The Mediterranean pine engraver, Orthotomicus (Ips) erosus (Wollaston) (Coleoptera: Scolytidae), was first detected in May 2004 in North America in baited flight traps in five counties of California (Kern, Tulare, Fresno, Madera, and Merced). Orthotomicus erosus is a pest of pines in the Mediterranean region, South Africa, and Chile. The adults infest recently fallen trees, standing trees under stress, logging debris, and broken branches with rough bark. They may also vector pathogenic fungi; the beetle has widely affected pines with bluestain fungus in South Africa. In California, O. erosus has been found to colonize and develop in Monterey, aleppo and Italian stone pine. Other frequently planted pines in the U.S. (Afghan, Canary Island, Coulter, Turkish, eastern white, scots, shortleaf, and slash pine) may potentially be affected as they are recorded hosts in other countries. To optimize early detection of this new invasive throughout the U.S., we began developing an attractive semiochemical bait based on preliminary studies abroad. In a series of experiments, we tested the attractiveness of 2-methyl-3-buten-2-ol, ipsdienol, and a-pinene in various combinations, release rates, and enantiomeric compositions. In late February 2005 when adult flight began, funnel traps were baited with each treatment and replicated in four sites. In the first experiment, treatments included: 1) unbaited control, 2) 2-methyl-3-buten-2-ol, 3) racemic ipsdienol, 4) a-pinene, 5) 2-methyl-3-buten-2-ol and racemic ipsdienol, and 6) 2-methyl-3-buten-2-ol, racemic ipsdienol, and a-pinene. Adult beetles responded synergistically to 2-methyl-3-buten-2-ol and racemic ipsdienol; a-pinene slightly enhanced the response to the two-component attractant.