Abstract
Mountain pine beetle (Dendroctonus ponderosae) has killed millions of hectares of pine forests in western North America. Beetle success is dependent upon a community of symbiotic fungi comprised of Grosmannia clavigera, Ophiostoma montium, and Leptographium longiclavatum. Factors regulating the dynamics of this community during pine infection are largely unknown. However, fungal volatile organic compounds (FVOCs) help shape fungal interactions in model and agricultural systems and thus may be important drivers of interactions among bark beetle-associated fungi. We investigated whether FVOCs can mediate interspecific interactions among mountain pine beetle’s fungal symbionts by affecting fungal growth and reproduction. Headspace volatiles were collected and identified to determine species-specific volatile profiles. Interspecific effects of volatiles on fungal growth and conidia production were assessed by pairing physically-separated fungal cultures grown either on a carbon-poor or -rich substrate, inside a shared-headspace environment. Fungal VOC profiles differed by species and influenced the growth and/or conidia production of the other species. Further, our results showed that FVOCs can be used as carbon sources for fungi developing on carbon-poor substrates. This is the first report demonstrating that FVOCs can drive interactions among bark beetle fungal symbionts, and thus are important factors in beetle attack success.
Highlights
Bark beetles (Coleoptera: Curculionidae, Scolityinae) are among the most destructive tree-killing insects in temperate and boreal conifer forests worldwide
Nine fungal volatile organic compounds (FVOCs), representing three classes of carbon-based chemicals, were detected in extractions of headspace volatiles of G. clavigera, O. montium, and L. longiclavatum adsorbed to activated carbon during a 24 h period: acetoin, ethyl acetate isoamyl acetate, and phenethyl acetate, cis-grandisol, isobutanol, 2-methyl1-butanol, 3-methyl-1-butanol, and phenethyl alcohol
non-metric multidimensional scaling (NMDS) showed that G. clagivera was most closely associated with cis-grandisol and isobutanol, O. montium was associated with acetoin and 3-methyl-1-butanol, and L. longiclavatum was associated with ethyl acetate, isoamyl acetate, and phenethyl acetate (Fig 1)
Summary
Bark beetles (Coleoptera: Curculionidae, Scolityinae) are among the most destructive tree-killing insects in temperate and boreal conifer forests worldwide. Bark beetles remain at low densities for decades—suppressed by competitors, natural enemies, and host tree defenses—and are restricted to hosts with weakened defenses [1], which are typically rare in PLOS ONE | DOI:10.1371/journal.pone.0162197. Fungal Volatiles as Carbon Sources and Semiochemicals Bark beetles remain at low densities for decades—suppressed by competitors, natural enemies, and host tree defenses—and are restricted to hosts with weakened defenses [1], which are typically rare in PLOS ONE | DOI:10.1371/journal.pone.0162197 September 1, 2016
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