Decisions of developing parasitoids

Host acceptance may be the end of the mother parasitoid's decision trajectory in respect of a single host, but it is not the end of flexibility in parasitoid behaviour. After oviposition, decision-making is 'transferred to' the developing parasitoids. They now have to decide: (i) how to interact with siblings or other competitors (see Strand, Chapter 7, this volume); and (ii) when and how quickly to devour the host individual. Natural selection will act strongly on both processes and it goes beyond the scope of this chapter to discuss larval behaviour in detail. We want to mention only developmental timing, since this is a novel aspect for parasitoid behavioural ecology. The growth strategy of a parasitoid larva may have severe fitness consequences. The outcome will depend on the costs and benefits of a basic trade-off between developmental speed and adult wasp size at emergence. Early emergence can be highly advantageous in a growing population, while a large size at emergence can ensure greater survival, fecundity and foraging success. The developmental strategy has rarely been approached from an optimality point of view. Hemerik and Harvey (1999) show with a simulation model that developing parasitoids of Venturia canescens have to trade off their size as adults (which determines lifetime reproductive success) and development time. Especially in nutritionally suboptimal hosts, there is strong selection for longer development times, and a flexible growth strategy allows developing parasitoids to respond adaptively to such variation in host quality.

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