Scientific Note An improved synthetic attractant for the mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae: Scolytinae), in northeastern California

The mountain pine beetle, Dendroctonus ponderosae Hopkins 1902, is found in pine forests throughout the western U.S., north to northern British Columbia and Alberta, Canada and south to Mexico. It causes high levels of pine mortality throughout its range. Hosts include many species of Pinus (Pinaceae); in northern California, D. ponderosae is a pest of pine types dominated by P. ponderosa Douglas ex Lawson et C.Lawson, P. contorta Douglas ex Loudon, P. monticola Douglas ex D. Don, and in mixed conifer types where P. lambertiana Douglas is the principal host (Struble 1945). The extensive geographic range of D. ponderosae, and the variability in environments in which it occurs, create challenges for developing effective semiochemical tools for reducing beetle-caused tree mortality. Nonrandom genetic variation occurs among populations of D. ponderosae and has been attributed to both geography and host differences Variation has also been observed in D. ponderosae responses to host-produced pheromone synergists (Pitman & Vité 1969, Billings et al. 1976, Libbey et al. 1985, Miller & Lindgren 2000), leading to uncertainties in semiochemical deployment among locations and forest types. Semiochemical attractants (lures) can be used efficiently only when their effectiveness in different locations and host types is understood. For more than 20 years the standard lure for D. ponderosae has consisted of three components: two pheromones, trans-verbenol and exo-brevicomin, and myrcene, a host-based monoterpene synergist (Borden & Lacey 1985). This lure has generally caught greater numbers of D. ponderosae than other combinations of host compounds; however, most comparisons have been limited to British Columbia (e.g., Borden et al. 1987, Pureswaran & Borden 2005). In western U.S., uncertainty remains about the relative effect of individual monoterpenes for synergizing aggregation pheromones of D. ponderosae. This is especially true for terpinolene, which is commonly found as a minor component of oleoresin in hosts of D. ponderosae (e.g., Smith 2000), and has been found to catch similar numbers of beetles to myrcene in some forest types (Billings et al. 1976). Terpinolene appears to be less ubiquitous in western pines than myrcene, but in California is frequently present in the oleoresins of both P. ponderosa and P. lambertiana among others (Smith 2000, S. L. Smith et al. unpublished data). Because the effectiveness of terpinolene as a pheromone synergist for D. ponderosae has varied (Billings et al. 1976, Conn et al. 1983), its utility for particular applications (geographic regions and forest types) must be evaluated before …