FemalePlodia interpunctella(Hübner) reared and observed in a 12:12 h light: dark (L:D) regime exhibited a calling rhythm with a maximum calling beginning ca. 2 h after the initiation of scotophase and continuing until the initiation of photophase. When held in a constant light (L:L) regime, L:D-reared females lost their calling rhythm within 2 days. When reared and held in a L:L regime, females called continuously. With L:L females held in a L:D regime, a rhythm similar to that of L:D females held in L:D was entrained within 2 days.