Selective control of rangeland grasshoppers with prescribed fire

Abstract

Grasshoppers (Orthoptera: Acrididae) are considered among the most damaging rangeland pests, but are necessary for the survival of many wildlife species. Most grasshoppers species are innocuous, but control with insecticides is non-discriminatory among species. The objectives were to evaluate the effects of prescribed burning on the abundance and biomass of grasshoppers and to determine if species could be selectively controlled with prescribed fire. Twenty-four, 4-ha sites were selected in a sand sagebrush-mixed prairie near Woodward, Okla. and blocked by pasture. Plots were randomly assigned fall-, spring-, or non-burned treatments within block with 4 replications per treatment for each of 2 years. Grasshopper biomass and abundance were sampled in late July and early August by sweeping with canvas beating nets. Specimens were weighed to the nearest 0.1 mg and identified to species. Fire treatments had no effects on the total abundance or biomass of grasshoppers across species, with about 10 grasshoppers weighing 4,090 mg per 150 sweeps. Fire effects on the 4 most common species were variable and could be explained by the biology of the insects. Melanoplus bowditchi and M. flavidus were unaffected by fire treatment. Hesperotettix viridis is sensitive to damage to its host plants and was reduced about 88% by fire in either season. Ageneotettix deorum abundance was 65% lower on fall-burned plots. We hypothesize the reduction occurred because the species' eggs are laid near the soil surface and exposed to the heat of passing fire. Fire prescriptions may be developed to target species-specific vulnerabilities and reduce pest grasshoppers while maintaining the food base for grasshopper predators.