A test was conducted for 22 Aug. to 4 Sept., 1969, at Borrego Springs, Calif., to determine if pink bollworm males reared in the laboratory (Mangum et al. 1969) with no attempt to duplicate natural photoperiod would show the same pattern of response toward sex pheromones as the native moths. Nineteen modified Frick traps were distributed through a 5-acre plot of cotton where irradiated (25 krad) laboratory-reared pink bollworms were being released each day. These moths were reared on diet containing Calco Oil Red dye to mark them (Graham and Mangum 1971) and irradiated as adults at Brownsville, Tex., and shipped via air mail to Indio, Calif. The traps were baited each week with 10 mg of the synthetic sex attractant hexalure (Keller et al. 1969) on a filter-paper dispenser. On 6 nights during the trapping period, collections of the released and native males were recorded each hour from sunset to sunrise. Wind direction and velocity at plant height and temperatures beneath the canopy also were recorded.