Concentrations of the sex pheromone (Z,E)-9,12-tetradecadien-1-ol acetate present in superficial rinses of the sex pheromone gland of virgin female Plodia interpunctella (Hübner) at different times during a 14L:10D photoperiod fluctuated at least 10-fold. Maximum quantitites of pheromone, 1–2 ng/female, were obtained during the scotophase when ca. 90% of the females were calling. During the latter 1/2 of the photophase when calling was ca. 60%, less than 0.1 ng/female of the compound was detected. The corresponding alcohol, (Z,E)-9,12-tetradecadien-1-ol, showed a similar diel periodicity. Concurrent analyses of the pheromone levels in unmated females of Ephestia (= Cadra) cautella Walker revealed little Z,E)-9,12-tetradecadien-1-ol acetate and (Z)-9-tetradecen-1-ol acetate] at different times during the photoperiod. Ca. 46 and 30% of these females called during the scotophase and photophase, respectively.