318 Borden et al.: Verbenone Against the Mountain Pine Beetle Arboriculture & Urban Forestry 2007. 33(5):318–324. Operational Success of Verbenone Against the Mountain Pine Beetle in a Rural Community John H. Borden, Glen R. Sparrow, and Nicole L. Gervan Abstract. Pouches releasing verbenone, the antiaggregation pheromone of the mountain pine beetle, were stapled to 1191 lodgepole pines throughout 95 residential properties in four subdivisions at Lac le Jeune, British Columbia, in July 2005. Postflight assessment in October in three of the subdivisions, where almost all infested trees had been removed before beetle flight, revealed new mass attacks on 3.6% of 3857 available trees 17.5 cm or greater (7 in) dbh. In a fourth subdivision where no infested trees were removed, 19.6% of 634 available trees were mass-attacked. In contrast, 17.4% of 1145 available trees were mass-attacked within 25 m (27.5 yd) wide, verbenone-treated buffer strips on public forest land adjacent to the residential properties, and 48.3% of 4975 available trees were mass-attacked on untreated control areas beyond the buffer strips. We conclude that treatment with verbenone pouches at roughly 15 m (16.5 yd) centers is a useful tool for protecting trees from attack by the mountain pine beetle provided that verbenone is used as part of a multiyear integrated pest management program that also includes disposal of all infested trees on the area to be protected before beetle flight in midsummer. Key Words. Dendroctonus ponderosae; integrated pest management; lodgepole pine; mountain pine beetle; phero- mones; Pinus contorta var. latifolia; verbenone. Lac le Jeune (Figure 1) is a rural community comprised of five separate subdivisions clustered around a lake of the same name. It rests on a high plateau between the southern British Columbia (B.C.) communities of Kamloops and Merritt. The forest in which the community is laid out is dominated by mature to overmature lodgepole pine, Pinus contorta var. latifolia Engelmann. By the fall of 2004, it was apparent that the heavily forested lots in four of the subdivisions (North Shore East, Townsite, Lookout, and Little Lake), as well as much of the surrounding forest, had developing infestations of the mountain pine beetle, Dendroctonus ponderosae Hop- kins (Coleoptera: Curculionidae). The fifth subdivision (South Ridge) is in an immature stand and was not severely threatened. The risk outside the residential properties lay in growing infestations on Crown (publicly owned) land adja- cent to the residences and in Lac le Jeune Park situated be- tween the North Shore East and Townsite subdivisions. The mountain pine beetle is an obligate tree killer (Raffa and Berryman 1983). Mass attack of individual trees in mid- to late summer is synchronized by aggregation pheromones produced by the attacking beetles. As the beetles construct their galleries, they sever resin canals in the inner bark and sapwood, releasing the free-flowing resin that can protect vigorous trees by “pitching out” the attacking beetles. To counter this defense, the beetles inoculate pathogenic fungi ©2007 International Society of Arboriculture into the inner bark and sapwood. If the attack is synchronized and the attack density is greater than 40 new galleries per m2 (36 per yd2), the combined action of fungal growth and beetle mining will kill the tree before it can mount its secondary resistance mechanism, the production of large amounts of toxic resin. In contrast, an excessively high attack density will leave too little inner bark for each beetle brood to prosper. To prevent this negative effect, the beetles use the antiaggrega- tion pheromone verbenone (Ryker and Yandell 1983; Schmitz and McGregor 1990). It is produced in small amounts by oxidation of the host tree resin component -pi- nene by the attacking beetles and in major amounts by sym- biotic microorganisms associated with the beetles (Hunt and Borden 1990). As mass attack proceeds, verbenone, and certain other antiaggregation pheromones, surpass the ag- gregation pheromones trans-verbenol and exo-brevicomin as the predominant volatiles emanating from established galler- ies (Pureswaran et al. 2000; Pureswaran and Borden 2003). The progressive effect is to space out new attacks, deter in- coming beetles from attacking the source tree, and to direct attack to adjacent trees (Borden et al. 1987), creating the “spot” infestations characteristic of developing mountain pine beetle infestations (Geiszler and Gara 1978; Geiszler et al. 1980).
September 2007
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