Synergism of Beauveria bassiana and Phytoseiulus persimilis in control of Tetranychus urticae on bean plants

Tetranychus urticae Koch (Acari: Tetranychidae) causes severe damage in both greenhouse and field crops. Previous studies have found that a phytoseiid predatory mite, Phytoseiulus persimilis Athias-Henriot, and an entomopathogenic fungus, Beauveria bassiana (Balsamo) Vuillemin, are both potential candidates for the control of this pest and have shown varying degrees of success. We assessed the compatibility of these two biological control agents for control of T. urticae on potted bean plants, examining the following treatments: i) a low release rate of P. persimilis (10 prey: 1 predator), ii) a high release rate of P. persimilis (5: 1), iii) a single application of B. bassiana (1 x 108 spore/ml), iv) a single application of B. bassiana after application of the low release rate of P. persimilis, and v) a non-treatment control (no application of either B. bassiana or P. persimilis). A single application of B. bassiana reduced the egg and adult populations of T. urticae initially, but mite populations rebounded again after few days. Phytoseiulus persimilis at the high release rate eliminated the pest population completely, while the low release rate failed to control spider mites. The combined application of B. bassiana and low release rate of P. persimilis also successfully controlled T. urticae population (p < 0.001), with lowest corrected leaf damage (1.5%).