Geographic variation in chill coma recovery time across the US invasion front of the gypsy moth (Lymantria dispar)

Over the past 150 years, the invasion front of the gypsy moth (Lymantria dispar) in the United States has expanded to encompass a wide climatic gradient. Depending on the timing of hatch and location, early instar caterpillars may experience spring cold snaps that can impact survival or development. We measured chill coma recovery time to test the resiliency of gypsy moth to cold temperature stress during early stages of development. Populations were sourced from both the long-established range and along the current invasion front and were used to evaluate geographic variation in gypsy moth cold temperature tolerance. Second and third instar caterpillars from these populations were exposed to temperatures of 1°C and 2°C, respectively, for a period of 20 hours. The time taken for larvae to regain motor function after chilling was recorded as chill coma recovery time for each population. Our results indicate that gypsy moth from northern regions with colder mean annual temperatures recovered faster, and thus are likely more resilient to cold temperature stress than those from southern regions. The capacity to adapt to local climates during the course of the invasion may contribute to the future spread of this defoliating forest pest across the United States. As northern gypsy moth populations encounter more variable climate during the hatching period and early development, understanding cold tolerance will be an important factor for predicting further range expansion.