Hylastes opacus Erichson is a recently introduced bark beetle in North America (Bright and Skidmore 1997; Hoebeke 1994; Rabaglia and Cavey 1994; Wood 1992). It is widely distributed in the Palearctic region, where it usually breeds in stumps and roots of dead or dying pines (Pinus) and occasionally other conifers (Hoebeke 1994). Like many species of bark beetles, H. opacus uses host volatiles as cues to search for suitable host material for feeding and establishment of broods. Hoebeke (1994) reported the attraction of H. opacus to ethanol-baited logs of Scots pine (Pinus sylvestris L.) and red pine (Pinus resinosa Ait.) in New York, United States of America. In Sweden, Schroeder and Lindelöw (1989) observed H. opacus responding to (−)-α-pinene and to ethanol released separately, but a synergistic increase in response did not occur when these two compounds were released together. In later experiments, Lindelöw et al. (1993) found that traps baited with ethanol alone, ethanol + (−)-α-pinene, and spruce turpentine caught significantly more H. opacus than unbaited traps. In these experiments, (−)-α-pinene alone was not attractive, and when (−)-α-pinene was combined with spruce turpentine and ethanol, it reduced catches of H. opacus. In 2002, while investigating attractants for the pine shoot beetle, Tomicus piniperda (L.) (TM Poland, P de Groot, S Burke, D Wakarchuk, RA Haack, and RW Nott, unpublished data), we unexpectedly found significant numbers of H. opacus in one of our experiments. Here we report that H. opacus is strongly attracted to nonanal.