Collections of Beauveria bassiana isolates from Lygus spp. populations in the Mississippi Delta and San Joaquin Valley of California were evaluated for characteristics relevant to field efficacy and mycoinsecticide development. Evaluation criteria included; pathogenicity to L. lineolaris and L. hesperus , impact on beneficial insects, spore production, mycotoxin production, survival under solar radiation, and temperature tolerance. Based on these criteria one isolate from each collection was selected for field trials and comparison to the commercial B. bassiana isolate (GHA). Prevalence of infection and population change following application were determined for L. lineolaris and beneficial insect predators in wild host plants and cotton. Caged L. lineolaris adults were used to evaluate the persistence of B. bassiana conidia on plant surfaces. Results of field test conducted in 2004 and 2005 against L. lineolaris populations wild host plants and cotton will be presented