Abstract
The mountain pine beetle (Dendroctonus ponderosae; MPB) is an eruptive bark beetle species affecting pine forests of western North America. MPB are exposed to volatile monoterpenes, which are important host defense chemicals. We assessed the toxicity of the ten most abundant monoterpenes of lodgepole pine (Pinus contorta), a major host in the current MPB epidemic, against adult MPB from two locations in British Columbia, Canada. Monoterpenes were tested as individual volatiles and included (−)-β-phellandrene, (+)-3-carene, myrcene, terpinolene, and both enantiomers of α-pinene, β-pinene and limonene. Dose-mortality experiments identified (−)-limonene as the most toxic (LC50: 32 μL/L), and (−)-α-pinene (LC50: 290 μL/L) and terpinolene (LC50: >500 μL/L) as the least toxic. MPB body weight had a significant positive effect on the ability to survive most monoterpene volatiles, while sex did not have a significant effect with most monoterpenes. This study helps to quantitatively define the effects of individual monoterpenes towards MPB mortality, which is critical when assessing the variable monoterpene chemical defense profiles of its host species.
Highlights
The mountain pine beetle (Dendroctonus ponderosae; MPB) is an eruptive bark beetle that infests different pine (Pinus sp.) species in its native range of western North America
For the purpose of this study to assess and compare toxicity of individual monoterpenes, we focused on the exposure to monoterpene volatiles
It is important to note that there are limitations in the comparison of the LC50 values reported here, which are in units of relative volumes, with the absolute amounts of monoterpenes in host trees, which are typically determined after solvent extraction and reported as μg of monoterpene per g of dry weight of tissue sample
Summary
The mountain pine beetle (Dendroctonus ponderosae; MPB) is an eruptive bark beetle that infests different pine (Pinus sp.) species in its native range of western North America. The terpenoid profiles of the oleoresin vary substantially across different conifer species and between populations and individuals of the same species[11,12,13]. These variations may be explained, at least in part, by genomic variations of terpene synthase genes[14, 15]. For example the monoterpene profile of lodgepole pine has higher relative amounts of β-phellandrene and terpinolene compared to jack pine, which has higher relative amounts of (+) and (−)-α-pinene, (+)-3-carene, and (−)-limonene[16, 17]. (−)-α-pinene serves as the precursor to (−)-trans-verbenol[20], an aggregation pheromone produced and released by females upon initial attack of a host tree. As sex was not a significant factor in mortality for all monoterpenes tested, the data for both sexes was combined
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