Neurotoxic insecticides are widely used for crop protection. One consequence is that changes in behaviour can be expected in surviving beneficial insects because of an impairment of host perception and motor abilities. Under laboratory conditions, we studied the impact of deltamethrin, a pyrethroid, on the oviposition behaviour of two hymenopterous parasitoids of aphids, Aphidius matricariae (Haliday) and Diaeretiella rapae (McIntosh) (Hymenoptera: Braconidae). They both parasitize Myzus persicae (Sulzer) (Homoptera: Aphididae), which is the preferred host of A. matricariae, regardless of the host plant, whereas D. rapae is a major parasitoid of aphids on Cruciferae crops, including M. persicae. After exposure to deltamethrin, the different items of oviposition behaviour and the total time spent on the patch were recorded. The results showed that the patch time allocation by both parasitoid species was not significantly affected by deltamethrin treatment, when compared with the controls. Nor were the frequencies and sequences of behavioural items modified (e.g., frequency of sting). It therefore appeared that the patch use of A. matricariae and D. rapae on new colonies of M. persicae was not disturbed by deltamethrin at the three doses tested. The possibility that parasitoid strains are partially tolerant to deltamethrin is discussed.