This article was published originally on 1/17/2014
Iowa's recent experience with the Polar Vortex and extremely cold temperatures and wind chills has caused some people to ask, "Will this cold freeze out the EAB population in Iowa?"
The short answer: Probably not…
Cold hardiness research done in Minnesota by Robert C. Venette and Mark Abrahamson (2010) revealed that larvae that acclimated to winter temperatures over 3 months were able to survive lower temperatures (-13˚F / -25˚C) than larvae subjected to cold conditions in a short time (0˚F / 17.8˚C). This is referred to as supercooling. The supercooling point is a temperature far below freezing that insects can withstand through physical and chemical changes in their bodies. Survival varied from 5% in non-acclimated larvae to 90% acclimated larvae. Referring to northern Minnesota winter conditions, the authors stated, "cold temperatures may not completely eliminate the insect…may help to keep populations from building up quickly and may give ash trees some time to recover from initial attacks."
A key consideration in insect survival overwinter is how cold for how long. As an example, the northern 'expansion' of the bagworm, Thyridopteryx ephemeraeformis, is limited by freezing temperatures. When the temperature falls to 1˚F (-17˚C) and stays there for 24 hours, more than 75% of the eggs in the bag can be killed.
The brunt of central Iowa's extreme cold occurred on January 6 and January 7, 2014. Thirty-six hours of subfreezing temperatures (as low as -16˚F/-27˚C) probably weren't long enough to cause significant mortality to emerald ash borer larvae or native upper Midwestern insects. But, on a positive note, bagworm populations will probably be lower in 2014.