SEASONAL-VARIATION IN GENERATION TIME, DIAPAUSE AND COLD HARDINESS IN A CENTRAL OHIO POPULATION OF THE FLESH FLY, SARCOPHAGA-BULLATA

1. Generation time, diapause phenology and cold tolerance of the flesh fly, Sarcophaga bullata, were examined under confined natural conditions in central Ohio. In this locality, the fly can complete a maximum of four generations annually. 2. Very few pupae entered diapause in the first and second generations (May to July in 1988). In the third generation (August) 37% of the pupae entered an overwintering diapause, as did all pupae from the fourth generation (September). 3. The adult eclosion date in the spring and annual generation time can be predicted accurately from degree day data. 4. Cold tolerance of the field-overwintering portion of the population was high. After 30 days under field conditions, diapausing pupae readily survived a 7-day exposure to -17-degrees-C. Glycerol appears to be the major cryoprotectant in S.bullata, and glycerol concentrations in the field population (95-142 mM) remained high throughout the winter. 5. In contrast, diapausing flies reared under laboratory conditions (20-degrees-C, 12:12 LD) were less cold tolerant, and glycerol concentrations were lower (6.9-21.2 mM). Field conditions thus promote the acquisition of high levels of cold tolerance, presumably as a consequence of the accumulation of higher concentrations of glycerol. 6. In spite of differences in the cold tolerance of laboratory and field flies, the supercooling points of the two groups of flies were nearly the same, thus implying that the supercooling point is not a good indicator of cold tolerance.