Estimating Populations of Aphidophagous Coccinellidae (Coleoptera) in Winter Wheat

Abstract

Coccinellids are important natural enemies of aphid pests in wheat, Triticum aestivum em Thell, in the Great Plains of the United States. Coccinellid community development in wheat fields is unpredictable; therefore, precise, efficient sampling methods for coccinellids are needed for use in integrated pest management research and decision making. Our objectives were to compare removal sampling with quadrat sampling for estimating population density of adult and larval coccinellids in winter wheat, and to determine if timed count sampling and sweepnet sampling were useful for estimating adult and larval coccinellid densities. Removal sampling accurately estimated population density for adults of most species but consistently underestimated larval density. Timed count samples and sweepnet samples were significantly correlated with absolute density of both larval and adult coccinellids. Regression models were developed to convert estimates of relative to estimates of absolute population density. Depending on sampling method and life stage, models included the number of tillers per 0.3 m, wheat plant growth stage, plant height, and the number of aphids per tiller as variables; R2 values ranged from 0.89 to 0.93. Sweepnet sampling was more precise per unit of effort than timed count, quadrat, or removal sampling for estimating adult coccinellid density. Removal sampling (removing all coccinellids seen during 2 successive 15-min searches from each of 9 plots (25 m2) was the least efficient method.