The adult behavior and sex pheromone titers of Isoceras sibirica Alpheraky (Lepidoptera, Cossidae) were investigated to determine the diel periodicity of pheromone production during one scotophase and the effect of age on pheromone production. The results showed that females began to call on the first night after eclosion and called mainly during the second half of scotophase. The percentage of females calling was highest in 1‐ to 3‐day‐old females and lowest in 4‐ to 5‐day‐old females. The onset of scotophase calling occurred earlier as females aged. The responses to the pheromone source of males aged 1–5 days were monitored in a wind tunnel. Peak activity was observed in 3‐day‐old males, 4 h after the onset of the scotophase. The mating of all 1‐ to 3‐day‐old moths began after 6 h in scotophase and some 4‐ to 5‐day‐old moths began during the fourth hour. The average duration of copulation was 34.2 ± 18.2 min (N = 45) and ranged from 17.0 to 56.3 min. Gas chromatography–mass spectrometry (GC–MS) analysis of hexane extracts of pheromone glands revealed that the titers of the three sex pheromone components, (Z)‐9‐tetradecenyl acetate (Z9–14:Ac), (Z)‐7‐tetradecenyl acetate, and (Z)‐9‐hexadecadecenyl acetate were very low on the first night after eclosion, increased and peaked on the second night, then decreased with age. During the first 4 h of the scotophase, titers remained invariant, whereas from 4 to 6 h, pheromone titers increased sharply and peaked, with the greatest peak observed in the primary component, Z9–14:Ac. After the peak, all recorded titers declined until they reached a minimum between the ninth and tenth hours of the dark cycle. In field tests, most of the males were captured in traps during 00:00–02:00 h (13 ± 0.48), and females aged 2 days attracted more males than females of other ages. We infer that the I. sibirica mating system is organized around circadian control of mate calling and mating.