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

Abstract: The evaluation of side effects on natural enemies both as direct mortality and asshort and long-term sublethal alterations of their physiology and behaviour is stronglyrecommended when using chemical compounds in the framework of Integrated PestManagement. Trials have been conducted to evaluate the effects of two insecticides on adultsand young instars of the ectoparasitoid Aphytis melinus DeBach (Hymenoptera:Aphelinidae).The compounds tested were a narrow-range mineral oil and the insect growthregulator pyriproxyfen. Laboratory tests were carried out in order to measure the mortalityon adults and young instars, the effects on fertility and sex-ratio of the progeny as well as theresidual toxicity in terms of capacity of adults to parasitize treated hosts compared tountreated ones in a choice and a no-choice test. The results obtained in the trials highlightedthat mineral oil causes very high mortality of adult parasitoids, while a lower toxicity wasrecorded on young instars and their progeny. The parasitization level observed on treatedhosts was significantly lower than on untreated control both in the choice and in the nochoicetest. Pyriproxyfen proved to be less toxic than mineral oil on adults without anyreduction of fertility of survived females. However on young instars the same compound wasmore toxic, with a significant reduction of progeny produced by the adults emerged from thetreated 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.