Geographic structure with no evidence for host-associated lineages in European populations of Lysiphlebus testaceipes,an introduced biological control agent

Lysiphlebus testaceipes (Cress.) is an aphidiine parasitoid originally introduced to Europe as a biological control agent of citrus aphids in the Mediterranean. It has rapidly become widespread in coastal areas continuing gradually to expand inland. L. testaceipes exploited a large number of aphids in Europe, including new hosts and significantly changed the relative abundance of the native parasitoids. This behavior may reflect a broad oligophagy of the introduced parasitoid or it may require the evolution of host specialization that results in genetically differentiated subpopulations on different hosts. To address this issue we used the mitochondrial cytochrome oxidase subunit I and seven microsatellite loci to analyze the structure of genetic variation for L. testaceipes samples collected from 12 different aphid hosts across seven European countries, as well as some samples from Benin, Costa Rica, USA, Algeria and Libya for comparison. Only five COI haplotypes with moderate divergence were identified overall. There was no evidence for the association of haplotypes with different aphid hosts in the European samples, but there was geographic structuring in this variation. Haplotype diversity was highest in France, where L. testaceipes was introduced, but only a single haplotype was detected in areas of south-eastern Europe that were invaded subsequently. The analysis of microsatellite variation confirmed the lack of host-associated genetic structure, as well as differentiation between populations from south-western and south-eastern Europe. The parasitoid L. testaceipes in Europe is thus an opportunistic oligophagous species with a population structure shaped by the processes of introduction and expansion rather than by host exploitation.