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Horticulture and Home Pest News
Horticulture & Home Pest News is filled with articles on current horticulture, plant care, pest management, and common household pests written by Iowa State University Extension specialists in the Departments of Entomology, Horticulture and Plant Pathology.

Will Mild Winter Mean More Insects Next Summer?

This article was published originally on 2/8/2012

Iowa has set a new record for the latest winter day reached without hitting a temperature below zero and we have not had much snow in some parts of the state. While many of us are enjoying not shoveling our sidewalks and not worrying about the wind-chill, we have to wonder what this means for the other animals. We worry perhaps all this mild weather will make for a bad summer filled with lots of insects. 
 
How does winter weather affect insects? It depends.
 
We say 'it depends' a lot, which may sound like we have no clue but the reason we have no clue is that it is really complicated. Ok, it does mean we have no clue but there are good reasons we don't.
 
For instance how an insect is affected by the winter depends on where they are in the environment. Insects like bagworms and praying mantids that overwinter as eggs above ground and are highly exposed on branches may do better if the milder conditions continue.
 
Conditions underground experienced by insects such as white grubs are probably not all that much different this winter, though you could argue that lack of snow cover could have lessened their chances of survival. On the other hand, it has not been that cold this winter for frost to penetrate very deeply into the soil, or to persist.
 
Very warm days like we had in January can cause insects to become active at a time when they won't find food. That means they burned through fat stores and will not have enough energy reserves to survive the rest of the winter and be fit to resume activity in the spring. Insects that did not become active because they were in areas that stayed colder may be better off.
 
Soil moisture is another factor that affects insect survival. Insects can dry out and die. Some species are better at preventing water loss than others. On the other hand, many fungal pathogens that kill insects need moisture to thrive, so for some insects maybe dry conditions are better.
 
We don't even want to get started on the diseases, predators and parasites that have a strong effect on insect populations. All these natural enemies are also affected by the weather, some positively and some negatively and they may have more or less of an impact on the populations of our pest insects this summer.
 
Finally, there is the issue of reproduction. When spring does arrive and insects resume activity, the affect of local weather conditions at the time of reproduction (egg laying and emergence of first instar offspring) will probably overshadow any population changes that took place during the dormant period of winter.
 
Trying to predict what the population of Japanese beetles will be on your roses come mid-July would be about as accurate as predicting the weather in mid-July. I am not very good at predicting either several months in advance and if I were I would be very rich!
 
Unfortunately we are all going to just wait and see. I feel safe in saying that some insects might do better, some not as well, and overall we will probably not notice a huge difference. The insects will return. You can count on them!