Prolonged mate guarding and sperm competition in the weevil Diaprepes abbreviatus (L.)

The hypothesis that prolonged copulatory mate guarding coexistswith last male sperm precedence was tested for the sugarcanerootstalk borer weevil, Diaprepes abbreviatus (L.) (Coleoptera:Curculionidae). Male D. abbreviatus showed a long copulatoryguarding. Both males and females were less likely to rematewhen prolonged guarding occurred compared with terminating copulationearly. Guarding was generally terminated by the struggling behaviorof the female. Mating experiments using normal and sterile (X-rayirradiated) males revealed a similar value of last-male spermprecedence for both irradiated and normal males. The P₂ valuesof normal and sterile males were similar when all ovipositedeggs were counted over 30 days. These data made it possibleto calculate the expected gain to a male from prolonged guardingcompared with leaving a female early and seeking out an additionalmate. We show that guarding has the higher fitness. Eggs weredeposited in clutches in which normal fertilized eggs were groupedtogether and were attached to a group of sterile eggs. This,together with identifying the form of the cul-de-sac typespermatheca,allowed us to suggest a unique repositioning process, whichhas not been described elsewhere, as the likely mechanism bywhich last-male sperm precedence was achieved.