Pupal diapause of Helicoverpa armigera: Sensitive stage for photoperiodic induction

Helicoverpa armigera exhibits a facultative pupal diapause, which depends on temperature and photoperiod. Pupal diapause is induced at 20°C by short photoperiods and inhibited by long photoperiods during the larval stage. Sensitive stages for photoperiodic induction of pupal diapause were determined by transferring larvae of various instars between long and short photoperiods. When larvae reared at 20°C under a short photoperiod during egg to fourth instar were transferred to a long photoperiod at the early fifth instar, diapause was not induced. However, when larvae were transferred to a long photoperiod in the middle of fifth instar, diapause was induced. On the other hand, when larvae reared under a long photoperiod during egg to fourth instar were transferred to a short photoperiod at the early fifth instar, about 80 to 100% pupae entered diapause. These results show that the early fifth larval instar is the main sensitive stage for pupal diapause determination even though photoperiod has some effect in the third and fourth instars.