Mde. Fellowes et al., PUPAL PARASITOID ATTACK INFLUENCES THE RELATIVE FITNESS OF DROSOPHILATHAT HAVE ENCAPSULATED LARVAL PARASITOIDS, Ecological entomology, 23(3), 1998, pp. 281-284
1. The evolution of host resistance to parasitoid attack will be const
rained by two factors: the costs of the ability to defend against atta
ck, and the costs of surviving actual attack. These factors have been
investigated using Drosophila melanogaster and its parasitoids as a mo
del system. The costs of defensive ability are expressed as a trade-of
f with larval competitive ability, whereas the costs of actual defence
are exhibited in terms of reduced adult fecundity and size. 2. The co
sts of actual defence may be ameliorated by the host-choice decisions
made by Pachycrepoideus vindemiae, a pupal parasitoid. If larvae that
have successfully encapsulated a parasitoid develop into poorer qualit
y hosts, then these may be rejected by ovipositing pupal parasitoids.
3. Pupae developing from larvae that have encapsulated the parasitoid
Asobara tabida are smaller and have relatively thinner puparia. Thinne
r puparia are likely to be associated with a reduction in mechanical s
trength and possibly with a decrease in desiccation tolerance. 4. Pach
ycrepoideus vindemiae that develop in capsule-bearing pupae are smalle
r than those that emerge from previously unattacked hosts. This suppor
ts the prediction that ovipositing female P. vindemiae should avoid at
tacking capsule-bearing hosts. However, in choice experiments with 1-d
ay-old pupae, P. vindemiae females oviposited preferentially in hosts
containing a capsule, whereas there was no preference found with 4-day
-old hosts. This appears to be a maladaptive host choice decision, as
the female pupal parasitoids are preferentially attacking hosts that w
ill result in a reduction of their own fitness. 5. The increased likel
ihood of attack by a pupal parasitoid is another cost of actual defenc
e against larval parasitoid attack.