Sex attractant blends were developed for monitoring three conifer-feeding species of Eucosma Hübner found in pine seed orchards and plantations in Wisconsin and Ontario. Eucosma monitorana Heinrich, which attacks developing cones of red pine, Pinus resinosa Aiton (Pinaceae), preferred lures containing 100:5:15 (μg blend) of (Z)-9-dodecenyl acetate (Z9-12:Ac), (E)-9-dodecenyl acetate (E9-12:Ac), and (Z)-9-dodecen-1-ol (Z9-12:OH), respectively, over lures without the alcohol or with higher levels of E9-12:Ac. This blend was unattractive to sympatric Eucosma gloriola Heinrich, a species that feeds inside shoots of red pine and eastern white pine, Pinus strobus L. Eucosma gloriola was attracted to a 100:30 blend of Z9-/E9-12:Ac, and adding Z9-12:OH had no significant effect. Eucosma tocullionana Heinrich, which attacks cones of eastern white pine, was attracted equally to 10:3 and 10:5 μg blends of Z9-/E9-12:Ac, and adding Z9-12:OH had no effect. A ratio as low as 1:0.3 was attractive to E. tocullionana but not to sympatric E. gloriola, which preferred a 100-fold higher dosage of the same blend. The seasonal flight periods of the three species overlapped in all study areas. The flight of E. gloriola usually peaked in late May slightly before that of E. monitorana while the flight of E. tocullionana peaked about 1–3 weeks later. The results indicate that sex pheromones, seasonal flight periods, and host preferences are isolating mechanisms for these closely related sympatric species.