Field-based, degree-day model for pink bollworm (Lepidoptera: Gelechiidae) development

Lower and upper developmental temperature thresholds of 13.9 and 32.8 degrees C were determined for the pink bollworm, Pectinophora gossypiella (Saunders), using 21 occurrences documenting overwintering larvae to adult moth development in the field. The events were induced by irrigation of pink bollworm infested cotton bells held in emergence cages in experiments conducted from 1987 through 1991 in the Pale Verde Valley, CA. The whole day, sine wave method with a horizontal upper cutoff was found to be the best of several methods for calculating daily degree-days. Dates of beginning and peak spring moth emergence from overwintering diapaused larvae were determined from plots of male moth captures in 48 pheromone-baited survey traps situated along roadsides throughout the cotton producing area. Using the same method, degree-days from 1 February (determined to be the best starting date for heat accumulation) to the peak of spring moth emergence were calculated to be 510 DD (centigrade). Two weeks before peak infested cotton flowers was used as the date for initial in-field infestation. Numbers of male pink bollworm moths captured in held-situated pheromone traps were used to establish subsequent peak activity points for the Ist and 2nd generations. Using 12 of these generation events and the 13.9/32.8 degrees C thresholds, horizontal cutoff, and whole day sine wave method, the degree-days for 1 generation, adult to adult, were determined to be 492 DD. These field-derived thresholds corresponded well with thresholds obtained by some researchers using constant temperature laboratory trials.