Performance of gypsy moth at supraoptimal temperatures at the southern invasion front
Determining the factors that drive the extent of spatial spread in invasive species is fundamental for mitigating the negative impacts of damaging insect pests to forest ecosystems. For invasive species, climate change could open new habitats to invasion or impose environmental barriers to further spread. The gypsy moth (Lymantria dispar) is an invasive folivore in North American hardwood forests and represents one of the best documented biological invasions in the world. Spread rates across the invasion front are extremely dynamic, with some regions experiencing expansion while the invasion front in other regions is static or contracting. The southeastern edge of the invasion front in the Piedmont and Coastal Plain of Virginia is a region experiencing stasis and contraction of the gypsy range, potentially due to high temperature exposure during larval and pupal development. The objective of our research is to quantify the geographic variation in lethal and sublethal effects of supraoptimal temperatures on gypsy moth growth and development in a variety of experimental venues. Our work compares population responses to temperature in field experiments and growth chamber experiments, both at constant and fluctuating temperature regimes.
We present results for four populations span the latitudinal distribution of the gypsy moth invasion in North America: Quebec City, Quebec (QC), Amsterdam, New York (NY), Currituck, North Carolina (NC), and the New Jersey Standard Strain (NJSS) reared by the Animal and Plant Health Inspection Service Laboratory in Buzzards Bay, Massachusetts. Current work includes two southern invasion front populations from West Virginia and from Eastern Virginia. We compared the performance of these populations at three constant rearing temperatures: 28°C, 31°C, and 34°C. These rearing temperatures were based on fundamental research on gypsy moth development that identified 28°C as optimal for development. All populations experienced high survival at 28°C and 34°C was ultimately lethal. At 31°C, survival followed the latitudinal distribution of our populations with QC having the lowest survival and NC having the highest. All populations showed reduced relative performance at 31°C compared to 28°C, except for NC. Together our results indicate the potential for local adaptation for survival and development of gypsy moth under supraoptimal temperatures. Understanding the role of physiological tolerances and local adaption at the range edge of invasive species can inform the potential for further spatial spread.