Heliothis virescens (Lepidoptera: Noctuidae): Initiation of Summer Diapause

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Abstract
Summer diapause of the tobacco budworm, Heliothis virescens (F.), is a period of extended duration of the pupal stage, particularly of males, initiated by high temperature. In summer insectary studies, up to 95% of the male pupae exhibited delayed development. The number entering summer diapause was associated with high temperatures before pupation. Almost all pupae that had entered summer diapause over a period of several months emerged during the last part of September and the first part of October. In laboratory studies, high fluctuating temperatures caused the highest percentage of individuals to enter summer diapause. An analysis of variance showed that the effect of temperature was much greater than photoperiod, but with a significant interaction between these two factors. A daily 8-h exposure at 43°C caused an average bf 95.6% of males to diapause and 58.7% of females. Summer diapause only occurred when the maximum temperature exceeded 32°C When exposed to a fluctuating temperature of 23.9 to 40.6°C for all of the larval stage, all male pupae diapaused, while only 50% of the females entered summer diapause. When exposed for just the week before pupation, from 63 to 85% of the males diapaused compared to 15 to 50% of the females. Exposure of pupae 2 days after pupation still caused 24% of males to diapause (1% females) and 3 to 4 days after pupation, 8 to 9% to diapause (1–5% of females). Averaged across all photoperiods and temperatures, 61% of the males entered summer diapause, compared to 26.7% of the females. The substantial number of inviable eggs produced by females mated to males from pupae that did not enter summer diapause when exposed to high temperatures, compared to the low number of inviable eggs produced by females mated to males from pupae that did enter summer diapause, signifies the survival advantage of a physiological condition such as summer diapause.