Mating activity of pear psylla,Cacopsylla pyricola(Foerster), with emphasis on the morphologically distinctive overwintering winterform generation, was characterized in the laboratory. Generally, one spermatophore was passed per copulation. Presence of light, size of the mating arena, and the number of leaves in the arena affected mating frequency; the highest mean frequency observed was 9.18 matings per 24 h. Diapausing psylla males, after being conditioned under long photoperiod (16:8 [L:D]), mated significantly more often than those conditioned under a photoperiod of 12:12 or 10:14 (L:D). The photoperiodic experience of the female did not affect mating frequency. Visual observation of behavior revealed that the winterform males conditioned under short days made as many sexual advances as winterform males conditioned under long days, but diapause males were rejected by the females. Pairings of winterform females with summerform males had significantly fewer inseminations compared with pairings involving the same seasonal forms; there is a behavioral barrier to mating between the generations.