Non-target responses to Mormon cricket control measures in southwestern Idaho

Mormon crickets (Anabrus simplex) are native katydids can swarm at high densities that may reduce cattle forage in rangelands across the western United States. To control their populations, carbaryl bran bait, a neurotoxin, is applied along roadsides in Owyhee County, Idaho as part of the USDA APHIS’s Rangeland Grasshopper and Mormon Cricket Suppression Program. We investigated the impacts of carbaryl bait applications on three non-target responses: ants, grasshoppers, and plant biomass. During June and July 2024, we sampled 42 sites, half of which had been treated with carbaryl bait at least once from 2022 to 2024. The other 21 sites had not been treated with carbaryl since at least 2021. We collected 288 capture tubes containing ants from 12 native species and 406 grasshoppers using sweep nets from approximately 30 species. Treated sites compared to the control sites had lower ant species richness (P = 0.02) and different ant communities (P = 0.006), while the number of tubes with ants did not differ with treatment. Plant biomass was marginally lower in treated sites (P = 0.07) with approximately 135 g/m2 less biomass compared to the control sites, a 29% reduction. Grasshopper species richness (P = 0.08) and abundance (P = 0.07) were marginally higher at treated sites, but community composition and densities from ring counts did not differ. Declines in ant diversity and aboveground plant biomass represent unintended responses of biodiversity and rangeland forage that should be considered when managers seek to control Orthopteran populations.