Cold tolerance and factors affecting the duration of diapause in Ephestia kuehniella Zeller (Lepidoptera: Pyralidae)

Abstract

The duration of diapause in larvae of Ephestia kuehniella was studied in 10 population samples from flour mills or unheated stores in England, Egypt, Finland and Japan, and a laboratory stock from Japan under 11 combinations of temperature and photoperiod. The length of diapause varied considerably with little synchronization of pupation at any of the constant conditions tested but when larvae were transferred to 15°C LD 9:15 after 1 week at 25°C LD 16:8 there was a marked synchronization of pupation. At a constant 20°C or 25°C, the mean durations of diapause in different photoperiods ranged from 3 to 40 weeks with the majority of larvae spending at least 4 months in diapause. Larvae reared in continuous darkness remained in diapause for the longest periods, up to a maximum of 60 weeks. Cold tolerance was examined by leaving cultures of eight population samples from England, Scotland, Egypt and Japan in an unheated building over winter. All the cultures survived the winter during which a minimum mean monthly temperature of 4°C and a lowest daily minimum of 2°C were recorded. Pupal mortality, however, was high in some stocks. In laboratory experiments on the Scottish strain, 80% of diapausing larvae survived an exposure of 4 weeks at −2.5°C, whilst only 10% of non-diapausing larvae did so. These observations underline the importance of diapause as a factor to be considered when drawing up programmes for the control of Ephestia keuhniella Zeller.