Professor Simon Fraser University Burnaby, British Columbia, Canada
Population cycles in insects have intrigued ecologists for many years; many mechanisms have been proposed but the lack of detailed long-term data has made it difficult to identify the driving relationships. Here we use a unique set of population and life history data collected over several decades to elucidate the factors associated with the cyclic population dynamics of a forest insect, the western tent caterpillar, Malacosoma californicum pluviale. We have collected annual data on population size, fecundity, parasitism and infection with a virus, the host specific nucleopolyhedrovirus McplNPV from three island populations. These data are used to examine the population feedback structure and to try and elucidate the mechanisms driving the density-dependent feedbacks. We develop mechanistic models based on information from two island populations to simulate the dynamics in a third population. We found that incorporation of the impact of the virus could simulate realistic cyclic dynamics. Parasitoids, often implicated as drivers of population cycles of forest Lepidoptera, do not act in a density dependent manner but rather are observed only at low population densities when viral infection of western tent caterpillars does not occur.
