Release of Gypsy Moth 1 Populations from Innocuous Levels

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Abstract
Prior studies led to the premise that gypsy moth, Lymantria dispar (L.), populations tend to increase numerically from innocuous levels in environments where abundant, sheltered resting and pupation locations reduce the probability that the growing insects will be eaten by vertebrates. Although such locations may be found anywhere within the environment, and may either occur naturally or be introduced by man, they are usually above the forest floor, close to or part of a suitable host tree, and dark, dry, and rough. Test results described herein both supported this premise and led to the conclusion that environmental conditions that tend to produce or represent abundant sheltered locations for this pest also tend to produce or represent potential outbreak foci. Such environmental conditions include dry, rocky ridges, excessively drained sands, remnant “wolf-trees”, and ice storms. Other environmental conditions that may contribute to the release of gypsy moth populations from innocuous levels include changes in habitat or food sources of predators, tree age, nutrient and moisture deficiencies, air pollution, land abuse, and climate. Qualitative differences between individual insects may also contribute to population release from innocuous levels.