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In-Depth Information
attacks the sessile cocoon stage of the moth Cydia pomonella, did not find
any correlations between adult parasitoid size and host handling time
(
Bezemer and Mills, 2003
). The results of these studies suggest, for para-
sitoid species that utilise mobile hosts that exhibit aggressive defensive
behaviours, handling time costs associated with attacking a host are
related to the sizes of both the parasitoid and the host; however, for
parasitoids that attack sessile or juvenile host stages, size constraints on
handling ability do not playapartinforagingdecisions.
We can use parasitoid characteristics to predict relative costs associated
with searching and handling times according to knowledge of how
host choice is constrained by parasitoid life history. For example, mummy
hyperparasitoids are known to have much higher handling costs than koino-
biont endohyperparasitoids and should exhibit high levels of electivity
(
Sanders and Van Veen, 2010
). Evidence of the effect of handling time
restrictions in determining network structure is evident in a study by
Bukovinsky et al. (2008), in which an increase in the quality of aphid hosts
resulted in a proportionally greater increase in the species assemblage of the
highly elective mummy parasitoids, such as Pachyneuron aphidis, compared
to the specialist koinobiont hyperparasitoids, such as Alloxysta fuscicornis.
Similarly, idiobiont parasitoids must attack later, larger host stages, which
are better able to defend themselves and incur greater costs to handling time.
This suggests idiobionts that attack mobile stage hosts should be more
elective than koinobiont species, which typically attack poorly defended,
early stage hosts (
Hawkins, 1994; Henry et al., 2009
). Conversely, egg para-
sitoids have very short lives and incur very large fitness costs to foregoing
available host eggs, and we would expect these species to exhibit reduced host
electivity (
Boivin, 2010
).
While parasitoid size may have some influence on how parasitoid foragers
construct individual realised niches, the effect is dependent upon how
the parasitoid's fundamental niche is constrained by the life history of the
parasitoid. The analysis of quantitative network data could help elucidate on
the relative importance of different parasitoid life-history characteristics in
determining the structure of host-parasitoid networks (
Cagnolo et al., 2011;
Tack et al., 2011; van Veen et al., 2006
).
VII. SEX ALLOCATION AND HOST QUALITY
A. The Sex Allocation Process
Most parasitoid wasps exhibit arrhenotoky, a subtype of haplodiploidy, in
which female offspring develop from fertilised and males from unfertilized
eggs (
Heimpel and de Boer, 2008
). In this manner, the sex ratio of offspring
