Bionomics of Codling Moth: Diapause Induction in Codling Moth Larvae

Bionomics of Codling Moth

Diapause Induction in Codling Moth Larvae

Diapause is the principal mechanism for coordinating the life cycle of an insect with the dynamics of temperature and food conditions in the year. Diapause in the codling moth is facultative, although a certain proportion of larvae that display no photoperiod response is genetically univoltine (Riedl, 1983(). The codling moth overwinters as a diapausing larva in a cocoon under the bark or in the ground at the base of the tree. The diapausing state may continue for a very long time in the codling moth, sometimes as much as two years (Shel'Deshova, 1967). Dickson (1949) first showed that the decreasing photoperiods induced diapause in the larvae of codling moth. Some factors such as photoperiod, temperature, food quality, and others are known to play an important role in diapause. The induction of Dickson (1949) reported that the late instar larva was the photosensitive stage for the induction of diapause (Shel'Deshova, 1965). Jermy (1967) suggested that the early instars were the sensitive stage, but Saringer (1977; cited by Riedl, 1983) suggested that diapause could be induced by short periods throughout larval development although the earlier instars were more photosensitive. Temperature below 15°C during the summer months induced diapause in codling moth larvae. Jermy (1967) found that the photoperiod reaction of codling moth larvae from Hungary to diapause was practically temperature-independent.

Quality of apples could be a primary signal for diapause initiation (Gallick, 1948). Ciseros (1977; cited by Riedl, 1983) suggested that the relationships between photoperiod and maturity of apples were involved in diapause induction. Brown et al. (1979) noted that the number of larvae in the fruit was another factor that may contribute to diapause induction.

Shel'Deshova (1965) noted a gradual increase in obligatory diapause from south to the north. This increase in obligatory diapause in northern populations is advantageous to the species because the growing season is shorter and the food supply and weather tend to be more variable. Riedl and Croft (1978) observed that the population from throughout North America displayed a clinal-type variation with a latitudinal shift of 10° to the north corresponding to an increase of 1.25 hours in the critical photoperiod that induced diapause. Critical photophases for diapause induction for a site also are modified by prediapause temperatures.

In summary, the occurrence and maintenance of diapause is dependent upon both environmental and genetic factors. Environmental factors include temperature, photoperiod, food and population densities. The critical photoperiod for diapause induction varies among populations in different geographical areas. The codling moth has a facultative type of diapause but a gradual increase occurs in obligatory diapause from south to the north. This increase in obligatory diapause in the northern populations is advantageous to the species because the growing season is short and the food supply an weather tend to be more variable.