Continuous observations and measurements were made of adult flight, mating, and oviposition ofOrgyia pseudotsugataMcDunnough over a 31-h period in eastern Oregon. Male flight started at 1000 (P.S.T.), gradually increased to a peak period ca. 1700, and concluded at 1930. This coincided with peak mating activity with the wingless females. Oviposition occurred immediately after mating. Virgin females attached to sticky traps were very effective for attracting and capturing male moths. The female sex pheromone offers a possible technique for early detection of Douglas-fir tussock moth populations.