DIAPAUSE INDUCTION IN THE SESAMIA NONARGIOIDES (LEPIDOPTERA, NOCTUIDAE) EFFECT OF PHOTOPERIOD AND TEMPERATURE

The effects of several diel and nondiel photoperiods on the induction of larval diapause of the corn stalk borer, Sesamia nonagrtoides (Lefe bvre), were explored, The diapause induction curve was found to be of type III (short-long day type). The photoperiodic induction of diapaus e was not restricted to either specific light-dark ratios or to diel p hotoperiods. Instead, photoperiods of approximate to 6-13 h of photoph ase combined with approximate to 10-16 h of scotophase resulted in a h igh incidence of diapause. Light pulses of 1 and 2 h applied at differ ent successive points in time during the Ist part of the scotophase of a diapause-inducing photoperiod of 10:14 (L:D) h greatly reduced diap ause. Such pulses, applied to the last part of the scotophase, did not prevent diapause induction. Thus, 1 photosensitive time gate of the s cotophase, in which illumination prevents diapause induction, exists. No instar was found to be crucially sensitive to a diapause-inducing p hotoperiod of short day length. The 6th instar is a partial exception in the sense that its exposure to short day length is a necessary, but not a sufficient, condition for diapause induction. In general, as th e number of instars exposed to short-day photoperiod increases, the pe rcentage diapause also increases and vice versa. The commitment (irrev ersible process), however, to diapause and to nondiapause development were asymmetrical phenomena, as explained in the text. A synergistic e ffect of short-day photoperiods and low temperatures in the induction of diapause was demonstrated.