Data from: Are aphid parasitoids locally adapted to the prevalence of defensive symbionts in their hosts?

Background: Insect parasitoids are under strong selection to overcome
their hosts’ defences. In aphids, resistance to parasitoids is largely
determined by the presence or absence of protective endosymbionts such as
Hamiltonella defensa. Hence, parasitoids may become locally adapted to the
prevalence of this endosymbiont in their host populations. To address
this, we collected isofemale lines of the aphid parasitoid Lysiphlebus
fabarum from 17 sites in Switzerland and France, at which we also
estimated the frequency of infection with H. defensa as well as other
bacterial endosymbionts in five important aphid host species. The
parasitoids’ ability to overcome H. defensa-mediated resistance was then
quantified by estimating their parasitism success on a single aphid clone
(Aphis fabae fabae) that was either uninfected or experimentally infected
with one of three different isolates of H. defensa. Results: The five
aphid species (Aphis fabae fabae, A. f. cirsiiacanthoides, A. hederae, A.
ruborum, A. urticata) differed strongly in the relative frequencies of
infection with different bacterial endosymbionts, but there was also
geographic variation in symbiont prevalence. Specifically, the frequency
of infection with H. defensa ranged from 22 to 47 % when averaged across
species. Parasitoids from sites with a high prevalence of H. defensa
tended to be more infective on aphids possessing H. defensa, but this
relationship was not significant, thus providing no conclusive evidence
that L. fabarum is locally adapted to the occurrence of H. defensa. On the
other hand, we observed a strong interaction between parasitoid line and
H. defensa isolate on parasitism success, indicative of a high specificity
of symbiont-conferred resistance. Conclusions: This study is the first, to
our knowledge, to test for local adaptation of parasitoids to the
frequency of defensive symbionts in their hosts. While it yielded useful
information on the occurrence of facultative endosymbionts in several
important host species of L. fabarum, it provided no clear evidence that
parasitoids from sites with a high prevalence of H. defensa are better
able to overcome H. defensa-conferred resistance. The strong genetic
specificity in their interaction suggests that it may be more important
for parasitoids to adapt to the particular strains of H. defensa in their
host populations than to the general prevalence of this symbiont, and it
highlights the important role symbionts can play in mediating
host-parasitoid coevolution.