ABSTRACT
Cabbage root fly pupae overwinter in diapause and must receive a cold treatment to complete their diapause development. This must be followed by a period at warmer temperatures for their post-diapause development, which is complete when the flies emerge in the spring. To determine the time that diapause is terminated under field conditions, cabbage root fly pupae were extracted from field soil every two weeks from November to April during the winters of 1979–82. The pupae were extracted from the soil by flotation. A minimum of 500 pupae was collected at each sampling. In general, about 1 kg of soil had to be processed to obtain each pupa. In certain populations, cabbage root flies produced a bi-modal pattern of emergence in the spring which could possibly represent the contributions from the second and third generation of the previous year to the overwintering population.
