Climate, reproductive asynchrony, and mate-finding limitation in gypsy moth (Lymantria dispar)

Low density populations are prone to decline and possible extinction due to environmental and demographic stochasticity, and Allee effects. Allee effects collectively refer to decreases in the per capita population growth rate with decreases in population abundance. Understanding Allee effects can be critically important in the management of threatened and endangered species. In parallel, there is growing recognition of their important role in biological invasions. Whereas Allee effects can be a bane in conservation efforts, they can be a benefit if the rate of establishment or invasion speed of a non-native, invasive species is reduced. In many insect species, mate-location failures in sparse populations are a dominant cause of an Allee effect. This effect could be compounded by reproductive asynchrony in which individuals are reproductively active at different times within a larger population-level reproductive period. Because climate is a driver of insect seasonality, geographic variation in climate could influence the degree of reproductive asynchrony, which in turn could influence the strength of an Allee effect due to mate-finding failures. In 2010 and 2011, we measured the relationship among climatic conditions, reproductive asynchrony, and an Allee effect due to mate-location failure, using the non-native species Lymantria dispar (L) (gypsy moth) as a model system.