Rosa Rubicondior: Unintelligent Design - An Arms Race Between a Parasitic Beetle And a Parasitic Fungus

Adult spruce bark beetles in their galleries in the bark of a Norway spruce tree. The beetle in the middle is infected with the fungus Beauveria bassiana.

Fungus turns bark beetles’ defenses against them

A paper recently published in the Proceedings of the National Academy of Sciences of the USA (PNAS) has raised the spectre of evolutionary arms races for creationism. Evolutionary arms races are something of a nightmare for creationists because, within the paradigm of intelligent design by a single designer, having an arms race with yourself makes no sense at all.

Evolutionary arms races are among the strongest arguments against intelligent design, as I point out in my book, The Unintelligent Designer: Refuting the Intelligent Design Hoax. They epitomise stupidity. What on Earth is the point of designing a solution to a problem for one species, only to treat that solution as a problem to be solved for another? It is almost exactly as if two organisms are evolving in response to changes in their environments, of which their predator or prey is a key component. It makes less sense than a dog chasing its own tail – at least the dog gets some exercise.

The arms race reported in this paper, by a research team at the Max Planck Institute for Chemical Ecology in Jena, Germany, is between the spruce bark beetle, Ips typographus, and the pathogenic fungus Beauveria bassiana.

In fact, there are two arms races at work here. The first is between the Norway spruce, Picea abies, and its microbial environment. The tree produces antimicrobial phenolic compounds as a defence. The spruce bark beetle has evolved the ability to convert these compounds into an even more toxic derivative, which helps protect the beetle and enables it to successfully colonise the spruce.

The clever twist is that the fungus Beauveria bassiana has evolved a countermeasure. It converts the beetle’s toxic compound by binding a sugar molecule to it and adding a methyl group. This modification effectively neutralises the beetle’s antifungal defence, making it more susceptible to fungal infection.

Translated into creationist terms, a designer first designed a defence for the spruce that can be exploited by a parasitic beetle to protect itself from microbes, including a pathogenic fungus. The same designer then designed a pathogenic fungus capable of neutralising the beetle’s defences, allowing it to infect the beetle more efficiently.

What Is an Evolutionary Arms Race? An evolutionary arms race occurs when two or more species exert strong selective pressure on each other, leading to a cycle of reciprocal adaptations over many generations. As one species evolves a new defence, weapon, or strategy, the other evolves a counter-adaptation, which in turn selects for further change in the first.

Crucially, this process has no end point. There is no “perfect” solution, only temporary advantages that are eventually eroded by further evolution.

How Arms Races Arise

Arms races most commonly occur between:

Predators and prey (speed, camouflage, toxins, sensory acuity)
Hosts and parasites/pathogens (immune responses vs immune evasion)
Plants and herbivores (chemical defences vs detoxification mechanisms)
Competing species (resource acquisition, weaponry, behaviour)

Each adaptation alters the selective environment of the other species, driving further evolutionary change.

Why Arms Races Are Strong Evidence for Evolution

Evolutionary arms races:

Require ongoing, incremental change over long periods
Produce inefficient, jury-rigged solutions, not optimal designs
Frequently involve trade-offs, where gains in one trait cause losses in another
Show clear signs of historical contingency rather than foresight

These patterns are exactly what evolutionary theory predicts and exactly what purposeful, intelligent design does not.

Why Arms Races Are a Problem for Intelligent Design

Within the framework of Intelligent Design by a single, omniscient designer, evolutionary arms races are incoherent. They imply that:

A “designed” solution immediately becomes a problem requiring redesign
The same designer repeatedly undermines its own work
Harmful traits (toxins, immune evasion, parasitism) are deliberately engineered

This would amount to a designer endlessly designing around its own previous designs, a scenario that is indistinguishable from blind evolutionary processes and far less parsimonious.

The Bigger Picture

Evolutionary arms races are not rare anomalies. They are widespread, predictable, and measurable, and they occur at genetic, biochemical, physiological, and behavioural levels. Their existence is one of the clearest demonstrations that life evolves through natural selection acting on variation — not through foresight, planning, or design.

Creationist Claim vs Reality

Creationist claim:
Living systems are intelligently designed, with purposeful features carefully engineered to fulfil specific functions.

Reality:
Evolutionary arms races show organisms repeatedly modifying traits in response to each other, producing temporary, contingent, and often self-defeating solutions. Defences become vulnerabilities, countermeasures generate new problems, and harm is ubiquitous. This pattern is exactly what is expected from natural selection acting without foresight — and exactly what would not be expected from a single, intelligent, benevolent designer.

Bottom line:
Arms races make sense under evolution because no one is in charge. Under Intelligent Design, they imply a designer endlessly correcting its own mistakes.

This research is explained in a press release from the Max Planck Institute for Chemical Ecology in Jena, Germany.

Fungus turns bark beetles’ defenses against them
The insect-pathogenic fungus Beauveria bassiana detoxifies the defense substances of the beetles, which originate from plant precursors, and can successfully infect these insects

To the point:

Spruce bark beetles exploit the defenses of spruce trees for their own protection: they feed on the tree’s bark and convert the antimicrobial phenolic compounds it contains into even more toxic derivatives to protect themselves against pathogens.
The insect-pathogenic fungus Beauveria bassiana overcomes the beetles' antimicrobial defenses, enabling it to successfully infect spruce bark beetles.
Fungus-specific detoxification pathway includes glycosylation and methylation: Beauveria bassiana neutralizes the toxic phenolic compounds by binding a sugar (glycosylation) and adding a methyl group (methylation).
The beetles' susceptibility to infection depends on the functionality of this fungal metabolic pathway: If the pathway is blocked, the infection rate decreases.
This mechanism demonstrates the evolutionary adaptation of a pathogenic fungus to a host with complex chemical defenses, with potential benefits for biological pest control.

Spruce bark is rich in phenolic compounds that protect trees from pathogenic fungi. A research team at the Max Planck Institute for Chemical Ecology in Jena investigated how these plant defenses function within the food web, particularly in spruce bark beetles (Ips typographus), which ingest the compounds through their diet. Could the beetles use substances from the spruce's defenses to protect themselves against pathogenic fungi?

Beetles convert plant defenses into even more toxic forms

Using state-of-the-art analytical methods such as mass spectrometry and nuclear magnetic resonance (NMR), the team investigated which chemical compounds spruce trees produce for defense and how these compounds are metabolized by bark beetles. The team demonstrated that bark beetles infesting spruce trees utilize the trees' defensive substances found in the phloem, particularly phenolic glycosides such as stilbenes and flavonoids, to bolster their defense against pathogens. They convert these compounds into more toxic aglycones, which are sugar-free and have increased antimicrobial activity. These aglycones serve as an effective defense against fungi. "We did not expect the beetles to be able to convert the spruce's defenses into more toxic derivatives in such a targeted way," said the lead author Ruo Sun from the Department of Biochemistry.

The fungus neutralizes the beetles' defenses via specific detoxification pathways

Then, the scientists investigated how the beetle defense substances affected the fungus Beauveria bassiana.

Although this fungus has not been effective in controlling bark beetles in the past, we found strains that had naturally infected and killed them. We therefore wanted to investigate more closely how they were able to successfully infect the beetles.

Ruo Sun, lead author.
Department of Biochemistry
Max Planck Institute for Chemical Ecology, Jena, Germany.

Further analyses and enzyme assays revealed that the fungus employs a two-step detoxification process. First, there is glycosylation, which involves the re-addition of a sugar to the aglycones. Second, there is methylation, which involves the binding of a methyl group to the sugar. The resulting methylglycoside derivatives are not toxic to Beauveria bassiana. Interestingly, methylglycosylation increases fungal infestation, particularly in beetles that had previously consumed plant tissue with a high phenol content. Additionally, methylglycosides are resistant to beetle enzymes that would restore the compounds' toxicity through hydrolysis.

The scientists tested the function of the detoxification pathway in Beauveria bassiana by knocking out the genes responsible for methylglycosylation. Further experiments revealed that fungi lacking these genes, and thus the detoxification pathway, were far less effective at infesting bark beetles.

The successful infection of bark beetles with Beauveria bassiana depends on a highly specific detoxification pathway that neutralizes antimicrobial phenolics and increases the pathogen's virulence.

Ruo Sun.

An evolutionary balancing act with potential application

The study clearly shows that a tree's chemical defenses can undergo multiple transformations and retransformations throughout the food chain – with far-reaching consequences for the evolutionary arms race between hosts, pests, and pathogens.

We have demonstrated that a bark beetle can co-opt a tree's defensive compounds to make defenses against its own enemies. However, since one of the enemies, the fungus Beauveria bassiana, has developed the ability to detoxify these antimicrobial defenses, it can successfully infect the bark beetles and thus actually help the tree in its battle against bark beetles.

Jonathan Gershenzon, lead author
Department of Biochemistry
Max Planck Institute for Chemical Ecology, Jena, Germany.

These findings could lead to the development of more effective biological control agents against bark beetles.
Now that we know which strains of the fungus tolerate the bark beetle's antimicrobial phenolic compounds, we can use these strains to combat bark beetles more efficiently.

Ruo Sun.

The study emphasizes the importance of checking for resistance or detoxification strategies developed by the pest against its host when using biological pesticides.

In further experiments, the research team wants to determine how widespread the methylglycosylation detoxification pathway is in different strains of the fungus Beauveria bassiana and in other bark beetle pathogens. They also want to understand how this pathway interacts with other characteristics of pathogens that influence its effectiveness.

Publication:
R. Sun,B. Hu,Y. Nakamura,M. Reichelt,X. Jiang,K. Luck,C. Paetz, & J. Gershenzon
Detoxification of conifer antimicrobial defenses promotes entomopathogenic fungus infection of bark beetles
Proc. Natl. Acad. Sci. U.S.A. 123 (1) e2525513122, https://doi.org/10.1073/pnas.2525513122 (2026).

Significance
Plants produce antimicrobial compounds to defend themselves against pathogens, and herbivorous insects may gain protection from their own pathogens by consuming these compounds. We found that bark beetles enzymatically convert some antimicrobial phenolic compounds of spruce trees into more potent antimicrobial derivatives. However, an insect-killing fungus counters these phenolic compounds with a two-step detoxification pathway to produce methylglucoside derivatives. Knocking out this fungal pathway by genetic transformation reduces the virulence of the fungus on bark beetles, proving the pathway’s importance for successful fungal infection.

Abstract
After consumption by herbivores, plant antimicrobial defense compounds may enhance herbivore immunity to pathogenic microbes. In conifer-bark beetle interactions, beetles ingest large quantities of phloem tissue containing high concentrations of antimicrobial phenolic glucosides, such as stilbenes and flavonoids. It is not known, however, if these compounds increase bark beetle resistance to pathogens. We showed that Eurasian spruce bark beetles (Ips typographus) attacking Norway spruce (Picea abies) hydrolyze phenolic glucosides to their corresponding aglucones increasing their antifungal activity. However, the entomopathogen Beauveria bassiana, a natural fungal parasite of these beetles, detoxifies stilbene and flavonoid aglucones by forming methylglucoside derivatives. A two-step pathway involving a UDP-glycosyltransferase and an O-methyltransferase produces phenolic O-methylglucosides that are no longer toxic to B. bassiana and are stable to β-glucosidase action. Compared to wild-type strains of B. bassiana, mutant strains knocked out in the genes of this pathway exhibited decreased methylglucoside formation, slower growth on medium containing phenolic compounds, and reduced virulence toward bark beetles. Hence, methylglucosylation of plant-derived phenolics is a detoxification process that significantly increases the ability of B. bassiana to parasitize host insects consuming plant tissue high in phenolics, such as conifer phloem. This is one of the few examples of an entomopathogen that is able to resist the plant-derived defenses of an insect host.

R. Sun,B. Hu,Y. Nakamura,M. Reichelt,X. Jiang,K. Luck,C. Paetz, & J. Gershenzon
Detoxification of conifer antimicrobial defenses promotes entomopathogenic fungus infection of bark beetles
Proc. Natl. Acad. Sci. U.S.A. 123 (1) e2525513122, https://doi.org/10.1073/pnas.2525513122 (2026).

Copyright: © 2025 The authors.
Published by the National Academy of Science of the USA. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)

This study is yet another reminder that the living world is not the product of foresight, planning, or optimisation, but of relentless, unguided evolutionary processes. Evolutionary arms races arise inevitably when organisms interact over long periods, each responding to the selective pressures imposed by the other. No intelligence is required, only variation, inheritance, and differential survival.

For Intelligent Design, however, such systems are a conceptual dead end. Arms races imply waste, harm, redundancy, and constant retrofitting — precisely the opposite of what one would expect from a competent designer. They force creationists to invoke a deity that repeatedly undermines its own creations, engineers defences only to design ways around them, and produces suffering not as an unfortunate side effect, but as a built-in feature of the system.

As with so many discoveries in modern biology, this research fits seamlessly within evolutionary theory while presenting insurmountable problems for creationism. The more closely we examine the details of life — at the genetic, biochemical, and ecological levels — the clearer it becomes that life was not intelligently designed. It evolved, blindly and brilliantly, through natural selection acting over deep time.

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