That’s A Berry Good Question: SWD Survivability And Cold Weather

Mar 11, 2014

Q. Can we expect reduced SWD pressure this season due to our extremely cold weather? A. We didn’t have an answer to this one; and we weren’t alone on that. Dr. Greg Loeb, grape and small fruit entomologist at Cornell spearheading work on SWD in NY and the NE region, didn’t either, but provided the following thoughts on the topic:

Spotted Wing Drosophila on Raspberry

Spotted Wing Drosophila on Raspberry

“We really do not know. There are a few papers that I am aware of out of Japan looking at cold tolerance of SWD and also a paper out of Oregon. Both of these studies worked with non-adapted or poorly adapted SWD and found that adults were not able to handle temps much below freezing. Several groups are now looking at this question more carefully. We and others are showing that SWD does go into a non-reproductive phase (diapause) later in the fall and it’s likely the adults have improved capacity to tolerate cold temps, at least to some extent. Probably not enough to handle the kinds of temperatures we have seen this winter in unprotected places. Of course, we would expect adults to seek out protected places such as in the soil litter or in rotting wood, etc. But we really don't have any data on this yet. We did set up some cages without bottoms outdoors this winter (with leaf litter and with or without logs) and released flies reared from late season fruit. Around January 1 we pulled the cages off and allowed snow, etc. to accumulate. The plan is to put cages back on in March and monitor for emergence. I would guess survival will not be very good but we shall see.”

So, while we're tentatively hopeful that few SWD survived, protected locations such as compost piles, brush piles, or crawl spaces  may still have afforded them some protection.  We expect that Northern June-bearing strawberry crops will not be affected, or will be only minimally affected by SWD once again.  Numbers are still likely to increase sometime next summer, so stay tuned throughout the next growing season for updates.

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