Dispersal in the aphid parasitoid, Lysiphlebus cardui (Marshall) (Hym., Aphidiidae)

Dispersal of the aphid parasitoid Lysiphlebus cardui (Hym., Aphidiidae) between patches of its host, Aphis fabae cirsiiacanthoidis (Hom., Aphididae), was investigated in a field study and in laboratory and field experiments. Colonization patterns of thisle (Cirsium arvense L.) patches in the field suggested that most females of L. cardui parasitized A.f. cirsiiacanthoidis-colonies on ramets within an encountered plant stand of C. arvense while few females left to colonize new plant stands. In a release experiment L. cardui-females successfully travelled only up to 20 m to a new host patch. Observations and mummy counts suggest that a high proportion of the females released died without having laid any of their eggs. The behaviour of newly emerged parasitoid adults was observed in the laboratory and showed that, in contrast to two other aphid parasitoid species, L. cardui tended to stay and oviposit in the aphid colony in which it had developed. The dispersal patterns of L.cardui described in this study are discussed with respect to predictions of foraging models analysing the influence of mortality risks on parasitoid foraging behaviour.