Spread of Gypsy Moth (Lepidoptera: Lymantriidae) in the Central Appalachians: Comparison of Population Boundaries Obtained from Male Moth Capture, Egg Mass Counts, and Defoliation Records

Abstract

Since its introduction near Boston in 1869, the gypsy moth, Lymantria dispar (L.), has spread over 1,000 km to the southwest. To measure its current rate of spread through the central Appalachian Mountains we estimated population boundaries, which are lines that separate areas with population densities generally above and below a specific threshold. Population boundaries were estimated in northwestern Virginia and southeastern West Virginia using male moth counts (1988-1994), egg mass counts (1988-1991), and defoliation maps (1988-1994). The boundary of 1 moth per trap was on average 110 km from the boundary of defoliation, and the male moth capture rate increased 10 times per 29 km perpendicular to the population front. Approximately 11 yr separated the time when traps caught 1 moth per trap until defoliation first occurred in the same area. The rates of gypsy moth spread estimated using different census methods and from different population thresholds changed almost synchronously from year to year. Only spread rates estimated from defoliation data had a different temporal pattern. Gypsy moth spread rate declined from 1988 to 1994 by 35%, as measured from time series of spread rates and boundary compression (reduction of the distance between adjacent boundaries). Reduction in gypsy moth spread rate may have been the result of intensive population management in the area.