Population Regulation of Gypsy Moth (Lepidoptera: Lymantriidae) by Parasitoids: Does Spatial Density Dependence Lead to Temporal Density Dependence?

In 1987, four gypsy moth, Lymantria dispar, (L.) densities were established in eight 1-ha plots in western Massachusetts, ranging from 50,000 to 1.4 M neonates per hectare. Two tachinid parasitoid species, Compsilura concinnata (Meigen) and Parasetigena silvestris (Robineau-Desvoidy), exhibited spatial density-dependent parasistism and C. concinnata was the major source of gypsy moth mortality. This study investigated whether spatial density-dependent mortality in 1987 translated into temporal density-dependent mortality of experimental gypsy moth populations created the following year (1988). C. concinnata was responsible for the largest percentage of gypsy moth mortality again in 1988, however, overall mortality caused by C. concinnata in 1988 was considerably less than in 1987. Gypsy moth mortality caused by P. silvestris was greater in 1988. The killing power of either parasitoid in 1988 were not linearly related to the estimated density of the parasitoids produced in the previous year. We saw no evidence for a between-generation numerical response (1-ha scale) of either the generalist parasitoid, C. concinnata, or the specialist parasitoid, P. silvestris, between 1987 and 198