Seasonal change of cold hardiness in the codling moth, Cydia pomonella (Lepidoptera: Tortricidae).

To elucidate the relationship between diapause and cold hardiness, seasonal variations of supercooling point and low temperature survival of overwintering and non-diapausing larvae of codling moth were studied in two regions of Iran, Damavand and Karaj. In both regions supercooling point decreased gradually over the autumn. Supercooling point of field collected larvae in Damavand reduced from a mean value of -16.9 degrees C in early September to -19.9 degrees C in mid-October 2004. At the same time, supercooling point of overwintering larvae decreased from -19 to -21 degrees C in Karaj. Supercooling point decreased gradually until midwinter (January) in both regions and afterward increased gradually over the spring. Mean supercooling point for non-diapausing larvae was -13.4 degrees C, which was significantly higher than that of overwintering larvae. A high coincidence was observed between decrease of supercooling point and increase of low temperature survival rate in the overwintering larvae. Survival rate at -20 degrees C/24 h was lower than 20% in early autumn; that increased to upper than 50% during winter. Codling moth was shown to be a freeze susceptible and at the same time, a chill tolerant insect.