Diapause Induction And Termination In The Onion Maggot, Delia Antiqua

The onion maggot, Delia antiqua, is a serious pest of the onion, Allium cepa, and is widely distributed over Asia, Europe and North America. Besides its agricultural significance, D. antiqua can be easily induced in laboratory into both summer diapause and winter diapause, which occurrs at a comparable developmental pupal stage and can be easily reared with an artificial diet. Meanwhile, it is phylogenetically relatively close to Drosophila melanogaster, whose genomic information opens new possibilities for making association between diapause-associated genes and genes that have already been characterized in Drosophila. Thus, it is an ideal model species for diapause research. Diapause is one of the chief physiological mechanisms by which insects can survive under the adverse environmental conditions. An understanding of the physiological and biochemical mechanisms underlying diapause induction and termination is critical for the control of agricultural insect pests, the gene engineering in agriculture and biomedicine sciences. Numerous studies reported the research about diapause induction, maintenance and termination in many species, including the molecular research about the diapause induction, termiantion and coldhardiness. Up to now, there has been little datas about the sensitive stages for diapause induction, diapause maintenance and corresponding morphologic characters in pupal stage in D. antiqua.In the study, the eggs of D. antiqua were reared under the summer diapause conditions (25℃,16L-8D), the larve of 0D to 12D were transferred from SD conditions to ND conditions(17℃,16L-8D), and then pupae were transferred to SD, ND conditions respectively.till the adults eclosion; the eggs of the other group were reared under the nondiapause conditions, the larve of 0D to 14D were transferred from ND conditions to SD conditions, and then pupae were transferred to SD, ND conditions respectively till the adults eclosion and the sensitive stages to diapause induction were found; The summer diapausing pupae of 3D to 10D after pupariation were transferred form SD conditions to diapause termination conditions , the winter diapause pupae of 86D, 89D, 92D, 95D and 98D after pupariation were transferred from WD conditions (15℃,12L-12D) to diapause termination conditions till the adults eclosion; the pupae was also dissected to make the morphological characteristics observations as well. The study preliminarily got the sensitive stages for diapause induction, the necessary diapause maintenance phase and the morphologic characters for diapause termination. The primary results are as follows:1. The sensitive stages for diapause induction:There exists to be the sensitive phase for diapause induction in egg, larval and pupal stage of D. antiqua and the order of sensitive strength from strength to weakiness is pupal, larval and egg stage. The 5-6 D and 10-11 D of larvae reared under the summer diapause condition, the 7-8 D and 11-12 D of larvae reared the non-diapause condition, are the sensitive stage for diapause induction. Meanwhile, the photoperiod influences on the diapause induction cooperating with temperature.2. The necessary diapause maintenance phase:The necessary maintenance of summer diapause in Delia antiqua lasts to the 5D after pupariation approximately, and the necessary maintenance of winter diapause lasts to the 86D after pupariation at most.3. The morphologic characters for diapause in pupal stage:Six morphologic characters were observed under the stereomicroscope,and the whole pupal body can be divided into (1)prepupa;(2)cryptocephalic stages; (3) Head evagination;(4) Antennal stage;(5)Red-eye stage.;(6)Black bristle stage;(7)Adult eclosion.The diapause begins after head evagination and resume direct development once the antennal discs appear.