Density-Dependent Suppression of Experimentally Created Gypsy Moth, Lymantria dispar (Lepidoptera: Lymantriidae), Populations by Natural Enemies

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Abstract
(1) Experimental manipulation of densities of gypsy moths revealed a strong, positive spatially density-dependent reduction in population size, a response not evident in past studies of natural populations in North America (2) Positive density-dependent mortality occurred during the early and mid larval stages and was primarily due to Compsilura concinnata, a polyphagous parasitoid. (3) The oviposition rate of Parasetigena silvestris, an oligophagous parasitoid of gypsy moths, was initially inversely density-dependent but became positively density-dependent during the late larval period. (4) Phobocampe disparis showed an inversely density-dependent response, and predation by small mammals on pupae deployed in the liter was in plots with higher numbers of pupae. (5) We conclude that if gypsy moth population densities fluctuate asynchronously on a spatial scale of a few hectares, the density-dependent responses of C. concinnata and P. silvestris could suppress the populations to a point where small mammal predation would be able to prevent population increase. This phenomenon may explain the apparent stability of gypsy moth population on a region-wide basis for the many years between outbreaks.