Population cycles of forest Lepidoptera: a maternal effect hypothesis

1. Many species of forest Lepidoptera have cyclic population dynamics. Although there are numerous potential causes, including interactions with predators, parasitoids, pathogens, and food-plant quality, strongly density-dependent interactions are often difficult to demonstrate. Both autocorrelation analysis and attractorreconstruction methods have recently been applied to a number of species' time series. Results suggest that complex dynamics, i.e. cycles or deterministic chaos, may be more prevalent than once thought, and that higher-dimensioned models are necessary. 2. We develop a two-dimensional difference equation model that relates the average quality of individuals to patterns of abundance. The delayed density dependence is caused by transmission of quality through generations via maternal effects. We show that the maternal effect model can produce patterns of population fluctuations similar to those displayed by one class of host-parasitoid models. 3. We review empirical evidence for maternal and quality effects in dynamics of forest Lepidoptera. We fit the maternal effect and delayed logistic models to six species of forest moths for which delayed density dependence and maternal or quality effects have been found. The maternal effect model was a good predictor of the period of the oscillations for the species that we examined. We discuss why models of this type give better fits to moth cycles than do first order models with added delays.