It would be nice if cold temperatures killed pests but unfortunately they don’t. Trying to think on the bright side of our extended winter…
Cold temperatures not a cure-all for pests
If you have spent your winter looking for a silver lining behind the incredibly cold temperatures, we have both good and bad news for you. The good news is that some insect pests, like invasive gypsy moths, are not very cold hardy in the absence of snow. Gypsy moth females lay eggs on just about any surface, and when that surface is exposed to temperatures below -20°F, eggs die relatively quickly. When they lay eggs lower on a tree, more of them survive due to the insulating effects of snow. This winter we have seen temperatures reaching -20°F and lower in many places in northern Minnesota. In these areas, we can expect fewer gypsy moth eggs to survive.
The bad news is that these temperatures are not cold enough to kill off all gypsy moths or any other pest species entirely. Arthropods (insects, spiders, ticks, and related animals) have many ways of dealing with the cold, including the creation of their own antifreeze . Many insects and ticks are able to avoid the cold altogether and burrow into the soil to insulate themselves. While we can expect some emerald ash borers to die at temperatures as warm as -14°F, it takes temperatures of at least -30°F to kill a significant number of this invasive insect. This is because wood-boring pests like emerald ash borer spend the winter under the bark of trees. Bark provides insulation against the cold, and if temperatures rebound quickly, they are even less likely to experience mortality.
Overall, we may see lower numbers of a few insect species in 2018, like gypsy moths. This minor setback does not mean much in the long-term, however. This winter will not be enough to kill all emerald ash borer, gypsy moth, or any other pest of concern. For more information, listen to Jess Hartshorn’s interview on KAXE Phenology .