Long-Term, Large-Scale Effects of Insecticidal Control on Rangeland Grasshopper Populations (Orthoptera: Acrididae)

The characteristics of rangeland grasshopper outbreaks were assessed among adjacent border counties in Wyoming and Montana by the use of Markovian models. Based on about 30 yr of historical survey data, the probability, duration, and stability of economically damaging grasshopper populations were consistently greater in Wyoming counties than in adjacent Montana counties. These long-term, large-scale differences appear to be attributable to intensive insecticidal control efforts in Wyoming. Target pest resurgence, in which beneficial insects are eliminated by insecticides, thereby allowing rapid growth of a pest population, may be responsible for the counterproductive aspects of an intensive chemical control program against grasshoppers.