Effects of climate on emerald ash borer mortality and the potential for ash survival in North America

Non-native invasive insects such as the emerald ash borer (Agrilus planipennis Fairmaire; EAB) cause billions of dollars' worth of economic damage and unquantifiable but substantial ecological damage in North America each year. There are methods to mitigate, contain, control, or even eradicate some non-native invasive insects, but so far the spread of EAB across eastern North America appears to be unimpeded. Similar to the effect of chestnut blight (Cryphonectria parasitica (Murrill) Barr) on American chestnut (Castanea dentata (Marsh.) Borkh.) nearly 100 years ago, it is estimated that EAB will eventually decimate nearly all ash (Fraxinus spp.) in North America. Although previous literature suggests no impediment to the spread of EAB, we propose the possibility that obstacles to EAB population expansion into the northern ranges of ash could be formidable. We combined USDA Forest Service Forest Inventory and Analysis (FIA) 2010 ash data, historical climate data, beneath-snow and beneath-tree bark temperature modeling, and our current understanding of EAB physiology. We found that between 1945 and 2012, while some Canadian locations experienced temperatures potentially cold enough to kill all EAB, very few locations in the United States experienced such temperatures. However, more than 7% and 42% of weather stations located in the ranges of ash in the United States and Canada, respectively, experienced temperatures potentially cold enough to kill the majority of the EAB population. By killing the majority of the EAB population, EAB spread may be slower and EAB population may be held to densities to which ash trees can tolerate infestation. As in its native range in Asia, lower EAB densities may not cause ash mortality. This information should be helpful for the future sustainable management of ash.