Mountain pine beetle (MPB) has recently breached the geo-climatic barrier of the northern Rocky Mountains and invaded novel jack pine forests in western Canada. The mechanism underlying this host range expansion is unknown, but likely involves phytochemicals that play critical roles in the MPB biology. Thus far, studies have investigated both Scots pine and jack pine suitability to MPB as a host and examined compatibility of its chemicals with beetles and their microbial symbionts. Based on these studies, I have identified five phytochemical mechanisms that have likely facilitated the host and range expansion of MPB. First, relative to the historical host of MPB (lodgepole pine), novel hosts (Scot spine and jack pine) not only quantitatively lack toxic defense chemicals, but also contain large amounts of chemicals that promote MPB host colonization. Second, prior to the arrival to novel host forests, invasion of a zone of hybrids of jack and lodgepole pines by MPB likely improved their success in the jack pine as hybrids show chemical characteristics of both novel and historical hosts. Third, novel host chemistry is compatible for beetle pheromone production, aggregation on the host trees, and larval development. Fourth, compatibility of novel host chemistry with the microbial symbionts of MPB maintains beneficial interactions with their host. Finally, novel hosts contain low amounts of defense and attraction inhibitory compounds, and high amounts of pheromone precursor and synergistic compounds that make historical hosts susceptible to MPB. I conclude that compatibility of chemicals of novel hosts to MPB and its symbionts has likely facilitated the biological invasion.

Phytochemicals are key drivers of host and range expanding insect herbivores

2019 Fall National Meeting

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