Predicting Size and Change in Nonoutbreak Populations of the Douglas-fir Tussock Moth (Lepidoptera: Lymantriidae)

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Abstract
A range of nonoutbreak densities of the douglas-fir tussock moth, Orgyia pseudotsugata (Mcdunnough), were analyzed for 11 generations at four geographic locations. Simple correlation analyses of transformed data showed that, of the variation in early larval density, 69% was contributed by the density of early instars in the previous generation and 85% by late instars. In an alternate representation, 52% of the variation in intergeneration trend was contributed by the survival rate of larvae, even though survival was a poor predictor of trends in decreasing populations. For these data, a relatively high rate of larval survival is a good indicator of rapidly increasing populations; however, a causal mechanism is not identified.