Biological effects of three bacterial species on Tetranychus urticae (Acari: Tetranychidae) infesting eggplant under laboratory and greenhouse conditions

Abstract

This study evaluated the efficacy of three bacterial species. Acinetobacter sp. (concentration 2.237×108 cfu/ml), Bacillus subtilis (concentration 2.470×108 cfu/ml) and Bacillus qassimus (concentration 3.320×108 cfu/ml) were tested against the two-spotted spider mite, Tetranychus urticae, infesting eggplants under laboratory and greenhouse conditions. In addition, we studied their side effects on the predatory mite, Phytoseius plumifer. The highest efficiency rate on T. urticae was observed with Acinetobacter sp. sprays. Three days after treatment, mite mortality reached 87.15 and 77.29 % under laboratory and greenhouse conditions, respectively. Moreover, the mortality rates were significantly lower (72.22 and 67.11 % and 70.74 and 65.19 %) using B. subtilis and B. qassimus under lab and greenhouse conditions, seven days after treatment. The predatory mite, P. plumifer, showed higher tolerance than T. urticae to the three bacterial preparations. The results of this study indicated that Acinetobacter sp. has a strong efficacy on T. urticae and slightly affected the predatory species herein tested. This study introduces a potentially new strategy for biological control of phytophagous mites.