Leptoglossus occidentalis Heidemann is a serious pest of second-year cones in conifer seed orchards. We investigated the impact of this insect on first-year pine conelets. L. occidentalis adults and nymphs were caged on conelets of lodgepole pine, Pinus contorta var. latifolia Engelmann, and western white pine, Pinus monticola Dougl. ex D. Don. Abortion in lodgepole pine conelets was negligible, but feeding by nymphs reduced seed production by 75% compared with unexposed controls. Mortality of nymphs on lodgepole pine conelets was almost 100%, suggesting that conelets of this species are not a suitable food source for L. occidentalis. When nymphs had access to second-year cones, seed set in conelets was unaffected, and survival of nymphs greatly improved. Seventy-five percent of western white pine conelets exposed to L. occidentalis nymphs aborted, compared with none in unexposed controls. Seed set in surviving cones was reduced by 47%. Conelet abortion fell to 10% when nymphs were provided with an alternative food source. In pine seed orchards, damage to conelets probably is caused primarily by nymphs remaining on trees after second-year cones have been harvested.