Forecasting the distribution of an invasive, polyphagous moth, Epiphyas postvittana (Lepidoptera:Tortricidae), in a changing climate

Forecasting where invasive alien insects will spread is a vital component of many management and regulatory decisions. However, many challenges exist in constructing biologically relevant models that are meaningful over time and space, particularly in light of climate change. For much of North America, cold-temperature tolerance is especially important in defining the northern limits of insect survival and is often used as a key parameter in risk models. An insect’s response to cold, though, can be influenced by the type of host it consumes. For highly polyphagous species, host effects could significantly alter distribution projections based on cold. Projections could be further complicated by climate change.

Here, we used the invasive light brown apple moth, Epiphyas postvittana (Walker), to explore how the interaction between host plant and cold tolerance may affect forecasts of future distributions. Epiphyas postvittana is a recent, highly polyphagous invader to the contiguous United States and feeds on many plant species important to agriculture and forestry. The late instar larva is the purported overwintering stage and demonstrates partial freeze tolerance. We reared larvae on different host plants, and then, based on their supercooling and freeze tolerance capacities, estimated the temperature that kills 50% of each population. Using an ecological niche model, this threshold was then combined with each respective host distribution in the United States to plot potential distributions under certain climate change scenarios. We show that E. postvittana cold tolerance differs based on larval host plant, and consequently, alters forecasts of future geographic spread and establishment.