Compatibility of the entomopathogenic fungus Beauveria bassiana with etoxazole, spirodiclofen and spiromesifen against Tetranychus urticae

Abstract

In the Integrated Pest Management of Tetranychus urticae, it is important to use microbiological control agents and acaricides with differing modes of action in order to reduce the risk of resistance, so often reported for this mite. This study evaluates the effect of etoxazole, spirodiclofen, spiromesifen and their compatibility with Beauveria bassiana on the eggs and larvae of T. urticae. For etoxazole and spirodiclofen, the regression lines from the Probit Analysis were parallel in both cases for the two developmental stages. Both acaricides were more effective on eggs than larvae (2.5 and 4.6 times, respectively). The adjusted regression lines of efficacy produced from the bioassays with spiromesifen on eggs and larvae were neither equal nor parallel. However, the confidence intervals for eggs and larvae did overlap at LC, indicating equal sensitivity in both eggs and larvae at this concentration. The mixture of etoxazole with B. bassiana showed clear antagonistic interaction even though this effect was the result of interference with neither conidial germination nor with the fungus mycelial growth. On the other hand, the combinations of B. bassiana with spirodiclofen and with spiromesifen exhibited additive interaction. The results of this research show that the effectiveness of mixtures of B. bassiana with both spirodiclofen and spiromesifen requires product concentrations to be maintained with no possibility of reduction. Furthermore, the antagonistic effect of the mixture of B. bassiana and etoxazole precludes the combined use of these acaricides in the management of the eggs and larvae of this mite.