Factors influencing larval survival of the invasive browntail moth (Lepidoptera: Lymantriidae) in relict North American populations.

Scant attention has been paid to invasive species whose range and abundance has decreased after an initial range expansion. One such species is the browntail moth Euproctis chrysorrhoea L, which was discovered in the eastern United States in 1897. Its range expanded until 1914; after 1915, however, its range contracted and now it persists in only two isolated coastal locations. Although a biological control agent has been implicated in this range collapse, cold inland winter temperatures may also help to restrict browntail moth populations. We surveyed coastal versus inland habitats in Maine and Massachusetts for browntail moth overwintering mortality and larval density per web. We also performed an experiment assessing these same variables in coastal versus inland habitats on different host plant species and at different initial larval densities. We also analyzed temperature records to assess whether winter temperatures correlated with changes in the invasive range. Overwintering mortality was lower in coastal populations for both the experimental populations and in the Maine field survey. Experimental populations in Cape Cod coastal areas also had lower rates of fall mortality and higher larval densities, suggesting that coastal areas are better year-round habitats than inland areas. There were no consistent differences between coastal and inland populations in their response to larval density or host plant, although overall survival in both areas was higher at low initial larval densities and affected by host identity. There was also no difference in two measures of the coldest winter temperatures during browntail moth's expansion and contraction. Our results show that climate affects browntail moth, but suggest that winter temperatures cannot explain both the rapid expansion and subsequent collapse of this pest.