In the laboratory, diapause in adult Psylla pyricola Förster was induced by rearing nymphs with exposures to daily photoperiods of 13.5 h or less. The critical photoperiod that induced diapause was not influenced by temperature. Diapause was terminated in laboratory-reared adults and winter form adults collected from orchards in mid-October by exposure to photoperiods greater than 13.5 h. With adults collected from orchards during November, December, and January, diapause was terminated in the laboratory under both short and long photoperiods. With the earlier collections, long photoperiods markedly reduced preoviposition periods but with later collections the effect was not as pronounced because the preoviposition period under short photoperiods decreased markedly with the later collection dates. These results are discussed with relation to observations under natural orchard conditions.