Diapause induction in Ephestia elutella (Hübner) and Plodia interpunctella (Hübner) (Lepidoptera, Pyralidae) with a dawn-dusk lighting system

Abstract

The incidence of diapause in larvae of Ephestia elutella and Plodia interpunctella under two light systems operated by solar switches was observed at 25°C. Both switches gave progressively shortening daylength, as would be experienced from early July onwards at a latitude of 52°N. One of the light systems incorporated a device, which took 60 min to change to, or from, full light to near darkness, giving a dawn and a dusk with the photophase. The other was controlled directly by the time switch itself, without any extended periods of changing intensity. Maximal percentages of E. elutella larvae entering diapause under the two systems were obtained with photoperiods half way through development of less than 13 hr 25 min and 13 hr 10 min respectively, measurements of photoperiod in the dawn-dusk system including the 1 hr dawn and 1 hr dusk. The mean critical photoperiod, here defined as that photoperiod giving half the maximum percentage of insects that enter diapause in response to photoperiod at a fixed temperature, was found to be 14 hr 15 min under the dawn-dusk system, and 14 hr 5 min under the other shortening daylength system. Comparison of the above results with the incidence of diapause under a series of fixed daylengths confirmed that the principal sensitive phase in E. elutella occurred early in the last larval instar. Over 70 per cent emergence occurred in batches of P. interpunctella within 7 weeks of egg laying under all lighting conditions tested. Maximal percentages of larvae entered diapause after rearing in total darkness, continual light, or photoperiods of 13 hr or less. The sensitive phase occurred around 8 days after hatching at 25°C, and the mean critical photoperiod was found to be about 13 hr 15 min under both shortening daylength systems, and under fixed photoperiods. Photoperiods of over 13 hr, or increased temperature, appeared to inhibit diapause in P. interpunctella. Light intensities below 1 lux influenced diapause in both species.