Spatial variation among counts of gypsy moths (Lepidoptera: Lymantriidae) in pheromone-baited traps at expanding population fronts.

Geostatistics were used to quantify spatial variation in captures of adult male gypsy moths, Lymantria dispar (L.) in pheromone-baited traps in the central Appalachians. Spatial variation was analyzed in the infested zone, where yearly total capture was > 300 moths per trap; the transition zone, where moth capture ranged from 1 to 300 moths per trap; and the uninfested zone, where moth capture was < 1 moth per trap. The trend associated with gypsy moth spread was removed in each zone using linear and nonlinear regression. Spatial correlation among trap captures in the transition zone (correlogram sill, 0.544; range, 31.2 km) was much stronger than in the infested (sill, 0.269; range 23.9 km) and uninfested (sill, 0.222; range, 19.7 km) zones. Additional short-range correlation (range, 1.4 km) was detected in the uninfested zone. Differences in the spatial distribution of male moth populations among the 3 zones may be caused by different dominating population processes in each zone. Other factors, such as trap saturation, also may contribute to the difference in the patterns of moth captures. Obtained zone-specific geostatistical parameters can be used for interpolation of moth captures at unsampled locations and for improving gypsy moth monitoring.