Gypsy Moth (Lepidoptera: Lymantriidae) Egg Mass Distribution and Sampling in a Residential Setting

Abstract

The spatial distribution of gypsy moth, Lymantria dispar (L.), egg masses was determined in 60 developed lots in a residential community in Greenbelt, Md. The community was divided into low and high gypsy moth density sections, with average densities of 393.3 and 2,656.3 egg masses per ha, respectively. In the high-density lots, the proportion of egg masses found on trees, man made objects, and houses was 73.9, 21.6, and 4.5%, respectively. The distribution in the low density lots was similar. Oaks, Quercus spp., received the highest proportion of egg masses out of all tree species subcategories at both low and high population densities. The cost effectiveness of a number of potential sampling units, including entire lots, back yards, fixed area plots, and individual trees, was evaluated. The entire lot sampling units required the fewest samples to achieve a predetermined level of precision. However, cost (= sampling time) for these sampling units was also the highest, resulting in relatively low cost effectiveness. Fixed-area plot samples (0.01 ha) were in general the most cost effective sampling units. A binomial (presence-absence) sampling approach, in which the percentage of trees in each lot with >5 egg masses is determined, was nearly as cost effective as fixed-area plots, but its usefulness is limited because it does not provide direct estimates of absolute gypsy moth population density.