Gypsy moth (Lepidoptera: Lymantriidae) spread in the central Appalachians: Three methods for species boundary estimation

Estimation of the boundary of the geographic distribution of gypsy moth, Lymantria dispar (L.), populations is important for monitoring and controlling the spread of this species in North America. In this study, gypsy moth population boundaries were estimated from male moths counts in pheromone-baited traps and from egg mass counts in a 5.18-million-ha area in northwestern Virginia and southeastern West Virginia. Population boundaries were estimated for 5 yr (1988-1992) and for different population density thresholds using the following 3 methods: (1) best classification (minimizing the number of grid cell misclassifications), (2) 1st occurrence method, and (3) logistic regression of log population counts versus distance perpendicular to population boundary. All 3 methods generated similar boundaries for male moth counts, and boundaries obtained with the first 2 methods were most correlated. The regression method failed to estimate boundaries of egg mass populations because of their irregular spatial distribution. However, the 2 other methods were successful and yielded similar results. The average gypsy moth spread rate estimated using male counts was 10.7-11.9 km/yr. The minimum spread rate was 3.8-4.9 lan in 1991, and the maximum rate was 19.4-22.6 lan in 1989.