The effects of thermoperiods on diapause induction in continuous darkness or under a 12: 12h LD photoperiod were investigated in the cabbage beetle, Colaphellus bowringi Baly, a typical short-day species. The diapause response curves both at different constant temperatures and at the thermocycle of format CT x: (24-x) h (16: 28▫C) under continuously dark rearing conditions showed that the incidence of diapause depended mainly on whether or not the mean temperature was≤20▫C or ≥20▫C. If the mean temperature was≤20▫C, all individuals entered diapause; if >20▫C, the incidence of diapause declined gradually with increasing mean temperatures. The thermocycle (CT 12: 12h) with a series of different cryophases (8–22▫C) and thermophases (24–32▫C) under continuous darkness demonstrated a cryophase response threshold temperature of approximately 19▫C and a thermophase response threshold temperature of approximately 31▫C. Thermoperiodic amplitude (temperature difference between cryophase and thermophase) was shown to have a significant influence on diapause induction at the mean temperatures of 22, 23 and 24▫C, but not at ≥25▫C. Thermoperiodic responses under LD 12: 12h clearly showed that the incidence of diapause was influenced strongly by the photophase temperature. The thermoperiod under LD 12: 12h induced a much lower incidence of diapause than the thermoperiod with the same temperature in continuous darkness. The ecological significance of thermoperiodic induction of diapause in this species is discussed.

本文报道了用水稻和茭白分别饲养二化螟水稻种群和茭白种群的光周期反应。光周期反应曲线显示,用水稻饲养茭白种群或用茭白饲养水稻种群,无论是在短光照还是在长光照条件下,绝大多数幼虫被诱导进入滞育,丧失了各自原有的光周期反应特性,表明这两个种群已分化到仅适应其本身寄主的程度。用水稻饲养的茭白种群仅有5%～6%的个体化蛹,且其幼虫期较用茭白饲养的延长了15～18天;而用茭白饲养的水稻种群有30 %～40 %的个体化蛹,其幼虫期与水稻饲养的仅相差3～8天。茭白种群用水稻饲养时32日龄幼虫体重仅为茭白饲养的53.1 % ,而水稻种群用水稻饲养时32日龄幼虫体重为茭白饲养的79.5 %。这些结果表明,茭白种群不适应取食水稻,而水稻种群对取食茭白则有一定的适应能力。根据这些结果,我们认为: (1) 这两个种群已出现种下分化的迹象; (2) 茭白种植不会对水稻田二化螟的发生产生大的影响。

Pseudopidorus fasciata enters diapause as fourth instar larvae at short day lengths. Using 24-h light–dark cycles, the photoperiodic response curves in this species appeared to be similar with a critical night length of 10.5 h at temperatures below 30▫C. At an average temperature of 30.5▫C, the critical night length had shifted to between 15 and 17 h. In experiments using non-24-h light-dark cycles, it was clearly demonstrated that the dark period (scotophase) was the decisive phase for a diapause determination. In night interruption experiments using 24-h light–dark cycles, a 1-h light pulse at LD12:12 completely reversed the long night effect and averted diapause in all treatments.. At LD 9:15 light pulses of 1-h, 30- or 15-min also averted diapause effectively when both the pre-interruption (D1) or the post-interruption scotophases (D2) did not exceed the critical night length. If D1 or D2 exceeded the critical night length diapause was induced. The most crucial event for the photoperiodic time measurement in this species is the length of the scotophase. A 10-min light pulse placed in the most photosensitive phase reversed diapause in over 50% of the individuals. Night interruption experiments under non-24-h light–dark cycles indicated that the photoperiodic clock measured only D1 regardless of the length of D2, suggesting that the most inductive cycles are often those in which LD are close to 24 h. In resonance experiments, this species showed a circadian periodicity at temperatures of 24.5 or 26▫C, but not at 30.5 and 23.3▫C. On the other hand, Bünsow and skeleton photoperiod experiments failed to reveal the involvement of a circadian system in this photoperiodic clock. These results suggest the photoperiodic clock in this species is a long-night measuring hourglass and the circadian effect found in the final expression of the photoperiodic response in the resonance experiments may be caused by a disturbing effect of the circadian system in unnatural regimes.

The pine caterpillar, Dendrolimus punctatus (Walker) (Lepidoptera: Lasiocampidae), is a multivoltine pest of pine trees in China, overwintering as larvae. Winter diapause was induced by short day length. The critical night length was about 10 h 40 min at 25, 28, and 31°C in the field, showing a temperaturecompensated diapause induction. Transfer experiments from a short night (L16: D8) to a long night (L12: D12) or vice versa at different times after hatching showed that sensitivity to day length was restricted to the first 14 days; the required day number for a 50% response at 25°C was about 3.5 days for short nights but 7.5 days for long nights, indicating that short nights are photoperiodically more effective. When four successive short nights (L16: D8) were used to interrupt the long-night regime (L12: D12) at different development stages and vice versa, the results showed that the highest sensitivity to photoperiod occurred on the 4th−8th day, corresponding to the second larval instar. Experiments of alternating short-night (L16:D8) and long-night (L12:D12) cycles during the larval period showed that the information of short nights as well as long nights could be accumulated. By rearing the larvae under conditions other than 24-h light–dark cycles, we clearly showed that the dark period (scotophase) played a major role in the determination of diapause. The Nanda-Hamner and Bünsow experiments failed to reveal rhythmic fluctuations with a period of about 24 h in the occurrence of diapause. Therefore, the photoperiodic clock in D. punctatus is an hourglass timer or a damped circadian oscillator.