Interaction of temperature and photoperiod in control of reproductive diapause in the carrot weevil (Coleoptera: Curculionidae)

Laboratory-reared carrot weevil, Listronotus oregonensis (LeConte), adults were exposed to various temperature-photoperiod regimens (TPRs) to determine their effects on reproductive activity. The occurrence of reproductive diapause in females was regulated by interaction of photoperiod and temperature. Adults not sexually mature when placed at test regimens did not oviposit at certain TPRs, whereas reproductive diapause was induced in sexually mature females after periods of exposure to similar TPRs. Threshold photophases for oviposition were between 16 and 18 h at 16 degrees C, between 14 and 16 h at 20 degrees C, about 14.5 h at 24-25 degrees C, and between 10 and 12 h at 28-30 degrees C. Oviposition also occurred at short photophases (0 to 8 h), again modulated by temperature. Oviposition in the laboratory by field-collected adults that had overwintered was not influenced by photoperiod. Sexually mature adults mated at a TPR unfavorable to oviposition