The ambrosia beetle, Xyleborinus saxesenii Ratzeburg, infests physiologically stressed apple and peach trees in Korea. Dispersing females utilize the degradation product ethanol and host-related volatiles to locate and colonize new host trees. We examined the extent to which 12 chemicals emitted from fruit trees act synergistically with ethanol to attract X. saxesenii. The addition of benzaldehyde to ethanol significantly increased beetle attraction, although benzaldehyde was not attractive by itself. The addition of α-pinene, ethyl butyrate, ethyl isovalerate, limonene, 3-methyl-1-butanol, ethyl tiglate, aromadendrene, vanillin, 2-butanol, styrene, or ethyl 3,3-dimethylacrylate to ethanol had no effect on beetle attraction. In a dose-response test, the addition of 5–50% benzaldehyde doses synergistically increased the number of beetle captures; however, trap catches did not increase as the benzaldehyde dosage increased. The synergistic influence of benzaldehyde on beetle response to ethanol was lower in early spring than in late summer to early fall, probably because synthetic benzaldehyde emissions from field lures were overwhelmed by background levels of natural benzaldehyde emitted from peach twigs in the flowering stage.