PREY FINDING BY LARVAE AND ADULT FEMALES OF EPISYRPHUS-BALTEATUS

The prey-location behaviour of larvae of Episyrphus balteatus DeG. (Di pt.: Syrphidae) was investigated in two different experimental set-ups . First instar larvae exhibited directed search over short distances, guided by olfactory cues from aphids, but not from honeydew. However, second and third instars did not respond to aphid-plant-complex odours in a 4-arm-olfactometer. Aphid extracts, honeydew and sucrose were fo und to be feeding stimulants for the larvae. The oviposition behaviour of female syrphids was investigated in a series of two-choice experim ents: females were able to evaluate aphid numbers and adjust ovipositi on rates accordingly, with higher prey numbers eliciting increased ovi position, even when the aphids were removed at the start of the experi ment. The presence of conspecific syrphid larvae did not inhibit ovipo sition when the females were deprived of suitable oviposition sides be fore the experiments were conducted.