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Sunday, February 2, 2014

Impact of cold weather on insects

Jeffrey Hahn, Extension Entomologist



Jeff Hahn, Univ. of MN Ext.

Photo 1: Boxelder bugs aggregate into clusters and use supercooling to protect themselves from extreme cold

With the intense cold weather we have recently experienced,
a natural question to ask is what effect this will have on insects.  While the optimistic amongst us are hoping
that it will wipe them out, especially the types we like the least like
boxelder bugs and mosquitoes, the truth is it will probably have a minimal
effect on most insects, especially our native species.

Like their human counterparts, native insects have lived in
Minnesota a long time and know how to survive during the winter, even in extreme
weather conditions.  That is not to say
that some insects won't die as a result of temperatures around -20o
F or colder, but most will live to see spring. So how do they do that?  Insects
have several strategies for surviving cold. These options were nicely outlined in the fact sheet Tough Buggers: Insect strategies to survive winter in Minnesota by Cira et.al

First, insects
survive by avoiding the cold.  This could
be like boxelder bugs that find shelter in large numbers under the bark of a
dead tree or in our homes.  Some insects,
like monarchs, leave Minnesota, migrating to warmer weather for the winter.

Second, they can
avoid freezing.  Insects can go through a
process call supercooling, i.e. adding a chemical similar to antifreeze into
their blood (hemolymph).  This lowers the
temperature water will freeze and helps keep their body fluids liquid.  This is a common method for many insects in
Minnesota to protect themselves from extreme cold temperatures.  Forest tent caterpillar, a native insect,
supercools to protect itself during winter.


Jeff Hahn, Univ. of MN Ext.

Photo 2: Woolly bear caterpillars can seek shelter and alter their blood to tolerate freezing
Third, some
insects can tolerate freezing.  These
insects can release proteins into their blood to help control where, when, and
how much ice forms.  By controlling how their
bodies freeze, insects can minimize damage to their tissues.  Woolly bear caterpillar is an example of a freeze
tolerant insect.

It is not unusual for an insect to use more than one
strategy for surviving winter weather. Multicolored Asian lady beetles seek sheltered sites as well as using
supercooling.  Of course, some insects do
not even survive our Minnesota winters. Insects, such as aster leafhopper and striped cucumber beetle, migrate
into the state from the south during the growing season but are not able to
survive our winters.

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