Laboratory evaluation of toxicity and repellence of four microbial control agents on two phytoseiid species

Abstract: In laboratory trials, the toxicity and indirect harmful effects of 4 fungicides used in biological control strategies were evaluated on detached strawberry leaves (var. Selva), on the phytoseiids Phytoseiulus persimilis and Neoseiulus californicus, commonly used for the control of tetranychids. The microbial control agents tested were Bacillus subtilis strain QST 713 (Serenade Max®), Ampelomyces quisqualis isolate M-10 (AQ 10® WG), Trichoderma harzianum strain INAT 11 and Bacillus amyloliquefaciens strain D747 (Amylo-X®). The effects of these agents were tested on one commercial strain of P. persimilis, and on two different strains of N. californicus, one reared on Tetranychus urticae and the other on Quercus pollen. No adverse effects were recorded on female adult mortality, egg mortality, development of deutonymphs. Nor was the first oviposition of the predators affected by the fungicides. Furthermore, within three hours of exposure, no significant interference with the behaviour of the predators, such as repellence and first choice in location, was observed between treated and untreated control leaves. However, in choice-tests, the predators seemed to prefer leaves treated with T. harzianum to those treated with B. subitilis and B amyloliquefaciens, and finally with A. quisqualis. The possible implications of exposure to these substances over longer periods are discussed.