A predictive model for the survival of overwintering bean leaf beetles (Coleoptera : Chrysomelidae)

Survival of overwintering bean leaf beetle, Cerotoma trifurcata (Forster), populations in woodland and soybean habitats was studied for three consecut ive winters from 1996 through 1999. Four locations of soybean fields and th ree locations of woodlands were studied at Iowa State University farms near Ames, IA. In the winter of 1996-1997, woodlands and soybean fields were sa mpled monthly from mid-November through mid-April of the following year, wh ereas 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, t hree sampling units (1 m(2)) of leaf litter or crop residue was randomly co llected from soybean fields and woodlands at each location. The collected s amples were bagged and returned to the laboratory for estimates of overwint ering beetles. The beetles obtained from the samples were kept in individua l sample bags at 24 degrees C for 100 h to assess their survival. The beetl es were then kept in a freezer at -15 degrees C for investigation of potent ial fungal pathogen; and ectoparasitic mites. During the three-winter study , the mortality of overwintering beetles in soybean fields (77.04-88.89%) w as higher than those in woodlands (48.9-82.29%). The effects of winter temp erature on beetle mortality and a predictive model for the overwintering be etle survivorship are discussed.