Adaption of the life cycle o the codling moth to the seasonal rhythm
of the climate and the periodicity in the fruiting of the apple is maintained
by the geographical variability of its photoperiodic reaction. The temperature
reactions of the active stages and cold resistance remain permanent specific
attributes and are not subject to variability (Riedl, 1983).
Shel'Deshova (1965) reported that diapause termination was more uniform
in the northern than in the southern populations. In southern areas the
chill requirements for diapause termination may not get satisfied in all
individuals of a population and their development would not resume under
the short day lengths of early spring even if temperature was favorable.
However, the longer day lengths and high temperatures later in the season
provide an alternative mechanism to eventually terminate diapause in those
individuals which received inadequate chilling and thus ensure their emergence
the same year. The apple tree also requires a minimum duration of chilling,
about 1,000 to 1,600 hours below 7°C, for reactivation in the spring
(Westwood, 1978). Its reaction to inadequate chilling expresses itself
as increased variability in bud development and an extended bloom period
resulting in a fruit crop in various stages of maturity. Therefore, an
extended emergence period of the overwintering generation in areas with
mild winters could be advantageous to the codling moth in terms of synchronization
with fruit development.
To sum up, in its ecological need, the codling moth is similar to the apple. The northern range of both species is determined by lack of heat and cold resistance, and the southern range by the need for a period of dormancy at reduced temperatures. The adaptive potential of the codling moth is restricted by the fact that it must adapt to the seasonal nature of the fruits of the apple as well as to the climatic rhythm.