Biphasic effect of low temperature on completion of winter diapause in the onion maggot, Delia antiqua.

The effect of low temperature on completion of winter diapause was investigated in the onion maggot, Delia antiqua (Diptera: Anthomyiidae). Diapause was completed under constant diapause-inducing conditions of 15 degrees C and 12L-12D, without any exposure to lower temperature. The pupal period for 50% adult emergence was 117 days. None of the cold treatments at 5.6 degrees C examined in the present study advanced adult emergence; on the contrary, they delayed it. Detailed analyses of the results revealed that diapause development in D. antiqua comprises two phases which differ in sensitivity to low temperature, with the phase shift occurring at around day 60 at 15 degrees C and 12L-12D. In the first phase of diapause development, low temperature (5.6 degrees C) had no effect on diapause development. In the latter phase, by contrast, diapause development was retarded in proportion to the duration of cold treatment.