Insect Physiology and Toxicology - Insecticide Research and Development

Pesticides and Plant Protection Products (PPP)

  • Definition: Any substance or mixture intended for preventing, destroying, repelling, or mitigating any pest.
  • Scope: Includes insects, rodents, nematodes, fungi, weeds, terrestrial or aquatic plants or animals, viruses, bacteria, or other micro-organisms (excluding those on or in living humans or animals).
  • Also includes substances intended for use as plant regulators, defoliants, or desiccants (Ballantyne & Marrs, 2004).

EU Definition of Pesticide

  • A substance that prevents, destroys, or controls harmful organisms or diseases or protects plants/plant products during production, storage, and transport.
  • Classes:
    • Herbicides: Weeds/unwanted plants.
    • Fungicides: Fungi and fungal-like organisms.
    • Insecticides: Insects, mites, and other arthropods.
    • Acaricides: Ticks and mites.
    • Nematicides: Plant-parasitic nematodes.
    • Molluscicides: Mollusks, slugs, etc.
    • Rodenticides: Rodents and relatives.
    • Growth regulators: Plant hormones to modify plant growth.
    • Repellents: Repel pests.
    • Biocides: Chemical or microorganisms against organisms (European Union website, 2021).

Why Crop Protection is Required

  • High-yielding crop plants are susceptible due to:
    • Lack of co-evolution with pests & pathogens.
    • Loss of antimicrobial/insecticidal metabolites through breeding for digestibility.
    • Accumulation of substrate (carbohydrates, proteins).
    • Cultivation in annual cycles & in monoculture.
  • Increased demand for food, feed, fuel, and raw materials is estimated at 70-100% by the end of this century due to a population exceeding 10 billion.

Global Crop Production

  • Yield losses occur due to weeds, pathogens, viruses, and animal pests (E.C. Oerke, J. Agricult Science 144, 31-43, 2006).
  • The effect of crop protection and pesticide use on attainable yield.

Potential Positive Effects of Crop Protection

  • Global food security and reduction of hunger.
  • Reduction of land (forest) consumption for agriculture.
  • Reduction of risks from microbial contaminations of food with toxic (mycotoxins), allergenic, or carcinogenic fungal excretions.
  • Improved supply of fruits and vegetables at lower prices.
  • Securing agriculture in peripheral, less suitable areas.

Potential Negative External Effects of Continuous and Judicious Use

  • Pollution of ground and surface water.
  • Reduction of biodiversity/non-target organisms.
  • Health risk for users and consumers of plant products.
  • Resistance build-up in pest populations.

Insecticides defined

  • Chemicals that kill insects.
  • Longer and more noteworthy history due to the vast number of insects labeled as pests.
  • Occupy the biggest bulk of total pesticidal products, with extensive R&D programs by various chemical industries.

History of Insecticide Development

Inorganics

  • Sulfur: First recorded as insecticide (repellant) in 2500 BC.
  • Earliest insecticides were mainly inorganic compounds: inorganic sulfur (since 1000 BC) and arsenic (900 AD).
  • Other inorganics include lead arsenate (PbHASO4), calcium arsenate (Ca3 (AsO4)2), sodium arsenite (NaAsO2), sodium fluorides (NaF), cryolite or sodium fluoroaluminate (Na3AlF6), sodium fluorosilicate (Na3SiF6), and boric acid (H3BO_3).
  • 1855: Use of fine sulfur dust by Bequerel (France).
  • 1885: (Ca(OH)2) x CuSO4 (Bordeaux mixture, Pierre-Marie-Alexis Millardet) discovered in 1882.
    • Preventive treatment for grapevine downy mildew and potato blight.
    • Copper inhibits the germination of fungal spores.
    • Copper is a soil pollutant and bioaccumulates in organisms.
  • Circa 1915: Mercury compounds (e.g., (HgCl_2)).

Botanicals

  • Nicotine: First used in 1763; an alkaloid present in tobacco (Nicotiana tabacum: 2-5%) and its relative (Nicotiana rustica: 5-15%); highly toxic to mammals.
  • Rotenone: First rotenoid used before organosynthetic insecticides; isolated by Emmanuel Geoffroy in 1892 and named nicouline; isolated from Derris spp. and Tephrosia spp. and limited extent from yam bean (seeds) (Pachyrizhus erosus).
  • Pyrethroids: Natural pyrethroids are insecticides derived from flowering plants belonging to the genus Chrysanthemum, Family Asteraceae.
  • Flowers of C. cinerafolium and C. coccineum contain the highest concentration of the insecticidal metabolite pyrethrin.
  • Synthetic pyrethroids are based on the pyrethrum compounds consisting of six esters.

Milestones in history of chemical pesticides since 1800

  • 1810: Systematic testing of inorganic seed dressing against smuts
  • 1885: Copper sulfate seed dressing against wheat covered smut (bunt)
  • 1913: Bordeaux mixture (Copper sulfate + hydrated lime) by Millardet
  • 1942: Organic mercury against cereal smut and snow mold
  • 1948: DDT used as insecticide
  • 1948: Phosphoric acid esters (E605, Parathion), growth-regulating herbicides (2,4 D, first selective herbicide)
  • 1960: Dithiocarbamates (Maneb, Mancozeb), first organic funigicides
  • 1960: B. thuringiensis biologicals against Lepidopterans
  • 1966: Introduction of CCC as growth regulators in cereals
  • 1966: Carboxin, first systemic fungicide (loose smut)
  • 1986: Novel concept “Integrated Pest Management” (IPM) introduced into legal regulation
  • 1987: Herbicide tolerant cultivars of maize and soy bean (“GMO crops“)
  • 1987: Transfer of Bt gene into maize and other crop plants
  • 1993: Introduction of strobilurins
  • 1997: Registration of Contans®, first biological fungicide in Europe

Modern Insecticides

  • Chlorinated hydrocarbons
  • Organophosphorus
  • Carbamates
  • Pyrethroids
  • Neonicotinoids
  • Miscellaneous, newer generations of insecticides

Biorationals

  • Microbial, Spinosad, Insect Growth Regulators (IGR), Pheromones

Insecticide Production

  • Process from laboratory to market takes an average of 5 to 9 years at a cost of US$$50-90 million; in Europe, it takes 11 years and ~€200 million.
  • Undergoes rigorous testing and evaluation before approval from regulatory agencies (e.g., EPA in US, EFSA in Europe, FPA in Philippines).
  • The active ingredient has to undergo approximately 140 various environmental, ecological, and toxicological studies.
  • Process in Production of Insecticides
    • SYNTHETIC INSECTICIDES
  • Development and synthesis in the laboratory: extraction and synthesis of the chemical may be done via design, inspirations or by accident
  • Assay for biological activity
  • Mixing of promising chemicals to improve solubility, stability, ease of handling and performance
  • Development of a formulation (mixing of the bioactive compounds with anything to alter physical properties)
  • BIOLOGICAL INSECTICIDES
  • A new line in the pesticide industry for use in the integrated control of insects
  • Applies the techniques of industrial microbiology used in pharmaceutical (biotechnical) industry
  • Example are Bacillus thuringiensis (manufacturing process aimed a production of a “spore-crystal complex” which constitutes the active ingredient of the formulated biological insecticide

Players in Global Market of Pesticides (2020)

  • Top companies by 2019 revenue ($ billion):
    1. Syngenta (ChemChina) (Switzerland): 10.4
    2. Bayer Crop Science (Germany): 8.16
    3. BASF (Germany): 6.76
    4. Dow AgroSciences (United States): 4.66
    5. FMC (United States): 4.28
    6. ADAMA (Israel): 3.88
    7. Nufarm (Australia): 3.76
    8. Sumitomo Chemical (Japan): 3.14
    9. UPL (India): 3.14
    10. Huapont Life Sciences (China): 1.41

Insecticide Formulations

  • Definition: Physical mixture of one or more insecticide(s) (a.i.) and inert ingredients that provides effective and economical insect control.
  • Each formulation has one or several biologically active chemicals.
  • The form of an insecticide product in the market which is ready to use either as undiluted product or to be diluted with solvents (e.g., water or organic solvents) or other carriers such as inert clays or silicates.

Rationale in Making a Formulation

  • To make the insecticide easier to package, transport, store, and apply.
  • For chemical stability, prevention of corrosion of containers, and desirable physical properties.
  • For improved biological efficacy

Factors That Determine Formulation of Insecticides

  1. Chemical properties of pesticides (insecticides) e.g., hydro- or lipo-philic (phobic), stability of chemicals
  2. Physical properties of pesticides (insecticides) e.g., solubility, volatility, sublimation
  3. Reactivity of pesticides (insecticides)
  4. Mode of Action
  5. Probable physical or chemical properties of formulation affect only the activity, mode of action, desirability but also the sale of pesticide

Composition of an Insecticide Formulation

  1. Active ingredient (a.i.) (technical material): Any material in a pesticide (insecticide) formulation which has insecticidal activity. It is the most important component, either single or mixture
  2. Diluent: Inert materials used to dilute an active insecticidal chemical or the active ingredient, either solid, liquid, or gas (aerosols).
  3. Solvent: Substance in which the solute is dissolved, distributes the solute evenly throughout the solution system. Categories of Solvents
    • Solvents not miscible in water. Used in emulsifiable concentrates. Example: xylene (a solvent of choice in many emulsifiable concentrates).
    • Solvents miscible in water. Used in solution concentrates. Example: Isopropanol and Glycoethers
    • Important property of solvents is their miscibility in water
  4. Surfactant: Surface active agents Materials which facilitate and accentuate the emulsifying, dispersing, wetting and other surface-modifying properties of pesticide preparations
  5. Carrier: Liquid or solid material added to a chemical to facilitate its use
  6. Adjuvant: A non-toxic material added to a pesticide to improve toxicity and effectiveness May be added to a formulations by the manufacturer or to the final spray mixture by the user
  7. Synergist: Substance with little or no activity but may greatly improve the potency or activity of the active ingredient. May or may not be added
  8. Preservatives: (Usually an antioxidant) Materials usually added to slow down decomposition of a.i.
  9. Perfumes: Gives pleasant odor to the pesticides (insecticides), may or may not be added
  10. Coloring materials: Material added to differentiate them from non-toxic ones, may or may not be added

Types of Insecticide Formulation

  • Group 1: Concentrates for dilution with water
    • EC - Emulsifiable Concentrate
    • SC - Suspension Concentrate (Flowable Concentrate)
    • CG - Encapsulated Granule
    • SL - Soluble Concentrate
    • WP - Wettable Powder
    • WG - Water-Dispersible Granules
    • DC - Dispersible Concentrate
  • Group 2: Concentrates for dilution with organic solvents
    • OL - Oil Miscible Liquid
    • OF - Oil Flowable Concentrate (Oil Miscible Suspension)
    • OP - Oil Dispersible Powder
  • Group 3: Formulations Applied Undiluted
    • GR - Granules
    • DP - Dustable Powder
    • UL - Ultra Low Volume (ULV) Liquid
    • ED - Electro-chargeable Liquid
Conventional Formulation: Solid
  • Wettable Powder (WP)
    • Formulated to control bioavailability and physical behavior of the a.i. via containment within a polymer shell or matrix; applied by spraying.
  • Dustable Powder (DP)
    • Finely ground mixtures of the active ingredient with talc, clay, or powdered nut shells.
    • Used dry and never mixed with water. Some a.i. that may harm if applied as an EC can be applied without harm as a dust.
    • Percentage of a.i. is usually quite low, available for use on seeds, plants and animals.
  • Granules (GR)
    • Similar to dust formulations but with larger, heavier particles.
    • Composed of a.i., solid carrier (mineral or biological), and formulants to ensure bioavailability.
    • A.i. coats the outside or is absorbed into the granules.
    • The amount of a.i. is relatively low, usually ranging from 1 to 15 % by weight.
    • Designed to be applied to the soil, either onto the surface or in a furrow during planting, to provide control of the target pests. Once applied, granules release the active ingredient slowly.
  • Baits (BT)
    • A.i. mixed with food or other attractive substances.
    • Used to control household pests such as ants, roaches, flies, and other insects; also used for fruit flies.
    • Bait either attracts the pests or is placed where the pests will find it and insects are killed when they eat the bait that contains the active ingredient
    • The amount of active material in most bait formulations is quite low, usually less than 5%.
Conventional Formulation: Liquid
  • Emulsifiable Concentrate (EC)
    • A solution of a.i. in a non-water miscible solvent, usually organic in nature (benzene, xylene)
    • Insoluble, so an emulsifier is added to disperse the concentrate when water is added, and forms an emulsion
    • Emulsion – a system consisting of minute globules of one liquid dispersed in another (e.g., oil dispersed in water); a mixture of 2 liquids held together by a third chemical or emulsifier; turns milky when mixed with water
  • Suspension Concentrate (SC)
    • Stable suspension of a.i. in a fluid intended for dilution with water before use.
    • Developed for a.i. that are neither soluble in oil nor in water; a.i. is blended with a solid carrier, such as inert clay and a small quantity of water in a mixing mill to form a concentrated suspension.
    • Wetting agents, dispersing agents, and special additives may be added during the formulation process. Further diluted with water before application as a spray.
Conventional Formulation: Aerosol and Fumigants
  • Aerosols (A)
    • Contain one or more low content active ingredients and a solvent.
    • Two types of aerosol formulations: the ready-to-use pressurized sealed containers and those used in electrical or gasoline-powered aerosol generators that release the formulation as “smoke” of “fog."
    • Ready-to-use Aerosol: Formulations in a canister in which the insecticide is driven through a fine opening by an inert gas under pressure, creating fine droplets.
  • Fumigants
    • Form poisonous gases when applied
    • A.i are liquids when packaged under high pressure and change to gases when they are released; others are volatile liquids when enclosed in an ordinary container
    • Used for structural pest control, food and grain storage facilities, and regulatory pest control ports of entry. In agricultural control, fumigants are used in soil, greenhouses, granaries and grain bins.

New Generation Insecticide Formulations

  • Encapsulated Granule (CG)
    • A formulation of granule with protective and release-controlling coating.
    • Micro-encapsulation is a technique used to surround microscopic droplets of an a.i. with a thin, crosslinked polymeric plastic skin that forms the capsule wall.
  • Oil-in-Emulsion (EW)
    • Products prepared by dissolving the a.i. in oil, and the oil solution is then emulsified into a water carrier.
    • In addition to a.i. and the oil-water combination, EWs will require emulsifier surface active agents, and may typically contain other formulants to enhance emulsion stability and influence biological activity.
  • Suspoemulsion (SE)
    • Consists of solid particles or polymer capsules suspended in an emulsion system.
    • Typically, contains one or more solvent-soluble a.i. in an emulsion phase, with one or more low solubility a.i. in a continuous aqueous suspension phase.
  • Water-dispersible granule (WG)
    • Also known as dry flowables, are like wettable powders except instead of being dustlike, they are formulated as easily measured granule.
    • Appear as free-flowing small granules; the shape of which ranges from composite, popcorn-shaped to nearly smooth spheres, depending on their mode of manufacture. Must be mixed with water.
    • The granules break apart into fine particles similar to wettable powders. Formulation requires constant agitation to keep them suspended in water. The a.i. content is high as much as 90%.
  • Ultra-low-volume (ULV) liquids
    • Designed to be sprayed without dilution.
    • Easy to transport and to use. In addition to the a.i. and a solvent system in which the a.i. is very soluble. High concentration leads to low material-handling requirements.
  • Gelatinized Fluids (GW)
    • Differ from other liquid formulations in having higher viscosity
    • Water-Soluble Packets (WSP): Products package in precise amount of wettable powder or soluble powder formulations in a special type of plastic bag.
  • Attractants
    • Include pheromones, sugar and protein hydrolysate syrups, yeasts and rotting meats.
    • Used in sticky traps, capture bags and even customized collector containers. Attractants can also be combined with insecticides and sprayed onto foliage or other items in the treatments as an attract-kill formulation.
    • Attract-and-Kill Strategy for Wireworms

Data Generation and Safety Value

  • Crop protection industries are among the most highly regulated in the world.
  • The primary objective in regulating chemical pesticides is to provide man and the environment with maximum possible protection from potential adverse effects and facilitate international trade in food through the establishment of approved pesticide regulations.
  • Before a new pesticide reaches the market, extensive laboratory and field testing are being required by pesticide regulatory agencies.
  • Pesticide company has to identify uses, test effectiveness, and provide data on chemical structure, production, formulation, fate, persistence, and environmental impacts.

Regulatory Agencies

  • The continued use of a pesticide is supervised by the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) in the USA, enacted in 1947.
  • Environmental Protection Agency (EPA): responsible for regulating pesticides with public health uses and ensuring that it does not pose unintended or unreasonable risks to humans, animals, and the environment under FIFRA.
  • In the Philippines, the Fertilizer and Pesticide Authority (FPA) is mandated to regulate and ensure safety in the manufacture, formulation, importation, distribution, storage, sale, and use of pesticides and other agricultural chemicals.

Material Safety Data Sheet (MSDS)

  • MSDS is a form with data regarding the properties of a particular substance. It is available on most pesticide products and provides relevant health and safety information on hazardous chemicals.
  • Information provided in MSDS include:
    • Physical data (melting points, boiling point, flash point, etc.)
    • Toxicity
    • Health effects
    • First aid
    • Reactivity
    • Storage
    • Disposal
    • Protective equipment to be used in handling
    • Spill/leak procedures
  • Copies of MSDS on hazardous products, including insecticides products must be submitted to regulatory agencies.

Material Safety Data Sheet should contain 16 sections

  • I. Identification
  • II. Hazard(s) identification
  • III. Composition/information on ingredients
  • IV. First-aid measures
  • V. Fire-fighting measures
  • VI. Accidental release measures
  • VII. Handling and storage
  • VIII. Exposure control/ personal protection
  • IX. Physical and chemical properties
  • X. Stability and reactivity
  • XI. Toxicological information
  • XII. Ecological information
  • XIII. Disposal considerations
  • XIV. Transport information
  • XV. Regulatory information
  • XVI. Other information (date of preparation and revision).
  • Occupational Safety and Health Administration [OSHA] Standard 29 CFR 1910.1200, Safety Data Sheet
  • Sections 12-15 may be included in the SDS, but are not mandatory.
  • MSDS USA: EPA & OSHA (Occupational Safety and Health Administration), but in the Philippines: FPA & BAFS (Bureau of Agriculture and Fisheries Standards)

Maximum Residue Level (MRL)

  • Highest level of a pesticide residue that is legally tolerated in or on food or feed when pesticides are applied correctly (Good Agricultural Practice) = tolerance.
  • International trade of agricultural products is a major factor for increasing pesticide usage mainly due to strict phytosanitary and plant quarantine requirement.

Pesticide use in the Philippines

  • Davis, C.C. 1993. Environmental concerns about pesticide use in Philippine agriculture. The Science of Total Environment: 293-306.
  • 50% of the insecticides and 80% of the herbicides are used for rice production.
  • 55% Insecticides
  • 22% Fungicides
  • 16% Herbicides
  • 7% Others

Insecticides – nomenclature

  • Common name for active ingredient –1200 of these official common names for pesticides have been assigned by the International Organization for Standardization (ISO) –intention is to create short, distinctive, easily pronounced names –names reflect the chemical structure of the pesticide
  • Trade name –The name under which the product is sold, given by the producing company –A single chemical compound might have multiple trade names:
  • Chemical name (IUPAC) –Scientific name describing the chemical structure of the insecticide following the rules of the International Union of Pure and Applied Chemistry (IUPAC)

Insecticide – classification

  • Insecticides can be grouped by:
  • Based on chemical composition –Organic vs. inorganic
  • Mode of entry –stomach poisons, systemic insecticides, contact poisons, fumigants
  • Based on toxicity –Extremely toxic → highly toxic → moderately toxic → less toxic
  • Stage specificity –Ovicides, larvicides, pupicides, adulticides
  • Mode of Action (MoA)
  • **Chemical composition
  • Based on mode of entry
  • Based on toxicity
  • Stage specificity
  • Mode of Action
  • Acetylcholinesterase Inhibitors
  • GABA-gated chloride channel blockers
  • Sodium channel modulators
  • Nicotinic acetylcholine receptor competitive modulators
  • Nicotinic acetylcholine receptor allosteric modulators
  • Clutamate-gated chloride channel allosteric modulators
    *Juvenile hormone mimics
  • Microbial disruptors of insect midgut membranes
    *Inhibitors of chitin biosynthesis
  • Ecdysone receptor agonists
  • Ryanodine receptor modulators
  • Baculoviruses
  • Fungal agents
  • Insecticide Resistance Action Committee

Insecticide – classification Chemical composition

  • inorganic: without carbon (e.g., arsenic, sulfur, copper)
  • organic: with carbon (majority of insecticides)
    • Natural: extracted/refined from a naturally occurring substance (e.g., neem, pyrethrum)
    • Synthetic: developed and synthesized in a laboratory grouped by their active ingredient

Insecticide – classification Mode of Entry

  • stomach poisons: insecticide is ingested by feeding on treated plant or sucking plant sap and is then absorbed by the stomach
  • oldest insecticides only a few in use nowadays
  • Systemic Insecticides uptake into the plant tissue via leaves, shoots and roots, to be ingested by feeding insecticide seed coating or granule drench
  • Fumigants/respiratory poisons: insect is killed by inhaling toxic volatiles through its spiracles into the respiratory system
  • Contact poisons: insecticide penetrates the cuticle of the pest.
  • Residual insecticide: insecticide forms a residual film on the treated surface; insects pick up the toxic dose from the plant surface via their cuticle

Insecticide – classification Based on Toxicity/Hazard

  • The WHO recommended classification was approved by the 28th World Health Assembly in 1975.
  • The guide-points are now being aligned with the corresponding Acute Toxicity Hazard Categories from the Globally Harmonized System of Classification and Labelling of Chemicals (GHS).

Insecticide – classification Stage Specificity

  • Ovicides (Trichogramma); Larvicides (IGRs, CYD-X – granulosis virus, etc.); Pupicides (cardboard banding); Adulticides (mass trapping, mating disruption)

Classification of Insecticides: Target Sites and Mode of Actions

  • Targets:
    • Nerves & muscles
    • Growth & development
    • Respiration
    • Midgut

Group 1: Acetylcholinesterase (AChE) inhibitors

  • Inhibit AChE, causing hyperexcitation.
  • AChE is the enzyme that terminates the action of the excitatory neurotransmitter acetylcholine at nerve synapses.

Group 2: GABA-gated chloride channel blockers

  • Block the GABA-activated chloride channel, causing hyperexcitation and convulsions.
  • GABA is the major inhibitory neurotransmitter in insects.

Group 3: Sodium channel modulators

  • Keep sodium channels open, causing hyperexcitation and, in some cases, nerve block.
  • Sodium channels are involved in the propagation of action potentials along nerve axons.

Group 4: Nicotinic acetylcholine receptor (nAChR) competitive modulators

  • Bind to the acetylcholine site on nAChRs, causing a range of symptoms from hyper-excitation to lethargy and paralysis.
  • ACh is the major excitatory neurotransmitter in the insect central nervous system.

Group 5 Nicotinic acetylcholine receptor (nAChR) allosteric modulators

  • Allosterically activate nAChRs, causing hyperexcitation of the nervous system. Acetylcholine is the major excitatory neurotransmitter in the insect central nervous system.

Group 6 Glutamate-gated chloride channel (GluCl) allosteric modulators

  • Allosterically activate glutamate-gated chloride channels (GluCls), causing paralysis.
  • Glutamate is an important inhibitory neurotransmitter in insect.

Group 7 Juvenile hormone mimics

  • Applied in the pre-metamorphic instar, these compounds disrupt and prevent metamorphosis.
  • Application of eggs halted their development
    *Application of immatures stopped their metamorphosis
    ***Application to adult females produced sterile eggs
  • Adult males could transmit the paper factor venereally (transmitted during mating) to females causing sterile eggs.

Group 11 Microbial disruptors of insect midgut membranes

  • Protein toxins that bind to receptors on the midgut membrane and induce pore formation, resulting in ionic imbalance and septicemia.

Group 15 Inhibitors of chitin biosynthesis, type 0

  • Binds with the ecdysone receptor complex and transactivating a succession of molt initiating transcription factors that, in turn, induce the expression of a group of molt-related genes
  • Binds with the ecdysone receptor complex and transactivating a succession of molt initiating transcription factors that, in turn, induce the expression of a group of molt-related genes
  • Chitin inhibitors disrupt the synthesis of chitin and prevent the insect from further development.
  • Insects treated with chitin biosynthesis inhibitors become unable to synthesize new cuticle, and therefore unable to successfully molt into the next stage.

Group 17 Ecdysone receptor agonists

  • Mimic the molting hormone, ecdysone, inducing a precocious/premature molt. These agonists bind to the ecdysone receptors, thereby accelerating the molting process and thereby disrupting the insect hormonal balance (Lepidopteran-specific).

Group 28 Ryanodine receptor modulators

  • Activate muscle ryanodine receptors, leading to contraction and paralysis.
  • Ryanodine receptors mediate calcium release into the cytoplasm from intracellular stores.
  • Potent via ingestion of treated foliage → safe for most beneficial, since they are carnivores Structural difference between insect and mammalian ryanodine receptors (RyRs) → safer!

Group 31 Baculoviruses

  • Viruses which are known to infect insects.
  • This group represents about 60% of the 1,100 insect viruses which had been isolated by 1990: Baculoviruses are relatively large rod-shaped viruses having double stranded covalently closed circular DNA of approximately 80-180 KB
  • After ingesting NPV, infected larvae will eat normally for a couple of days before reducing feeding substantially. Diseased larvae typically climb to the top of the plant to die