Regulation of outbreaking populations of winter moth (Operophtera brumata) by density dependent dispersal

Winter moth  (Lepidoptera:Geometridae) is an invasive defoliator in North America, which is currently a serious pest in the New England.  Winter moth populations have alternately been suggested to be regulated by pupal predation, parasitoids, and host plant resistance in its native Europe.  Life tables have shown that winter moth populations in New England are largely regulated by density dependent larval mortality.  Density dependent larval mortality has been suggested from earlier work on winter moth in Canada, and the causes of mortality were assumed to be competition and starvation.  Using a combination of manipulative and observational laboratory and field studies, we show that winter moth larval populations disperse in a density dependent fashion, possibly mediated by changes in host plant quality induced by heavy herbivory.  This dispersal process commonly results in the prevention of complete defoliation of host plants, and is a novel proposed regulatory mechanism in winter moth population dynamics.