Modeling airborne transport of gypsy moth (Lepidoptera: lymantriidae) larvae

Wind structure and dispersal of gypsy moth larvae, Lymantria dispar (L.), were simulated using a three-dimensional wind and dispersion model. In particular, the springtime wind patterns of coastal California near Monterey Bay, an area of current infestation, were simulated using climatological data. These mass-conserved winds were then used to simulate the trajectories of gypsy moth larvae with terminal velocities ranging from 40 cm per second to 120 cm per second. Small-scale convective processes which would carry the larvae aloft were simulated through the random location of buoyant plumes in the modeled area. Three hundred simulations were made in order to determine the probability of long-range airborne transport of larvae. The larvae were carried aloft and transported more than a few hundred meters in only 2% of the cases. Dispersal under these 2% of the cases in which long-range transport occurred was then examined in detail for larvae with terminal velocities of 40, 80, and 120 cm s −1. Model results showed that the larvae with a 120 cm s −1 terminal velocity were transported 7 km and resulted in a maximum concentration of 49 larvae per hectare based on 1 million larvae at the source. The larvae with a terminal velocity of 40 cm s −1 were transported 21 km with a maximum concentration of 14 larvae per hectare. While the results shown in this paper are geographically specific, the model is fully exportable since it is based on a direct solution of the equations describing those physical processes.