Effect of multiple concentrations and rates of an insecticidal bait on grasshoppers (Orthoptera : Acrididae) of mixedgrass prairie

A field study was conducted to determine the effects of multiple concentrat ions and rates of carbaryl bran bait on grasshopper populations on mixedgra ss prairie. Fifty-one, 16.2-ha plots were randomly treated with insecticida l baits at the following concentrations and rates: 2% carbaryl at 0.56, 1.1 2, 2.24, 5.60, and 11.21 kg/ha; 5% carbaryl at 0.56, 1.12, and 2.24 kg/ha; and 10% carbaryl at 0.56, 1.12, and 2.24 kg/ha. An additional eight plots w ere used as controls. Densities of total grasshoppers, bran-accepting, and bran-rejecting species were estimated in each plot before treatment and 2, 4, and 7 days after treatments. Bran accepters and rejectors are those spec ies that will either feed on or not feed on bran, respectively. Results ind icated that all treatments, except the 2% carbaryl at 0.56 kg/ha, caused si gnificant reductions of 37-86% in total grasshoppers. Grasshopper populatio ns were affected by the amount of bait applied, but were generally not affe cted by the concentration of carbaryl on the bait. The highest mean mortali ties of total grasshoppers (72-86%) occurred in plots treated with 2% carba ryl at 5.60 and 11.21 kg/ha, 5% carbaryl at 1.12 kg/ha, and 10% carbaryl at 2.24 kg/ha. Applications of 0.56 kg bait per ha were generally ineffective . Mortality of bran-accepting species, which constituted 72% of all grassho ppers, ranged from 45 to 97%. Treatments had no significant effect on popul ations of bran rejectors.