Determination of the virulence of Beauveria bassiana mixed with acaricides against two-spotted spider mite Tetranychus urticae and its field control efficiency
To explore the control efficacy of Beauveria bassiana and acaricide on two-spotted spider mite Tetranychus urticae,we used the Munger cell method to determine the toxicity and synergism in-doors with B.bassiana ZJU435,bifenazate,and cyetpyrafen.Additionally,we determined the field effi-cacy of different combinations among B.bassiana and acaricides.Indoor results revealed the following toxicity order to T.urticae:cyetpyrafen＞bifenazate＞B.bassiana ZJU435,with LC50 values of 2.68,9.31,and 29.37 mg/L,respectively.B.bassiana ZJU435 combined with bifenazate and cyetpyrafen showed significant synergistic effects at the ratios of 1∶9,3∶7,5∶5,7∶3 and 9∶1.The highest co-toxici-ty coefficients of B.bassiana ZJU435 mixed with bifenazate and cyetpyrafen at a ratio of 9∶1 were 324.61 and 391.80,respectively,indicating moresignificant synergistic effects.Field experiments showed that the control efficacy of B.bassiana ZJU435 mixed with bifenazate at concentrations of 12.50,9.50,and 8.00 mg/L for ten days were 84.13％,81.94％and 77.96％,respectively.Similarly,the control effects of B.bassiana ZJU435 mixed with cyetpyrafen at concentrations of 8.60,3.60,and 2.40 mg/L for 10 days were 89.38％,83.08％and 79.95％,respectively.These results suggest that com-bining B.bassiana ZJU435 with low doses of bifenazate and cyetpyrafen could enhance the control effi-cacy while reducing the amount of chemical acaricides required.
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