The Life-Histories of Parasitoid Wasps Developing in Small Gregarious Broods

Abstract

Theory predicts that small gregarious brood sizes are evolutionarily unstable in parasitoid wasps due to the evolution of brood reduction behaviour in larvae competing for developmental resources. Despite this, many species of parasitoid wasp develop in small gregarious broods. Here, I catalogue the life-history properties of 87 such species, and attempt to explain their apparent stability in brood size. Small gregarious broods are taxonomically widespread, occurring in at least 15 of the 26 families containing gregarious species. The life-histories represented in this species list are extremely varied. Several species display properties consistent with an increase in the stability of non-siblicidal behaviour, but few of these properties are common to a large proportion of species. This suggests that either several factors contribute towards clutch size stability, or some important unknown variable is responsible. I discuss stochasticity in brood size as a novel but widespread factor contributing to the stability of non-siblicidal behaviour.