Biopesticides Cheatsheet

Cheatsheet Content

Biopesticides: Overview and Advantages Definition: Biopesticides are naturally occurring substances or organisms that control pests by non-toxic mechanisms. They are derived from animals, plants, bacteria, and certain minerals. Their use is a cornerstone of Integrated Pest Management (IPM) strategies, aiming to reduce reliance on synthetic chemical pesticides. Components: The active ingredients can be living microorganisms (bacteria, fungi, viruses, nematodes), biochemicals (plant extracts, pheromones), or plant-incorporated protectants (PIPs) where plants are genetically engineered to produce pesticidal substances. EPA Classification: The U.S. Environmental Protection Agency categorizes biopesticides into three main groups: Microbial Pesticides: Consist of a microorganism (e.g., bacterium, fungus, virus, protozoan) as the active ingredient. They control pests by producing toxins, causing disease, or outcompeting pest organisms. Plant-Incorporated Protectants (PIPs): Pesticidal substances that plants produce from genetic material that has been added to the plant. For example, the Bt toxin produced by genetically modified corn. Biochemical Pesticides: Naturally occurring substances that control pests by non-toxic mechanisms. Examples include insect sex pheromones that interfere with mating, and various plant extracts. Advantages of Biopesticides: Environmental Safety: Generally less toxic to non-target organisms (humans, wildlife, beneficial insects) and the environment compared to conventional pesticides. Biodegradability: Break down quickly in the environment, reducing concerns about persistent residues in food and water. Target Specificity: Often highly specific to their target pests, minimizing harm to beneficial insects and pollinators, which are crucial for ecosystem health. Reduced Residues: Leave minimal to no harmful residues on crops, making them suitable for pre-harvest application. Resistance Management: Can be rotated or combined with chemical pesticides to manage or delay the development of pesticide resistance in pest populations. Organic Farming Compatibility: Many biopesticides are approved for use in organic agriculture, supporting sustainable food production. Worker Safety: Generally pose lower risks to agricultural workers due to their reduced toxicity. Limitations and Desirable Properties Disadvantages/Limitations: Slower Action: May have a slower kill rate compared to fast-acting chemical pesticides, which can be problematic for acute pest outbreaks. Environmental Sensitivity: Efficacy can be highly dependent on environmental conditions like temperature, humidity, and UV radiation, which can degrade active ingredients. Storage and Shelf Life: Many microbial biopesticides require specific storage conditions (e.g., refrigeration) and have a shorter shelf life than chemical pesticides. High Specificity: While an advantage, it can also be a disadvantage if the pest identification is incorrect or if multiple pests need to be controlled. Limited Standalone Use: Often work best as part of an Integrated Pest Management (IPM) program rather than as a sole control method. Cost and Production: Production can sometimes be more complex and costly than synthetic alternatives, although this is improving. Resistance Development: Although less common than with chemical pesticides, pests can still develop resistance to biopesticides over time. Desirable Properties of Biological Control Organisms: To be effective and commercially viable, a biological control agent should possess these qualities: High Virulence: Capable of causing significant harm or death to the target pest. Host Specificity: Pathogenic to the target pest but non-pathogenic to non-target organisms (humans, animals, beneficial insects, crops). Rapid Action: Needs to act quickly enough to prevent significant crop damage. Predictable Efficacy: Consistent and reliable pest-killing ability under field conditions. Safety Profile: Safe for handlers, consumers, and the environment. Production Scalability: Amenable to cost-effective mass production on an industrial scale. Stability: Maintain viability and efficacy under various environmental conditions (e.g., temperature, UV light) during application. Shelf Stability: Viable for reasonable periods during storage and transport. Persistence and Recyclability: Ideally, able to persist in the environment or reproduce within the pest population for ongoing control. Host Searching Ability: For mobile agents, the capacity to actively seek out and infect target pests. Biopesticide Classification & Modes of Action Microorganism-based pesticides: These utilize living microbes or their by-products. Biofungicides, Bioinsecticides, Bioherbicides: Examples include bacteria, fungi, viruses, and protozoa. They control pests through various mechanisms such as: Infection: Directly infecting and causing disease in the pest. Toxin Production: Releasing specific toxins that are harmful to the pest. Competition: Outcompeting pest organisms for resources or colonization sites. Antagonism: Suppressing pest growth or activity. Plant-incorporated protectants (PIPs): These are genetically modified plants that produce substances to protect themselves from pests. Transgenic Products: Plants are engineered to express genes from other organisms (e.g., Bacillus thuringiensis genes) to produce insecticidal or disease-resistant proteins within their tissues. This provides built-in pest protection. Biochemical-based pesticides: These are naturally occurring substances that control pests through non-toxic mechanisms. Plant Essential Oils & Extracts: Compounds derived from plants that can repel, deter feeding, or disrupt pest development (e.g., neem oil, pyrethrins). Pheromones: Chemical signals used by insects for communication (e.g., sex pheromones used for mating disruption). Insect Growth Regulators (IGR): Mimic or interfere with hormones that regulate insect growth and development, preventing them from maturing or reproducing. Mechanisms: Act through non-toxic ways like anti-feeding (deterring pests from eating), mating disruption (preventing reproduction), desiccation (drying out pests), suffocation (blocking breathing), or repellency. Advanced Technologies in Biopesticides: RNA Interference (RNAi): A molecular biology technique where double-stranded RNA (dsRNA) is introduced into a pest. This dsRNA triggers a natural cellular process that silences specific genes essential for the pest's survival, leading to its death or impaired development. Can be delivered via engineered bacteria or as a spray. Nanotechnology: Involves the use of materials at the nanoscale (1-100 nm) to encapsulate, deliver, or enhance the stability and efficacy of biopesticides. Bionanopesticides use biologically derived nanoparticles or encapsulate biopesticides within nano-carriers for improved targeting, controlled release, and protection against environmental degradation. Bacterial Biopesticides Bacteria are among the most common and effective microbial biopesticides, primarily targeting insect pests. Mode of Action: They typically produce toxins that disrupt the pest's digestive system or cause systemic infection. Common Genera: Key bacterial genera used in biopesticides include Bacillus , Pseudomonas , Burkholderia , Xanthomonas , Enterobacter , Streptomyces , and Serratia . These bacteria exhibit diverse mechanisms, including toxin production, antibiotic synthesis, and competitive exclusion. Bacillus thuringiensis (Bt): The Leading Bacterial Biopesticide Prevalence: Accounts for approximately 75% of all commercial bacterial biopesticides due to its high efficacy and specificity. Key Components: During sporulation, Bt produces characteristic protein crystals (parasporal bodies) alongside spores. These crystals contain insecticidal proteins known as Cry (crystal) toxins and Cyt (cytolytic) toxins . Cry Toxins: A diverse family of proteins, each encoded by specific cry genes. Different Cry toxins target different insect orders (e.g., lepidopteran, coleopteran, dipteran). Cyt Toxins: A smaller family of toxins that are cytolytic (cell-lysing) and can enhance the activity of Cry toxins, particularly against dipteran pests. Specificity: Bt toxins are highly selective, acting only on specific insect species that possess the necessary gut conditions and receptors for activation and binding. This makes them safe for beneficial insects and vertebrates. Genetic Diversity: The presence of plasmids carrying cry genes allows for genetic exchange between Bt strains, leading to a wide variety of toxin combinations. Transposons (jumping genes) further contribute to this genetic plasticity, enabling the evolution of novel toxin repertoires. This natural diversity is exploited to develop biopesticides effective against a broad spectrum of pests. Other Notable Bacterial Biopesticides: Bdellovibrio bacteriovorus: A predatory bacterium that invades and consumes other Gram-negative bacteria. It shows promise in controlling bacterial phytopathogens (plant disease-causing bacteria). Lysinibacillus sphaericus: Known for its larvicidal activity against mosquitoes, it also exhibits potential in controlling plant diseases like rice sheath blight and has plant growth-promoting properties. Pseudomonas aeruginosa: Certain strains produce antimicrobial compounds and can induce systemic resistance in plants, offering protection against fungal pathogens like Colletotrichum capsici in chili plants. Mode of Action of Bt Toxin (Detailed Pathway) Ingestion: The insect pest, typically a larva, ingests the plant material treated with Bt, consuming the inactive protoxin crystals and spores. Solubilization in Mid-gut: In the highly alkaline environment of the insect's mid-gut (pH typically > 9.5, unlike the acidic mammalian gut), the insoluble protoxin crystals (molecular weight 130-140 kDa) dissolve. Proteolytic Activation: Once dissolved, the protoxins are cleaved by specific proteases (enzymes) present in the insect's gut into smaller, active toxin fragments (molecular weight approximately 60 kDa). These active fragments are often referred to as delta-endotoxins. Receptor Binding: The activated toxin binds with high affinity and specificity to unique receptor proteins located on the brush border membrane of the insect's mid-gut epithelial cells. Key receptors include Cadherin, GPI-anchored aminopeptidases, and ABCC2 transporters. The presence and specific type of these receptors determine the host specificity of different Bt toxins. Pore Formation: Upon binding, the toxin molecules undergo a conformational change and insert into the cell membrane, forming ion-permeable pores or channels. Disruption of Osmotic Balance: The formation of pores leads to the leakage of ions and water into the epithelial cells, causing swelling and ultimately lysis (bursting) of the cells. This disrupts the osmotic balance of the mid-gut. Cessation of Feeding: The damage to the mid-gut epithelium and the disruption of ion transport cause the insect to stop feeding within hours of ingestion. This is often the first visible symptom. Systemic Infection: The damaged gut wall allows the Bt spores (also ingested) and other gut bacteria to penetrate the insect's hemocoel (body cavity). The disrupted gut pH further facilitates the germination of Bt spores. Lethal Septicaemia: The proliferation of bacteria in the hemocoel leads to a fatal systemic infection (septicaemia), ultimately killing the insect within a few days. Specificity Explained: The strict requirement for alkaline conditions to solubilize the protoxin and the presence of highly specific receptors on the mid-gut cells are the primary reasons for Bt toxin's remarkable specificity to certain insect orders, making it harmless to most other organisms. Production of Biological Insecticides Submerged Fermentation (SMF): This is the most common method for producing bacterial biopesticides like Bt, especially for facultative pathogens that can grow in liquid culture. Medium Composition: Typically uses inexpensive carbon sources like molasses or dextrose, nitrogen sources such as corn steep liquor or soya bean meal, and mineral supplements like $\text{CaCO}_3$, $\text{MgSO}_4$, $\text{FeSO}_4$, $\text{ZnSO}_4$. Process Flow: Inoculum Preparation: A small amount of microbial culture is grown in a primary culture vial. Seed Culture: This is scaled up in shake flasks and then in a seed fermentor to produce a sufficient volume of active inoculum. Main Fermentation: The seed culture is transferred to a large-scale SmF bioreactor, where optimal conditions (temperature, pH, aeration, agitation) are maintained for maximum microbial growth and toxin production. Downstream Processing: After fermentation, the culture broth is harvested. Centrifugation is used to separate microbial cells (and associated toxins/spores) from the spent medium. The concentrated product is then formulated (e.g., as wettable powders, granules, or liquid concentrates) with stabilizers and adjuvants to enhance shelf life and efficacy. Surface or Semi-solid Fermentation (SSF/Koji process): This method is particularly suitable for fungi and spore-forming bacteria, mimicking their natural growth on solid substrates. Medium Composition: Utilizes readily available agricultural by-products such as wheat bran, rice husk, or soybean meal, often supplemented with dextrose and mineral salts. Process: Inoculation: The organism is first grown in a seed tank to produce a liquid inoculum. Substrate Loading: This broth is then sprayed onto thin layers of the solid substrate, which are spread in shallow bins or trays with perforated bottoms. Incubation & Aeration: The thin layers ensure good aeration and heat dissipation. Hot air is often passed through the substrate for drying. Harvesting & Formulation: The dried, colonized substrate is then ground into a powder, assayed for active ingredient concentration, and compounded with inert carriers to produce the final biopesticide product. In vivo Production: This method is necessary for obligate pathogens, such as many insect viruses (e.g., baculoviruses), which can only replicate within living host cells or organisms. Process: Involves infecting live insect larvae or insect cell cultures with the pathogen. The host insects are reared under controlled conditions, infected, and then harvested once the pathogen has replicated sufficiently. Harvesting: Infected insects are typically homogenized, and the pathogen (e.g., viral occlusion bodies) is extracted and purified. Extraction and Formulation Technologies: Recovery Methods: Active components (e.g., spores, toxins, viral particles) are recovered from fermentation broths or homogenized infected hosts using techniques like centrifugation, vacuum filtration, or precipitation (e.g., with $\text{CaCl}_2$, ammonium sulfate, or acetone). Formulation: The concentrated active ingredients are then formulated into various delivery systems (e.g., wettable powders, emulsifiable concentrates, granules) with additives that protect them from degradation, enhance spread, and improve shelf life. Viral Biopesticides (Baculoviruses) Viruses, particularly those in the Baculoviridae family, are highly effective and environmentally safe biopesticides due to their insect specificity and lack of pathogenicity to vertebrates. Family: Baculoviridae is the most well-studied and utilized family of insect viruses for pest control. Mechanism: Baculoviruses primarily infect and kill insect larvae by disrupting their physiology and causing systemic disease. They can also be engineered to express insect-specific toxins for faster action. Baculovirus Characteristics: Structure: Double-stranded, circular DNA genome encased in a rod-shaped nucleocapsid. Virion Types: Produce two distinct types of virions during their life cycle: Budded Virions (BVs): Responsible for systemic infection within the host insect. Occlusion-Derived Virions (ODVs): Responsible for primary infection of the mid-gut cells and for environmental transmission between hosts. Occlusion Bodies (OBs): A hallmark of baculoviruses. These are proteinaceous protective structures that encapsulate many ODVs. OBs provide environmental stability, protecting the virions from UV radiation and desiccation, and are crucial for the transmission of the virus. OB Composition: OBs are primarily composed of a single viral protein: Polyhedrin: Forms the matrix of OBs in Nucleopolyhedroviruses (NPVs), which are typically polyhedral (many-sided) in shape. Granulin: Forms the matrix of OBs in Granuloviruses (GVs), which are smaller and ovocylindrical (granule-like) in shape. NPVs vs. GVs: Nucleopolyhedroviruses (NPVs): Contain multiple virions (ODVs), each with one or more nucleocapsids, within a single OB. They are further classified as multiple nucleocapsid NPVs (MNPVs) or single nucleocapsid NPVs (SNPVs) based on the number of nucleocapsids per envelope within the ODV. Granuloviruses (GVs): Contain only a single virion (ODV) with a single nucleocapsid within each small, granule-like OB. Mode of Action (Baculovirus Life Cycle and Infection): Ingestion: Susceptible insect larvae ingest the stable OBs (polyhedra or granules) present on contaminated plant foliage. Dissolution in Mid-gut: In the alkaline environment of the insect's mid-gut, the protein matrix of the OBs dissolves, releasing the occlusion-derived virions (ODVs). Primary Infection: The ODVs infect and replicate within the epithelial cells of the insect's mid-gut. Systemic Spread (Budded Virions): Newly produced virions, known as budded virions (BVs), bud from the infected mid-gut cells and enter the hemocoel (insect body cavity). These BVs then spread the infection systemically to other tissues and organs (e.g., fat body, epidermis, tracheal matrix). Secondary Replication and OB Formation: In these secondary infected cells, the virus undergoes further replication, and large numbers of ODVs are produced and encapsulated within newly synthesized OBs in the cell nucleus. Host Death and Liquefaction: The massive viral replication and accumulation of OBs lead to the breakdown of host tissues. The infected larva typically becomes sluggish, stops feeding, and often climbs to elevated positions before dying. The cadaver often liquefies, releasing billions of OBs onto the plant surface, ensuring environmental transmission to new hosts. Advantages as Biopesticides: Highly effective against specific target pests, host-restricted (safe for non-targets), relatively easy to produce (via in vivo insect rearing), and environmentally stable due to OBs. Fungal Biopesticides Entomopathogenic fungi (insect-killing fungi) are important natural enemies of insects and mites. They infect insects through their cuticle, making them effective against a wide range of pests that may not ingest pesticides. Mechanism of Action: Fungi infect and grow inside the insect, producing toxins or causing mechanical damage, leading to the host's death. Common Genera: Widely used fungal biopesticides include species from Beauveria , Metarhizium , Isaria (formerly Paecilomyces ), Verticillium , and Trichoderma (primarily for plant diseases but some strains have insecticidal properties). Detailed Mode of Action (Entomopathogenic Fungi): Attachment: Conidia (spores) of the fungus adhere to the insect's cuticle (outer surface). Germination: Under favorable conditions (high humidity), the conidia germinate and produce a germ tube. Penetration: The germ tube forms an appressorium (a specialized infection structure) and penetrates the cuticle using a combination of mechanical pressure and enzymatic degradation (chitinases, proteases, lipases). Invasion and Growth: Once inside the hemocoel (insect's body cavity), the fungus proliferates, typically as hyphae or yeast-like cells (blastospores), absorbing nutrients from the host's hemolymph. Toxin Production: Many entomopathogenic fungi produce insecticidal toxins (e.g., destruxins from Metarhizium , beauvericin from Beauveria ) that contribute to the host's death by disrupting physiological processes. Host Death: The insect dies from a combination of nutrient depletion, tissue damage, and toxemia (toxin poisoning). Sporulation: After the host's death, under humid conditions, the fungus often grows out of the cadaver and produces new conidia on the insect's surface, turning it into a "mummy" and facilitating further spread to other insects. Specific Examples and Mechanisms: Beauveria bassiana: A broad-spectrum entomopathogenic fungus used against a wide range of insects, including whiteflies, thrips, aphids, and beetles. Metarhizium anisopliae: Effective against soil-dwelling insects and various pests like locusts, grasshoppers, and weevils. For example, it is used to control fall armyworm by causing mycosis. Trichoderma spp.: Primarily known as biofungicides and plant growth promoters, some strains exhibit mycoparasitism (parasitizing other fungi), competition for nutrients, and produce lytic enzymes against plant pathogens. Indirectly, they can enhance plant resistance to pests. Paecilomyces lilacinus (now Isaria lilacinus ): A well-known nematophagous fungus, effective against plant-parasitic nematodes, particularly root-knot nematodes. It colonizes nematode eggs and juveniles. Arthrobotrys flagrans: A nematode-trapping fungus that forms adhesive nets or constricting rings to capture and kill nematodes in the soil. Biochemical Pesticides (Plant-Based and Pheromones) Biochemical pesticides are naturally occurring substances that control pests through non-toxic mechanisms, often by disrupting behavior, growth, or reproduction rather than directly killing them. Plant Extracts & Oils (Botanical Pesticides): These are derived from plants and have been used for centuries due to their repellent, antifeedant, growth-disrupting, or direct pesticidal properties. Pyrethrins: Extracted from the flowers of Chrysanthemum cinerariifolium (pyrethrum daisy). Mechanism: Act as neurotoxins, disrupting nerve impulse transmission in insects. They cause rapid knockdown but insects can recover if not exposed to synergistic compounds. Properties: Fast-acting, low mammalian toxicity, and rapidly degrade in sunlight, minimizing environmental persistence. Target Pests: Broad-spectrum, effective against many flying and crawling insects (e.g., mosquitoes, flies, ants, cockroaches). Rotenone: Derived from the roots of certain legumes (e.g., Derris , Lonchocarpus ). Mechanism: Inhibits cellular respiration in insects and fish. Target Pests: Used as an insecticide for leaf-eating insects and as a piscicide (fish poison). (Note: Its use has declined due to toxicity concerns for non-target organisms). Neem ( Azadirachta indica ): Extracts (e.g., Azadirachtin) from the neem tree. Mechanism: Acts as an antifeedant (deters feeding), insect growth regulator (disrupts molting), and repellent. Target Pests: Broad-spectrum, effective against over 200 insect species. Sabadilla: Derived from the seeds of Schoenocaulon officinale . Mechanism: Contains alkaloids (veratrine) that affect nerve cell membranes, leading to paralysis and death. Target Pests: Effective against squash bugs, thrips, and stink bugs. Nicotine: An alkaloid derived from tobacco ( Nicotiana tabacum L.). Mechanism: Acts as a neurotoxin, mimicking acetylcholine and causing uncontrolled nerve firing, leading to paralysis and death. Target Pests: Used as a contact and stomach insecticide. (Note: Highly toxic to mammals and its use is restricted). Other Plant-derived Compounds: Limonene, Linalool: Terpenes found in citrus and other plants, used as repellents and insecticides against fleas, mites, and aphids. Garlic ( Allium sativum L.): Extracts contain sulfur compounds that act as repellents against insects and birds. Lantana camara: Extracts show promise in immobilizing and killing root-knot nematodes. Insect Pheromones: These are chemical substances released by insects to communicate with others of the same species. They are used in pest control to disrupt mating or to monitor pest populations. Mechanism: Pheromones are typically highly species-specific. For pest control, synthetic versions of sex pheromones are most commonly used. Applications: Mating Disruption: Large amounts of synthetic pheromone are released into the environment, confusing male insects and preventing them from finding females, thereby reducing successful mating and subsequent pest populations. Mass Trapping: Pheromones are used as lures in traps to capture large numbers of pests, reducing their population. Monitoring: Pheromone traps are used to detect the presence of pests and monitor their population levels, helping farmers decide when and if to apply other control measures. Advantages: Extremely specific, non-toxic, and effective at very low concentrations. Biopesticide Bioformulations The efficacy, stability, and ease of application of biopesticides are highly dependent on their formulation. Formulations protect the active ingredients from environmental degradation, ensure uniform application, and enhance their interaction with the target pest. Solid Carrier Formulations: These are dry formulations where the active ingredient is adsorbed or incorporated into a solid carrier material. Granules (G), Microgranules (MG): Small, uniform particles applied to soil or water. Provide slow release and are less prone to drift. Dispersible Granules (WG/WDG): Dry granules that disperse readily in water to form a suspension for spraying. Dry Powders (DP): Fine powders applied directly or mixed with water. Wettable Powders (WP): Fine powders that form a suspension when mixed with water; contain wetting agents to aid dispersion. Peat, Dust, Pellets, Tablets: Various forms for specific applications (e.g., soil amendments, seed treatments, water treatments). Tablets can be effervescent (dissolve with fizzing), water dispersible, floating (for aquatic pests), or bait forms. Liquid Formulations: These are liquid preparations ready for dilution or direct application. Ultra-low Volume Suspension (ULV): Concentrated liquid formulations applied in very small volumes without dilution, often used in aerial spraying. Oil Dispersion (OD): Active ingredient dispersed in oil, often used for better cuticle penetration in insects. Oil-miscible Flowable Concentrates (OF): Liquid formulations that mix easily with oil-based carriers. Emulsion (EW, EC): Active ingredient dissolved in an organic solvent and then emulsified in water (Emulsion, Water in oil - EW) or an oily solution forming an emulsion when diluted in water (Emulsifiable Concentrate - EC). Suspension Concentrate (SC): Fine particles of active ingredient suspended in a liquid, designed to be diluted with water before spraying. Polymer Entrapped Formulations (Encapsulation): Involve enclosing the active ingredient within a protective polymer matrix. Capsule Suspension (CS): Microcapsules containing the active ingredient suspended in a liquid. Provides controlled release and protection from degradation. Encapsulation (Micro/Macro Encapsulation): Techniques that enclose small particles (micro) or larger quantities (macro) of the biopesticide within a protective barrier, improving stability, enhancing UV protection, and enabling slow, sustained release. Fluidized Bed Dry Formulation: A specialized drying technique that produces dry, free-flowing granules or powders with enhanced stability and solubility by fluidizing the active ingredient particles with hot air.