Physiological development time and zero development temperature of the codling moth (Lepidoptera: Tortricidae)

The physiological development time was determined for the immature stages of summer form codling moth, Cydia pomonella (L.), when reared at both constant and field-simulated temperatures. The phenological data thus obtained was used to examine the zero temperature threshold to model codling moth development. Two procedures were used to determine the base or zero development temperature for codling moth. They were the x-intercept, i.e., an extrapolation of the best-fit linear approximation of the reciprocal of time for development (days or hours) at each of a series of constant temperatures; and second using thermal units, i.e., physiological development time (degree-hours). The thermal unit was a constant at any logical rearing temperature when using the correct base (zero development) temperature. Physiological development time became increasingly curvilinear as the base temperature deviated from the correct value. Errors in base temperature, particularly at lower temperatures, introduce large errors into phenology models, reducing their reliability when used to time pest management procedures. Thermal units may be used to directly determine the base temperature or to validate the precision of the x-intercept. When reared at constant temperature, mean development time was 2,100, 6,100, and 5,800 degree-hours, but when reared under held-simulated (variable) temperatures the mean development time was reduced by 0, 500, and 1,100 degree-hours for eggs, larvae, and pupae, respectively. Development was retarded at 35 degrees C when reared at constant temperature, but not when reared at field-simulated temperatures that were as high as 35 degrees C for a few hours each day. There was no evidence for an upper temperature threshold using field-simulated temperatures. Modeling codling moth development in the field using field-simulated temperature data more accurately represents true development time. Fifteen percent of the larvae reared under long-daylength at 14.8 degrees C entered diapause; whereas, there was no diapause at higher temperatures. Diapause induction at low temperature under long-daylength has not been previously reported.