Methods for monitoring the spread of gypsy moth (Lepidoptera: Lymantriidae) populations in the Appalachian mountains

Gypsy moth, Lymantria dispar (L.), is gradually spreading in North America from New England to the west and south. Monitoring this expansion is important for evaluating effects of population management on the rate of gypsy moth spread, for planning areas regulated by domestic quarantine, and for accurate timing of preventive silvicultural measures. Spread rate was measured as the distance between population boundaries in consecutive years. Gypsy moth population boundaries from 1988 to 1995 were estimated in northwestern Virginia and southeastern West Virginia using counts of male moths in pheromone-baited traps. Population boundaries estimated using the 10 moths per trap threshold were most stable in space and time compared with the boundaries estimated for other thresholds ranging from 1 to 300 moths per trap. Thus, the 10 moths per trap threshold is reliable for the monitoring of gypsy moth spread. Local spread rates were significantly autocorrelated in space (range, 80 km) but not in time. The rate of gypsy moth spread decreased from 16.9 km/yr in 1984-1990 to 8.8 km/yr in 1991-1996. An 8-km intertrap distance was adequate for detecting this decline in the rate of gypsy moth spread.