Modeling the influence of forest characteristics and ant (Formicidae:Hymenoptera) predation on dispersal and survival of neonate gypsy moths (Lymantriidae: Lepidoptera)

A deterministic model was developed that predicts dispersal distance and survival of neonate gypsy moth, Lymantria dispar (L.), larvae as functions of host tree acceptability, tree density, tree canopy size, and intensity of ant predation. This model was compared with output from a more realistic, individual-based computer model. The outputs of both models were similar, implying that the deterministic model assumptions were reasonable. In both models, the number of larvae killed by ants and the distance larvae dispersed increased as tree separation increased. Conversely, predation and dispersal decreased as the size of tree canopies increased. Predation also decreased as trees became more palatable to larvae, and increased as ant numbers and their effectiveness as predators increased. Model outputs were quite sensitive to some ranges of predator effectiveness. Changes in number of dispersal episodes, tree acceptability, ant predation intensity, and unimpeded dispersal distance (i.e., theoretical dispersal distance in the absence of trees) had little effect on actual distances larvae dispersed. Only forest geometry (tree density and canopy size) had substantial effects on dispersal distance. These effects on dispersal were unexpected, but suggest that information about natural dispersal of neonate gypsy moth larvae can be inferred from simple forest measurements