Some Effects of Gypsy Moth1 Density on Rate of Development, Pupation Time, and Fecundity

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Abstract
In the gypsy moth, Lymantria dispar (L.), subpopulations studied in an overall outbreak area near Glenville, N. Y., the rate of larval development and the time of pupation were directly related to larval density at the start of stadium IV. Avg pupation time differed by as much as 3 wk. Most of the variation in avg egg mass size was also associated with variation in larval density. Possible adaptations by this insect to a numerically bimodal way of life include reductions in the duration of the larval stage as density increases, which result in earlier pupation; reductions in fecundity as larval density increases; the abrupt behavioral shift during instar III, which occurs most dramatically in sparse populations and virtually disappears during outbreaks; and an expanded variety of acceptable host plants as the larvae mature. Results disagree with certain theoretical expectations on relationships between population density and the duration of the 1st instar. The possible confounding influence of density on the timing of monitoring or control work should be considered when such operations are planned.