Distribution Pattern and Sampling of Eggs of the Western Hemlock Looper (Lepidoptera: Geometridae) in Mature Western Hemlock Stands

Abstract

An egg sampling study of the western hemlock looper, Lambdina fiscellaria lugubrosa (Hulst), was conducted in mature western hemlock stands from 1992 to 1994 in British Columbia, Canada. Egg density of the looper was homogenous within a tree crown, Suggesting that lower-crown sampling is effective for egg density estimation on the entire tree. Both the Taylor power law and the Iwao patchiness regression described egg distribution as aggregated. This aggregated distribution was further delineated as negative binomial distribution by chi-square test. Based on the Iwao model, the optimal sample size required to reach a predetermined precision level was calculated. To reduce egg-counting time, the relationship between mean egg density and proportion of lichen samples containing a specified number of eggs was established. The effect of tree height, diameter at breast height, crown width, crown length, and presence of heartrot on egg density was also examined. The results indicated no significant effect on egg density of these variables.