Synchronisation of pre‐imaginal development and reproductive success in the winter moth, Operophtera brumata L

The phenology of a winter moth population originating from tributaries of the river Rhine (50°30′ N) was investigated. The eggs spend winter in the canopy of the trees without chilling to be necessary for larval eclosion. Larval development was temperature dependent with a theoretical development null point at 1.5 and 1.8 °C., calculated according to time of development as well as larval growth rate (R.G.R.). Photoperiod had no effect. Influence of the host plant (Salix spp.) was obvious (p < 0.01) in only 1 of 21 examples. In the field, pupal aestivation was a mean of 171 d. Aestivation period differed between sexes, with aestivation 7 d shorter in males (p < 0.001). Photoperiod had a minor effect with 4 d shorter at short‐day (LD 8/16) comparing to long‐day (LD 16/8) (p < 0.05). An influence of temperature was evident during the initial phase of aestivation resulting in a time of pupation which deviated by a maximum of 10 d (p < 0.05). When temperatures differed during the terminal phase of aestivation, the effect on time of pupation was more pronounced. The shortest aestivation period was found at 10°C (= 169 d). At lower temperatures (5 °C) and higher temperatures (20 °C) time of adult emergence was retarded to > 200 d. Host plants, in the main did not influence pupation period. Within the population two different reaction patterns were found which may synchronize the development of individuals: 1. When larval development was accelerated by high temperatures resulting in an early date of pupation, the subsequent aestivation period was prolonged. 2. When larvae fed on young leaves later in the season rather than on leaves growing earlier, time of larval development was shortened. Fecundity of females was temperature dependent with an optimum value at 10 °C. At lower and higher temperatures the mean number of eggs/ ♀ decreased. Photoperiod did not influence fecundity and the host plants the larvae fed on, mostly had no effect.