Quantitative analysis of gypsy moth spread in the Central Appalachians
Gypsy moth, Lymantria dispar (L.), is an introduced forest pest in North America that has been expanding its range to the west and south. In attempt to slow its spread, the USD A Forest Service has established several barrier zones in which isolated colonies are detected and eradicated. To evaluate the effect of barrier zones on the rate of gypsy moth spread, we measured the rate of spread as the average distance between population boundaries in consecutive years which were estimated using male moth counts in pheromone traps, egg mass counts, and defoliation maps in the central Appalachian Mts. in 1984-1995. In 1988-1992, the boundary of 1 moth per trap was on average 108.5 km from the boundary of defoliation, and male moth capture rate increased 10 times per 29 km perpendicular to the population front. Since 1990, the average rate of gypsy moth spread declined from 20.78 km/yr to 8.6 km/yr. This reduction of spread rate may have been due to eradication of isolated colonies in the study area that started in 1990. We developed a model of gypsy moth spread that considered establishment of isolated colonies beyond the moving population front. The model predicts that the barrier zone in the Appalachian Mts. should reduce the rate of gypsy moth spread by ca. 53% which is consistent with our data.