Generally speaking, warmer winters mean more insects are likely survive because they aren’t exposed to lower lethal temperatures. An early spring can also benefit insects, particularly those species we consider field crop pests, because they are physically larger when crops emerge and can cause significant seedling injury. Multigenerational insects have extra time to produce more offspring, and may produce higher pest densities later in the season.
I’ve been at ISU since 2009, and this is the most extreme winter I’ve had yet. Sometimes it was snowing and cold, at times it was raining and on occasion people were wearing shorts. These inconsistent conditions are difficult for insects. Insects need time to gradually prepare for winter, and repeated cold and warm cycles can eventually burn up all their stored energy reserves.
But what happens if spring comes too fast? Most insects stop diapausing and become active when temperatures are above 50 degrees (I talked a bit about diapause in my previous blog post). According to the ISU Mesonet, some areas of the state have already accumulated 40 growing degree days! In some years, the insects emerge from overwintering sites and have nothing to feed on because the crops aren’t planted and weeds/grasses haven’t resumed growth. This could end up being an important starvation tactic.
Ultimately, I think there will be more field crop insects this spring compared to the last couple seasons. I also expect to see more seed/seedling injury this year due to the insects getting the edge on development before planting. This means getting out and starting scouting efforts even sooner than normal to understand potential pest activity this growing season.
(Source – http://www.farms.com/news/was-does-a-mild-winter-and-early-spring-mean-for-field-crop-pests-104769.aspx)