The effect of pesticides used in strawberries on the phytophagous mite Tetranychus urticae (Acari: Tetranychidae) and its fungal natural enemy Neozygites floridana (Zygomycetes: Entomophthorales)

Neozygites floridana is an important natural enemy of the two-spotted spider mite, Tetranychus urticae. Pesticides used in strawberries that might affect the conservation and enhancement of this beneficial fungus were therefore studied. This was done in a laboratory study by letting non-inoculated (healthy) mites and mites inoculated with N. floridana feed on strawberry leaf disks treated with one of the following pesticides: the fungicides tolylfluanid, fenhexamid or cyprodinil + fludioxonil or the acaricide/insecticide/molluscicide methiocarb. The effect of these pesticides on mortality and egg production of T. urticae and on the killing capacity and sporulation of N. floridana were determined. Tolylfluanid increased the mortality of non-inoculated mites (75.3%) compared to the non-inoculated control (27.5%). Methiocarb also killed non-inoculated mites. Fenhexamid did not have any effect on the mortality of non-inoculated mites (19.2%), neither had cyprodinil + fludioxonil (19.1%). Tolylfluanid did not reduce the mortality of mites inoculated with N. floridana (89.3%) compared to the inoculated control (80.0%). Neither did methiocarb, it rather increased the mortality of inoculated mites (93.2%). Fenhexamid did, however, reduce the mortality of inoculated mites (66.7%). The same was true for cyprodinil + fludioxonil (48.7%). In addition, cyprodinil + fludioxonil increased the time to death of inoculated mites (6.69 days) compared to the control (6.10 days), and inhibited sporulation of N. floridana (7.9% sporulation) compared to the control (42.4% sporulation). Tolylfluanid also reduced sporulation of N. floridana (15.5% sporulation). Results from this study indicate that the use of the fungicides tested will potentially reduce the survival and efficacy of the natural enemy N. floridana in the field.