Seedcorn Maggot (Diptera: Anthomyiidae) Phenology in Central Iowa and Examination of a Thermal-Unit System to Predict Development Under Field Conditions

Two generations of seedcorn maggots (SCM)occurred in central Iowa in 1980 and 1981. In both years, overwintering flies appeared in late April (at 181/198°D c ; 1980–1981) and the F 1 generation appeared in early June (at 494/490 degree-days C; 1980–1981). SCM were uncommon or absent in the summer and fall, strongly suggesting aestivation by flies in the F 2 . Air temperatures were useful in predicting SCM development in the field; however, both air and soil temperatures overestimated SCM development. Our results indicate that low-risk planting periods could be identified with additional knowledge of SCM population biology.