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

The physiological development time was determined for the immature stages o f summer form codling moth, Cydia pomonella (L.), when reared at both const ant and field-simulated temperatures. The phenological data thus obtained w as used to examine the zero temperature threshold to model codling moth dev elopment. Two procedures were used to determine the base or zero developmen t temperature for codling moth. They were the x-intercept, i.e., an extrapo lation of the best-fit linear approximation of the reciprocal of time for d evelopment (days or hours) at each of a series of constant temperatures; an d 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 d evelopment time became increasingly curvilinear as the base temperature dev iated from the correct value. Errors in base temperature, particularly at l ower temperatures, introduce large errors into phenology models, reducing t heir reliability when used to time pest management procedures. Thermal unit s may be used to directly determine the base temperature or to validate the precision of the x-intercept. When reared at constant temperature, mean de velopment time was 2,100, 6,100, and 5,800 degree-hours, but when reared un der held-simulated (variable) temperatures the mean development time was re duced by 0, 500, and 1,100 degree-hours for eggs, larvae, and pupae, respec tively. Development was retarded at 35 degrees C when reared at constant te mperature, 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 a n upper temperature threshold using field-simulated temperatures. Modeling codling moth development in the field using field-simulated temperature dat a more accurately represents true development time. Fifteen percent of the larvae reared under long-daylength at 14.8 degrees C entered diapause; wher eas, there was no diapause at higher temperatures. Diapause induction at lo w temperature under long-daylength has not been previously reported.