Laboratory bioassays and field-cage trials of Metarhizium spp. isolates with field-collected Mormon crickets (Anabrus simplex)

Authors: KEYSOR, CHAD - Utah State University; FERNANDEZ, E.K. - Federal University Of Goias; RANGEL, D.E. - Universidade Federal Da Paraiba (UFPB); FOSTER, R. - Animal And Plant Health Inspection Service (APHIS); JECH, LARRY - Animal And Plant Health Inspection Service (APHIS); REUTER, K. - Animal And Plant Health Inspection Service (APHIS); BLACK, LONNIE - Animal And Plant Health Inspection Service (APHIS); Jaronski, Stefan; FLAKE, D. - Utah State University; EVANS, EDWARD - Utah State University; ROBERTS, DONALD - Utah State University

Submitted to: BioControl
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/12/2016
Publication Date: 1/18/2017
Publication URL: http://handle.nal.usda.gov/10113/5757332
Citation: Keysor, C.R., Fernandez, E.K., Rangel, D.N., Foster, R.N., Jech, L.E., Reuter, K.C., Black, L.R., Jaronski, S., Flake, D.D., Evans, E.W., Roberts, D.W. 2017. Laboratory bioassays and field-cage trials of Metarhizium spp. isolates with field-collected Mormon crickets (Anabrus simplex). Biocontrol. 62(2):257–268. doi:10.1007/s10526-016-9782-8.

Interpretive Summary: The Mormon cricket is an important pest in the western United States, particularly in Utah, Nevada and Wyoming. This study sought to evaluate the efficacy of a number of Metarhizium spp. isolates against the insect in both laboratory bioassays and outdoor field cages. Seven days after exposure to fungal spores in the lab, at temperatures ideal for the fungi, all of the treated insects had greater than 80% mortality. Three of the best domestic Metarhizium isolates were subsequently tested outdoors in field cages, in two successive years. In the first year one isolate performed better than two others, which were no better than the control. In the second year all four isolates tested resulted in greater and faster mortality than the control but were not significantly different from each other. In all cases, however, the fungi took much longer to kill their hosts outdoors than in the laboratory. These isolates performed poorly when the insects could properly thermoregulate their body temperatures to levels above the upper thermal tolerances of the fungi.

Technical Abstract: The Mormon cricket, Anabrus simplex, is an important pest in the western United States. This study evaluates the virulence of 32 isolates of Metarhizium towards field-collected Mormon crickets. Additionally, several isolates were tested in outdoor field-cage studies. All 32 Metarhizium isolates were pathogenic towards the insect in laboratory assays, including four isolates of the grasshopper-specialist species M. acridum, but virulence varied considerably among isolates. The field study, conducted in 2008 and 2009, showed a significant effect of treatment in both years. However, a pairwise comparison of the survival curves revealed that several of the isolates did not differ statistically from the control treatment. In 2009, M. robertsii isolate DWR 346 had the shortest median survival of 16 days. We hypothesize that the observed poor field performance resulted from a combination of environmental effects and isolate trait, particularly upper temperature limits for growth. Further field studies with additional isolates are necessary to continue seeking an efficacious biocontrol agent for the Mormon cricket.