Studies on codling moths (Carpocapsa pomonella (L.)) caged in the greenhouse showed that the moths are capable of mating in the first 12 hours after emergence. Mating was found to occur equally Well under conditions of complete darkness as in periods of alternating dark and light. with and without twilight. By the use of varied sex ratios in the mating and oviposition tests it appears that a reduction in the ability of females to attract males occurs after the females have been mated. The occurrence of multiple matings was determined by dissecting the field-captured moths each week and counting the number of spermatophores present in the females. The incidence of multiple-mated females increased in the field as the season progressed. In laboratory tests, the preoviposition period was approximately 1 day. The peak of oviposition occurred by the fourth day and the females were reproductively old after the sixth day. Dissection of field-captured codling moths from black-light traps revealed that more than 90% of the females attracted to the black light were ready to oviposit or were reproductively young. This suggests that blacklight traps are more efficient than bait pans for the timing of codling moth sprays. The sex ratio of the codling moths captured in the black-light traps was very nearly the same as the sex ratio found in the laboratory thus indicating that the codling moths attracted to the black light lire representative of the sex ratio which actually occurs in the field.