Biology of Hessian fly (Diptera: Cecidomyiidae) in the southeastern United States: geographic variation and temperature-dependent phenology

Population dynamics of the Hessian fly, Mayetiola destructor (Say), were studied in volunteer and sown fields of soft red winter wheat, Triticum aestivum L. em Thell, in the Piedmont region of Georgia and the Coastal Plain regions of Georgia and South Carolina. The Hessian fly estivated during the summer at all locations with the initial emergence occurring about 1 September. Eggs, larvae, and puparia, however, were collected in August in some years indicating that limited activity is possible during the summer. The primary difference in Hessian fly phenology between the two regions was the occurrence of a winter brood and second spring brood in the Coastal Plain. Typically, two fall and one spring brood occurred in the Piedmont region, and two fall, one winter, and one to two spring broods occurred in the Coastal Plain region. The 1985-1986 season was substantially warmer than 1986-1987 and 1987-1988, and a third fall brood was observed in both regions with a seasonal total of four and six broods occurring in the Piedmont and Coastal Plain regions, respectively. The first fall brood at all locations and the second fall brood in the Coastal Plain occurred before normal wheat plantings; consequently, these broods developed primarily in volunteer wheat. An average (+/-SD) of 638 +/- 110 centigrade degree-days (DD) accumulated between most broods, but some broods required substantially more degree-days to complete development. The variability in degree-day accumulations indicated that further refinement will be needed before specific management activities can be timed using degree-day calculations. This research demonstrated that volunteer wheat is the primary interim host before wheat is normally planted, and indicated that delayed planting of wheat is of limited utility for controlling the Hessian fly in the southeastern United States.