Short-time effects of water sprinkling on the two-spotted spider mite predator Phytoseiulus persimilis in strawberry

Combining two tools for an integrated pest management (IPM) was the reason for investigating the potential use of predatory mites (Phytoseiulus persimilis) in addition to water sprinklers in order to reduce spider mite (Tetranychus urticae) populations in tunnel grown strawberries. To determine the short-time effects of irrigation on the predatory mite, 26 strawberry plants were infested with spider mites as a prey, and 2 weeks later predatory mites were introduced. Leaves were sampled before, immediately after, and twenty-four hours after, irrigation of one minute from overhead water sprinklers in a tunnel. The number of predatory mites was counted on the abaxial of the leaves sampled. On a control plant, not receiving irrigation, the number of mites was counted at the same times as in the experiment. This experiment was repeated four times. To compare the water tolerance of spider mites and predatory mites, leaves with both spider mites and predatory mites were hand sprayed in a laboratory experiment. Number of mites and eggs was counted before and after spraying. The water sprinkling in tunnel significantly increased predatory mite populations up to nearly 2-fold, compared to before irrigation. Predatory mite eggs increased statistically different from before irrigation to one minute after irrigation, while total mobile stages (larva, nymphs and adults) larvae and nymphs increased significantly after twenty-four hours. Control plants had no significant increase, except from larvae. In the laboratory experiment, predatory mites (average of 11 % reduction of mobile stages and eggs) tolerated water spraying to a greater extent than spider mites (average of 22 % reduction of mobile stages and eggs). Both mites had higher reductions when sprayed on the abaxial side, compared to sprayed on the adaxial side of leaves. The findings confirm that water sprinklers combined with biological control by predatory mites is a promising IPM strategy to suppress spider mites in tunnel grown strawberries.M-LU