The role of autoxidation of α-pinene in the production of pheromones of Dendroctonusponderosae (Coleoptera: Scolytidae)

Abstract

The monoterpene α-pinene, a major component of the terpene composition of Pinus spp., has been reported to act as a host-produced kairomone for a variety of bark beetle species, including the mountain pine beetle, Dendroctonusponderosae Hopkins. However, our experiments indicate that α-pinene autoxidizes under normal temperature and atmospheric conditions to form significant quantities of trans-verbenol, an aggregation pheromone for many species of bark beetles. The quantities of α-pinene present in the resin that can flow from small wounds in pine trees appear to be sufficient to produce trans-verbenol at rates similar to those by female beetles that are actively synthesizing the compound.trans-Verbenol can then autoxidize rapidly to form verbenone, with the content of this compound reaching 8% within 13 weeks of exposure to air. Verbenone is often used by scolytids as an antiaggregation pheromone. Approximately 1.9% of the trans-verbenol and 2.7% of the verbenone found in Porapak Q aerations of phloem with boring spruce beetle, Dendroctonusrufipennis (Kirby), females, as well as 0.8% of the trans-verbenol and 0.8% of the verbenone found in aerations of phloem with boring D. ponderosae females, was due to the autoxidation of α-pinene and (or) the release of oxygenated compounds found in the phloem before bark beetle attack. The natural interconversion of α-pinene, trans-verbenol, and verbenone under ambient conditions suggests that many experiments involving the behavioral activity of these compounds require re-evaluation.

Semiochemicals in the Natural History of Southern Pine Beetle Dendroctonus frontalis Zimmermann and Their Role in Pest Management

“…Verbenone (and verbenol) can be generated through autoxidation of host-released α-pinene coming into contact with atmospheric oxygen (Hunt et al, 1989;Moore et al, 1956). Microbes including bark beetle symbionts and incidental associates are also capable of oxidizing α-pinene to verbenol and/or verbenol to verbenone Brand et al, 1975;Hunt and Borden, 1990;Xu et al, 2015).…”

“…Rather, these and additional common oxygenated monoterpenes may be more general infochemicals which indicate the early stages of a decaying and thus unsuitable host (Flechtmann et al, 1999;Lindgren and Miller, 2002). As with verbenone, many may be generated through the enzymatic oxidation activities of microbes in the host tissues or autoxidation of host resin (Flechtmann et al, 1999;Hunt et al, 1989;Sullivan, 1997;Sullivan et al, 2000).…”

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

“…When tested in Lindgren funnel traps baited with aggregation pheromones, verbenone significantly reduced trap capture of the mountain pine beetle, and two secondary bark beetles that attack pine, the pine engraver, Ips pini Say and I. latidens (LeConte) (Coleoptera: Curculionidae: Scolytinae) (Miller et al 1995). In the mountain pine beetle, verbenone is produced by autooxidation (Hunt et al 1989) and oxidation of verbenol by microbial associates of the female beetles (Hunt and Borden 1990) late in the colonisation process (Pureswaran et al 2001). Therefore, this compound may better be described as a kairomone that signals the breakdown of plant tissues (Lindgren and Miller 2002) and hence elicits broad antiaggregation response from insects that rely on relatively fresh plant tissue for survival and brood production.…”

Protection of lodgepole pine from attack by the mountain pine beetle, Dendroctonus ponderosae (Coleoptera: Scolytidae) using high doses of verbenone in combination with nonhost bark volatiles

“…In nature verbenone is produced in small amounts by autoxidation of the monoterpene α-pinene (Hunt et al 1989), but the principal route of production is through metabolic conversion by bark beetles of inhaled and ingested α-pinene to the terpene alcohols cis-and trans-verbenol, which are then metabolized by yeasts in the beetles' guts and galleries to verbenone (Leufvén et al 1984;Hunt and Borden 1990). Despite its production by autoxidation and by microorganisms, verbenone is so closely associated with the galleries of bark beetles and is so consistently repellent (to at least 10 species known to date) that it is generally classed as an antiaggregation pheromone or interspecific synomone, inferring that it is produced by the beetles themselves (Borden 1997).…”