Side effects of pesticides on Aphytis melinus DeBach adults and young instars

The evaluation of side effects on natural enemies both as direct mortality and as short and long-term sublethal alterations of their physiology and behaviour is strongly recommended when using chemical compounds in the framework of Integrated Pest Management. Trials have been conducted to evaluate the effects of two insecticides on adults and young instars of the ectoparasitoid Aphytis melinus DeBach (Hymenoptera: Aphelinidae).The compounds tested were a narrow-range mineral oil and the insect growth regulator pyriproxyfen. Laboratory tests were carried out in order to measure the mortality on adults and young instars, the effects on fertility and sex-ratio of the progeny as well as the residual toxicity in terms of capacity of adults to parasitize treated hosts compared to untreated ones in a choice and a no-choice test. The results obtained in the trials highlighted that mineral oil causes very high mortality of adult parasitoids, while a lower toxicity was recorded on young instars and their progeny. The parasitization level observed on treated hosts was significantly lower than on untreated control both in the choice and in the no-choice test. Pyriproxyfen proved to be less toxic than mineral oil on adults without any reduction of fertility of survived females. However on young instars the same compound was more toxic, with a significant reduction of progeny produced by the adults emerged from the treated instars. The parasitization level on treated hosts was lower than on untreated control, with significant differences in the choice test and not significant ones in the no-choice test. None of the insecticides tested significantly affected the sex-ratio of the F1.