Effect of Chilling of Diapause Pupa on Adult Emergence in the Sweet Potato Hornworm, Agrius convolvuli (LINNÉ) (Lepidoptera; Sphingidae)

Abstract

The effect of chilling of diapause pupae on adult emergence was studied in Agrius convolvuli. When diapause pupae were kept at 5-20°C for 60 days, the pupal period was shortened compared to that of pupae kept at a constant 25°C. The optimum temperature for diapause termination was 10-15°C. The pupal period decreased with the duration of chilling up to about 50 days, indicating that chilling accelerated diapause development. In contrast, at more than 50 days of chilling, the pupal period increased linearly with the duration of chilling, indicating that chilling blocked the initiation of adult development. Chilling at 10 or 15°C for more than 60 days terminated pupal diapause in all individuals because adult emergence occurred uniformly within 40 days when the pupae were transferred to 25°C. When diapause pupae were chilled for 30 days beginning 20, 40 and 60 days after pupation, the earlier the chilling was started, the more effectively it shortened the pupal period. It is concluded that although exposure to low temperature is not necessary to break diapause, (i) low temperature (10-15°C) promotes diapause development and (ii) the sensitivity to low temperature changes during diapause.