The Clock Mechanism Of And Physiological Response To Diapause Induction In Chilo Suppressalis (Walker)

Chilo suppressalis Walker (Lepidoptera: Crambidae), is one of the main insect pest in rice production and widely distributes in all the regions in China. Photoperiod is the most main factor for diapause induction in C. suppressalis. In this dissertation, the critical night length and the photosensitivity as well as the clock mechanism of diapause induction in C. suppressalis larvae reared with artificial diet were determined. Physiological parameters were also measured in larvae reared at long-day and short-day cycles to determine physiological changes in diapause-destined larvae and the period in which the changes occur.Diapause induction and photoperiodic clock mechanism were investigated in C. suppressalis larvae reared on an artificial diet in the present study. The critical night length for diapause induction was about 9 h 53 min to 10 h 39 min at 22 to 28°C. The third-instar larvae were found to be relatively sensitive to diapause induction. Photoperiodic response under non-24-h light–dark cycles showed that scotophase length played an essential role in the induction of larval diapause in C. suppressalis, and consecutive exposure to long-night cycles was necessary for a high diapause incidence. In the Nanda–Hamner experiment, diapause incidence peaked at scotophase of 12 h and dropped rapidly at scotophases > 24 h. In the Bünsow experiment, diapause incidence was clearly suppressed, especially at the light pulse located 8 h in the scotophase. Both the Nanda–Hamner and Bünsow experiments showed no rhythmic fluctuations with a period of about 24 h; thus the photoperiodic clock in C. suppressalis is a non-oscillatory hourglass timer or a rapidly damping circadian oscillator.For physiological response to diapause induction in C. suppressalis, weight and dry weight of old larvae reared under short-day cycle (LD 12:12) were both slightly lower than those under long-day cycle (LD 16:8); but for the 13d old larvae, weight and dry weight were significantly heavier in LD 12:12 treatment than in LD 16:8 treatment. Water content in larvae was generally lower in LD 12:12 treatment than in LD 16:8 treatment, and differed significantly in 10,19 and 22d old larvae. Concentration of glycerol, glucose and trehalose showed similar change patterns with the increase in larval age in larvae reared at LD 12:12 and LD 16:8; but glycerol concentration in 10 and 31d old larvae was significantly higher in LD 12:12 treatment than in LD 16:8 treatment; glucose concentration of 10 and 34 d larvae were significantly higher in LD 12:12 treatment than in LD 16:8 treatment; and trehalose concentration was different between LD 12:12 treatment and LD 16:8 treatment in 4,7and 16d larvae. These results show that larvae reared at LD 12:12 show physiologically adaptative responses to diapause induction photoperiod, and this occurs at the photosensitive stage.