Effects of Chlorpyrifos and Lambda- and Gamma-Cyhalothrin on Suppression of Aster Leafhoppers, Macrosteles quadrilineatus (Hemiptera: Cicadellidae) in Spring Wheat1

Abstract

ABSTRACT Unexpected outbreaks of the aster leafhopper, Macrosteles quadrilineatus Forbes (Hemiptera: Cicadellidae), in wheat in the spring of 2012 across the Northern Plains of the U.S. prompted extensive applications of insecticides to suppress their populations. Aster leafhoppers are infrequent pests of wheat in the Northern Plains early in the spring, and data on insecticide efficacy for aster leafhoppers in wheat were unavailable at the time of the outbreak. Thus, our goal was to test several insecticides commonly used against key pests in wheat for their efficacy against aster leafhoppers. We examined the effects of chlorpyrifos and lambda- and gamma-cyhalothrin in greenhouse and field. These insecticides are not currently registered for suppression of aster leafhoppers in wheat, but they are used frequently to control potato leafhoppers in alfalfa. We found that all insecticides reduced numbers of aster leafhoppers four days after application (DAA) in the field, but not seven and 14 DAA, likely due to an influx of resident aster leafhoppers present in high numbers in the field surrounding the experimental plots. We also noted lack of effect of insecticides on total yield or the grain weight. We conclude that all insecticides effectively suppressed this pest immediately following applications, but the small-plot experiment obscured efficacy beyond the initial knockdown of the populations. These conclusions were supported by greenhouse experiments, which revealed that the insecticides killed 90% of the leafhoppers up to 14 days after application. This study will provide valuable efficacy data for new research-based chemical management recommendations for the aster leafhopper in wheat.