Variations in foliar monoterpenes across the range of jack pine reveal three widespread chemotypes: implications to host expansion of invasive mountain pine beetle.

Spencer Taft,Ahmed Najar,Nadir Erbilgin,Jean Bousquet,Julie Godbout

doi:10.3389/fpls.2015.00342

Abstract

The secondary compounds of pines (Pinus) can strongly affect the physiology, ecology and behaviors of the bark beetles (Coleoptera: Curculionidae, Scolytinae) that feed on sub-cortical tissues of hosts. Jack pine (Pinus banksiana) has a wide natural distribution range in North America (Canada and USA) and thus variations in its secondary compounds, particularly monoterpenes, could affect the host expansion of invasive mountain pine beetle (Dendroctonus ponderosae), which has recently expanded its range into the novel jack pine boreal forest. We investigated monoterpene composition of 601 jack pine trees from natural and provenance forest stands representing 63 populations from Alberta to the Atlantic coast. Throughout its range, jack pine exhibited three chemotypes characterized by high proportions of α-pinene, β-pinene, or limonene. The frequency with which the α-pinene and β-pinene chemotypes occurred at individual sites was correlated to climatic variables, such as continentality and mean annual precipitation, as were the individual α-pinene and β-pinene concentrations. However, other monoterpenes were generally not correlated to climatic variables or geographic distribution. Finally, while the enantiomeric ratios of β-pinene and limonene remained constant across jack pine's distribution, (−):(+)-α-pinene exhibited two separate trends, thereby delineating two α-pinene phenotypes, both of which occurred across jack pine's range. These significant variations in jack pine monoterpene composition may have cascading effects on the continued eastward spread and success of D. ponderosae in the Canadian boreal forest.

Highlights

In pine trees, monoterpenes are a prominent class of phytochemicals that play a significant role in tree-insect interactions (Phillips and Croteau, 1999; Franceschi et al, 2005; Raffa et al, 2005, 2013; Moore et al, 2014)
Due to importance of monoterpenes in bark beetle biology and ecology, in our investigations we focused on monoterpene composition of jack pine in both natural and provenance stands
While the impacts of our findings on bark beetles should be interpreted cautiously, as monoterpene composition varies between tissues of an individual tree (Latta et al, 2000; Erbilgin and Colgan, 2012) there is reason to believe that our defined jack pine chemotypes will have important implications for the biology and ecology of D. ponderosae in the jack pine boreal forest

Summary

Introduction

In pine trees (genus Pinus), monoterpenes are a prominent class of phytochemicals that play a significant role in tree-insect interactions (Phillips and Croteau, 1999; Franceschi et al, 2005; Raffa et al, 2005, 2013; Moore et al, 2014). Monoterpenes are a central aspect of pines’ constitutive and inducible defenses and are an essential component of pine defensive resins that are toxic to many herbivorous insects, including subcortically-feeding bark beetles. The influence of pine monoterpenes on bark beetles is critical as about 500 species of these subcortical herbivorous insects feed on pine trees, including many tree species of significant ecological and economic importance (Wood, 1982; Bentz et al, 2010; Safranyik et al, 2010; Raffa et al, 2013). Host plant volatiles can attract bark beetle predators or mediate predator attraction to bark beetle pheromones (e.g., Erbilgin and Raffa, 2001)

Results

Discussion

Conclusion