Comparative toxicity of botanical and reduced-risk insecticides to Mediterranean populations of Tetranychus urticae and Phytoseiulus persimilis (Acari Tetranychidae, Phytoseiidae)

The spider mite Tetranychus urticae and its predator Phytoseiulus persimilis are widely spread in the Mediterranean area. Predator–prey interactions may be affected by pesticides used to control various pests, and knowledge of pesticide side-effects is essential when managing spider mite populations following IPM tactics. Toxicological studies evaluating the effects of pesticides on both predator and prey can better predict their impact in field conditions. A number of botanical and reduced-risk insecticides were evaluated on T. urticae and P. persimilis in the laboratory. Mite populations were collected on unsprayed vegetables. Females were treated by micro-immersion and then reared on treated leaves in holding cells. Then the survival, fecundity and fertility of mites were assessed. All pesticides affected mite survival and/or fecundity. Some of them (e.g. pyrethrins and rotenone) were more toxic to P. persimilis than to T. urticae. Azadirachtin, B. bassiana and pymetrozine showed opposite results. Imidacloprid had a similar impact on predator and prey. Toxicological trials were conducted with T. urticae and P. persimilis eggs. Beauveria bassiana reduced dramatically the hatching of T. urticae treated eggs and rotenone significantly affected P. persimilis egg hatching. Implications for IPM are discussed.