VARIABILITY IN POSTDIAPAUSE DEVELOPMENT PERIODS OF GEOGRAPHICALLY SEPARATE OSTRINIA-NUBILALIS (LEPIDOPTERA, PYRALIDAE) POPULATIONS IN PENNSYLVANIA

Postdiapause developmental periods of overwintering European corn borer, Ostrinia nubilalis (Hubner), larvae collected at five geographically separate locations in Pennsylvania (Bradford, Centre, Lancaster, Lycoming, and Mercer counties) were compared. Larvae were reared under constant 25-degrees-C and 16-h light conditions in growth chambers after collection, and the days for each individual larva to complete the larval stage were recorded. Degree-days (DD) from 1 january to pupation were calculated. The Mercer and Lancaster populations completed the postdiapause developmental period within 450 DD; whereas the Centre and Lycoming populations required 650 DD, and the Bradford population required more than 900 DD. Although the termination day of a population's pupation period varied greatly between geographic locations, the degree-days for initiation of spring pupation among populations were very similar. The study results suggested that a mixture of univoltine and bivoltine individuals coexist in Centre, Lycoming, and Bradford counties, leading to a prolonged postdiapause developmental period and continual emergence over the growing season. The data also suggested that postdiapause developmental periods may be correlated with length of growing season.