Laboratory investigations revealed that black cutworm (BCW), Agrotis ipsilon (Hufnagel), developmental rates on a meridic diet did not differ from developmental rates on seedling corn leaves, the principal economic host in Iowa. The same investigations, however, demonstrated that fluctuating temperatures of 4.4-26.7, 10.0-26.7, 15.6-26.7, and 21.1-26.7(DEGREES)C accelerated BCW developmental rates when compared to development under the constant means of the fluctuations (15.6, 18.4, 21.1, and 23.9(DEGREES)C);The performance of a BCW developmental model was evaluated during several field trials. In all cases, the model did not perform accurately. Similar to the laboratory results, BCW development was seemingly accelerated by natural, fluctuating temperatures. The results of the field studies suggested that natural Iowa photophases of spring, summer, and autumn did not alter BCW developmental rates. Further, it was speculated that soil moisture may have affected BCW developmental rates during some of the field trials;A modified model, based upon field-determined Centigrade Degree Day requirements, was proposed for use in Iowa.