Changes in the responsiveness during two phases of diapause termination in Bruchidius atrolineatus Pic (Coleoptera: Bruchidae)

The tropical bruchid Bruchidius atrolineatus (Pie) is in reproductive diapause during the dry season, Previous experiments demonstrated that diapause terminates when beetles are exposed to a short photophase (11:13h L:D), a high humidity (70-80% r,h,) and to the presence of pods of the host plant Vigna unguiculata. The structure of the ovarioles changes during the course of diapause termination, The previtellogenesis phase corresponds to the beginning of the ovarian maturation process. In the germarium of the ovarioles, the trophocytes initiate secretory activity, and nutritive cords transfer the secretory material into the oocytes, Despite the presence of vitellogenin in the haemolymph, the growth of the oocytes is minimal, Some females produce a sex pheromone and exhibit reproductive behaviour, The vitellogenesis phase is characterized by completion of the ovarian maturation process and marks the end of diapause termination, The presence of V. unguiculata pods does not induce the previtellogenesis phase but stimulates the transition from previtellogenesis to the vitellogenesis phase and allows the production of mature oocytes, The diapause intensity is high at the beginning of female imaginal life and decreases with age, This decrease in diapause intensity prevents a;premature termination of the diapause at the beginning of the dry season and enables sexual maturation of the females when the conditions are suitable for reproduction and development of their offspring. Copyright (C) 1996 Elsevier Science Ltd