Fungal Biopesticide Detoxifies Plant Compounds That Protect Bark Beetles
- Gauri Khanna
- 3 hours ago
- 3 min read
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Researchers at the Max Planck Institute identified Beauveria bassiana strains capable of detoxifying plant defence compounds that bark beetles weaponise against fungal infection
The fungus neutralises toxic phenolic compounds through a two-phase process: restoring sugars to aglycones, then methylation to create harmless methylglucosides
Climate change has triggered bark beetle population explosions in temperate forests, creating demand for alternatives to chemical insecticides
Wood-boring insects inflict substantial economic and ecological damage through structural infestations and forest devastation. Eurasian spruce bark beetles (Ips typographus) have experienced population surges in temperate forests due to climate change, overwhelming Norway spruce (Picea abies) populations. Conventional pest control relies on synthetic insecticides, yet research from Germany's Max Planck Institute for Chemical Ecology demonstrates that specific fungal strains can eliminate these pests through sophisticated biochemical mechanisms.
Beetles Hijack Plant Defences
Norway spruce produces phenolic compounds (stilbenes and flavonoids) as chemical defences against pathogenic fungi and herbivorous insects. These organic molecules function as antioxidants and antimicrobials, linked with sugar molecules that moderate their toxicity. When bark beetles ingest spruce bark, their metabolism removes these sugars through hydrolysis, converting the compounds into aglycones: versions considerably more toxic to microorganisms.
This metabolic transformation effectively weaponises plant defences for beetle protection. The enhanced antimicrobial potency theoretically renders beetles immune to fungal infection, as the very compounds meant to protect trees now shield the insects consuming them. Biochemist Ruo Sun, who led the research team, noted that insect herbivores have long been known to accumulate plant defence metabolites from their diet as defences against their own enemies.
Two-Phase Detoxification Strategy
Despite these formidable chemical barriers, certain strains of Beauveria bassiana, an entomopathogenic fungus naturally infecting various insect species, demonstrate capability to infect and kill bark beetles in wild populations. Sun's team isolated fungal strains from deceased beetles, cultivated them under laboratory conditions, and identified the genetic mechanisms enabling detoxification of beetle-borne phenolic compounds.
The detoxification proceeds through two distinct phases. First, the fungus restores sugars to the toxic aglycones, weakening their antimicrobial properties. Subsequently, methylation occurs—the sugar is chemically bonded to a methyl group (CH₃), forming methylglucosides that pose no threat to fungal growth. In simpler terms, the fungus reverses the beetles' chemical modification of plant compounds, then adds another molecular component rendering them harmless.
To confirm this mechanism's essentiality, researchers created mutant fungal strains with detoxification genes knocked out—essentially disabled. These modified strains could not produce methylglucosides and demonstrated drastically reduced infection rates and lethality against beetles, confirming the detoxification pathway's critical role in fungal pathogenicity.
Beyond Beauveria: Broader Implications
Beauveria bassiana is not alone in this capability. Other entomopathogenic fungi, including Cordyceps militaris, notorious for its portrayal in fictional dystopian scenarios despite posing no threat to humans, also produce methylglucosides from stilbenes, flavonoids, and similar defensive compounds.
Sun suggested fungi such as B. bassiana could possess additional resistance mechanisms beyond direct detoxification. Some fungi reportedly excrete compounds like resveratrol from fungal cells, potentially contributing to enhanced growth and virulence on substrates containing toxic compounds.
The research team proposes that genes enabling B. bassiana to detoxify antifungal substances might facilitate metabolism of other defensive plant compounds ingested by harmful insects. This versatility suggests potential application against diverse pest species beyond bark beetles.
Commercial and Environmental Considerations
Translating these findings into practical pest management requires addressing several challenges. Identifying and cultivating the most virulent fungal strains, developing stable formulations maintaining viability during storage and application, and demonstrating field efficacy under varying environmental conditions all demand substantial development investment.
Regulatory approval for biological control agents typically requires comprehensive safety assessments, though fungal biopesticides generally face less stringent requirements than synthetic chemicals. Beauveria bassiana already features in some commercial biopesticide formulations targeting agricultural pests, providing regulatory precedent.
Whether fungal biopesticides can replace chemical insecticides depends on cost competitiveness, application convenience, and efficacy under diverse conditions. The vision of exterminators arriving with petri dishes rather than chemical sprayers remains aspirational, though climate-driven pest pressures and regulatory restrictions on synthetic insecticides may accelerate adoption of biological alternatives based on naturally occurring entomopathogenic fungi.