Overview
- What are microbial biopesticides?
- How do they work: modes of action
- Advantages and impact on sustainable agriculture
- Types of microbial biopesticides
- How are they applied?
- Bridging the gap: Microbial biopesticides and sustainable agriculture
- Challenges and future prospects of biopesticides
What are microbial biopesticides?
Microbial biopesticides, or microbials, are biological control products that contain microscopic living organisms (or their by-products) as the main active ingredient.
The application of microbial biopesticides is similar to other pest control products – such as with a spray bottle, in the soil, or on foliage, to name a few examples. They are particularly effective in controlling pests with little harmful effects unlike synthetic pesticides.
Some examples of microbial pesticides are:
- BETK-03®(BETK-03® CL, BETK-03® PE)
- Serenade® (BR)
- BioCeres EC®(US, CA)
- Attracap® (DE)
- Capex® (FR, GB)
- Nexy® (FR, US)
- V10® (DE, GB, CA, ES)
Microbial biopesticides are just one type of biocontrol agent. There are others, such as:
Microbial biopesticides are typically based on viruses, bacteria or fungi, but they can also contain oomycetes or algae.
We can separate microbials into two groups based on their functionality:
- antagonist microbials – microbials that control pathogens, including parasitic nematodes
- entomopathogenic microbials – microbials that control insect pests
How do they work: modes of action
Microbial biopesticides are specific in their modes of action and usually target one or small range of pests and pathogens. The effects and modes of action of a microbial depend on the targeted pest or pathogen and the microorganism contained in the product. There are also both direct and indirect ways these biopesticides can suppress pests and pathogens.
Direct mechanism
Some microbial biopesticides directly kill or inhibit the pest or pathogen, for example:
- Entomopathogenic microbes can work against insect and mite pests. Typically, the insect host gets infected by either eating (ingestion) of microbes or by the penetration of microbes through its skin (cuticle). The insect can die from either direct infection or from toxins released.
- Microbial antagonists that control plant pathogens, both above and below ground, also have direct modes of action:
- Parasitism: the antagonist “eats” the pathogen. For example, some fungi can gain nutrients from other fungi and thereby limit the growth of the disease.
- Antibiosis (or the production of inhibiting products): inhibitory compounds produced by the antagonist limit or reduce the activity and growth of the pathogen.
Indirect mechanism
This refers to modes of action through which the biopesticide does not directly kill or inhibit the pest or pathogen but instead creates conditions that reduce the pest’s or pathogen’s ability to thrive.
Microbial antagonists can indirectly control pathogens indirectly through two main modes of action:
- Competition (or competitive exclusion): the antagonist can compete with the plant disease for food or space, eventually outcompeting it. This works well against fungal pathogens that colonize plant roots.
- Induction of plant resistance: the antagonist can improve the ability of the plant to fight diseases. The application must precede the detection of the disease. For example, using seed treatment products.
Advantages and impact on sustainable agriculture
Microbial biopesticides have many benefits in addition to controlling pests and diseases effectively.
These include:
- They leave little to no toxic residues
- They decompose quickly
- Many have a zero or low re-entry (REI) and preharvest intervals (PHI)
- They have complex modes of action that make it difficult for pests and pathogens to develop resistance
- They are specific in their activity and target one or a small range of pests
- They are compatible with most biological products and synthetic pesticides and can therefore be incorporated within Integrated Pest Management (IPM) programmes.
Unlike synthetic chemical pesticides, microbial biopesticides pose little risk to the environment and play a key role in sustainable agriculture. They can protect biodiversity, soil health and water quality while effectively controlling pests. When incorporated in IPM programmes, these biopesticides reduce the need for chemicals and increase crop yield. Microbial biopesticides can therefore foster a resilient and healthy ecosystem, ultimately promoting sustainable agriculture.
Types of microbial biopesticides
Bacterial biopesticides
Bacterial biopesticides are the most common and used form of microbial biological control. Most of these products are insecticides, meaning that they fight insect pests such as moths, caterpillars, beetles and flies.
Entomopathogenic bacteria
Bacterial biopesticides are often applied directly to the crop. Once ingested by an insect pest, it infests its host. The bacteria release toxins inside the insect that attack gut cells, perforating the insect’s gut. The insect dies within a couple of days.
Common entomopathogenic biopesticides contain the bacteria of the genus Bacillus.
- For example, BETK-03® (CL, PE) is a wettable powder that contains bacteria from the Bacillus thuringiensis (var. Kurstaki) species. The powder is mixed with water and sprayed on foliage attacked by the pest. This product targets caterpillars of butterflies and moths (Lepidopteran), including the tomato leaf miner (Tuta absoluta), the oriental fruit moth (Cydia molesta) and the codling moth (Cydia pomonella). When caterpillars ingest the product, the bacteria act on the insect’s gut, leading to its paralysation. Caterpillars can no longer feed and eventually die.
Antagonist bacteria
Bacillus bacteria are also common in products that target soil and plant leaf (foliar-borne) pathogens. These include parasitic nematodes as well. They can prevent and control diseases through various mechanisms, such as competition and antibiosis.
- For example, the Serenade® (BR) biopesticide contains the bacterial species Bacillus subtilis. It limits the growth of numerous foliar-borne pathogens, such as the ones causing powdery mildew, early blight, botrytis and more. It works by antibiosis, meaning that the bacteria produce inhibiting compounds that limit the growth of the pathogen.
Fungal biopesticides
Entomopathogenic fungi
Fungal insecticides enter insect pests’ bodies once they come into contact. The fungus multiplies inside the insect and paralyses it via the fungal toxins produced and then eventually kills it. Four genera are common amongst the entomopathogenic fungi: Beauveria, Isaria, Metarhizium and Paecilomyces.
- BioCeres EC®(US, CA) is a biopesticide that contains spores of the Beauveria bassiana fungus. It targets pests such as whiteflies, thrips and aphids. Once sprayed on the insects, it infects them and, after a few days, causes mortality.
Antagonist fungi
Many fungal products targeting diseases contain fungi from the genus Trichoderma spp.. They work against root pathogens such as Fusarium root rot and powdery mildew.
Some products like Nexy® (FR, US) contain yeasts that will compete with plant pathogens for nutrients. It is active against the grey mould (Botrytis spp.) or some pathogenic Penicillium species.
Afla-Guard GR® (US) is another fungal biopesticide that outcompetes and controls a pathogenic fungus growing in maize.
Viral biopesticides
Entomopathogenic viruses
Insects need to eat the virus before it can take effect. Insects ingest the virus by feeding on the plant where the product has been applied. The virus then infects the insect’s gut and spreads through the insect, which dies in a couple of days. Once the insect dies, its body eventually bursts and releases the virus into the environment, which can infect new hosts.
Viral biopesticides typically contain baculoviruses. Nucleopolyhedrosis viruses (NPVs) and Granuloviruses (GVs) are the most frequently used genera of Baculoviruses.
For example, Capex® (FR, GB) is a product based on a granulovirus that works against the summer fruit tortrix (Adoxophyes orana), a pest that feeds on various fruit crops.
Cryptex® (KE, UG) is another viral product that controls the false codling moth (Thaumatotibia leucotreta) in citrus fruits.
Antagonist viruses
Some viruses can tackle plant diseases by improving the plant’s ability to fight pathogens, including other viruses.
This is the case for the V10® (DE, GB, CA, ES) biopesticide, a viral biopesticide that controls the Pepino Mosaic Virus (PepMV) in tomatoes. This product works like a vaccine for the plant. The virus contained in the product is the same virus that attacks the plants but is a less virulent variant. You can use this product preventively and help the plant “prepare” for an eventual attack from a harmful virus variant.
How can microbial biopesticides be applied?
There are many ways of applying microbial biopesticides to the target pests. The application method depends on the active ingredient (bacteria, fungi, viruses, etc.), the target pest or disease and the formulation of the product.
Microbial biopesticides come in various formulations, including wettable powders (WP), water-dispersible granules (WDG) and suspension concentrates (SC). Liquid formulations tend to be sprayed or incorporated into the irrigation system, for example. Microbials can be delivered to the seeds, soil, cuttings, seedlings or maturing/mature plants.
Some application methods include:
- Seed treatment: the microbial biopesticide is applied to seeds before sowing. It prevents pathogens from colonizing the roots and protects the crop during its early stages. You can dip the seeds in the microbe or sprayed with it.
- Seedling dipping: you can dip seedlings or roots of seedlings in a mixture containing the microbial product.
- Soil application: the microbial biopesticide can be applied directly in the soil to control soil-borne diseases and root pests. You can incorporate the product into the soil as is (for example, granules) or mixed with water first.
- Foliar spray application: the product is directly sprayed on plant leaves, targeting foliar diseases and pests feeding on the plant’s top parts. With this method, you must pay attention to environmental conditions, such as rain, UV rays and temperature, which can significantly impact a product’s efficacy.
Bridging the gap: microbial biopesticides and sustainable agriculture
Connecting green chemistry with sustainable development
Microbial biopesticides are made from naturally occurring microorganisms. Their targeted action makes them safer for beneficial organisms and biodiversity, while their quick degradation in the environment prevents long-term soil and water contamination. By enhancing soil health and preserving biodiversity, microbial biopesticides contribute to more sustainable agricultural practices. Integrating these microbial biopesticides into farming systems supports sustainable food production and ensures a healthier ecosystem.
Biopesticides in Integrated Pest Management (IPM)
The low risk and effectiveness of microbial biopesticides make them a valuable element to incorporate into IPM programmes. They are compatible with many other biological products, including macrobials like predators, and they perform even better when combined with scouting and monitoring methods. The use of microbial products in IPM can help decrease the reliance on chemical pesticides and, by doing so, farmers can establish more productive and environmentally sustainable agricultural systems, ensuring food security and ecosystem health.
Challenges and future prospects of biopesticides
The adoption of biopesticides faces challenges such as limited shelf life or variable efficacy due to environmental conditions. Additionally, lack of awareness among farmers can hinder their widespread use. However, ongoing research is always looking at enhancing the stability and efficacy of biopesticides. Technology advances in the field are expected to overcome current limitations.
Easier accessibility to information and increased knowledge on biopesticides can further boost adoption, making biological plant protection products a fundamental component of sustainable agriculture. Tools like the CABI BioProtection Portal raise awareness and facilitate the use of biocontrol and biopesticides products by providing free access to information about registered products and offering educational content to farmers on sustainable pest control practices.
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