Induction and Termination of Winter Diapause in a Californian Strain of the Cabbage Maggot (Diptera: Anthomyiidae)

Populations of the cabbage maggot, Delia radicum (L.), occur in the field during all seasons in coastal northern California because the climate is mild, hosts are available, and a percentage of the population does not enter diapause. Laboratory experiments on this population of the cabbage maggot showed the following 6 results: (1) criteria for diapause vary with the conditions that induce diapause, (2) the proportion of larvae entering diapause is highest at low temperatures across all photoperiods and at short photoperiods across all temperatures, (3) developmental times of larvae producing diapause pupae were longer than for those producing nondiapause pupae, (4) rearing larvae at high temperatures and short photoperiods increased the diapause period for the pupal stage, (5) average pupal weights of diapause pupae (20.20 ± 2.27 mg) (mean ± SD) were higher than for nondiapause pupae (18.01 ± 3.31), and (6) fresh pupae weighing <15.5 mg did not complete diapause. The results support previous findings that field populations of D. radicum are induced into winter diapause mainly by short photoperiods, whereas temperature has a lesser effect.