Effects of host size on progeny sex and survivorship of Hymenoepimecis pinheirensis

Parasitoid larvae consume their hosts to obtain the nutritional resources required for their development. Parasitoid wasps can optimally select the size of their hosts by laying unfertilised and fertilised eggs according to the amount of biomass available for consumption by the larvae. However, parasitoids may eventually experience low host availability within the optimal range of body sizes, affecting the survival of their offspring. In this study, we identified a situation in which all available hosts (Leucauge volupis) were smaller than those previously observed to be parasitised by Hymenoepimecis pinheirensis at the same study site. Therefore, we investigated how these parasitoids can bypass the scarcity of ideal hosts. Female wasps biased their oviposition toward the largest L. volupis females available. In this suboptimal scenario, they did not oviposit only unfertilised eggs, which developed into relatively small offspring (males). In this situation, they lay fertilised eggs mainly on larger spiders. Larval mortality was high, but the larvae attached to the larger spiders were more likely to complete their development. In general, H. pinheirensis females managed to target the best hosts available, but could not delay the oviposition of fertilised eggs or avoid offspring mortality. Here, we discuss the potential causes of asynchronies in the life cycles of parasitoid wasps and their hosts, the availability of optimal hosts, and how these factors may affect their populations