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

Grasshoppers continue to be a major pest on rangeland and pastures in the western U.S. with millions of acres treated annually.  USDA ARS, APHIS, and Utah State University are researching biological alternatives to the current chemical grasshopper control measures. Here we report the results of field evaluation of a number of native isolates of Metarhizium anisopliae s.l., chosen for specific UV- and high temperature tolerance characteristics. Because of grasshopper mobility, typical experimental plot size is a minimum of several acres, up to the maximum of 10 acres allowed under FIFRA.  We used a non traditional evaluation method: confining grasshoppers in thermally transparent cages (in which grasshoppers can normally thermoregulate) to replicated small plots of treated ground and monitoring insect survival within those cages. Addition of cages at intervals after fungus application allowed us to determine conidial persistence in the face of UV.