Bean leaf beetle adults are susceptible to cold weather and most will die when the air temperature falls below 14°F (-10°C). However, they have adapted to winter by protecting themselves under plant debris and loose soil. An overwintering survival model developed at ISU in 2000 is helpful for predicting winter mortality based on accumulating subfreezing temperatures. Predicted mortality rates in Iowa were low during the 2015-2016 winter and ranged from 35-68%. This is a big contrast to the 2013-2014 winter, where most beetles were not predicted to survive.
Figure 1. Predicted mortality for bean leaf beetle during the 2015-2016 winter.
Since 1989, we have predicted bean leaf beetle mortality at ISU. In central Iowa, the average mortality for over 25 years is 72%. If you like to plant soybean on the early side and had issues with overwintering beetles causing severe defoliation and/or vectoring bean pod mottle virus, I recommend scouting fields as plants emerge.
Figure 2. Predicted mortality for bean leaf beetle from 1989-2016.