Comparison of techniques to survey populations of cereal aphids (Homoptera: Aphididae) in winter cereals during autumn and spring with special consideration of sample size

Abstract

Cereal aphid populations (Homoptera: Aphididae) in winter wheat and winter barley were evaluated in the autumn and early spring of two subsequent vegetation periods (2004/ 2005 and 2005/2006) by D-VAC mobile suction sampler, visual counts, and plant sampling in order to compare the efficiency of different cereal aphid survey techniques. Plant sampling (i.e. collecting whole plants from fields for evaluation in laboratory) generally detected the highest numbers of instars per m2 and enabled the most accurate aphid classifications while additionally permitting further laboratory analysis (e.g. immunosorbent assays). Visual counts (in situ) were most effective for producing quick, rough estimates of overall population density. D-VAC, which detected the lowest numbers of aphids/m2, was the least effective technique and was determined to be unsuitable for cereal aphid monitoring in autumn crops. Coefficients of variation confirmed this trend for the three sampling techniques. The minimum sample sizes required for estimation of aphid populations at different levels of precision (50%, 30%, 20% and 5%) were determined using different calculation methods (FENG and NOWIERSKI 1992; GREENWOOD and ROBINSON 2006) based on visual count data. The results of this study have important implications for the selection of appropriate techniques for surveying cereal aphid populations in winter wheat and winter barely in autumn and early spring.