Diapause Termination and Postdiapause Development in Eggs of Hydraecia immanis Guenée (Lepidoptera: Noctuidae)

Abstract

Most diapause eggs of Hydraecia immanis Guenée stored in environmental chambers at 1.7 and 4.4°C terminated diapause after ca. 2 or 3 mo. After diapause was completed, mean egg hatch occurred in ca. 12 or 13 d at 21.1°C. About 0.1% of eggs held continuously at 21.1°C hatched without exposure to cold storage, which indicates that low temperatures are not required to terminate diapause for all eggs. Diapause eggs laid between 16 August and 4 September 1985 in a greenhouse under conditions of natural daylight and placed in an outdoor weather shelter in Champaign, Ill., on 4 September, generally terminated diapause by the end of the year, although some eggs did not complete diapause until later in winter. To achieve 50% hatch under field conditions, 119.5 degree days above a threshold temperature of 9.43°C were required by eggs that had completed diapause.