Technical Abstract: Post-diapause winterform pear psylla, Cacopsylla pyricola (Förster), exhibit a highly clumped distribution in late winter in pear orchards. The reasons for this behavior are unknown. Choice tests and assays with an olfactometer were done to test whether male psylla of the overwintering morphotype are attracted to pear shoots infested by post-diapause females and to shoots previously occupied by females. Paired choice tests showed that males accumulated on pear shoots occupied by females or previously occupied by females if those shoots were paired with uninfested shoots or shoots previously occupied by males. Cues associated with infestation or previous infestation that attracted the males are not known. Assays with an olfactometer showed that males were attracted to volatile odors from female-infested or previously infested shoots. The source of the attractants (i.e., the infested shoot, female psylla, eggs of the female psylla, or a combination of these sources) remains to be determined. Our results appear to be only the second published account at least consistent with the hypothesis that a species of Psyllidae emits a sex attractant.