Volatile Organic Compounds Emitted by Fungal Associates of Conifer Bark Beetles and their Potential in Bark Beetle Control

Abstract

Conifer bark beetles attack and kill mature spruce and pine trees, especially during hot and dry conditions. These beetles are closely associated with ophiostomatoid fungi of the Ascomycetes, including the genera Ophiostoma, Grosmannia, and Endoconidiophora, which enhance beetle success by improving nutrition and modifying their substrate, but also have negative impacts on beetles by attracting predators and parasites. A survey of the literature and our own data revealed that ophiostomatoid fungi emit a variety of volatile organic compounds under laboratory conditions including fusel alcohols, terpenoids, aromatic compounds, and aliphatic alcohols. Many of these compounds already have been shown to elicit behavioral responses from bark beetles, functioning as attractants or repellents, often as synergists to compounds currently used in bark beetle control. Thus, these compounds could serve as valuable new agents for bark beetle management. However, bark beetle associations with fungi are very complex. Beetle behavior varies with the species of fungus, the stage of the beetle life cycle, the host tree quality, and probably with changes in the emission rate of fungal volatiles. Additional research on bark beetles and their symbiotic associates is necessary before the basic significance of ophiostomatoid fungal volatiles can be understood and their applied potential realized.Electronic supplementary materialThe online version of this article (doi:10.1007/s10886-016-0768-x) contains supplementary material, which is available to authorized users.

Symbiont selection via alcohol benefits fungus farming by ambrosia beetles

“…Bacteria ( Acinetobacter spp., Pseudomonas aeruginosa ) ( 48 , 49 ), many yeasts ( 50 , 51 ), and the fungal tree pathogen Armillaria mellea ( 52 ) have also been proposed to use ethanol as a carbon source. In addition to detoxifying ethanol, ambrosia beetle fungal symbionts are known to produce ethanol, among other alcohols ( 53 and 54 ), which may maintain an alcohol-rich gallery environment even after its production by plant cells has ceased (i.e., because of tree death). Such consumption, production, and environmental accumulation of ethanol has been reported so far from only three lineages of yeasts, in which it has been shown to be a potent tactic for securing their food resource against other microbial and possibly also arthropod competitors ( 50 , 51 , 55 ).…”

Performance of the tree‐killing bark beetles Ips typographus and Pityogenes chalcographus in non‐indigenous lodgepole pine and their historical host Norway spruce

“…The presence of enemies in the non‐indigenous lodgepole pine may be a result of most bark beetle enemies being generalists that utilize several bark beetle species reproducing in different tree species and, generally, they do not appear to rely on species‐specific host tree cues when locating bark beetle‐attacked trees. Instead, they may be attracted by bark beetle pheromones, host tree volatiles such as α‐pinene that are present in many tree species, or volatiles from host‐associated fungi (Kenis et al ., ; Kandasamy et al ., ).…”

Optimizing the attractiveness of pheromone baits used for trapping the four‐eyed spruce bark beetle Polygraphus poligraphus

“…Frontalin was tested since it has been shown that P. poligraphus responds to it. 1‐Hexanol was tested as it has been identified as a reppelent for other bark beetle species (Kandasamy, Gershenzon, & Hammerbacher, ). Since n ‐nonane was used as a solvent in the “wick‐bait” dispensers, it was also tested along with two potential alternatives, n ‐octane and n ‐decane.…”