Endo, K., T. Ito and Y. Chiba (1986)
Photoperiodic control of pupal diapause in the swallowtail, Papilio xuthus L. (Lepidoptera, Papilionidae) - Sensitive stage and number of required cycles.
Zool. Sci. 3, 351-356 (1986).

Fifty percent of diapause pupae was induced by the exposure to 8 short days. When the short-day exposure was continued for 12 days, the majority of insects entered diapause. Besides, in induction of non-diapause pupae, 50 % and 100 % were reached by the exposure to 5 and 10 long days, respectively. When a same length of exposure to daylength was made on larvae during the stages between the day of the 2nd instar and the middle day of the 5th instar, insects were found to show a large response almost corresponding to the maximum response to the cycles of long or short days. The response became small when the exposure was started before the first larval ecdysis or continued after the middle day of the 5th instar.

The results indicated that the responsive stage of P. xuthus to daylength covers about 13 of 20-21 days required for larval development at 25 oC. The sensitive stage begins on the day of the 2nd instar and ends on the middle day of the 5th instar. Long days and short days have opposite effects on the induction of diapause, but may have almost the same efficiency in the determination of diapause.