Phytochemicals as mediators for host range expansion of a native invasive forest insect herbivore

Abstract

Summary Mountain pine beetle (MPB) has recently invaded jack pine forests in western Canada. This invasion signifies a climate change‐induced range expansion by a native insect. The mechanism underlying this invasion is unknown, but likely involves phytochemicals that play critical roles in MPB biology. Thus far, studies have investigated the compatibility of jack pine chemistry with beetles and their microbial symbionts. I have identified three phytochemical mechanisms that have likely facilitated the host range expansion of MPB. First, jack pine chemistry is overall similar to that of the historical hosts of MPB. In particular, jack pine chemistry is compatible with beetle pheromone production, aggregation on host trees and larval development. Furthermore, the compatibility of jack pine chemistry maintains beneficial interactions between MPB and its microbial symbionts. Second, compared with historical hosts, the novel host not only has lower concentrations of toxic and repellent defense chemicals, but also contains large concentrations of chemicals promoting host colonization by MPB. These patterns are especially pronounced when comparing novel hosts with well‐defended historical hosts. Finally, before MPBs arrived in jack pine forests, they invaded a zone of hybrids of novel and historical hosts that likely improved beetle success on jack pine, as hybrids show chemical characteristics of both hosts. In conclusion, the phytochemistry of jack pine has likely facilitated the biological invasion of this novel host by MPB.

A niche perspective on the range expansion of symbionts

“…In addition, the novel host has lower concentrations of defensive chemicals than historical hosts and large concentrations of chemicals that promote host colonisation. Further, the existence of a hybrid zone between lodgepole and jack pine forest likely facilitated host switch (Erbilgin, ). The parasitic mite Varroa destructor expanded its geographical range worldwide after a host switch from its Asian original host, Apis cerana , to the cosmopolitan A. mellifera (Navajas, ).…”

Nitrogen and Ergosterol Concentrations Varied in Live Jack Pine Phloem Following Inoculations With Fungal Associates of Mountain Pine Beetle

“…latifolia Engelm. ex S. Watson) forests; however, the beetle has recently expanded into jack pine (Pinus banksiana Lamb) forests in British Columbia and southern Alberta and threatens to move toward eastern boreal forests (Cullingham et al, 2011;Erbilgin, 2019). The life cycle of MPB is well described (Safranyik et al, 2010).…”

Caterpillars on a phytochemical landscape: The case of alfalfa and the Melissa blue butterfly

“…As technological limitations have dissipated, the opportunity now exists for a more comprehensive understanding of the challenges faced by herbivores, with the possibility of discovering, among other things, novel compounds and synergistic interactions among compounds (Prince & Pohnert, 2010; Richards, Dyer, Smilanich, & Dodson, 2010; Sardans, Penuelas, & Rivas‐Ubach, 2011). More generally, an important task is to quantify the phytochemical complexity of the antagonistic interaction between plants and herbivores, with an eye toward understanding constraints on the evolution of both players (Fordyce & Nice, 2008; Macel, van Dam, & Keurentjes, 2010) and predicting the formation of new plant‐herbivore interactions (Erbilgin, 2018). Here we use the example of a specialized herbivore and a recently colonized host plant to investigate the phytochemical landscape from the perspective of developing caterpillars.…”