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 I hate to be the bearer of bad news, or perhaps good news
(depending on your thoughts on insects) but, for the most part,
most insects will survive just fine. Insects use a variety of
strategies to survive through the winter.
The first strategy some insects will use is to avoid the cold
altogether. Some insects that we find in Illinois won't survive
our freezing winter temperatures. So, instead of trying to make
it through the winter here, they'll survive elsewhere. An
example of this would be monarch butterflies. As we approach
fall, monarchs will begin to migrate south and will eventually
reach Mexico where they will overwinter. As temperatures begin
to warm again come spring, they will begin migrating north and
their children or grandchildren will arrive in Illinois. Others,
like armyworms and potato leafhoppers, survive in Southern
states and will migrate north as temperatures begin to warm.
For those insects that stick around, low temperatures aren't
necessarily the problem; the formation of ice crystals in their
bodies is what makes survival difficult. If ice crystals rapidly
form in their bodies, their cells will burst, resulting in
damage and likely death. Some insects, like woolly bear
caterpillars, will avoid this by using chemicals to control the
way in which and where they freeze and therefore minimize damage
to their cells (these insects are called freeze tolerant).
The other strategy insects that stick around for the winter use
to survive is to produce chemicals in their bodies to avoid
freezing altogether (these insects are called freeze
intolerant). As temperatures begin to cool, these insects will
start creating anti-freeze chemicals. These chemicals allow the
insects bodies' to supercool (reach temperatures below freezing,
32ᵒF). Therefore the insects won't freeze until they reach their
supercooling point. Some insects that take this approach include
Japanese beetles (supercooling point is 19ᵒF), emerald ash borer
(supercooling point is -13ᵒF), and codling moth (supercooling
point is -10ᵒF).
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Just because temperatures don't hit the supercooling
point of an insect it doesn't mean some won't be killed. Perhaps the
insect people are most excited about being 'wiped out' by the cold
is emerald ash borer. A study by the U.S. Forest Service showed that
5% of the insects die at 0ᵒF, 34% at -10ᵒF, 79% at -20ᵒF and 98% at
-30ᵒF. That being said it's important to note that emerald ash borer
doesn't overwinter in exposed areas.
While air temperatures in many places in Illinois got colder than
the above supercooling points, most insects will overwinter in
protected areas where temperatures did not get nearly as cold. For
example, white grubs (like Japanese beetles) in the soil will not be
exposed to extremely cold temperatures because the soil will
insulate them. Others will seek shelter under leaf litter (codling
moth), under bark (emerald ash borer), or even in your home. All of
these will provide some protection from cold temperatures. Snow is
also an excellent insulator, and all of our snow offered another
layer of protection. While the brutally cold temperatures may have
seemed like they lasted forever, in reality, they only lasted a
relatively short time and likely didn't drop temperatures in these
protected areas low enough to 'wipe out' these pest insects.
While the cold temperatures we've had have likely killed some
insects, come spring it should be business as usual.
[Ken Johnson, Horticulture Educator,
University of Illinois Extension] |
