Population dynamics and biological control of outbreak populations of winter moth in the eastern United States
Winter moth, Operophtera brumata L. has recently invaded the northeastern United States and caused widespread defoliation. We embarked on a ten year project to collect life table data which involved estimating densities of different winter moth life stages at multiple research plots. We wished to understand what factors regulated the outbreak populations of winter moth that we observed in this region. We also began introduction of the tachinid parasitoid, Cyzenis albicans, which has controlled winter moth at other locations in North America. We wished to find out if we could established the fly in winter moth populations and whether it would result in much lower densities of winter moth, as it has elsewhere.
An analysis of 10 years of life table data collected from outbreak populations of this species has revealed that populations are regulated by density dependent mortality primarily in the larval stage. This mortality constitutes direct and overcompensating density dependence, resulting in distinct two year cycles of density. The dynamics contrast strongly with classic analyses of low-density populations of this insect. Introductions of the parasitoid Cyzenis albicans have resulted in successful establishment at several locations and sharp reductions in winter moth density at one location so far.