Review of Scientific Research Publications and Biocontrol Advances
How Trichoderma asperellum strain T34 stands out as a strategy for ragweed beetle control.
The present entry corresponds to a review based on two publications by researchers of the University of Catania: “Microbial mutualism suppression by Trichoderma and Bacillus species for controlling the invasive ambrosia beetle Xylosandrus compactus” and “Exploring the potential of synthetic and biological fungicides for managing the fungus-farming ambrosia beetle Xylosandrus compactus”.
Different possible control strategies are compared and T34 Biocontrol® stands out stands out in the control of the ragweed beetle, showing a significantly superior effect compared to other products evaluated, with very relevant results.
Based on this evidence, we initiated this review to further explore the findings and potential of this biocontrol strategy.
A tiny beetle with a big impact
Xylosandrus compactus (known as borer black twig borer o black ambrosia beetle) is an ambrosia beetle native to Asia that has become an invasive pest in other regions. It measures barely 2 mm, but can infest a wide variety of trees and shrubs of ornamental and agricultural importance, boring galleries in their young branches. In Europe it was first detected in 2011 (Italy) and arrived in Spain in 2019 (Mallorca), then spreading to Catalonia in 2020. This insect causes wilt, breakage of branches y decay in the trees it attacks, affecting forests, fruit plantations, nurseries and urban areas. Its small size and life habit hidden inside at the wood make control with conventional methods difficult, as contact insecticides hardly reach hidden pests. Therefore, X. compactus is considered a serious phytosanitary threat wherever it becomes established.
Crops and plants affected
Main agricultural crops:
Ornamental orchids
Various species of ornamental and forest trees:
It also affects many other species such as Macadamia, Mango, among others.
Mediterranean plants in Europe:
The ambrosia beetle's secret partner: an indispensable fungus
The success of X. compactus is not only due to the beetle itself, but also to its alliance with a symbiont fungus, Ambrosiella xylebori. Female beetles carry spores of this fungus in special structures on their bodies. They bore into the wood and start a gallery, fungus is planted on the walls of the tunnel. Ambrosiella xylebori grows inside the wood feeding on plant tissue and plugs the galleries with its mycelium and spores. The larvae of the beetle do not feed directly on woodThey consume the cultivated mushroom, obtaining its nutrients from it. In other words, X. compactus is a “farmer beetle”: it grows its own fungal food inside the tree. This mutualistic relationship is so close that the development and reproduction of the beetle are totally dependent on the fungus; without it, the larvae cannot thrive and the insect’s life cycle isWithout it, the larvae cannot thrive and the insect’s life cycle is interrupted.
However, X. compactus is not only associated with Ambrosiella xyleboribut also with other species of saprotrophic fungi (Ambrosiella macrosposa) y pathogens (Fusarium solani, Epicoccum nigrum), which may influence the symptoms observed in infested plants.
On the other hand, in many cases the fungus Ambrosiella Ambrosiella can also act as a tree pathogen, amplifying the damage: it causes tissue necrosis (dark lesions in the wood) and contributes to the wilting of the host. Thus, this insect-fungus pair is doubly damaging: the beetle bores and spreads the fungus, and the fungus weakens or kills the invaded plant.
Searching for a biological solution: attacking the fungus
Traditionally, pest control strategies focus on attacking the insect (e.g., with insecticides). However, in the case of ambrosia beetles such as X. compactus, conventional methods often fail due to their cryptic lifestyle within the wood and their rapid dispersal. This is where an innovative idea arises: what if instead of attacking the beetle directly, we attack its feeding fungus? If we succeed in suppressing or eliminating Ambrosiella xylebori, we would be “cutting off the food supply” for X. compactus, preventing it from breeding new generations. This indirect biological control approach seeks to exploit the beetle’s Achilles heel: its vital need for a mutualistic fungus.
A promising candidate for this task is another fungus, Trichoderma asperellumspecifically strain T34. Trichoderma are benign fungi widely known in agriculture for their ability to antagonize other fungi (they are “mycoparasitic”), compete for space and nutrients, and even stimulate plant defenses. The T. asperellum T34 strain in particular is used commercially as a biofungicide in crops because of its efficacy in controlling soil pathogens. The researchers hypothesized that T34 could colonize the same habitat as Ambrosiella (the wood or rhizosphere of the plant) and displace or inhibit it, thus disrupting the insect-fungus mutuality. In short: use a good fungus to defeat a bad fungus and thereby defeat the pest beetle naturally.
Surprising results: Trichoderma vs. Ambrosiella
Researchers at the University of Catania (Italy) conducted laboratory studies to test this strategy. In 2022, Gugliuzzo et al. evaluated different biocontrol agents, including T . asperellum strain T34, against X. compactus and its fungus. The trials included in vitro (culture plates confronting the beneficial fungus against A. xylebori) and in vivo (twigs infested with beetles, treated with the biofungicides) tests. The results were very encouraging: T. asperellum T34 was able to stop the growth of the Ambrosiella fungus significantly, both on the plate and inside the wood. In Petri dishes, T34 inhibited about 80% of A. xylebori mycelial growth due to its rapid overgrowth and competition. But the most important thing occurred in infested twigs: T34-treated galleries hardly developed any fungus and, consequently, many X. compactus females failed to rear any larvae in those galleries. Trichoderma was observed to colonize inside the tunnels or nearby, leaving Ambrosiella without space and nutrients.
In the laboratory, X. compactus females produced on average more than 20 offspring each on untreated branches (gray bar, control). In contrast, when branches had been treated with T. asperellum T34, beetle offspring were drastically reduced to only ~1-4 offspring per female (green bar). This experiment demonstrates that, by preventing the growth of the mutualistic fungus, T34 treatment leaves X. compactus larvae without their food source, causing a collapse in their reproduction. In many cases the galleries treated with T34 directly had no viable larvae, only the mother and perhaps some undeveloped eggs. The difference is remarkable: without the nutritive fungus, the beetle can hardly bring forth its progeny.
Trichoderma were not the only ones evaluated. In the 2022 study, a couple of beneficial bacterial strains (Bacillus) were also tested, which also showed potential in suppressing Ambrosiella. Indeed, Bacillus amyloliquefaciens D747 was able to reduce the presence of the fungus in the galleries and decrease brood production by ~82% at high doses. However, T. asperellum strain T34 stood out as one of the most consistent agents: with proper application, it achieved up to 95% reduction in the number of beetle broods. In other words, where a beetle would normally produce about 20 offspring, with T34 it produced barely 1. This level of efficacy in vitro and in vivo was a powerful proof of concept that sabotaging the fungus-insect relationship is feasible.
From the laboratory to the field: a future integrated biological control
Encouraged by these results, in 2025 Costanzo et al. published a study extending the research, including tests with chemical fungicides alongside biological fungicides, and simulating conditions closer to the field. In these experiments, young laurel plants (a host plant) were treated with different fungicides before exposure to the beetle. Synthetic fungicides (such as thiophanate-methyl and azoxystrobin) showed the greatest reduction of the beetle population, because by infiltrating the wood they effectively eliminated the cultured fungus and significantly reduced the number of galleries with broods.
However, among the biological options, Trichoderma asperellum T34 again stood out: it was the only one that succeeded in significantly slowing down the mutualistic fungus in the treated plants. Specifically, the application of T34 in the rhizosphere of infected laurels halved the length of fungal lesions inside the wood (29.47 mm with T34 vs. 60.65 mm in control plants). This “lesion” is basically the dark patch of dead tissue caused by Ambrosiella as it spreads; its smaller size indicates that the fungus was much less active on the T34 plants.
The other two products evaluated, based on two Trichoderma strains and one Bacillus, showed a tendency to reduce lesion length (44.11 mm and 50.40 mm, respectively), although without significant differences with respect to the control. According to the authors of the study, root colonization by T. asperellum T34 could have induced systemic resistance in the plant, modifying the mutualistic interaction between the beetle and the fungus. This study expands the knowledge on the use of biofungicides to break the interaction between X. compactus and its main mutualist, A. xylebori.
Why did T34 work particularly well? The researchers propose two complementary mechanisms. First, T. asperellum T34 competes directly with A. xylebori: it grows faster, occupies gallery space, and can secrete enzymes or compounds that inhibit the other fungus. Second, T34 stimulates the natural defenses of the host plant. Evidence for this was that the application of T34 to the roots of the laurel induced a systemic response in the tree, making it less conducive to fungal colonization in its vessels. In other words, the tree “defends itself better” when its roots are colonized by T34, a phenomenon known as induced systemic resistance. This dual effect makes T34 a valuable ally.
A promising strategy to control the pest
Taken together, these studies demonstrate an innovative concept: controlling an insect pest by attacking its essential microbiota. This integrated pest management strategy opens up a more selective and ecological way of combat: biocontrol by altering the insect’s mycobiome.
Disrupting ambrosia mutualism represents an interesting paradigm shift in forest and agricultural protection. Instead of applying broad-spectrum fungicides or insecticides (which can damage biodiversity), a beneficial organism is introduced that naturally disarms the pest.
In conclusion, the use of Trichoderma asperellum T34 against Xylosandrus compactus is a promising and environmentally friendly biotechnological strategy. The studies by Gugliuzzo et al. (2022) and Costanzo et al. (2025) provide strong proof-of-concept that targeting the fungus-insect symbiosis does work, representing a ray of hope in the fight against a devastating invasive beetle. With biofungicides like T34 fungus on our side, it is possible to protect forests and crops without resorting so much to chemicals, but by harnessing the natural rivalries between microorganisms themselves. A tiny green Trichoderma spore could be the key to stopping this tiny but destructive ragweed beetle.
Bibliography
- Costanzo, M. B., Gugliuzzo, A., Vitale, A., Puglisi, I., Visentin, S., Pane, A., Cascone, P., Pappalardo, V., Guerrieri, E., & Conti, E. (2025). Exploring the potential of synthetic and biological fungicides for managing the fungus-farming ambrosia beetle Xylosandrus compactus. PLOS ONE, 20(7), e0329063. https://doi.org/10.1371/journal.pone.0329063
- Gugliuzzo, A., Vitale, A., Puglisi, I., Pane, A., Pappalardo, V., Cascone, P., Guerrieri, E., & Conti, E. (2022). Microbial mutualism suppression by Trichoderma and Bacillus species for controlling the invasive ambrosia beetle Xylosandrus compactus. Biological Control, 170, 104929. https://doi.org/10.1016/j.biocontrol.2022.104929
- Leza, M., Nunez, L., Riba, J. M., Comparini, C., Roca, A., & Gallego, D. (2020). First record of the black twig borer, Xylosandrus compactus (Coleoptera: Curculionidae, Scolytinae) in Spain. Zootaxa, 4767(2), 337-340. https://doi.org/10.11646/zootaxa.4767.2.9
- EPPO (European and Mediterranean Plant Protection Organization) (n.d.). Xylosandrus compactus. EPPO Global Database. https://gd.eppo.int/search?k=Xylosandrus+compactus.
- Generalitat de Catalunya. Department of Climate Action, Food and Rural Agenda. (2023). Phytosanitary affectations. Dried Fruit Sectorial Roundtable . https://ruralcat.gencat.cat/documents/20181/11400265/punt+3-+Afectacions+fitosanitaries+Taula+Sectorial+FS+2023.pdf/0b3aa598-f30a-4bc6-a916-32718d078d0c
- Generalitat de Catalunya. Departament d’Acció Climàtica, Alimentació i Agenda Rural. (n.d.). Fitxa tècnica de Xylosandrus compactus. https://agricultura.gencat.cat/web/.content/ag_agricultura/ag02_sanitat_vegetal/ag02_02_plagues/documents_fulls_informatius/fitxers_estatics/fi-xylosandrus-compactus.pdf
- Ruralcat (n.d.). New pests affecting ornamental plants: Ripersiella hibisci. Xylosandrus compactus . https://ruralcat.gencat.cat/documents/20181/9596914/punt+5.2.-+RH+i+XC+TS+Flor_.pdf/775e4f19-78cc-4bcd-90d9-6ee4e8cba6fc
