Impact of botanical pesticides derived from Melia azedarach and Azadirachta indica on the biology of two parasitoid species of the diamondback moth

The effect of two botanical pesticides was tested on two species of parasitoids, Cotesia plutellae 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 a 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. plutellae remains unknown. The impact of the botanical extracts on the fitness of D. collaris could not be investigated because the pesticides resulted in a high mortality of P. xylostella hosts. In the glasshouse a significantly higher proportion of P. xylostella were parasitised by C. plutellae 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. xylostell