Notes on Factors Influencing Diapause in the Cabbage Maggot, Hylemya brassicae (Bouché)

Abstract

Factors inducing diapause and methods foe breaking diapause in the cabbage maggot, Hylemya brassicae (Bouché), are discussed. The pest was reared continuously in the greenhouse during the winter months (when pupae normally enter diapause) by fluctuating the air temperature from 60 to 65 °F. at night to between 75 and 80 °F. during the day and maintaining the soil temperature (in which the eggs, larvae and pupae were reared) at about 68 °F. Pupae produced by flies kept at constant temperatures entered diapause. Fluctuating the soil temperature (for rearing larvae and pupae) did not markedly influence entry into diapause, but when larvae and pupae were reared at above 72 °F. high mortality occurred. Intensity of diapause in the pupae also depended on the temperature at which the flies were reared, with the shorter period of dormancy occurring when flies were kept at low temperatures. Diapause development proceeded more rapidly at 45-50 °F. than at higher or lower temperatures but proceeded to completion at any temperature from 34 to 70 °F. At above about 72 °F., diapause development appeared to be inhibited. The period for completion of development was about 3-8 months, depending on storage temperatures and on intensity of diapause. Preliminary tests indicated that light intensity is a major factor influencing entry into diapause, and results of tests reported in this paper show that this influence can be offset by temperature.