Pitfall traps were used to monitorCalosoma sayiDeJean (Coleoptera: Carabidae) populations in soybean fields to determine the species' seasonal history, patterns of colonization, and response to insecticides.C. sayiadults were detected from mid-July into mid-Oct. Adults of the 1st and 2nd generations were separated by ca. 4 wk. Usually only 1 generation developed annually, but a 2nd generation developed in some instances.C. sayiadults quickly established populations in most areas where noctuid larvae were plentiful. However, noC. sayiwere detected, even though abundant prey were available, in 2 relatively isolated soybean fields which had not been previously planted to soybeans.Methyl-parathion and methomyl treatments reduced the numbers ofC. sayilarvae when these insecticides were applied when these forms were active. However, applications made beforeC. sayiactivity began often resulted in higher adult and larval numbers later. Insecticide induced reductions of the beetles' biotic control agents and, more likely, a resurgence of noctuid prey in treated areas may have led to the increase in numbers ofC. sayiafter insecticide treatment.