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Tough Buggers: Insect strategies to survive winter in Minnesota

T. Cira, L. Christianson, A. Hanson, A. Hefty, A. Morey, K. Nail, D. Rosenberger, R.C. Venette
University of Minnesota, Department of Entomology
Dept. of Conservation Biology, USDA-Forest Service

Minnesota winters are too cold for most insects to survive without special strategies and adap- tations (see below). Learning how insects cope with cold temperatures is helpful in many ways. We can more accurately forecast when and where insects are active, and predict where invasive species may establish in the future. We can also better understand the different ways in which pest and beneficial insects will be impacted by climate change. Warmer winters could allow more insects to survive, expanding or shifting their habitats to new areas. Other insects may be less likely to survive because of reduced snow cover, which can serve as an insulative layer. Below, you see just how cold Minnesota is, for how long, and how much snow falls.

 

Strategy #1: Avoid the cold Strategy #2: Don't let yourself freeze Strategy #3: Let yourself freeze
Many insects find shelter, often in aggregations with insects of the same species. Other insects will migrate to warmer climates. Most insects die when they freeze. But some supercool by making chemicals to prevent freezing until temperatures below the freezing point of water. Some insects can survive freez- ing. They survive by using special proteins to regulate the way their body freezes and to minimize damage to cells.
Some insects will use more than one strategy to battle the cold. For example, the woollybear caterpillar (below right) avoids the cold by finding shelter under leaf litter and snow, produces chemicals to supercool, and can also survive
Strategy 1 Strategy 2 Strategy 3

The table below lists brief facts about the overwintering strategies of common insects that are, or might one day be, found in Minnesota. Overwintering notes include what physiological (e.g. lowering supercooling point) and/or behavioral adaptations (e.g. burrowing under the soil and snow) they use, and the lifestage in which they spend the winter.

Strategy Species Overwintering habitat Winter lifestage
---- Striped cucumber beetles Die in MN, spring migrants from southern states Adult
---- Corn earworms Die in MN, spring migrants from southern states Pupa
Avoid cold 1 Monarch butterflies Migrate to Mexico Adult
1 Common green darners Migrate to the Southern US and Mexico Adult
1 European honey bees Aggregate in hives All stages
1 & 2 Multicolored Asian lady beetles Aggregate in sheltered areas Adult
1 & 2 Nothern house mosquitoes Find protected sites with high humidity Adult
1 & 2 Bean leaf beetles As individuals under leaf litter and snoq Larva
1&2 Japanese beetles As individuals under soil and snow Larva
Don't freeze 2 Codling moths As individuals under bark; supercool to -10°F Larva
2 Emerald ash borers As individuals under bark; supercool to -26°F Larva
2 Mountain pine beetles* As individuals under bark; supercool to -31°F Larva
2 Gypsy moths On bark; supercool to -17°F Egg mass
2 Forest tent caterpillars On bark; supercool to -22°F Egg mass
2 Soybean aphids On buckthorn near leaf buds; On bark; supercool to -29°F Egg
Freeze 2 & 3 Asian long-horned beetles* As individuals under bark Larva
2 & 3 Goldenrod gall flies As individuals in goldenrod stem Larva
1, 2& 3 Woollybear caterpillars As individuals under leaf litter and snow Larva
*Species not yet found in Minnesota
Soybean aphid Japanese beetle Honey bee Monarch Butterfly
Overwintering habitat Overwintering soybean aphid Overwintering Japanese beetle Overwintering honey bee Monarch butterflies
Most recognizable stage Aphid normal Japanese beetle normal Honey bee normal
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