We investigated the possibility of overwintering of the diamondback moth, Plutella xylostella L., in central Michigan. In the spring of 1993, counts of immature stages on brassicaceous weeds in a field previously planted to broccoli revealed a small but significant number of late instars that could not be attributed to oviposition of immigrant moths from the southern United States. We suggest that crop debris and snow cover played an important role in sheltering the larvae, which are known to tolerate sub·freezing temperatures. There was no indication of adult survival.
Idris, A. B. and Grafius, Edward J.
"Evidence of Pre-Imaginal Overwintering of Diamondback Moth, Plutella Xylostella (Lepidoptera: Plutellidae) in Michigan,"
The Great Lakes Entomologist, vol 29
Available at: https://scholar.valpo.edu/tgle/vol29/iss1/4