Mate guarding and sperm displacement in the water strider Gerris lateralis Schumm. (Heteroptera: Gerridae)

SUMMARY. 1. Field and laboratory observations on the mating behaviour of Gerris lateralis Schumm. allowed three distinct phases to be distinguished: (i) a precopulatory phase (1.5min, SD=1.3), (ii) copulation (16.2min, SD=12.9), and (iii) a postcopulatory phase. The duration of the postcopulatory phase, during which the male rode passively on the back of the female without genital contact, varied considerably (11 min to > 48h). Females appeared reluctant in all matings, and matings were forced by males.
2. Laboratory experiments showed that the females were able to store sperm for more than 30 days without decrease in fertilization rate. In double mating experiments, where partially sterilized males were used, it was demonstrated that sperm displacement was extensive. The last male to mate fertilized approximately 80% of the eggs.
3. It is concluded that the postcopulatory behaviour is beneficial to males in terms of paternity assurance, and it is interpreted as a mate guarding behaviour.