Reproduction and Immature Development of Egg Parasitoids

Abstract

In this chapter I review the recent advances on egg parasitoids reproduction and immature development. Sperm production in adult male parasitoids varies depending on the status of their testes at emergence and these differences in sperm production are described by the spermatogeny index. Polygyny is common in Hymenoptera parasitoids and males that mate with several females in succession may temporarily (synspermatogenic species) or definitely (prospermatogenic species) deplete their sperm supply. Sperm-depleted males that continue to mate are not transferring any sperm to females, but they can still obtain some fitness. Egg parasitoid females use sperm parsimoniously, releasing one or a few sperm each time a female progeny is about to be laid. The temporal distribution of oocyte production is described by an ovigeny index. As in most Hymenoptera species, it is mostly the female that attracts the male from a distance and mate choice by females is predicted when mating or mate searching involves costs and when there is variability in mate quality. Egg parasitoids are defined by the fact that all their immature stages develop within host eggs and it is therefore the immature stages that have to deal with the constraints imposed by the host. All egg parasitoids are idiobiont, killing the host egg at the beginning of its development, and the developing immature has thus a finite reserve of food. The size of the host egg has a major effect on the available resource and ultimately on the size and fitness of the emerging parasitoid. The egg, larval and pupal stages of egg parasitoids are described.