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 vicious cold snaps.
1. Emerald ash borer suffer some losses when it is very cold. 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. 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 and Long Island, New York. Good news! It dies out when winters reach -8F / -22C for at least a season or two. For more on bark beetles and when they freeze their tarsi off, try this article.
Please note: cold events do not eradicate populations of insects- they just reduce them to much lower levels for a season or two. 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 survival in there, too.
And finally: Entomology Today posted an excellent blog in January 2014 titled, Falling Temperatures do not Necessarily Mean Fewer Insects. I highly suggest anyone interested in this subject also read that article.
BLOG EDITED JANUARY 2016 TO REFLECT NEW ARTICLES AND INFORMATION