Oviposition site selection of Episyrphus balteatus

The oviposition behaviour of Episyrphus balteatus DeGeer (Diptera: Syrphida e) was investigated in four-choice experiments in screen cages and in exper iments with direct behavioural observations. Females laid hardly any eggs i n the absence of aphids and preferred larger aphid colonies to small ones. Honeydew attracted the females via olfaction and elicited oviposition. Fema les were able to perceive the presence of conspecific eggs and oviposited l ess often in aphid colonies in which eggs were present. The oviposition det erring stimulus was also active when the eggs were removed, hence, the dete rrent did not act visually, but probably olfactorily.