Abstract
The mountain pine beetle, Dendroctonus ponderosae, is a significant pest of lodgepole pine in British Columbia (BC), where it has recently reached an unprecedented outbreak level. Although it is native to western North America, the beetle can now be viewed as a native invasive because for the first time in recorded history it has begun to reproduce in native jack pine stands within the North American boreal forest. The ability of jack pine trees to defend themselves against mass attack and their suitability for brood success will play a major role in the success of this insect in a putatively new geographic range and host. Lodgepole and jack pine were sampled along a transect extending from the beetle’s historic range (central BC) to the newly invaded area east of the Rocky Mountains in north-central Alberta (AB) in Canada for constitutive phloem resin terpene levels. In addition, two populations of lodgepole pine (BC) and one population of jack pine (AB) were sampled for levels of induced phloem terpenes. Phloem resin terpenes were identified and quantified using gas chromatography. Significant differences were found in constitutive levels of terpenes between the two species of pine. Constitutive α-pinene levels – a precursor in the biosynthesis of components of the aggregation and antiaggregation pheromones of mountain pine beetle – were significantly higher in jack pine. However, lower constitutive levels of compounds known to be toxic to bark beetles, e.g., 3-carene, in jack pine suggests that this species could be poorly defended. Differences in wounding-induced responses for phloem accumulation of five major terpenes were found between the two populations of lodgepole pine and between lodgepole and jack pine. The mountain pine beetle will face a different constitutive and induced phloem resin terpene environment when locating and colonizing jack pine in its new geographic range, and this may play a significant role in the ability of the insect to persist in this new host.
Highlights
The primary host of the mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae) in its native range in western Canada is lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.), but the insect is capable of utilizing other species of pine, including jack pine (P. banksiana Lamb.) (Furniss & Schenk, 1969; Safranyik & Linton, 1982; Cerezke, 1995; Cullingham et al, 2011; Erbilgin et al, 2013)
With only one exception, all of the trees sampled at sites considered to be occupied by jack pine had a higher percentage of α-pinene compared with β-phellandrene; and all of the trees from sampling locations occupied by lodgepole pine had a higher percentage of β-phellandrene compared with α-pinene
Comparison of bark resin terpene compositions of lodgepole and jack pine sampled in our study showed that lodgepole pine have higher constitutive levels of most terpenes than does jack pine, including 3-carene, myrcene, and terpinolene (Table 2)
Summary
The primary host of the mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae) in its native range in western Canada is lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.), but the insect is capable of utilizing other species of pine, including jack pine (P. banksiana Lamb.) (Furniss & Schenk, 1969; Safranyik & Linton, 1982; Cerezke, 1995; Cullingham et al, 2011; Erbilgin et al, 2013). The northeastern portion of the range of lodgepole pine is contiguous with jack pine in Alberta. Where the two species’ ranges overlap, they form a hybrid zone (Moss, 1949), which in recent years has been successfully invaded by the mountain pine beetle (Langor, Rice & Williams, 2007 ). Its recent invasion of the pine forests east of the Rocky Mountains in north-central Alberta (Langor, Rice & Williams, 2007 ; Cullingham et al, 2011) has raised concerns that it may have the capacity to spread eastward through Canada’s extensive jack pine forest (Logan & Powell, 2001; Safranyik et al, 2010)
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