Bionomics of Codling Moth
Diapause Termination
Chilling and photoperiod, or a combination of both, play a role in diapause
termination (Petterson and Hamner, 1968). Although some population do not
always require chilling for diapause termination as in the case of Michigan
population (Garcia-Salazar, 1984). Townsend (1925) was able to terminate
diapause by exposing larvae to 10°C. In short day conditions, diapause
termination can happen only under the influence of low temperature between
0° and 10°C (Shel'Deshova, 1967). Petterson and Hamner (1969) observed
that twenty days chilling at 4.5°C cause diapausing larvae to pupate
even under a short day length of LD 8:16. A long photoperiod alone can
terminate diapause but only under exposure to high temperatures (Shel'Deshova,
1967). Cisneros (1971; cited by Riedl, 1983) reported that long photoperiod
and no chilling caused scattered adult emergence over a long period of
time. Short chilling prior to long photoperiod and high temperature enhanced
diapause termination and shortened the emergence period. A short photoperiod
regardless of temperatures maintains diapause of the codling moth (Russ,
1966). Phillips and Barnes (1975) suggested that the first larvae entering
diapause will also be the first to emerge in the following year.
The ecological features of the diapausing caterpillars play a large
role in the distribution of the codling moth. These larvae are different
from the active caterpillars because of high resistance to adverse conditions,
in particular to temperatures below 0°C.
To sum up, chilling and photoperiod or a combination of both play a
role in diapause termination. Although some population do not always require
chilling for diapause termination, and some larvae in a population that
are univoltine never show a photoperiodic response. Short chilling prior
to long photoperiod and high temperature enhanced diapause termination
and shortened the emergence period. A short photoperiod, regardless of
temperature, maintains the diapause of codling moth.
