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This flexibility in behaviour is strikingly common in insect parasitoids

and allows them to adaptively respond to crucial variation in their

environment. We make it the focus of our chapter.

The success in encountering hosts directly determines the female

wasp’s Darwinian fitness: her searching strategy can make or break

her. During her lifetime, each individual female has to make repeated

decisions on whether to forage for hosts or for food, which cues to use and

how to search, where to go and how long to stay. Having found a host, she

needs to decide whether to use it for host feeding or for oviposition. If she

accepts it for oviposition, she has to decide how many eggs to lay and

which sex ratio. Figure 3.1 depicts these aspects of decision-making as

discussed in the chapter. Through this direct link between behaviour

and fitness, insect parasitoids are highly suitable model systems for

asking evolutionary questions about behaviour and they have been

very important in the development of behavioural ecological methods

(Godfray, 1994). Behavioural ecology would not be where it is now with-

out insect parasitoids. Throughout the chapter, we shall address both the

mechanism and the function of flexibility in behaviour, since we strongly

believe a combination of both approaches is needed in behavioural ecol-

ogy. We shall point to the importance of learning and the leading role of

olfaction and plants in patch and host finding. We shall also address the

food ecology of parasitoids and how the need to forage for food interacts

with foraging for hosts. Furthermore, we specify which factors play a role

Flexibility in Host-search and Patch-use Strategies 41

Parasitoid

life cycle

Leaving

food source

Searching

for food

Finding food

source

Finding host Searching

for hosts

Leaving

host/patch

Assessing hostAssessing food

Feeding Oviposition

Mating

Pre-imaginal

development

Parasitoid

emergence

Fig. 3.1. The life cycle of a parasitoid with food and host search as main behaviours during

adult life.