Biopesticides and Biocontrol agents

Biopesticides and biocontrol agents are integral components of sustainable agriculture and integrated pest management (IPM) strategies. They offer environmentally friendly alternatives to chemical pesticides, reducing the impact on non-target organisms and the environment while managing pests and diseases effectively. They are generally less toxic to humans and have less impact on the environment. Biopesticides are natural, biologically occurring compounds that are used to control various agricultural pests infesting plants while Biocontrol Agents are the natural enemies which play an important role in controlling the plant pests like nematodes weeds, insects, and mites.

Biopesticides

Biopesticides are natural or biologically derived agents used to control pests, including insects, weeds, and plant diseases. Biopesticides are developed from naturally occurring living organisms such as animals, plants, and microorganisms (e.g., bacteria, fungi, and viruses) that can control serious plant- damaging insect pests They are typically less toxic than conventional pesticides and target specific pests, thereby minimizing harm to beneficial organisms. 

Types of Biopesticides:

1. Microbial Pesticides:
• Description: These are composed of microorganisms such as bacteria, fungi, viruses, or protozoa that target specific pests.
• Examples:
• Bacillus thuringiensis (Bt): A bacterium that produces toxins lethal to certain insect larvae, particularly caterpillars. Bt is used extensively in agriculture and horticulture.
• Trichoderma spp.: Fungi used to control soil-borne pathogens by outcompeting them for nutrients and space, as well as producing antifungal compounds.
• Beauveria bassiana: A fungus that infects and kills a wide range of insect pests, including aphids, whiteflies, and beetles.
• Nucleopolyhedrovirus (NPV): A virus that specifically targets and kills caterpillar pests, such as the cotton bollworm.
2. Botanical Pesticides:
• Description: These are derived from plants and contain natural compounds that have insecticidal, fungicidal, or herbicidal properties.
• Examples:
• Neem oil: Extracted from the seeds of the neem tree (Azadirachta indica), it contains azadirachtin, which disrupts the life cycle of insects by inhibiting feeding, molting, and reproduction.
• Pyrethrins: Derived from the flowers of the chrysanthemum plant, pyrethrins are natural insecticides that affect the nervous system of insects, leading to paralysis and death.
• Rotenone: Extracted from the roots of certain legumes, rotenone is used as an insecticide and piscicide (fish poison).
3. Biochemical Pesticides:
• Description: These are naturally occurring substances that control pests by non-toxic mechanisms, such as interfering with mating, growth, or development.
• Examples:
• Pheromones: Chemicals used to disrupt the mating behavior of insects. For example, sex pheromones can be used in traps to attract and capture male insects, preventing reproduction.
• Insect Growth Regulators (IGRs): Compounds like methoprene and pyriproxyfen mimic insect hormones, disrupting molting and development processes, leading to the death of immature insects.
4. Plant-Incorporated Protectants (PIPs):
• Description: PIPs are made by introducing genetic material from a bacterium into a plant's genome. The plant then manufactures the pesticide, which is toxic to certain pests but not to mammals or other non-target organisms.
• Examples:
• Bt corn: Corn genetically engineered to express Bt toxins, making it resistant to certain insect pests, such as the European corn borer.

Advantages of Biopesticides:

·   Environmental Safety and Low toxicity: Biopesticides are generally less harmful to the environment than synthetic chemicals. They degrade more quickly and have lower toxicity to non-target species, including humans, animals, and beneficial insects.

·  Target Specificity: Many biopesticides are highly specific, targeting only the intended pest species, reducing the risk of harming beneficial organisms.

·  Resistance Management: Biopesticides often have unique modes of action that differ from chemical pesticides, helping to manage and reduce the development of pest resistance.

·   Integration with IPM: Biopesticides can be integrated with other pest management strategies, such as cultural practices, mechanical controls, and the use of natural predators, to create a more sustainable approach to pest control.

·  Improve soil: Biopesticides enhance soil microflora, which improves root and plant growth.

Disadvantages of Biopesticides

·  Slower effects: Biopesticides can take longer to work than chemical pesticides.

·  More expensive: Biopesticides are usually more expensive than synthetic pesticides.

· Spreading over a larger plot takes time: Spreading biopesticides over a larger plot can take time.

· Limited effectiveness: Biopesticides are only effective against target species and may not be effective under certain conditions.

·   Short shelf life: Some biopesticides have a short shelf life.

·  Knowledge required: Biopesticides require a greater level of knowledge to use effectively.

Examples of Microbial Bio pesticides

Bacteria - Bacillus thuringiensis

Bacillus species such as Bacillus thuringiensis israelensis (Bti) and Bacillus  sphaericus (Bs) are particularly effective against mosquito and other dipteran larvae.

Bti was first discovered to have increased toxicity against mosquito larvae in 1975. Bt produces crystalline proteins (δ-endotoxins, and kills few target insect pest species like lepidopteran species.  These toxins, when ingested by the larvae, can damage the gut tissues, leading to gut paralysis. After that, the infected larvae stop feeding and finally they die from the combined effects of starvation and midgut epithelium impairment

Mode of action of Bti against lepidopteran insects  

(https://images.app.goo.gl/jasoEzTij17kj3fT7)

Bt is marketed worldwide for the control of different important plant pests, mainly caterpillars, mosquito larvae, and black flies. Commercial Bt -based products include powders containing a combination of dried spores and crystal toxins. They are applied on leaves or other environments where the insect larvae feed. Toxin genes from Bt have been genetically engineered into several crops.

Fungi -  Metarhizium anisopliae

M.anisopliae are hyphomycete entomopathogenic fungi most widely used for insect pest control and are ubiquitous worldwide. Under natural conditions, Metarhizium are found in the soil, where the moist conditions permit filamentous growth and production of infectious spores, called conidia, which infect soil-dwelling insects upon contact. M. anisopliae has the potential to be used as a biocontrol agent, particularly for malaria vector species.

Mode of action of entomopathogenic fungi against lepidopteran insects

 

Virus – Baculovirus

Baculoviruses are double-stranded DNA viruses present in arthropods, mainly insects. Baculoviruses are usually highly pathogenic and have been used as biocontrol agents against numerous insect pests such as cotton bollworm and budworm, caterpillars that are mainly dangerous insect pests of corn, soybean, and other vegetables.  Baculoviruses need to be ingested by the larvae to initiate infection. After ingestion, they enter the insect’s body through the midgut and from there they spread throughout the body.  Although in some insects, infection can be limited to the insect midgut or the fat body. Two groups of baculoviruses are the nucleopolyhedroviruses (NPVs) and granuloviruses (GVs). In NPVs, occlusion bodies comprise numerous virus particles, but in GVs, occlusion bodies ordinarily contain just one virus particle.

Mode of action of Baculoviruses against lepidopteran insects

 

Protozoa - Nosema

Some protozoan species like Nosema locustae are pathogenic for grasshoppers.  Protozoans produce spores, which are the infectious phase in susceptible insects. Nosema spp. spores are assimilated by the host and develop in the midgut. Germinating spores invade host target cells, inducing massive infection and destroy organs and tissues. Sporulation process begins again from the infected tissues and, upon ingestion by a susceptible host, induces an epizootic infection. Parasitoids and insect predators act as vectors.

 

Nematodes -  Steinernema (Rhabditida)

Various effective entomopathogenic nematodes from two genera, Steinernema and Heterorhabditis (Nematoda: Rhabditida), are used as a biocontrol agent against insects.

Insect-parasitic nematodes may encroach upon soil-dwelling stages of insects and kill them within 48 h through the expulsion of pathogenic bacteria. The parasitic cycle is initiated by the third-stage Infective juveniles.  IJs infest suitable insect host and enter through the insect’s natural body openings like the anus, mouth, and spiracles. Once they have entered inside the host, nematodes infest the hemocoel and then release their symbiotic bacteria into the intestine, the bacteria cause septicemia and kill the host within 24–48 h.  The nematode feed on the cadaver and 2-3 generations will be developed and once the nutritents are depleted, they move on to a new host.

 Mode of action of entomopathogenic nematodes

(https://images.app.goo.gl/17966VzhoAVYDz5u6)

Biocontrol Agents

Biocontrol agents are living organisms that are used to control pest populations through predation, parasitism, herbivory, or other natural mechanisms. They play a crucial role in maintaining ecological balance and reducing reliance on chemical pesticides.

Types of Biocontrol Agents:

1. Predators - Predators are organisms that hunt and consume multiple prey organisms during their lifetime.
• Examples:
• Ladybugs (Coccinellidae): Feed on aphids, mites, and other soft-bodied insects, making them effective in controlling these pests in crops and gardens.
• Lacewings (Chrysopidae): Their larvae, known as "aphid lions," are voracious predators of aphids, caterpillars, and other pests.
• Spiders: Generalist predators that feed on a wide range of insect pests.
2. Parasitoids - Parasitoids are insects whose larvae develop inside or on a host insect, ultimately killing it.
• Examples:
• Trichogramma spp.: Tiny wasps that lay their eggs inside the eggs of pest insects, such as moths and butterflies, preventing them from hatching.
• Aphidius colemani: A parasitoid wasp that targets and parasitizes aphids, helping to control their populations.
• Encarsia formosa: A parasitoid wasp used to control whiteflies in greenhouse crops.
3. Pathogens - Pathogens are microorganisms, such as bacteria, fungi, viruses, or nematodes, that cause disease in pests, leading to their death.
• Examples:
• Metarhizium anisopliae: A fungus that infects and kills insects like locusts, termites, and beetles.
• Steinernema spp.: Nematodes that infect and kill insect larvae, such as those of rootworms and caterpillars.
• Paecilomyces lilacinus: A fungus used to control nematodes that attack plant roots.
4. Herbivores -  These are organisms that feed on weeds, reducing their growth and spread.
• Examples:
• Cactoblastis cactorum: A moth whose larvae feed on prickly pear cactus, effectively controlling its invasive spread in regions like Australia.
• Chrysolina quadrigemina: A beetle used to control the invasive weed St. John’s Wort (Hypericum perforatum).

Advantages of Biocontrol Agents:

• Environmental Compatibility: Biocontrol agents are a natural part of the ecosystem and help maintain ecological balance without introducing harmful chemicals.
• Self-Sustaining: Once established, biocontrol agents can often sustain their populations without repeated human intervention, providing long-term pest control.
• Reduced Chemical Use: The use of biocontrol agents can reduce or eliminate the need for chemical pesticides, lowering the risk of environmental contamination and human health issues.
• Resistance Management: Biocontrol agents help manage resistance development in pests, as they often have complex and multi-faceted modes of action that are difficult for pests to overcome.

Disadvantages of Biocontrol Agents:

• Specificity and Efficacy: While biopesticides and biocontrol agents are often target-specific, their effectiveness can vary based on environmental conditions, pest population levels, and timing of application.
• Cost and Availability: Some biopesticides and biocontrol agents may be more expensive or less readily available than conventional pesticides.
• Regulatory and Adoption Barriers: The registration and approval process for biopesticides can be lengthy, and adoption by farmers may be slow due to lack of awareness or perceived efficacy compared to synthetic pesticides.
• Potential Non-Target Effects: While generally safer, some biopesticides and biocontrol agents can still impact non-target organisms if not used properly.