with a suitable carbohydrate source. These parasitoids have to alternate
their search for hosts (reproduction) with bouts of food foraging, which
requires a clear task differentiation. The latter group faces the issue of
whether to stay in a host patch, thereby optimizing short-term repro-
ductive success, or to leave the host patch in search of food sources, a
strategy that could optimize reproduction in the long term.
Parasitoids are equipped with a number of mechanisms that enable
them to deal with the dichotomy between searching for hosts (repro-
duction) and foraging for sugar sources (energy). They possess separate
categories of innate responses, which are expressed relative to their
physiological needs (Wäckers, 1994). Food-deprived parasitoids typically
seek out stimuli that are associated with food, such as floral odours or
colours. Following feeding, parasitoids lose interest in these food stimuli
and start responding to host-associated cues (Wäckers, 1994). Associative
learning of host- and food-associated information is also organized
according to the parasitoid’s physiological state (Takasu and Lewis, 1993).
When parasitoids are conditioned using two distinct odours (vanilla or
chocolate) in association with feeding and oviposition, respectively, they
will learn both. When pitted against each other, they will choose between
the two in accordance with their predominant physiological needs
(Takasu and Lewis, 1993).Epilogue
Our chapter has highlighted the behaviour of insect parasitoids in respect
of patch finding, host finding, host acceptance, patch leaving and food
ecology. We discussed the prominent role of olfaction and other sensory
modes in foraging, placed behavioural variation in a functional context
and looked at the connection between the experimental and theoretical
approach. Throughout the chapter, we emphasized the flexibility of
parasitoid foraging behaviour, i.e. variation in individual behaviour,
which we think is one of the most intriguing characteristics of insect
parasitoids. Especially through learning, parasitoids can alter their behav-
iour in an optimal way. They can enhance their response to temporarily
important stimuli, alter their innate preferences and even acquire
responses to novel stimuli that have proved to be reliable indicators of
host presence. Stephens (1993) argues that learning is most beneficial
when the environment is unpredictable between generations, but predict-
able within generations. For many insect parasitoids, this is a likely
scenario. The primary source of information for foraging parasitoids is not
the host itself, but the host’s direct environment, such as its food. Mothers
will often (have to) forage for different host food resources from those
foraged for by their daughters, but within the lifetime of the individual
there will certainly be short-term temporal regularities to detect. Hence
learning can be expected as a likely adaptive mechanism for foraging
parasitoids under natural conditions.58 L.E.M. Vetet al.