From the Ground Up - Does Cold Weather Impact Insects?


When we’ve been experiencing a mild winter, how many times have you heard someone comment that we need to have some freezing weather to kill some of the bugs that had been pestering us during the fall and summer?

Spencer Behmer is a Texas A&M Agrilife entomologist and professor.

“They actually have these clocks, that actually measure and record the length of a day, based on how much light there is, and this basically tells them, O.K. it’s time for me to prepare for winter. I need to change my physiology, my behavior. I need to get ready for these changing conditions.”

Behmer says that if an insect is to survive winter it most likely migrates.

“The biggest response if it’s going to survive through those conditions is to migrate, if it can, so Monarch butterflies migrate to avoid the cold weather, so they’re moving south, there’s a population that goes to California. There’s a population that goes to Mexico City.”

A huge number of insects don’t migrate.

“Instead, what they do, is that they have these seasonal life cycles, and so mom will lay eggs in the ground, and it’s the eggs that over winter and don’t have to deal with that extreme cold temperature because they’re in the soil, where there’s less fluctuation in extremes in the temperature.”

The eggs react to a different stimulus.

“So they also have a time keeping mechanism, but it’s independent of light because obviously anything that’s underneath the ground can’t respond to day length, so what it has to respond to is temperature.”

The eggs are able to internally track how many degrees it is above a minimum threshold.

“And once they sort of accumulate to a certain threshold number, then their developmental program kicks in and says. O.K. it’s probably warm enough out there for me, that I should go ahead and start developing from an egg, developing as an embryo, and it’s going to develop to the point then that it can emerge and come out of the ground.”

So really nothing short of a late cold spell, say in April, would suppress the upcoming year’s insect population.


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