Populational variation in diapause-induction and -termination of Helicoverpa armigera (Lepidoptera: Noctuidae)

Diapause induction and termination were compared among three different geographic populations of Helicoverpa armigera from Ishigaki (24.3 degrees N; 124.2 degrees E), Okayama (Ushimado, 34.6 degrees N; 134.1 degrees E) and Kanazawa (36.6 degrees N; 136.7 degrees E) in Japan. The critical daylength for pupal diapause induction among the three populations was between 12L:12D and 14L:10D in the larval stage. No clinal latitudinal variation in the critical daylength was found among the three populations. Most of the diapausing pupae emerged when they were continuously maintained at 20 degrees C under 12L:12D, suggesting that cold exposure (chilling) is not necessary to break the pupal diapause. Furthermore, the time required for diapause termination of the Okayama population was the longest (214 days), followed by the Ishigaki (149 days) and Kanazawa (73 days) populations at 20 degrees C (without chilling) under the 12L:12D photoperiod. These results showed no clinal latitudinal variation in diapause termination.