Laboratory bioassays and field-cage trials of Metarhizium spp. isolates with field-collected Mormon crickets (Anabrus simplex) Chad A. Keyser . E ´ verton K. K. Fernandes . Drauzio E. N. Rangel . R. Nelson Foster . Larry E. Jech . K. Chris Reuter . Lonnie R. Black . Stefan Jaronski . Darl D. Flake II . Edward W. Evans . Donald W. Roberts Received: 19 February 2016 / Accepted: 12 December 2016 / Published online: 18 January 2017 Ó International Organization for Biological Control (IOBC) 2017 Abstract The Mormon cricket (MC) is an important pest in the western United States. This study evaluated the virulence in the laboratory of 32 isolates of Metarhizium spp. towards field-collected MCs. Addi- tionally, four isolates were tested in outdoor field-cage studies. All 32 Metarhizium isolates were pathogenic towards the MC (could induce some mortality in the laboratory), including four isolates of the grasshopper- specialist species M. acridum. Virulence varied con- siderably among the isolates. Field studies, conducted in 2008–2009, showed a statistically significant effect of fungal treatments in both years. Pairwise comparison of the survival curves, however, revealed that, in 2008, three of the isolates did not differ statistically from the non-fungus control treatment. In 2009, all three of the isolates tested had significantly lower survival rates than the control treatment: MCs exposed to M. robertsii isolate DWR 346 had the lowest survival with a LT 50 of 16 days. We hypothesize that the poor field perfor- mance resulted from a combination of negative envi- ronmental effects and isolate selection, and propose that further field studies with additional isolates are needed to identify an efficacious fungal agent for MC biocontrol. Keywords Metarhizium spp. Á M. acridum Á Orthopteran Á Virulence Á Biological control Á Anabrus simplex Á Mormon cricket Handling Editor: Nicolai Meyling Electronic supplementary material The online version of this article (doi:10.1007/s10526-016-9782-8) contains supple- mentary material, which is available to authorized users. C. A. Keyser (&) Á E ´ . K. K. Fernandes Á D. E. N. Rangel Á E. W. Evans Á D. W. Roberts Department of Biology, Utah State University, Logan, UT 84322-5305, USA e-mail: chadaltonkeyser@gmail.com E ´ . K. K. Fernandes Á D. E. N. Rangel Instituto de Patologia Tropical e Sau ´de Pu ´blica, Universidade Federal de Goia ´s, Goia ˆnia, GO 74605-050, Brazil R. N. Foster Á L. E. Jech Á K. C. Reuter Á L. R. Black USDA APHIS PPQ CPHST, 3645 E. Wier Ave., Phoenix, AZ 85040, USA S. Jaronski Pest Management Research Unit, USDA ARS NPARL, 1500 N. Central Ave., Sidney, MT 59270, USA D. D. Flake II Department of Mathematics and Statistics, Utah State University, Logan, UT 84322-3900, USA 123 BioControl (2017) 62:257–268 DOI 10.1007/s10526-016-9782-8