Severely cold weather can greatly reduce populations of both native and non-native forest pests, giving the trees a temporary reprieve. Here's a quick round up of three forest pests very likely to freeze into tiny larvae-sicles during the Eastern and Central USA cold snap this week.
1. Emerald ash borer is going to suffer. The larvae of emerald ash borer contain a natural antifreeze- but it only works to around -13F / -25C. After that, they freeze and die. Read this Minnesota Public Radio article, or this technical scientific paper, to glory in their frozen demise. Added 27 Jan 2014: On the other hand, some of the parasitoid wasps that kill and eat emerald ash borer are also vulnerable to extreme cold. Read all about that in this scientific paper if you want to get deep into the details.
2. Hemlock woolly adelgid might not be woolly enough. It needs to be fully -22F / -30C to start killing hemlock woolly adelgids under their tiny wool coats, but that'll do it. Read the scientific paper here.
3. Southern pine beetle. It is native to the Southern US, but it is increasingly creeping north and becoming a pest of more northerly forests, like in New Jersey. Good news! It dies out when winters reach -8F / -22C. For more on bark beetles and when they freeze their tarsi off, try this article.
Please note: cold events like this do not eradicate populations of insects- they just reduce them to much lower levels temporarily. Even just being insulated by snow can be enough to keep a few larvae alive at the base of a tree. And of course, you can't count on the cold to render your firewood safe to move, either- the wood in the center of the pile might be a lot less cold than the wood at the edges, permitting some survival in there, too.
Edited 27 January 2014 to add: Entomology Today posted an excellent blog in January titled, Falling Temperatures do not Necessarily Mean Fewer Insects. I highly suggest anyone interested in this subject also read that article.
H/T to twitter.com/foresthealth for the HWA article!