Field observations were made on the timing of sexual activity of the navel orangeworm,Amyelois transitella(Walker), for 18 nights, from early April through October, 1979 and 1980. Throughout most of the summer, female calling and male attraction to calling females occurred from 1 to 3 h before sunrise but shifted to earlier, warmer hours on cool spring and autumn nights. A linear relationship existed between temperature and time of onset of female calling when measured from sunrise. Male activity was limited to temperatures>11°C and may have been inhibited by the increasing light intensity of approaching sunrise.