Age‐dependent foraging behaviour and host‐instar preference of the aphid parasitoid Lysiphlebus cardui

Foraging behaviour and host‐instar preference of young and old females of the solitary aphid parasitoid, Lysiphlebus cardui Marshall (Hymenoptera: Aphidiidae), were studied in the laboratory. The analysis of interactions between parasitoids and different stages of Aphis fabae cirsiiacanthoidis Scop. (Homoptera: Aphididae) revealed that encounter rates between aphids and parasitoid females and defence reactions of the aphids influenced the degree to which a particular aphid age class is parasitized. Encounter rates between hosts and parasitoid females depended on the foraging pattern of the parasitoid, which varied with age. In mixed aphid colonies patch residence time increased with parasitoid age. Furthermore, younger parasitoids (≤ 1 day old) laid more eggs into second and third instars, while older parasitoids (≥ 4 days old) did not show distinct host instar preferences. It is suggested that the oviposition behaviour of L. cardui is influenced by the physiological state, i.e. the age of the wasp. 1994 The Netherlands Entomological Society