Spatial population dynamics of a specialist aphid parasitoid, <i>Lysiphlebus hirticornis</i> Mackauer (Hymenoptera: Braconidae: Aphidiinae): evidence for philopatry and restricted dispersal

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