2014 field evaluation of candidate Metarhizium fungi for grasshopper control on the U.S. Northern Plains

A series of domestic Metarhizium robertsii isolates were subjected to field evaluation of grasshopper efficacy in Montana in the summer of 2014. These isolates were chosen to represent a range of spore tolerances to UV-B radiation and to transient exposure to 45^o C. , to determine the relevance of such laboratory testing to field performance. All fungi were applied in a simulated ULV aerial application of an oil flowable formulation, using the APHIS “FAASST” spray system, to discrete replicated plots of prairie grassland. The plots were then caged with small, cylindrical wire cages, which allow normal grasshopper thermoregulation, and the cages infested with grasshoppers, either immediately after spray or three days later. Survival of the grasshoppers was followed for 21 days. In parallel experiments the persistence of the fungi was followed on sprayed pots of wheat grass subsequently exposed to normal sunlight, and bioassayed at intervals to determine the half-life of each isolate based on bioassay efficacy.