Photoperiodic control of diapause termination was systematically investigated in Pseudopidorus fasciata. In 24 h light-dark cycles, the rate of diapause termination in this species depended on photoperiod. The critical night length (CNL) for diapause termination was 10 h, 0.5 h shorter than that for diapause induction. Night-interruption experiments with T = 24 showed that diapause was effectively terminated when the scotophases separated by light pulse were shorter than the critical night length (10 h); no developing individuals were found if the duration of the pre-interruption scotophase or the post-interruption scotophase exceeded the CNL. A 15-min light pulse was sufficient to reverse the effect of long night when it was placed 8 h after lights-off. Resonance experiments with a constant photophase of 12 h or 16 h and various scotophases of 4-80 h showed an hourglass-type photoperiodic response, where no rhythmicity was found. In another resonance experiment with constant scotophase of 8 h and various photophases of 4-72 h, all individuals developed into cocoons. In the Bünsow experiment, the response curve showed two apparent peaks for diapause termination, one being 8 h after lights-off, and another 8 h before lights-on. However, there was no periodic rhythmicity, which again indicates an hourglass principle. The results lead to the conclusion that the same photoperiodic clock mechanism (a long-night measuring hourglass) is involved in both diapause induction and termination.
In the field, the blister beetle Mylabris phalerata Pallas (Coleoptera: Meloidae) undergoes larval diapause in the ground, which lasts for nearly six months. The effect of the soil environment on this diapause was examined. Final instar larvae kept at temperatures of >= 26°C do not enter diapause and continued to develop regardless of the soil water content and photoperiod. Below 25°C the final instar larvae entered diapause regardless of soil water content and photoperiod. The early stages, particularly L2, appeared to be more important for diapause induction than the later stages. However, the other instars were also sensitive. Temperature, rather then photoperiod was the main factor influencing pupal duration.