Evaluation of two repellent semiochemicals for disruption of attack by the mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Scolytidae)

Journal of the Entomological Society of British Columbia, Dec 2004 by Borden, John H, Pureswaran, Deepa S, Poirier, Lisa M

ABSTRACT

When released from attractant-baited multiple-funnel traps, 3-methyl-2-cyclohexen-1-one (MCH) reduced catches of male and female mountain pine beetles, Dendroctonus ponderosae Hopkins, by 67.4% and 71.8%, respectively. 2-Phenyl ethanol reduced the respective catches by 96.6% and 95.1%, but only verbenone and all three compounds together reduced catches to levels no different from those in unbaited control traps. In another experiment, all three binary combinations of the above compounds, plus the ternary combination, reduced catches of both sexes by >96%. In comparable tree protection experiments near Princeton BC, MCH and 2-phenyl ethanol alone and together significantly reduced the percentages of pheromone-baited lodgepole pines that were attacked by 16.0%, 33.3% and 40.0%, respectively, but verbenone alone totally protected baited trees, and many trees within 5 m of them, from attack. In identical experiments near Prince George BC, where mountain pine beetle populations were much higher, adding MCH, 2-phenyl ethanol or both together to verbenone did not cause attack to be reduced significantly beyond that achieved by verbenone alone. Our results confirm that 2-phenyl ethanol is an antiaggregation pheromone for the mountain pine beetle, and that MCH is an interspecific synomone. However, because neither was as effective as verbenone in protecting pheromone-baited trees from attack, and adding either or both to verbenone did not improve protection, neither compound warrants further consideration as a potential tool for operational disruption of attack.

Key Words: Dendroctonus ponderosae, semiochemicals, pheromones, verbenone, 2-phenyl ethanol, 3-methyl-2-cyclohexen-1-one, attack disruption

INTRODUCTION

Although the antiaggregation pheromone verbenone has long been known to disrupt attack by the mountain pine beetle (MPB), Dendroctonus ponderosae Hopkins (Amman et al. 1989; Lindgren et al. 1989a), its efficacy has been inconsistent between years, target species of trees, and geographic areas (Bentz et al. 1989; Lister et al. 1990; Gibson et al. 1991; Shea et al. 1992). Part of the reason for variable efficacy may be that verbenone is transformed to the inactive compound chrysanthenone when exposed to ultraviolet radiation (Kostyk et al. 1993). Adding repellent nonhost volatiles from angiosperm tree bark to verbenone has been shown to increase the efficacy of protecting lodgepole pines, Pinus contorta var. latifolia Engelmann, from attack (Huber and Borden 2001), and combining a seven-component nonhost volatile blend with an increased release rate of verbenone has raised the efficacy even higher (Borden et al. 2003). However, at an effective 10 x 10 m spacing, the latter treatment would cost $1,250 per ha, excluding labor, limiting its potential use.

One means of reducing the cost would be to replace the repellent nonhost volatile blend with cheaper materials. Two such semiochemicals are the antiaggregation pheromone 2-phenyl ethanol (Pureswaran et al. 2000) and 3-methyl-2-cyclohexen-1-one (MCH). MCH is an antiaggregation pheromone of Douglas-fir and spruce beetles, Dendroctonus pseudotsugae Hopkins and D. rufipennis (Kirby), respectively (Rudinsky et al. 1972; Lindgren et al. 1989b) that was recently shown to be a repellent synomone for the mountain pine beetle (Pureswaran and Borden 2004). Our objectives were to confirm the bioactivity of 2-phenyl ethanol and MCH, and to determine in trapping and tree protection experiments whether they are potential adjuvants that could increase the efficacy of verbenone.

MATERIALS AND METHODS

Two randomized complete block, 12-replicate, field trapping experiments (Exp. 1 and 2) were set up on 31 July and 13 August 2002, respectively, near the East Gate of Manning Park BC (49° 19' N, 120° 35' W). Tree protection experiments (Exp. 3A and 4A) with treatments identical to those in the trapping experiments were set up on 5-7 July 2002 in the valley of Whipsaw Creek near Princeton BC (49° 9' N, 120° 41' W), and two additional identical experiments (Exp. 3B and 4B) were set up on 24-27 July 2002 on the 1400 Road south of Prince George BC (53° 21' N, 123° 10' W).

For trapping experiments, 12-unit multiple-funnel traps were deployed at least 15 m apart along logging roads that passed near infested stands. For the tree protection experiments, lodgepole pines with a minimum diameter at breast height (dbh = 1.3 m) of 20 cm were selected at least 25 m apart in rows at least 50 m apart through cut blocks designated for harvest in the fall of 2002.

Treatments (Tables 1, 2) in Exp. 1, 3A and 3 B were an unbaited trap or tree (negative control), and an attractive bait alone (positive control) or with MCH, 2-phenyl ethanol, verbenone, or all three together. In Exp. 2, 4A and 4B, the control treatments were the same, but the three disruptants were deployed in all three possible binary blends and the ternary blend. All semiochemicals and release devices were purchased from Phero Tech Inc., Delta BC. The attractive trap bait consisted of the host kairomone myrcene released from a 20 mL polyethylene bottle at 95 mg/24 h, determined at 23 °C, and the aggregation pheromones 82% (-)-transverbenol and (±)-ero-brevicomin respectively released from bubble caps and polyurethane flexlures at 1.2 and 0.3 mg/24 h, determined at 20 °C. The attractive tree bait was identical to the trap bait, but with myrcene deleted (Borden et al. 1993). MCH, 2-phenyl ethanol and 80% (-)-verbenone were released from bubble caps at 4.0, 4.2 and 1.8 mg/24 h, determined at 20, 25, and 20 °C, respectively. Devices were hung in the central funnel of traps and affixed to the north face of trees at maximum reach from the ground. The dbh of all baited trees was measured, and varied among experiments (mean ± SE) as follows: 30.9 ± 1.3 cm to 35.1 ± 1.2 cm in Exp. 3A and 4A near Princeton, and 23.0 ± 0.5 cm to 25.3 ± 0.9 cm in Exp. 3B and 4B near Prince George.