Expression of early and late‐emerging phenotypes in both diapausing and non‐diapausing Delia radicum L. pupae

Abstract

AbstractThe presence of early and late phenotypes of Delia radicum L. (Diptera: Anthomyiidae) has been attributed to the existence of differences in development after diapause. The criteria for the early phenotype is emergence in less than 20 days at 20 °C (320 DD above 4 °C) and more than 30 days at 20 °C (280 DD above 7 °C + 320 DD above 4 °C) for the late phenotype. The emergence pattern of 10008 non‐diapausing D. radicum pupae reared at 20 °C, L16:D8 and 60% r.h. showed an asymmetrical bimodal distribution similar to the emergence pattern of 477 (1994) and 326 (1995) diapausing pupae from the field. When reared individuals were segregated based on their emergence pattern and reared separately, the proportion of early phenotype increased from 61 to 96% in three generations, while the proportion of late phenotype stayed at 78 to 80% during three generations. These results indicate clearly that diapause is not necessary for the expression of the early and late phenotypes. The presence of these two phenotypes probably enables D. radicum to optimize the use of the available resources, to ensure that a sizeable proportion of the larval population enters diapause and to maintain its distribution throughout the holarctic region (35 to 68 °N).