Hemlock Woolly Adelgid (Homoptera: Adelgidae) Dispersion and the Failure of Binomial Sampling to Estimate Population Density

Abstract

Data collected in 1994 and 1995 from eastern hemlock stands in Pennsylvania and Virginia were used to evaluate the binomial sampling method for hemlock woolly adelgid. An empirical distribution model and a model based on the negative binomial distribution were used to describe the relationship between mean hemlock woolly adelgid density ( x ) and the proportion of samples with at least T hemlock woolly adelgid ( P _T ). There were significant differences in the x versus P _T relationship between locations and hemlock woolly adelgid generations regardless of the value of T (1–10) or model used. The inconsistency of the relationship may be a result of the respective phenologies of hemlock woolly adelgid and eastern hemlock, and of the effect that continued hemlock woolly adelgid feeding has on the production of new foliage. Binomial sampling procedures have been successfully developed for many pests of agricultural crops. The technique may not be suitable for long-lived hosts where pest attack significantly alters the food resource.