Supercooling point of bean leaf beetle (Coleoptera: Chrysomelidae) in Minnesota and a revised predictive model for survival at low temperatures

Integrated pest management (IPM) programs for the bean leaf beetle, Cerotoma trifurcata (Förster), could benefit from an ability to forecast the magnitude and timing of early-season infestations. The objectives of this study were to examine the supercooling point (SCP) of adult C. trifurcata as an index of its cold hardiness, monitor overwintering survival, and revise an existing model used to predict the overwintering survival of this pest in wooded areas as a function of low-temperature accumulation. Within a year, the mean SCP of C. trifurcata ranged from -8.9 to -6.0°C. Soil temperatures dropped below the lowest mean SCP (i.e., -8.9°C) in only 2 of 11 yr (1994-2004). In-field survivorship studies showed that adult C. trifurcata successfully overwintered in Minnesota (34-59% survival). This species survived well in years when the existing model predicted zero or low survival. In contrast, our revised model predicted more closely the overwintering survival of this species in southern Minnesota. However, other overwintering mortality factors should be studied to improve our understanding of how well C. trifurcata overwinters in temperate regions.