Compatibility in Vitro and in Vivo of the Entomopathogenic Fungi Beauveria bassiana and Hirsutella citriformis with Selected Insecticides

Compatibility, measured as insecticidal effect on conidial germination, vegetative growth, and conidial production of strains of three B. bassiana (Bals.) Vuill. and seven H. citriformis Speare strains was evaluated with selected insecticides (abamectin, cypermethrin, imidacloprid, and malathion) at field (commercial) application rates. Potential insecticidal synergism of imidacloprid with B. bassiana against adults of potato/tomato psyllid, Bactericera cockerelli (Sulc.), also was investigated. For vegetative growth of B. bassiana, abamectin was compatible with all strains; imidacloprid, cypermethrin, and malathion slightly inhibited the growth of two strains (11.4-28.3%), while another strain was inhibited by imidacloprid and malathion (9.9-41.0%). Vegetative growth of Hirsutella strains was inhibited significantly, particularly by malathion (as much as 88% less growth). Yield of conidia of B. bassiana indicated no inhibition to severe reduction (74.0%) with some insecticides, depending on the fungal strain and insecticide combination. For Hirsutella, abamectin and imidacloprid dramatically increased yield (as much as 306.0 and 624.0%, respectively) in three strains; smaller or no increases were observed for the remaining strains. Insecticides did not significantly inhibit germination of B. bassiana spores, while all insecticides evaluated significantly inhibited germination of conidia of H. citriformis strains (60.5-97.33%). When B. bassiana strains were applied mixed with 83.3, 125, and 166 mu l per liter of imidacloprid, significantly more (81.2-95.0%) B. cockerelli adults were killed than with insecticide (15.0-32.6%) or fungus (72.5-83.9%) alone. Results indicated that at the tested concentrations, B. bassiana was compatible with most insecticides evaluated, but H. citriformis was not compatible.