The factors affecting trap capture of adult Aphelinus mali (Haldeman) (Hymenoptera: Aphelinidae) were studied in 2010–2011 in eastern Washington apple (Malus spp.) orchards infested with its host woolly apple aphid, Eriosoma lanigerum (Hausmann) (Hemiptera: Aphididae). The initial study of white sticky cards indicated that traps stapled to the trunk in a vertical orientation had the highest capture. A factorial experiment of three colors (clear, white, and yellow) by three orientations (trunk, scaffold, and hanging) indicated that yellow traps and traps on trunks caught higher numbers of A. mali. For this reason, the recommended trap for this natural enemy is a yellow trap stapled to the trunk. Having a readily available and effective sampling method for this species may be helpful in implementing biological control programs and assessing the impact of different spray regimes.