Egg size affects larval performance in a coleopteran parasitoid

1. Optimal progeny size models assume that the more eggs a female produces, the lower the amount of resource allocated per egg. As egg size generally correlates with the fitness of the emerging immature, this trade-off can be expressed as a choice between the production of numerous low quality or fewer high quality progeny. 2. The first-instar larvae of the coleopteran parasitoid Aleochara bilineata have to search for and parasitise dipteran pupae. The present study found a positive correlation between egg size and larval weight, but not between egg size and development time. Larger first-instar larvae survived longer, were more active, and found and parasitised their host more rapidly. 3. Female A. bilineata may invest smaller larvae in conditions of high host density and low intraspecific competition, but investing fewer, larger larvae would bring them more fitness when hosts are scarce and competition high.