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

摘要

The entomopathogenic fungus, Beauveria bassiana (Balsamo) Vuillemin, was evaluated in alfalfa seed plots for control of lygus bug (primarily Lygus hesperus Knight) in comparison with conventional chemical insecticides and a water control. B. bassiana applications reduced lygus bug nymphs relative to the water control during one of three prebloom (June) trials but not during any bloom (July) trials. A single application of conventional insecticides reduced lygus bug populations more frequently and to a greater extent compared 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 canopy closed. Faster nymphal growth rates relative to growth of B. bassiana hyphae at field temperatures could also explain seasonal differences in the effectiveness of B. bassiana.