The effect of two botanical pesticides wits tested on two species of parasitoids, Cotesia plittellae and Diadromus collaris. Aqueous leaf extracts from the syringa tree, Melia azedarach and commercial formulations from the neem tree, Azadirachta indica, Neemix 4.5 were investigated in the laboratory and in it glasshouse. No direct negative effect was recorded on the longevity of the parasitoid species. However, hind tibia length was found to be significantly shorter in male C. plutellae that emerged from Plutella xylostella that had been exposed to syringa extracts. Whether this negatively affects the fitness of male C plittellae remains unknown. The impact of the botanical extracts on the fitness of D. collaris could not be investigated because the pesticides resulted in it high mortality of P. xylostella hosts. In the glasshouse a significantly higher proportion of P. xylostella were parasitised by C plittellae on plants treated with botanical pesticides than on the control plants. However, there were no significant differences between the treatments for the proportion of P. xylostella parasitised by D. collaris. Results indicate that these botanical pesticides have the potential to be combined with biological control programs for P. xlylostella. [copyright] 2005 Elsevier Inc. All rights reserved. Plutella xylostella (Plutellidae) : Host Cotesia plutellae (Braconidae) : Parasite Diadromus collaris (Ichneumonidae) : Parasite Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Ecology; Population dynamics; Abiotic factors; Chemical factors Cotesia plutellae; Diadromus collaris; Lepidopteran hosts; Plutella xylostella; Survival; Fertilizers and pesticides; Effect on parasitoid biology; lepidopteran host; Botanical pesticides Plutella xylostella; Hymenopteran parasites; Botanical pesticides effect on parasitoid biology; Cotesia plutellae & Diadromus collaris none