female that arrives first on the patch is more likely to retain the overall
possession of the patch (Field and Calbert, 1999). The winner of the
fight gets the ownership, after which the non-owner will retreat to the
periphery of the patch. While the owner searches for hosts, the non-owner
tries to return to the patch and gain an opportunity to superparasitize
already parasitized hosts or to parasitize healthy ones. Finally, the owner
ceases searching for hosts and starts guarding the patch to prevent the
non-owner from superparasitism. This guarding is called ‘the waiting
game’ (Fieldet al., 1998). At first sight, this guarding seems a waste of
valuable search time, but, by extending the period between the deposition
of the first and second egg in a host, the guarding parasitoid guarantees a
certain number of offspring.
Optimal foraging not only demands good host-finding ability (sensory
abilities and patch-choice decisions), but also efficient decision rules
for patch leaving. During all steps in the foraging cycle, parasitoids have
to choose between different alternatives. The early theoretical models
assuming parasitoids to behave in an optimal manner did not always
predict what was found in experiments. Most of the time, there was
qualitative agreement between model and data, but the average parasitoid
is not always as omniscient as assumed by theoreticians. The combination
of practical and theoretical approaches enhances our insight into how
animals are able to make flexible decisions.Feeding versus Reproduction
While the broad variation in parasitoid–host associations makes general-
izations about parasitoid reproductive strategies difficult, the feeding
associations of the adult stages are less diverse. Virtually all parasitoids
require carbohydrates as a source of energy, especially for flight.
Parasitoids cover their energetic needs by feeding on accessible sugar
sources, such as (extra)floral nectar or honeydew. Carbohydrates can
have a strong impact on several key fitness parameters. Sugar feeding is
indispensable to parasitoid survival, a factor applying to both females and
males. In addition, sugar feeding can also raise a female’s fecundity, as
well as her propensity to search for herbivorous hosts. While parasitoids
as a group share a requirement for carbohydrates, hymenopteran
parasitoids can be categorized on the basis of two fundamental feeding
characteristics, each representing a distinct trade-off between repro-
duction and feeding.Host-feeding versus oviposition
The issue of host-feeding constitutes a first divide. On the one hand, there
are numerous parasitoid species that do not feed on the haemolymph of
their host and as a result are entirely dependent on sugar-rich substrates56 L.E.M. Vetet al.