Ethanol tolerance of fungal strains underlies biocontrol of invasive ambrosia beetles

Authors: Moore, Megan; Cure, Anne; JOHNSON, THOMAS - Indiana University; BIDDLE, GREGORY - University Of California; Baniszewski, Julie; Ranger, Christopher; Milbrath, Lindsey; Lovett, Brian

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/2026
Publication Date: 5/29/2026
Citation: Moore, M.E., Cure, A.E., Johnson, T.W., Biddle, G., Baniszewski, J.A., Ranger, C.M., Milbrath, L.R., Lovett, B.R. 2026. Ethanol tolerance of fungal strains underlies biocontrol of invasive ambrosia beetles. Journal of Economic Entomology. 2026. toag144. https://doi.org/10.1093/jee/toag144.
DOI: https://doi.org/10.1093/jee/toag144

Interpretive Summary: Ambrosia beetles are a substantial threat to tree crops such as apples, stonefruits, avocados, and ornamental trees. These beetles damage the tree by digging tunnels into the wood, where they create symbiotic fungal gardens. Because of this unique natural history, ambrosia beetles are difficult to manage with chemical pesticides, which require contact or ingestion to be effective. Insect-killing fungi are a promising solution for biological control, as their infective spores have evolved to adhere to insect cuticle and can be carried with the beetle into its tunnels. Here, we tested the ability of three commercially available biocontrol fungi to kill three prominent species of ambrosia beetle in the northeastern United States. We found that the most important consideration for the effectiveness of the insect-killing fungi was its tolerance to ethanol; ethanol is produced by flood-stressed trees that ambrosia beetles preferentially attack, and is a potent antimicrobial chemical. Different strains of the same biocontrol fungi, from the same product and manufacturer, have different levels of ethanol-tolerance, which impacted their pathogenicity against ambrosia beetles in the presence of ethanol. Our work highlights the importance of considering the natural history of targeted pests, and provides a screening tool that can be used to identify new species and strains of fungi for the biological control of ambrosia beetles.

Technical Abstract: Entomopathogenic fungi are an effective form of biological control and show promise against insect pests that are difficult to manage with chemical pesticides. Invasive ambrosia beetles threaten a wide variety of tree crops and prove challenging to manage with chemical pesticides due to their unique life history; entrenched in the wood of tree hosts, feeding on symbiotic fungi. Many ambrosia beetle species attack trees that are flood-stressed and producing ethanol, a key component of growth for their fungal symbiont. Ethanol causes osmotic and chaotropic stress in microbes and could prevent successful biocontrol of ambrosia beetles using insect-killing microbes. To investigate the potential of entomopathogenic fungi to manage ambrosia beetles, we conducted a series of experiments using three species in eastern North America (Xylosandrus germanus, Xylosandrus crassiusculus, and Anisandrus maiche). We tested the efficacy of three commercially available biopesticides (Botanigard 22 WP: Beauveria bassiana; Met52: Metarhizium brunneum; and PFR-97 20% WDG: Cordyceps javanica) in a series of environments with and without ethanol. We found that B. bassiana was the most effective against all three beetle species, but that its pathogenicity was heavily dependent on the ethanol-tolerance of the strain used. We isolated two strains of B. bassiana from separate batches of Botanigard that demonstrated significant differences in ethanol tolerance, as well as pathogenicity, radial colony growth, and spore production in the presence of ethanol. Our results emphasize the importance of pest natural history in control methods, while revealing that strain differences in biocontrol products fundamentally alter their performance across applications.