A multifactorial experiment was conducted to determine the relative influence of photoperiod, temperature, water content of the diet, and parental age on the induction of diapause in an Arizona strain ofPectinophora gossypiella(Saunders) reared on a wheat germ-casein diet. The highest level of diapause (100%) occurred when the following conditions were combined: (1) 11-h daily photoperiod; (2) 19°C; (3) low water content of the larval diet; and (4) larval progeny were derived from eggs laid by young (3-day-old) females. If larval progeny were derived from older (10-day-old) parents or the larvae were reared on diet containing a higher water content, there was a significant reduction in the incidence of diapause. Photoperiod and temperature were the predominant factors in the induction of diapause, but dryness of the larval diet and parental age significantly influenced the overall level of response.