A Predictive Model for the Survival of Overwintering Bean Leaf Beetles (Coleoptera: Chrysomelidae)

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Abstract
Survival of overwintering bean leaf beetle, Cerotoma trifurcata (Förster), populations in woodland and soybean habitats was studied for three consecutive winters from 1996 through 1999. Four locations of soybean fields and three locations of woodlands were studied at Iowa State University farms near Ames, IA. In the winter of 1996–1997, woodlands and soybean fields were sampled monthly from mid-November through mid-April of the following year, whereas in the winters of 1997–1998 and 1998–1999, both habitats were sampled twice a month from mid-October through mid-April. On each sampling date, three sampling units (1 m2) of leaf litter or crop residue was randomly collected from soybean fields and woodlands at each location. The collected samples were bagged and returned to the laboratory for estimates of overwintering beetles. The beetles obtained from the samples were kept in individual sample bags at 24°C for 100 h to assess their survival. The beetles were then kept in a freezer at −15°C for investigation of potential fungal pathogens and ectoparasitic mites. During the three-winter study, the mortality of overwintering beetles in soybean fields (77.04–88.89%) was higher than those in woodlands (48.9–82.29%). The effects of winter temperature on beetle mortality and a predictive model for the overwintering beetle survivorship are discussed.