togo hemipterus (Scott) (Heteroptera: Lygaeidae). All mated females laid eggs, even after a short mating duration (10 min). After a short mating duration, however, only approximately half of the females laid fertilized eggs, possibly because they did not receive sufficient sperm to fertilize all their eggs. These results showed that female egg laying was induced by such physical stimuli as penis insertion and stretch reception in the bursa copulatrix, or by male seminal products other than sperm. Males must continue ejaculation for 20 min or more to ensure fertilization of the female’s eggs. Although males ejaculated all their sperm within 20 min, a single insemination did not fertilize all of a female’s eggs throughout her lifetime. Females that copulated once laid eggs for approximately 40 days, but laid fertilized eggs for approximately the first 20 days only; we believe the sperm were depleted or became inactive. The positive correlation between mating duration and lifetime fecundity (including both fertilized and unfertilized eggs) and rate of oviposition (the number of eggs laid per day) indicated that the seminal substances stimulated female egg production and/or egg laying, and were transferred to females in a time-dependent manner. Males manipulated females by use of seminal substances. Mating duration did not affect female longevity. T. hemipterus males affected female reproductive traits in several ways. These seemingly manipulative substances are likely to be costly to females because they laid unfertilized eggs when sperm were depleted or became inactive.