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 concentrations and rates of carbaryl bran bait on grasshopper populations on mixedgrass prairie. Fifty-one, 16.2-ha plots were randomly treated with insecticidal baits at the following concentrations and rates: 2% carbaryl at 0.56, 1.12, 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 were 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 acceptors and rejectors are those species that will either feed on or not feed on bran, respectively. Results indicated that all treatments, except the 2% carbaryl at 0.56 kg/ha, caused significant reductions of 37-86% in total grasshoppers. Grasshopper populations were affected by the amount of bait applied, but were generally not affected by the concentration of carbaryl on the bait. The highest mean mortalities of total grasshoppers (72-86%) occurred in plots treated with 2% carbaryl 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 grasshoppers, ranged from 45 to 97%. Treatments had no significant effect on populations of bran rejectors.