Abstract: The non-diapausing (ND), winter-diapausing (WD) and summer-diapausing (SD) pupae have distinguishable physiological and developmental process. In the present study, the developmental duration and morphological changes of ND, WD and SD pupae were comparatively investigated with the onion maggot Delia antiqua as the model species through anatomic and photographed observation and measurement, with emphasis on the head evagination- and diapause-related characteristics. The study aims to understand the differences of developmental and morphological characteristics of ND, WD and SD pupae, and lays a morphological base for the distinguishment of diapause developmental stage and study of diapause molecular mechanism. The developmental durations of pre-diapause, diapause and post-diapause of WD pupae were 4, 85 and 27 d, respectively, while those for SD pupae were 2, 8 and 22 d, respectively. The pre-diapause begins at the pupation stage, and ends when the free fat body appears in the central area of eyes, which happens 10 h after the completion of head evagination. The completion of head evagination is the premise of diapause occurrence, the head evagination of ND, SD and WD pupae happened at 48, 36 and 83 h after pupation, and there was no morphological difference observed in the developmental process of head evagination between these three kinds of pupae. During the process of head evagination, firstly, the head capsule and thoracic appendages turned out from thorax capsule, and the head got to the location and shape of matured pupae; then, the abdominal muscles continued contraction to push the haemolymph and fat body into the head capsule and thoracic appendages. The pupae entered SD and WD when approximate 15% total effective accumulated temperature was obtained at the pupal stage. In the duration of diapause, the pupal morphology remained in the form of the appearance of free fat body in the central area of eyes, and no difference was observed between these two kinds of diapausing pupae in morphology in the diapause stage. The WD pupae had the largest body length, width and weight, followed by SD pupae and then ND pupae. At the post-diapause stage, malpighian tubules of ND pupae were green and clearly visible during the existence of the yellow body, whereas they were almost invisible in the diapausing pupae. This study provides basic data for understanding diapause physiology and inferring diapause development process of insects through developmental duration and morphology.

Key words: Delia antiqua, diapause, winter diapause, summer diapause, comparative morphology, developmental duration, effective accumulated temperature