Abstract:
Within insect communities, the population ecology of organisms
representing higher trophic levels, for example, hymenopterous
parasitoids, may be influenced by the structure of
their insect hosts. Using microsatellite markers and ecological
data, we investigated the population structure of the specialist
braconid wasp parasitoid, Lysiphlebus hirticornis Mackauer
attacking Metopeurum fuscoviride, a specialist aphid feeding
on tansy, Tanacetum vulgare. Previous studies revealed that
M. fuscoviride has a classic metapopulation structure with
high subpopulation turnover. In this study, up to 100% of
ramets within a host plant genet colonized by aphids were
colonized by the parasitoid, yet plants with aphids but
no parasitoids were also observed. Genetic differentiation
measured by FST, actual differentiation (D) and relative
differentiation (GST) indicated highly structured parasitoid
population demes, with restricted gene flow among and
between parasitoid subpopulations at the various sites.
Interestingly, both field data and population assignment
analysis showed that the parasitoid is highly philopatric. Thus,
despite the frequent local extinctions of the aphid host, the
parasitoid continuously exploits its aphid host and contributes
to the demise of local aphid subpopulations, rather than
spreading its genes over many aphid populations. FST values
for the haplodiploid parasitoid were similar to those found in an
independent study of the diploid aphid host, M. fuscoviride,
hence supporting the view that an insect herbivore’s population
structure directly influences the ecology and genetics of
the higher trophic level, in this case the wasp parasitoid.
