Prolonged copulation: A male ‘postcopulatory’ strategy in a promiscuous species,Lygaeus equestris (Heteroptera: Lygaeidae)

Summary Copulation in Lygaeus equestris L. (Heteroptera, Lygaeidae) is known to last 0.5–24 h. Variations in copula duration of field-collected insects were studied in the laboratory, and different hypotheses concerning the significance of prolonged copulations were tested.Through reciprocal matings with normal and sterile (irradiated) males, sperm displacement was estimated at about 90%. A male could thus increase his fitness by preventing subsequent matings of an inseminated female.Copulations with virgin insects, observed over 15 h, were classified in two categories: short (0.5–8.0 h) and long (> 15 h) duration (Fig. 1). No difference in the number of fertilized eggs was found between long and short copulations, and the insemination rate was highest during the first hour of a couplation (Fig. 2). Long-lasting couplations did not give rise to increased sperm displacement (Table 2). These results indicate that there is no difference in the amount of sperm transferred during short and long copulations and that no insemination takes place during the latter part of a prolonged copulation.Longer lasting copulations occurred when the sex ratio was male-biased than when it was female-biased (Fig. 1). The frequency of prolonged copulations was higher when the female was gravid than when she contained no eggs (virgin) (Figs. 3 and 4). Support is thus given to the hypothesis that prolonged copulation is a male postinsemination strategy to prevent subsequent matings of a female.Females subjected to male competition over a longer period, laid fewer eggs and died earlier than females that were mated but subsequently isolated from males (Fig. 5). Egg batches from females living with males were larger than batches from mated, isolated females (Table 3). This is probably due to a combination of many matings with short intermissions and prolonged copulations, both of which postpone oviposition.Comparisons between copulations of males with either gravid or virgin females during these experiments, led to the conclusion that short copulations with virgin females result from a male decision to terminate copulation after insemination is completed, whereas copula duration with gravid females is more likely to depend on a combination of male and female behavior.