Changes in non-target arthropod populations following application of liquid bait formulations of insecticides for control of rangeland grasshoppers

This study was undertaken to determine the non-target impacts of rangeland grasshopper control using liquid bait formulations of insecticides (canola and corn oil as carriers of carbaryl, diflubenzuron, and malathion). The research was conducted on native rangeland in Wyoming under drought conditions. Three collection methods (pitfall traps, yellow sticky cards, and sweep nets) were used to estimate non-target arthropod densities. The formulated insecticides were applied according to the protocol of reduced agent-area treatments, an application method designed to reduce economic and environmental costs by applying insecticides at low rates with incomplete coverage via alternating treated and untreated swaths). Canola and corn oils are vegetable oils high in linolenic and linoleic acids which function as attractants and phagostimulants for many species of grasshoppers. Crop oil is a biologically inert paraffin-based petroleum product that served as a control. Although all treatments markedly reduced grasshopper population densities, non-target populations were nominally affected. There were no consistent, significant differences in the responses of non-target populations to treatments with the liquid baits (canola and corn oil carriers) relative to those observed with the standard carrier (crop oil). Only one taxonomic group (Formicidae) showed a significant negative response to treatment relative to untreated controls. Logistical and ecological factors associated with grasshopper control methods may account for the nominal effects on non-target taxa. Sweep net and sticky trap sampling were more sensitive to treatment effects and time-by-treatment interactions. Temporal changes in population densities may have made treatment effects difficult to distinguish in several taxonomic groups.