The connection between variable synchrony of insect eclosion with host budburst and variability in insect densities was investigated. Experiments with gypsy moth (Lymantria dispar L.) larvae determined the duration of acceptable foliage after budbreak of nine hardwood species. Four competing conceptual models of environmental influences on the timing of budburst were compared and evaluated. The best budburst model was combined with an eclosion model to estimate the frequency of asynchrony and its correlation with density. Synchrony with budburst has a smaller effect than weather after hatch, on the population size of the gypsy moth, but neither is the driving force behind density changes. However, comparison of traits of 300 species of Macrolepidoptera showed that 50% of outbreak species, but only 24% of nonoutbreak species begin feeding at the time of budburst; this suggests a stronger relation between synchrony and population dynamics than was found with the gypsy moth.

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