Beauveria bassiana review

Can a fungus weaken a hornet colony from the inside? This review collects the evidence for using Beauveria bassiana (Bb), a naturally occurring insect-killing fungus, against Vespa velutina (yellow-legged hornet) delivered by contaminating hornet workers through selective traps and baits.

• A Vespa velutina enters a selective trap.
• She drinks sugar bait or takes protein bait carrying Beauveria bassiana spores (conidia), or picks them up from the trap surface as she passes. She flies back to the nest.
• Nestmates pick up spores by contact.
• The spores grow through the cuticle into the body cavity. That can kill the hornet, alter her behaviour, or be cleared by her immune system.
• A dead hornet may sporulate and generate new conidia.
• The ideal outcome is colony collapse. The more realistic target is colony weakening: less damage this season, fewer queens and drones for the next.

1. EU products and NL use. Six Bb strains hold EU active-substance approval. Whether any product is authorised in the Netherlands for trap or bait delivery is on the to-do list.
2. Kill or weaken V. velutina. One Bb isolate from a wild foundress killed hornets in the lab (half died in about 6 days); field efficacy of commercial available Bb and on V. velutina colonies remains untested.
3. Selective delivery. Both passage-contact dispensers and sugar/protein baits load spores onto insects in lab and field trials. Protein baits has been validated for V. velutina and 0.01% fipronil (Barandika2023). No studies with fungi.
4. Horizontal transfer to nestmates. Social wasps transfer spores by contact; species differ in nestmate response to exposed individuals (recognition, aggression, avoidance). The minimum spore load a returning V. velutina forager must carry is unknown.
5. Fungal growth in the nest. Bb grows best at 23-28 °C with high humidity; nest temperature and humidity of V. velutina have yet to be measured.
6. Colony-level impact. Bb caused colony failure in Polistes dominula in the lab; colony weakening or collapse from catch-infect-release in V. velutina is an open question.

Note: Direct research on Vespa velutina and Beauveria bassiana (Bb) is scarce. To fill this gap, evidence from related insects—such as other wasps, bees, and ants—has been included. Data from more distantly related species, which are often the focus of commercial Bb products, are labelled as proxies (see the phylogenetic tree). Workflow can be found in workflow.md.

Assay shorthand and jargon are expanded in the glossary (LD50, LC50, LT50, conidia, catch-infect-release, proxies, regulation, and nest biology). Short index:

1. Which Bb strains are commercially available in the EU, what formulations exist, and what use is allowed in the Netherlands?
2. Can Bb kill or weaken V. velutina and non-target species under field conditions, not only in a lab assay?
3. How can Bb be delivered so V. velutina picks up spores and carries them (formulation, dispenser design)?
4. Can a treated hornet transfer spores to nestmates, and at what concentrations?
5. Does nest temperature and humidity allow the fungus to grow after transfer?
6. Is the resulting infection strong enough to reduce queen and drone production, or to collapse the colony?

Exact search strings: search log.

Each row lists two links when both exist: first jumps to the summary section in this README, second opens the full literature extract in results/.

• Terms used in this review · glossary
• Background (background)
• 1 EU-available products, strains and formulations (eu-products)
• 2 Effect on Vvel, Vespidae, other Hymenoptera, other insects (effects)
• 3 Mechanics and delivery (mechanics-delivery)
• 4 Horizontal spread in the Vvel nest (horizontal-spread)
• 5 Fungal growth on the Vvel (fungal-growth)
• 6 Effect of fungi on Vespidae nests (nest-effects)
• Study selection
• Methods: lab journal · search log · commercial affiliations
• Attachments: glossary · references · phylogenetic tree · workflow
• Data: input-phase0 (input-rayyan, input-cc-rr) · input-phase1 · input-phase2 (include list, download links, excluded) · pdfs (excluded, inbox)

Beauveria bassiana is a soil fungus found worldwide. Infection follows seven steps (Valero-Jimenez2016):

1. The spore sticks to the insect cuticle
2. It germinates and grows into the outer shell
3. Inside, it multiplies as single cells (blastospores) in the blood
4. It colonises the body and eventually kills the host
5. The insect's immune system may fight back, sometimes clearing the infection
6. After death, fungal threads emerge and produce new spores that can infect others

Bb infection cycle on a hornet: A) spore penetrates the cuticle and multiplies in the blood; B) after death, new spores emerge from the body Original diagram based on Valero-Jimenez2016

Efficacy in the field depends on humidity, temperature, UV exposure, and rainfall (Mascarin2016).

Bb has many strains, each with its own killing power, growth speed, and stress tolerance. Even batches of the same commercial product can differ (Moore2026), and laboratory-recultured spores can behave differently from the commercial product (Nouri-Aiin2021).

Full background extract: background.

Six Bb strains hold EU active-substance approval under Regulation (EC) No 1107/2009. They are sold as sprays, wettable powders, granules, or electrostatic powder, mostly for protected crops, storage pests, and palm weevils. Whether any product label covers trap or bait-station use is an open question, and EU approval may not automatically mean a product is authorised in the Netherlands. Full strain table and product details: eu-products.

Crop spray trials (conventional crop use)

• BotaniGard ES (GHA): 48-71% chilli thrips reduction on roses (Aristizabal2017; abstract).
• BotaniGard (GHA) plant dips: 81-86% corrected whitefly mortality on mint (Aristizabal2018; abstract).

Product quality and batch variation

• balEnce (HF23) germinated poorly where BotaniGard ES (GHA) and Mycotrol O (GHA) killed house flies (Weeks2016).
• Velifer ES (PPRI 5339) and BotaniGard ES (GHA) killed tea shot-hole borer faster (6-8 d) than wettable-powder products; cadaver sporulation was highest on Velifer ES (Chavez2023; beetle proxy).
• Even between batches of the same commercial product (Botanigard, GHA), ethanol tolerance, pathogenicity, and spore production differed (Moore2026).

Direct evidence on V. velutina and Bb is limited to one isolate (wild strain) from a single research group:

• Bb strain from a naturally infected foundress in Brittany; growth fastest at 20-28 °C, optimum about 20-22.6 °C (Poidatz2019; funded by Bayer Crop Science).
• Lab bioassay of that isolate on adult hornets at about 10⁷ spores/mL: half died in 6.25 ± 0.67 days; direct inoculation gave the highest mortality (Poidatz2018). Application above 20 °C recommended.

An other entomopathogenic fungus (Metarhizium robertsii)

• V. velutina, Vespula vulgaris, and Bombus terrestris: hornets consistently the most susceptible, even at low spore concentrations (Lacombrade2025; CIFRE doctoral co-funding with M2i Biocontrol, disclosed in COI section as non-influential).

Bb kills other social wasps in the lab, but results vary by species and life stage:

• Vespula germanica: sugar bait at 1 × 10⁸ spores mL⁻¹ killed 79-95% of workers and 66-73% of males (Merino2007; Chilean isolates, outside EU commerce; co-funded via agreement with Controladora de Plagas Forestales S.A., a pest control service company).
• V. germanica and Polistes dominula larvae, lab: Eco-Bb (R444) killed all tested larvae by day 7 (VanZyl2024).
• Same species, field in-nest spray: EPF+EPN mixture gave ~31% larval infection and ~3% pupal infection; pupae were largely spared (VanZyl2024).
• Mischocyttarus metathoracicus: Boveril (ESALQ PL63), half died by day 19, slower than imidacloprid (DeSouza2023).
• P. dominula: Naturalis (ATCC 74040) caused colony failure with brood ejection and reduced foundress reproduction (Cappa2024; topical dose 1 μL of 10⁶ spores/μL).

Polistes and Mischocyttarus build open-comb nests where brood is directly exposed. V. velutina nests are enclosed in a paper envelope, so spores must travel through returning workers rather than landing directly on brood.

Open-comb Polistes nest: brood cells are directly exposed to the environment Photo: Root Simple, CC BY-NC

Framing asymmetry

• Safety-framed studies tend to report little Bb effect on bees (Zimmermann2007; Omuse2022; Meikle2008).
• Pathogenicity-framed studies report high mortality (Portilla2017; Leite2022) and sublethal disruption of nestmate recognition and cognition (Cappa2019; Carlesso2020).
• Leite2022 flags the tension: hive-level varroa studies found no colony damage while individual-level lab assays on the same fungus found considerable mortalities.

Selected outcomes

• Honey bee contact mortality with ICIPE 284: at most 17.4% under hive-simulated conditions (Omuse2022).
• Stingless bee Meliponula ferruginea: at most 11.0% (Omuse2022).
• Direct application and ingestion of commercial Bb reduced survival of Apis mellifera and Bombus terrestris; oral exposure can exceed topical (Leite2022).
• Isolate NI8: 98.2% honey bee mortality at the highest lab concentration at 10 d (Portilla2017).
• Hive-mounted bumblebee dispensers: detectable Bb on 97-99% of Bombus impatiens workers, no epizootic, no adverse colony impact (Al-Mazraawi2006; Bb from Emerald BioAgriculture, predecessor to Laverlam/BotaniGard).
• Meikle2008: mite fall increased with Bb05002 + carnauba wax carrier, but colony weight, adult mass, and brood were similar to controls. GHA material supplied by S.T. Jaronski of Mycotech Corp. (USDA-ARS study).

Hymenopteran proxy

• Apple sawfly (Hoplocampa testudinea): soil-applied BotaniGard GHA gave 49-68% lab mycosis but only 17% in field soil cages (Swiergiel2016).

Broad efficacy (proxies)

• High spray or contact mortality in aphids, whiteflies, beetles, flies, thrips, and moths (Wraight2010; Parker2015).
• Wraight2010: co-author S.T. Jaronski affiliated with Mycotech Corp., a Bb product company and predecessor to the Laverlam/BioWorks BotaniGard line.

Autodissemination (proxies)

• Sap beetles (Dowd2003, USDA-ARS), kissing bugs (Forlani2011, CONICET-UNLP), bed bugs (Barbarin2012, Penn State).

Field failure

• Three Bb applications did not reduce spotted lanternfly numbers (Keller2023, Penn State; PA Dept of Agriculture and USDA APHIS/NIFA funding). Co-author Nina Jenkins: lead author of US Patent 14/810,137 (Aprehend) and co-founder of ConidioTec LLC (disclosed in acknowledgements).

Full effects extract: effects.

Two pickup modes sit side by side: contact on a passage surface (1- or 2-way dispenser) and spores mixed into sugar or protein bait. Both work for pollinators; neither is established as the better option for Vespidae.

Dispensers and baits

• Hive-mounted 1- and 2-way dispensers move Bb onto crops via bumblebees (Al-Mazraawi2006; Kapongo2025).
• Maize flour carried more spores through bee dispensers than coarser meals (Al-Mazraawi2007; Bb from Emerald BioAgriculture).
• NZ protein baits with Metarhizium and Bb reduced Vespula nest traffic; infected larvae recovered from both fungal treatments (Brownbridge2009).
• Red-palm-weevil pheromone traps with Broadband: half dead by day 4 at 10⁸ spores/mL (Hajjar2015; weevil proxy).

Formulation

• Oil formulations improve infection at low humidity, extend thermal stress tolerance, and protect against UV (Mascarin2016).
• HEC and alginate hydrogels kept Bb viable up to 24 d in a mosquito ovitrap assay (Friuli2025).
• Carnauba wax in dry powder raised virulence in a blowfly assay (Muniz2020).
• Corn-oil coating improved granular thermotolerance (Kim2010).
• Longifolene at 0.2-0.4 mmol mL⁻¹ reversed spore repellence in a termite bait (Lin2026).

UV

• After simulated sunlight, spores showed a half-life of about 2 hours (Zimmermann2007).
• An archaeal photolyase transgene raised spore survival after 4-7 h natural sunlight up to 44-fold and preserved virulence on Anopheles gambiae (Fang2012; engineered mosquito proxy).

Full delivery extract: mechanics-delivery.

Catch-infect-release design proxies (fipronil trials)

• Catch-treat-release with fipronil demonstrates the social-wasp design pattern (Buczkowski2024).
• Protein bait with 0.01% fipronil reduced V. velutina pressure at apiaries for at least two weeks in one trial (Barandika2023; co-authors R. Fananas and E. Arroyo are employees of D+S-OABE, which partially funded the study, disclosed in the COI section).

Nestmate response to Bb-exposed social insects

• Mischocyttarus metathoracicus: cuticular hydrocarbon (CHC) profiles similar 24 h after Boveril exposure; nestmates did not discriminate exposed from unexposed individuals (DeSouza2023).
• Polistes dominula: Bb altered CHC profiles and increased aggression toward exposed nestmates (DeFazi2025).
• Stingless bees: Tetragonisca guards exclude pathogen-exposed nestmates (Almeida2022ao; proxy).
• Ants: susceptibility and autogrooming vary; concentrations about six orders of magnitude above natural levels did not give 100% mortality (Bos2019).

Bee pathogen carriage in V. velutina nests (Santos2026)

• qPCR survey of 38 nests in Portugal: bee- and bumblebee-associated pathogens (DWV, Nosema ceranae, BQCV, CBPV, and others) occurred in larvae, pupae, adults and queens at similar prevalence. Authors attribute this mainly to predation on infected prey (bees fed to larvae), with additional routes via flowers and direct contact. Nests bioaccumulate bee pathogens over the season. The concern is interspecific transmission and spillback (hornet harbours replicative bee pathogens). The study does not address Bb or trap-delivered inoculum on returning foragers.
• The required load (spores per returning forager) for introducing Bb into a V. velutina nest remains an open question.

Full horizontal-spread extract: horizontal-spread.

Temperature and moisture (general Bb)

• Germination on the cuticle and sporulation after death both require high moisture (Zimmermann2007).
• Optimum temperature for Bb is about 23-28 °C; isolate-dependent minimum is about 5-10 °C, maximum about 30-38 °C (Zimmermann2007).
• The Poidatz foundress isolate was better adapted to intermediate temperatures (Poidatz2019).
• Fu2026 isolate WZS5 (melon fly proxy) remained active at 35 °C with half dead by day 5 at 1.0 × 10⁸ spores mL⁻¹.

Nest climate

• Honey-bee hives: in-hive temperature near 35 °C abolished germination of formulated spores while forager mortality was high at 25 °C (Peng2020ao; honey-bee nest climate proxy).
• Nest temperature and relative humidity of V. velutina are an open question.
• Nest paper of P. dominula is hydrophobic (VanZyl2024).

Full fungal-growth extract: fungal-growth.

Colonies remove sick individuals, isolate the dead, and can compensate with more brood; capped cells may shelter pupae (Rose1999). [project inference] A contaminated returning forager alone is insufficient for nest collapse.

Colony-level Bb outcomes in social wasps

• P. dominula in lab/colony boxes: colony failure after topical Naturalis, with brood ejection and reduced foundress reproduction (Cappa2024).
• M. metathoracicus: half died by day 19 with no avoidance behaviour; the authors flag a possible threat to colony survival (DeSouza2023).
• P. dominula / V. germanica field nests: inundative spray; EPF+EPN mixture performed better than Bb alone; pupae largely spared (VanZyl2024).
• P. chinensis: oral Beauveria malawiensis at 2.68 × 10⁶ cfu mL⁻¹ raised adult mortality across three treatment nests (Reason2022).

Full nest-effects extract: nest-effects.

The catch-infect-release idea: traps and baits can load spores onto insects, social wasps pass them to nestmates, and Bb can kill wasps and damage colonies in the lab. Each link in the chain has at least some evidence from related species.

The chain has gaps specific to V. velutina: field efficacy is untested, the minimum spore load for nest introduction is unknown, nest temperature and humidity have yet to be measured, and the question of whether a commercial EU strain works or a Vespidae-isolated strain is needed remains open. Oil formulation, UV protection, and application temperature all constrain reliability.

For our project, this means: the biology is promising enough to warrant field trials, but there is no ready-to-use product or validated method for V. velutina today.