Thawing and freezing: will the winters volatile weather kill off the stink bugs?

During late January, from January 29-31, the high temperature in Washington ranged from 66 to 72 degrees. It felt like spring. Stink bugs across the area, sensing the warmth, emerged from their overwintering locations in dead trees, attics, and under shingles. They buzzed around clumsily, often inside of our homes and offices.

Then, on February 1, cold air rushed back into the Washington area behind a strong cold front. Reagan National Airport recorded a high of 36 with a low of 21 and light snow coated the area.

The stink bugs, caught off guard by the sudden cold and snow, moved quickly to get back into their overwintering locations and resume a state which closely resembles hibernation.

Is it possible that the January thaw followed by cold temperatures and snow harmed the stink bugs? Are stink bugs weakened or killed when they become active during mid-winter and then quickly encounter Arctic blasts? Can extreme temperature changes during a winter season reduce an entire stink bug population?

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I asked two entomologists who specialize in stink bugs for answers to these questions.

Below is the response from Thomas P. Kuhar, Associate Professor in the Department of Entomology at Virginia Tech:

My guess is that the warm spell this January probably did not impact the bug very much. The brown marmorated stink bug’s seasonal biology is triggered by diel [24 hour period involving day and night] patterns in light and dark phases. This is why the bugs seem to stop feeding on plants in September and very synchronously begin aggregating on large trees and manmade structures and begin to seek dark sheltered places to spend the winter.

After nestling under siding or shingles, or in garages, and attics, this is how the bug ends up in our houses. At this time bugs will change their physiology to endure freezing temperatures. They will not feed during this time.

They typically increase polyol cryoprotectants [substance that protect bugs from freezing damage] in their hemolymph (or blood). This prevents their body fluids from crystallizing. We have determined in my lab that [stink bugs] can endure temperatures below -20 degrees C.

After January, prolonged warm temperatures can cause the bugs to become active. This is why they end up flying around in houses in the winter.

Most will not leave their natural overwintering sites, which are typically dead standing trees, until May. The bugs will not become reproductively active until another light-dark phase trigger in late May.

So, while a warm stretch in the middle of winter might cause a few bugs to become active and possibly burn up some of their winter energy reserves, most of the bug population remains dormant in a state of diapause until around May, when they will seek out trees to feed upon and to begin a new generation.

I also asked Kim Reynolds, entomologist with HomeTeam Pest Defense, for her opinion on the January thaw and refreeze scenario for stink bugs. Below is Kim's response:

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Temperature is one of several environmental factors that can influence insect activity.

The 70 degree weather probably did not last long enough to bring large numbers of stink bugs out from overwintering. (Insects do not actually hibernate). If insect activity was present and a hard freeze occurred, it could potentially kill off a portion of the population.

I couldn’t specifically say if winters with extreme changes in temperature reduce the stink bug or any other insect population, but temperature changes do impact insect activity. It would probably depend on the extremity of the temperature changes, how long those changes last, and other environmental conditions.

Typically consistently colder winters will decrease insect activity more than a milder winter.

The Conclusion

Our recent January thaw followed quickly by cold and a little snow probably did not harm the Washington area stink bug population. Most of the bugs can survive our changeable winter weather, particularly since they can endure temperatures below minus 20 degrees C.

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But, if we notice less stink bugs this spring and summer, perhaps the weather did play a role. We’ll have to wait and see.

For a good summary on stink bugs, check out this document from George Hamilton which was published in American Entomologist.

Explanation of the lead photo

The stink bugs in the top photo emerged from my attic or walls during the recent January thaw and buzzed around inside my house. I used the BugZooka (see photo to the left) to catch them with a suction blast after they landed.

A few days later, on February 3, I decided to let the stink bugs go. Yes, I know; I’m very kind-hearted for releasing stink bugs. I could see that some of the bugs were still crawling around inside the BugZooka’s clear, plastic chamber.

I went to my backyard and shook the bugs out of the BugZooka onto the snow-coated ground. The temperature at the time was hovering near 25 degrees. The bugs were free again!

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After the release, the stink bugs didn’t fly away or even move that much. A few of them wiggled their little legs on the crusty snow. I took a photo for this article and I went back inside.

Two days later, the bugs were gone. Did the stink bugs fly back into my attic? Did they crawl away? Perhaps they were eaten by birds? Or, maybe, they were victims of the Stink Bug Freeze of 2013!

Thanks to Thomas P. Kuhar, Kim Reynolds, Ann Davis, and HomeTeam Pest Defense for help with this article.

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