FIELD-EVALUATION OF A REDUCED RATE OF CARBARYL SPRAY ON RANGELAND GRASSHOPPERS (ORTHOPTERA, ACRIDIDAE)

A modified formulation of carbaryl insecticide was aerially applied to contiguous 65-ha plots of rangeland in South Dakota in 1989. The appl ication rate contained 25% less active ingredient than the standard fo rmulation used in the U.S. Department of Agriculture's (USDA) Animal a nd Plant Health Inspection Service (APHIS) rangeland grasshopper progr am. The experimental plan was a four-replicate randomized block design with the experimental plots grouped by pretreatment grasshopper densi ties. Reduced rates of application resulted in control statistically e qual to the standard carbaryl rate. Within 7 days of treatment, grassh opper populations were reduced by 95% or more for each of the treatmen ts. The four dominant grasshopper species, comprising 81.5% of the ove rall population, were each significantly reduced by all of the treatme nts after one week.