Diapause inHeliothis armigera(Hübner) andH. fletcheri(Hardwick) (Lepidoptera: Noctuidae) in the Sudan Gezira

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Abstract
Diapause induction inHeliothis armigera(Hb.) from the Sudan Gezira was investigated under controlled conditions. A maximum incidence of diapause occurred in response to exposure to low temperature (22°C) and short daylength (12 h) during the larval stage. However, the prepupal and early pupal stages were also sensitive to temperature; if they were exposed to 26°C, diapause was averted. After more than two months at low temperature, some pupae remained in diapause for more than two months after transfer to high temperature (34°C) and only commenced developing when the temperature was lowered again. This may provide a mechanism to bridge the hot dry season and to synchronise emergence with the start of the rainy season. A high incidence of diapause inH. fletcheri(Hardwick) was observed to occur at the end of the rainy season under ambient conditions in the Sudan. Emergence from these diapause pupae occurred in the following rainy season. The different phenologies of diapause in the two species are discussed in relation to their distribution in rain-fed and irrigated vegetation in the Sudan.