Self‐superparasitism, oviposition order, and delay: does offspring survival explain host exploitation strategies of females under interspecific competition in a solitary parasitoid wasp?

Abstract

AbstractIf the risk of larval competition is high and its consequence on offspring mortality is important, we expect female behavioural strategies favouring the survival of their offspring to be selected for. In parasitoids, hosts can be parasitized several times, in some cases by females of different species (i.e., multiparasitism). In solitary parasitoids, only one offspring can develop per host: supernumerary individuals are eliminated through larval competition. Under these conditions, mothers can lay additional eggs in/on the same host (i.e., self‐superparasitism) to increase the chances of one of their offspring winning the competition. They can also aggressively protect their offspring against competing females to prevent them from multiparasitism and ovicide. Both strategies (self‐superparasitism and host defence) are observed in females of the solitary ectoparasitoid wasp, Dinarmus basalis Rondani (Hymenoptera: Pteromalidae), when facing females of another solitary ectoparasitoid species, Eupelmus vuilleti (Hymenoptera: Eupelmidae), during host exploitation. Here, we aimed to explore whether D. basalis females' behaviours relate to their offspring survival chances during larval competition: we expect mothers to defend their hosts only during the vulnerability period of their offspring and self‐superparasitize to increase the chances of their offspring winning the larval competition. We thus measured the effect of oviposition order (D. basalis females oviposited first or second), delay between ovipositions (30–60 min or 3–4 h) and the occurrence of D. basalis females' self‐superparasitism on D. basalis offspring survival when competing with E. vuilleti juveniles. Our results showed D. basalis offspring constantly had a lower survival probability than E. vuilleti offspring. Only being laid first increased D. basalis offspring survival rate, whereas the time delay between ovipositions and self‐superparasitism did not significantly increase it further. The fact that offspring survival chances under interspecific competition may not be the main driver of maternal host protection and self‐superparasitism is discussed.