The influence of photoperiod on the life-cycles of Ephestia calidella (Guenée) and Ephestia figulilella Gregson (Lepidoptera: Phycitidae)

Abstract

When reared at 30°C 70% r.h. and fed on a diet of wheat-feed, glucose and yeast, some larvae of Ephestia calidella and E. figulilella entered diapause at photoperiods of 13 hr light and less per day. In continuous darkness for 60 days, no E. calidella larvae exhibited diapause, but two E. figulilella larvae showed some delay in development in food infested by psocids. Under a light regime of 13 hr light followed by 11 hr darkness ( 13L 11D ), 45 per cent of E. figulilella but only 3 per cent of E. calidella larvae entered diapause. The critical photoperiod for both species was between 12L 12D and 13L 11D . For both species, survival was good in continuous darkness and poor in continuous light. Wherever diapause was detected, it delayed adult emergence by an average of 48 days for E. calidella and 74 days for E. figulilella. When reared at 20°C 70% r.h. in continuous darkness for 140 days, 96 per cent and 91 per cent of E. calidella and E. figulilella larvae, respectively, entered diapause. In neither species was diapause observed at 20°C 16L 8D . In E. figulilella diapause did not appear at photoperiods longer than 13L 11D at this temperature. Transfer of larvae which were in diapause after 60 days at 30°C in a 12L 11D photoperiod to one of 16L 8D reduced the range of emergence period for E. calidella by 15 days and for E. figulilella by 75 days, compared to controls left at 12L 12D . Mean development periods were shortened by 13 days and 54 days respectively. Insertion of a 30 day cold period at 5°C did not significantly hasten the termination of diapause. Similar effects were obtained when E. calidella larvae entered diapause at 12L 12D and 20°C. In this case, transferring diapause larvae to the longer photoperiod reduced the development period range by more than half that of controls at 12L 12D . Mean development period was reduced by 63 days. E. calidella larvae entering diapause at 20°C appeared to possess a more intense diapause than those entering at 30°C. The significance of diapause in these species in relation to their potential as pests is discussed.