PUPAL DIAPAUSE IN HELIOTHIS-ARMIGERA (HUBNER) (LEPIDOPTERA, NOCTUIDAE) IN BOTSWANA - ITS REGULATION BY ENVIRONMENTAL-FACTORS

Heliothis armigera (Hb.) has been shown to develop continuously in tropical areas but to become more dependent with increasing latitude on a pupal diapause to survive the winter. The changes that occur in pupal period under ambient conditions in Botswana were examined. Pupae formed in May were able to survive the winter period and produce adults in September. Laboratory work using artificial environments showed that this extended pupal period is not simply a response to low pupal temperatures but is induced by the low temperatures and short daylengths experienced by the larva. Pupae from larvae reared at 27° C and a 14-h daylength (non-diapause pupae) initiated adult development even at 13° C. Pupae from larvae reared at 18° C and a 9-h daylength (diapause pupae) had similar pupal periods to non-diapause pupae at 33 and 27° C. However, at 18 and 13° C, diapause pupae had much longer developmental periods than non-diapause pupae. More diapause pupae were produced at 18° C from larvae reared in a 12-h daylength than from those in 15- or 9-h daylengths. The variation and importance of this temperature-labile facultative diapause over the extensive geographical range of H. armigera is discussed. © 1979, Cambridge University Press. All rights reserved.