The Douglas-fir beetle (Dendroctonus pseudotsugae Hopkins) (Coleoptera: Curculionidae) antiaggregation pheromone, 3-methylcyclohex-2-en-1-one (MCH), has been used since 2000 to protect high-value trees and stands throughout western North America. Operational treatments involve placing individual releasers on a 12 m × 12 m grid throughout the area to be protected. In this study, six widely spaced trap lines were established with aggregation attractant–baited traps located 1, 3, 9, 27, and 81 m from a location where an operational MCH release device was alternately either present or absent, and changes in catches caused by the MCH device were assessed at all distances. Trap catches were suppressed by about 70% at one and three metres, by 50% at nine metres, by 30% at 27 m, and not at all at 81 m. Inhibition by the MCH device varied with distance (m) from the source according to the function 0.79 − 0.092x0.51 (R2 = 0.986). Decline of attractant inhibition with distance from the MCH device was much less steep than would have been expected if catch inhibition had varied directly with the average airborne concentration of MCH.

This paper reviews the literature on the identification of 3-methylcyclohex-2-en-1-one (MCH) as the antiaggregation pheromone of the Douglas-fir beetle (Dendroctonus pseudotsugae Hopkins) (Coleoptera: Curculionidae) and the development of successful management applications using the pheromone. Previously unpublished data from two studies on novel uses of MCH are included. The successful development of antiaggregation pheromone-based treatments for the Douglas-fir beetle is discussed in relation to efforts to develop similar treatments for other bark beetle species, and opportunities for future research on MCH and the Douglas-fir beetle are suggested.

Western hemlock, Tsuga heterophylla (Rafinesque) Sargent (Pinaceae), trees growing in a clonal, commercial seed orchard on Whidbey Island, Washington, United States of America were assessed for Adelges tsugae (Annand) (Hemiptera: Adelgidae) infestation levels to determine whether there was any evidence of resistance to this herbivore. Join-count statistics revealed that A. tsugae infested trees were not clumped, but instead were randomly distributed throughout the seed orchard. Chi-square analyses suggested that there is a genetic basis for different levels of A. tsugae infestation among the genets represented in the orchard. However, since none of the genets were completely free of A. tsugae infestation, differences among genets seem to be related more to susceptibility or tolerance than complete resistance. Among the 17 genets that had five or more ramets in the seed orchard, only one had more than one ramet free of A. tsugae. That genet had four of five ramets that were free of A. tsugae. However, it is not possible to say whether that was due to chance or inherent tree characteristics that make it less susceptible to A. tsugae infestation.

The hemlock woolly adelgid (Hemiptera: Adelgidae: Adelges tsugae Annand) is an invasive insect, introduced from Japan to eastern North America, where it causes decline and death of hemlock trees. There is a closely related lineage of A. tsugae native to western North America. To inform classical biological control of A. tsugae in the eastern USA, the density and phenology of three native western adelgid specialist predators, Leucopis argenticollis (Zetterstedt), Le. piniperda (Malloch) (Diptera: Chamaemyiidae), and Laricobius nigrinus Fender (Coleoptera: Derodontidae), were quantified in the Pacific Northwest. Infested branches were collected from western hemlock (Pinaceae: Tsuga heterophylla (Raf.) Sarg.) at four sites around the Puget Sound, Washington and three sites in Oregon. Immature Leucopis were identified to species using DNA barcodes. Leucopis argenticollis was roughly twice as abundant as Le. piniperda. Laricobius nigrinus larvae were more abundant than the two species of Leucopis during the egg stage of the first adelgid generation, but Leucopis were present as feeding larvae during the second adelgid generation when La. nigrinus was aestivating in the soil, resulting in Leucopis being more abundant than La. nigrinus across the entire sampling period. Adelges tsugae and La. nigrinus densities were not correlated, while A. tsugae and Leucopis spp. densities were positively correlated. Leucopis spp. and La. nigrinus densities were negatively correlated. These results support the complementary use of La. nigrinus and the two Leucopis species for biological control of A. tsugae in the eastern USA, and point to the need for further investigation of spatial and temporal niche partitioning among the three predator species.

The female-produced sex pheromone blend of the pandora moth, Coloradia pandora pandora Blake, a pest responsible for periodic defoliation of pine forests in the western United States, has been identified. The pheromone consisted of a mixture of E10,Z12-hexadecadienal, E10,Z12-hexadecadienyl acetate, and E10,E12-hexadecadienyl acetate. All three components were essential for optimal attraction. E10,Z12-Hexadecadienol, tentatively identified in trace amounts in pheromone gland extracts, elicited strong responses from male antennae in coupled gas chromatography – electroantennogram analyses but had no apparent effect as a pheromone component at physiologically relevant levels. Hexadecanal, octadecanal, and hexadecyl acetate also were identified in extracts of female pheromone glands but elicited no responses from male antennae, nor did they appear to be components of the attractant blend. In field trials, each trap baited with the optimized three-component blend of E10,Z12-hexadecadienal, E10,Z12-hexadecadienyl acetate, and E10,E12-hexadecadienyl acetate captured an average of more than 40 male moths per night.

Two mark–recapture experiments and a trap interference experiment were conducted to determine the sampling range and range of attraction, respectively, of Dendroctonus pseudotsugae Hopkins (Coleoptera: Scolytidae) pheromone-baited traps in northern Idaho. To determine the sampling range, either live beetles or logs containing brood were marked with one of four colors of fluorescent powder. Colored beetles or logs were placed along transects oriented away from a central pheromone-baited trap at distances of 50, 100, 200, and 300 m. A release distance of 400 m was added to one mark–recapture experiment during the 2nd year. To determine the range of attraction, a trap interference study was conducted. For this experiment, groups of three traps were oriented in equilateral triangles with distances of 50, 100, 200, and 300 m between the three traps. Distances between traps were changed daily to allow for adequate replication. Mark–recapture studies indicated that most D. pseudotsugae were recaptured from distances less than or equal to 200 m from the pheromone-baited trap. On average, 95% of beetles recaptured were males. Results of the trap interference experiment provided no insight into the range of attraction of D. pseudotsugae pheromones. Natural resource managers should attempt to place pheromone-baited suppression traps within 200 m of target D. pseudotsugae populations. Also, to minimize undesirable beetle-caused tree mortality, traps should be placed as far as possible from live trees that managers wish to protect.

The Douglas-fir beetle (Dendroctonus pseudotsugae) antiaggregation pheromone, 3-methylcyclohex-2-en-1-one (MCH), was applied to stands at high risk for infestation. The MCH was applied in a bubble capsule formulation to plots ranging from 2.1 to 2.6 ha in size at rates of 45–76 g/ha. Catches of Douglas-fir beetles in attractant-baited Lindgren funnel traps located at the plot centers were significantly lower on MCH-treated plots compared with untreated plots. In contrast, catches of the most abundant predator, Thanasimus undatulus (Say), were unaffected by the MCH treatment. The percentage of Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] trees ≥20 cm dbh that were mass attacked was significantly lower on treated plots (0.2%) compared with untreated plots (8.5%). MCH alone was effective in reducing the probability of Douglas-fir beetle infestations occurring in high risk stands.