Factors affecting Beauveria bassiana for control of lygus bug (Hemiptera :Miridae) in alfalfa seed fields

The entomopathogenic fungus, Beauveria bassiana (Balsamo) Vuillemin, was ev aluated in alfalfa seed plots for control of lygus bug (primarily Lygus hes perus Knight) in comparison with conventional chemical insecticides and a w ater control. B. bassiana applications reduced lygus bug nymphs relative to the water control during one of three prebloom (June) trials but not durin g any bloom (July) trials. A single application of conventional insecticide s reduced lygus bug populations more frequently and to a greater extent com pared to three applications of B. bassiana. Infection rates were relatively high in treated plots despite lower spray coverage than expected. Reduced B. bassiana infection during the bloom trial compared to the prebloom trial may be attributed to reduced spray penetration within alfalfa as the canop y closed. Faster nymphal growth rates relative to growth of B. bassiana hyp hae at field temperatures could also explain seasonal differences in the ef fectiveness of B. bassiana.