Technical Abstract: Three entomopathogenic fungi, Beauveria bassiana Strain GHA, Metarhizium anisopliae Strain F52 and M. anisopliae Strain DWR346 (discovered by Utah State University) were evaluated for their efficacy against Mormon Cricket, Anabrus simplex, in an outdoor cage trial in northeastern Montana. Fungal materials were applied with APHIS PPQ CPHST’s newly developed Field Aerial Application Spray Simulation Tower Technology (FAASSTT) that simulates liquid ULV aerial application to 0.25 yd2 plots. Each sprayed plot was immediately enclosed with a newly designed, thermally transparent, wire mesh cage and a Mormon cricket introduced into that cage. Insect mortalities were observed for 50 days. Potential cricket body temperatures were continuously monitored using thermal surrogates fitted with thermocouples. Mormon crickets moved to the laboratory from the treated plots after two days confirmed that lethal doses of all 3 isolates had been applied. However, outdoors, response to body temperatures, which were permissive for fungal development to yield rapid mortality in the field, varied greatly among the isolates. The strain, M. anisopliae DWR 346, demonstrated significant mortality against immature Mormon crickets within 7 days after treatment and reached mortality levels expected of current chemical treatments (90%) at about 3 weeks after treatment. Metarhizium anisopliae F52 only produced statistically significant mortality 39 days after treatment. Field mortality from the Beauveria paralleled that of F52, but was lower and not significantly different from control mortality. The thermal growing degree model being developed by ARS accurately predicted the onset of mortality for DWR 346 but dramatically overestimated onset for the other isolates.