Female egg dumping and the effect of sex ratio on male egg carrying in a coreid bug

Abstract

Phyllomorpha laciniata Vill (Heteroptera, Coreidae) is unique among terrestrial insects in that females glue eggs on the backs of other conspecifics. Egg carrying by P. laciniata males has previously been considered as paternal care. We explored female oviposition with respect to previous mating experience of females and tested whether sex ratio affects male egg-carrying. The hypothesis that male egg-carrying is a form of paternal care predicts that a male should always accept eggs after mating with a female. However, if male egg-carrying is a form of postcopulatory mate guarding rather than paternal care, egg carrying should increase in the presence of other males. When two couples were placed together, females laid eggs on the backs of all individuals enclosed, including the backs of other females. However, when a female was accompanied by 2 males, 22 out of 26 females oviposited on their mating parmer. Thus, sexual competition rather than paternity alone, affects a male's eagerness to carry eggs. However, even if males sometimes carry their own eggs, females lay eggs on the backs of all conspecifics they can easily acquire. Thus, egg carrying in P. laciniata is partially voluntary and partially the result of female egg dumping.