Synergistic Blends of Monoterpenes for Aggregation Pheromones of the Mountain Pine Beetle (Coleoptera: Curculionidae)

Abstract

The superiority of the host monoterpene myrcene as a synergist for trans-verbenol and exo-brevicomin, aggregation pheromone components of the mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae), suggests that the ancestral host of the mountain pine beetle is a pine rich in myrcene. A field trapping experiment in British Columbia testing reconstituted bole oleoresin of whitebark pine, Pinus albicaulis Engelmann, composed of mainly myrcene (20.7%), terpinolene (6.8%), and 3-carene (61.9%) showed it to be a better pheromone synergist than reconstituted bole oleoresin of lodgepole pine, Pinus contorta variety latifolia Engelmann, which contained only 2.7, 1.0, and 6.0%, respectively, of the above-mentioned three compounds. In the same experiment myrcene alone was the best synergist. In subsequent experiments, testing myrcene, terpinolene and 3-carene alone and in all possible binary and ternary combinations, a 50:50 blend of myrcene and terpinolene released at the same rate as either compound alone generally resulted in trap catches approximately 3 times higher than with myrcene as a synergist. This result held as long as the terpinolene was free of contaminants, and the traps were in the open, well away from potential interference of semiochemicals emitted by newly attacked trees. 3-Carene seemed to be inert or slightly inhibitory. No single monoterpene tested alone or in binary or ternary combination in the absence of pheromones was attractive. There was no effect of doubling or tripling the release rate of myrcene or terpinolene. In five of nine experiments, adding terpinolene to myrcene caused a significant increase in the percentage of female mountain pine beetles captured. Among host pines, the presence of highly synergistic monoterpenes at various levels in combination with other monoterpenes that are apparently either inert or inhibitory could account for different degrees of pheromone synergism, and thus host preference. The highly synergistic effect of combining myrcene plus terpinolene with the mountain pine beetle aggregation pheromone components opens up the potential for suppression of populations through semiochemical-based mass trapping.

Effect of Water Stress and Fungal Inoculation on Monoterpene Emission from an Historical and a New Pine Host of the Mountain Pine Beetle

“…All volatile monoterpenes emitted by lodgepole and jack pine seedlings in the study can be detected by the MPB (Huber et al, 2000;Pureswaran et al, 2004b). Some of these host monoterpenes synergize MPB response to the aggregation pheromones trans-verbenol and exo-brevicomin in trapping studies (Borden et al, 2008). There is strong evidence that myrcene, 3-carene, terpinolene, and α-pinene synergize MPB aggregation pheromone response (Borden et al, 2008).…”

“…Some of these host monoterpenes synergize MPB response to the aggregation pheromones trans-verbenol and exo-brevicomin in trapping studies (Borden et al, 2008). There is strong evidence that myrcene, 3-carene, terpinolene, and α-pinene synergize MPB aggregation pheromone response (Borden et al, 2008). In olfactometer tests, 3-carene was most attractive to MPB out of 20 tested compounds (Conn, 1981).…”

“…MPB is able to distinguish between host and non-host volatiles, and may also use host volatiles to identify weak hosts and avoid the risks associated with trying to overcome tree defenses of a healthy host (Keeling and Bohlmann, 2006). Jack pine emits about three times more 3-carene than lodgepole pine, suggesting that it may be more prone to MPB attacks (Conn, 1981;Borden et al, 2008). Further, jack pine bark contains higher concentrations of α-pinene than lodgepole pine, and α-pinene can be a synergist for the MPB aggregation pheromone, and it is also a precursor for production of transverbenol, the primary component of MPB aggregation pheromone (Borden et al, 2008).…”

“…Jack pine emits about three times more 3-carene than lodgepole pine, suggesting that it may be more prone to MPB attacks (Conn, 1981;Borden et al, 2008). Further, jack pine bark contains higher concentrations of α-pinene than lodgepole pine, and α-pinene can be a synergist for the MPB aggregation pheromone, and it is also a precursor for production of transverbenol, the primary component of MPB aggregation pheromone (Borden et al, 2008). This study enabled us to compare VOC emission and monoterpene content between lodgepole and jack pine exposed to water stress and different biological treatments under controlled and easy to manipulate conditions.…”

The influence of Canadian research on semiochemical-based management of forest insect pests in Canada

“…Additional information about the population can be garnered from closer examination of the trapped insects, such as sex ratio (Borden et al 2008), mating status (Bergh et al 1988), size and disease status (Sweeney and McLean 1987;Jones and Evenden 2008). These factors can be useful in determining the population phase of forest insects that undergo cyclical changes in population density.…”