Can nano-silver made with Beauveria bassiana stop caterpillars? What a 2024 study found
Beauveria bassiana is a fungus that kills insects, and farmers already use it as a biopesticide. A 2024 study co-authored by Dr. Abhishek Mathur used an extract of this fungus to make silver nanoparticles, and tested them on caterpillars that attack cauliflower. Here is what it found, and what it did not show.
Key points
- Researchers made silver nanoparticles using an extract of Beauveria bassiana, a natural fungus that infects and kills insects.
- Tested on caterpillars that attack cauliflower, the stronger dose (20 ppm) cut their numbers by 52% in five days. The weaker dose (10 ppm) cut them by 20%.
- The same study found four Streptomyces soil bacteria that held back four common crop-disease fungi on lab plates.
- Key details are missing: the paper does not name the caterpillar, report an untreated comparison, or measure the particles. This is early research, not a product.
- What to do today: against caterpillars, use registered biopesticides such as Beauveria or Bt, with trap crops and pheromone traps, as your KVK advises.
Beauveria bassiana: a fungus that kills insects
Beauveria bassiana is a fungus found naturally in soil. Its spores stick to an insect's body, grow into it and kill it within days. Because it attacks insects and not crops, it is widely used as a biopesticide. It can infect many pests, including caterpillars, whiteflies, aphids and beetles, and in India it is sold as a registered biopesticide.
Live spores have limits: they need humid weather, and strong sunlight and heat kill them. The fungus also makes its own insect-killing substances, and some researchers study these instead of the living spores. This study combined those substances with silver.
Silver nanoparticles are specks of silver far smaller than a cell. Extracts of fungi and plants can turn dissolved silver into such particles, a method often called "green synthesis". Silver is known to kill many microbes, and several research groups are now testing silver nanoparticles against insect pests.
What the researchers tested
The study was published in 2024 in the Journal of Advanced Zoology. Its authors are Rashmi Jain of Veer Madho Singh Bhandari Uttarakhand Technical University, Dehradun; Devendra Singh of JBIT College of Applied Sciences, Dehradun; and Dr. Abhishek Mathur, then at the R&D department of Prathista Industries. Dr. Mathur was the second author and the corresponding author, the researcher who handles the paper with the journal.
- Collected soil: 25 samples from around the roots of rice, wheat, pulses and local vegetables in the Chamoli and Pauri Garhwal districts of Uttarakhand.
- Grew the microbes: from 56 microbes, they kept 14 beneficial ones, among them Bacillus, Pseudomonas, Rhizobium, Trichoderma, mycorrhizal fungi, four Streptomyces strains and Beauveria bassiana.
- Tested the Streptomyces against disease fungi: each strain's culture was placed in wells cut into plates of four crop-disease fungi, and the clear zone where the fungus could not grow was measured.
- Made nano-silver: they grew Beauveria bassiana for five days, drew out its substances with solvents, and mixed the extract with silver nitrate. A change of colour showed that nanoparticles had formed.
- Tested the nano-silver on caterpillars attacking cauliflower, at 10 and 20 ppm, and recorded the fall in their numbers each day for five days.
What they found on caterpillars
The nano-silver reduced caterpillar numbers, and the higher dose worked better. At 20 ppm, numbers fell by 5% on the first day and by 52% by the fifth. At 10 ppm, they fell by 20% by the fifth day. In both cases the effect grew day by day.
In simple words: the stronger dose cut the caterpillars by about half in five days, and the weaker dose by about a fifth. That is a start, but at the stronger dose about half the caterpillars were still there after five days.
A second finding: soil bacteria against crop-disease fungi
Streptomyces are common soil bacteria, well known as the source of many antibiotics. In this study, the cultures of all four Streptomyces strains held back all four disease fungi on lab plates.
| Strain | Wilt | Collar rot | Anthracnose | Root rot |
|---|---|---|---|---|
| Streptomyces AM101 | 41 | 32 | 45 | 26 |
| Streptomyces AM102 | 32 | 25 | 41 | 22 |
| Streptomyces AM103 | 33 | 26 | 27 | 26 |
| Streptomyces AM104 | 28 | 35 | 22 | 28 |
| Fluconazole (comparison) | 45 | 40 | 25 | 27 |
A bigger zone means a stronger effect. Green marks a zone larger than the comparison's. Fungi tested: Fusarium oxysporum (wilt), Sclerotium rolfsii (collar rot), Colletotrichum (anthracnose) and Rhizoctonia solani (root rot). Fluconazole is a medical antifungal, not a farm fungicide.
Strain AM101 did best overall. Against the anthracnose fungus, three of the four strains made larger clear zones than fluconazole. Against root rot, most strains were about level with fluconazole, and against wilt and collar rot fluconazole stayed ahead.
In simple words: these soil bacteria make substances that stop disease fungi on a plate. Whether they protect crops in a field was not tested.
What this study does not tell us
- The paper does not name the caterpillar, or say whether the test was in a lab or a field, how many caterpillars were used, or how the nano-silver was applied.
- No untreated comparison is reported, and the fungus extract and the silver were not tested on their own. So we cannot tell how much of the fall came from the fungus, from the silver, or would have happened anyway.
- The particles were judged only by a change of colour. Their size, shape and silver content were not measured.
- The disease-fungi results come from lab plates, not plants, and the comparison was a medical antifungal, not a farm fungicide.
- No statistics are given for the caterpillar test, and no yield or residue was measured. Some counts in the paper also disagree, such as the number of soil samples.
- The paper's conclusion suggests such nanoparticles could work at lower doses than conventional inputs. That was not tested: nothing was compared with a standard fertilizer or insecticide.
The authors present this as a first step. Its most useful message is that a well-known biocontrol fungus and common soil bacteria make substances worth studying further.
Is nano-silver safe on farms?
For use as an insecticide, that has not been shown yet. Silver kills microbes, and that cuts both ways: research reviews report that silver nanoparticles can also harm helpful soil microbes, earthworms and water life, especially at higher doses or with repeated use. Before any nano-silver insecticide could be used on food crops, its effects on soil and water, and any silver left on the harvest, would need testing.
In India, any product sold to kill insect pests must be registered with the Central Insecticides Board and Registration Committee (CIB&RC). Use only registered products, at the dose on the label.
What you can do about caterpillars today
- Check the crop twice a week. Look under the leaves for eggs and young caterpillars. While numbers are small, pick off and destroy egg masses and early caterpillars by hand.
- Use trap crops and traps. For diamondback moth on cabbage and cauliflower, Indian IPM advice is to grow rows of mustard as a trap crop and to set pheromone traps to watch for the moths.
- Choose registered biopesticides first. Products based on Bacillus thuringiensis (Bt), Beauveria bassiana or neem are widely used against caterpillars. Buy only products with a CIB&RC registration number, and follow the label dose.
- Spray Beauveria in the evening. Sunlight and heat kill its spores, and it works best when the air is humid. Do not mix it with chemical fungicides, which can kill it.
- Ask before you spray. Your KVK or agriculture officer can confirm which caterpillar you have and which registered products work on it. Avoid unregistered "nano" pest products.
What comes next
To take this further, the nano-silver would need to be measured (particle size and silver content), tested on named caterpillars against untreated plants and a standard biopesticide, and checked for residues and effects on soil life. Dr. Mathur's wider work on microbial biocontrol and formulations is part of that path.
NanoKheti sells colloidal-silver products for plant diseases and hygiene (the NanoFOR range). They are not insecticides, and they were not part of this study.
