Pesticide side-effects on predatory mites: the role of trophic interactions

Abstract

The control of spider mites in protected crops is often critical due to the development of mite resistance to acaricides. Studies of the side-effects of pesticides on beneficial mites are required in order to improve integrated spider mite management. Pesticide side-effects on predatory mites of the family Phytoseiidae can be studied at the field or laboratory level. In the field, phytoseiid abundance can be related to the presence of prey and/or alternative foods, which can affect the response of predatory mites to pesticides. We investigated whether pesticide side-effects on phytoseiids may be mediated by trophic interactions. In the laboratory we evaluated the effects of two insecticides (derived from pyrethrins and Beauveria bassiana) on the predatory mite Phytoseiulus persimilis by testing the same under various exposure conditions (leaf residues, treated prey, topical application). The effects of these insecticides on P. persimilis were higher when the predators were fed with treated prey. Furthermore, we investigated the effects of pyrethrins on the predatory mite Amblyseius andersoni on vines with low or high incidence of the plant pathogenic fungus Plasmopara viticola (grape downy mildew, GDM). GDM mediated interactions between pyrethrins and A. andersoni since it is alternative food for this predatory mite. The implications of these studies for the development of toxicological methods and integrated pest management are discussed.