⚗️ Insecticide Classification & Chemical Control
Chemical method history, insecticide formulations, toxicity colour coding, classification by mode of entry/action/chemical nature, newer groups, antidotes, spraying equipment, semiochemicals, pheromones for CUET Agriculture
Chemical Method (रासायनिक विधि)
The chemical method involves using synthetic or natural chemical compounds (insecticides) to kill or repel pest insects. While highly effective and fast-acting, chemical control is considered the last resort in IPM because of potential environmental damage, residue issues, and development of pest resistance.
History of Insecticides
- Plants have been used as pesticides for over 100 years — early examples include sulphur, tobacco, and neem, which were applied long before modern chemistry
- Arsenic-based compounds have been used since approximately 40 AD — among the earliest known mineral insecticides
- The modern era of synthetic insecticides began in 1939 when P.H. Muller discovered the insecticidal properties of DDT (Dichloro Diphenyl Trichloroethane), for which he won the Nobel Prize
- After the DDT discovery, a rapid proliferation of synthetic insecticides occurred — organochlorines, organophosphates, carbamates, and pyrethroids were developed in succession
- In 1962, Rachel Carson published Silent Spring, a landmark book that warned the world about the harmful effects of indiscriminate pesticide use on wildlife, ecosystems, and human health. This book catalysed the modern environmental movement.
Types of Pesticides (कीटनाशक)
Pesticides are classified by the type of organism they target:
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Chemical Method (रासायनिक विधि)
The chemical method involves using synthetic or natural chemical compounds (insecticides) to kill or repel pest insects. While highly effective and fast-acting, chemical control is considered the last resort in IPM because of potential environmental damage, residue issues, and development of pest resistance.
History of Insecticides
- Plants have been used as pesticides for over 100 years — early examples include sulphur, tobacco, and neem, which were applied long before modern chemistry
- Arsenic-based compounds have been used since approximately 40 AD — among the earliest known mineral insecticides
- The modern era of synthetic insecticides began in 1939 when P.H. Muller discovered the insecticidal properties of DDT (Dichloro Diphenyl Trichloroethane), for which he won the Nobel Prize
- After the DDT discovery, a rapid proliferation of synthetic insecticides occurred — organochlorines, organophosphates, carbamates, and pyrethroids were developed in succession
- In 1962, Rachel Carson published Silent Spring, a landmark book that warned the world about the harmful effects of indiscriminate pesticide use on wildlife, ecosystems, and human health. This book catalysed the modern environmental movement.
Types of Pesticides (कीटनाशक)
Pesticides are classified by the type of organism they target:
| Type | Target |
|---|---|
| Insecticides (कीटनाशी) | Insects |
| Miticides/Acaricides (बरूथीनाशी) | Ticks & Mites |
| Nematicides (सूत्रकृमिनाशी) | Nematodes |
| Rodenticides (कृत्तकनाशी) | Rats & Mice |
| Molluscicides (मोलस्कनाशी) | Snails & Slugs |
| Fungicides (कवकनाशी) | Fungi |
| Bactericides (जीवाणुनाशी) | Bacteria |
| Weedicides/Herbicides (शाकनाशी/खरपतवारनाशी) | Weeds |
Insecticide Formulations (कीटनाशी संरूपणा)
The active ingredient (AI) of an insecticide is rarely used in pure form. It is mixed with carriers, solvents, and additives to create a formulation that is safe to handle, easy to apply, and effective in the field.
A. Solid Formulations (ठोस संरूपण)
| Type | Details |
|---|---|
| Dust (धूलि) | AI concentration 0.1-25%; applied @ 20-25 kg/ha; best applied in the morning when dew is present (dew helps dust adhere to plant surfaces) |
| Granules (दानेदार) | Granule size 0.25-2.38 mm; AI 2-10%; examples: Carbofuran 3G, Phorate 10G — placed in soil near plant roots for systemic uptake |
| Wettable Powder (WP) | Contains a wetting agent to help the powder mix with water; AI 25-50%; mixed with water for spray application |
B. Liquid Formulations (तरल संरूपण)
| Type | Details |
|---|---|
| Emulsifiable Concentrate (EC) | Oil + Emulsifier + Solvent; forms a milky emulsion when mixed with water; e.g., Chlorpyrifos 20 EC (the number indicates 20% AI) |
| Solution | AI dissolved directly in water (water-soluble) or organic solvent |
| Concentrate insecticide liquid | Highly concentrated liquid for dilution before use |
| Aerosol | Fine mist for spot treatment in enclosed areas (like household mosquito sprays) |
C. Fumigants (धूमक)
Fumigants are insecticides in gaseous form used primarily for stored grain pest control. Their gaseous nature allows them to penetrate into all crevices and spaces within a grain mass, reaching pests hidden deep inside.
- Aluminium Phosphide (AlP): The most commonly used fumigant worldwide; it releases phosphine gas (PH3) on contact with moisture. Trade names include: Celphos, Phostoxin, Quickphos, Delphia
- A single 3 gm AlP tablet releases 1 gm of phosphine gas
- Other fumigants: EDCT, EDB, Methyl Bromide, HCN
WARNING
Aluminium Phosphide is extremely toxic (Red label). Phosphine gas is lethal to humans even in small concentrations. Fumigation must be carried out by trained personnel with proper safety equipment and in well-sealed structures.
| Fumigant | Composition |
|---|---|
| EDCT | 3:1 ratio of Ethylene Dichloride + Carbon Tetrachloride |
| ECO-fume | Phosphine + CO2 |
| Durafume | EDB + MB (1:1) |
| Grain-O-Cide | CO2 + CTC |
Toxicity Identification — Colour Coding of Insecticides
India uses a colour-coded labelling system to indicate the toxicity level of pesticide formulations. This system helps farmers and applicators quickly identify how dangerous a product is.
| Colour | Toxicity Level | LD50 Oral (mg/kg) | LD50 Dermal (mg/kg) |
|---|---|---|---|
| Red (लाल) | Extremely Toxic (अत्यंत विषाक्त) | 1-50 | 1-200 |
| Yellow (पीला) | Highly Toxic (अत्यधिक विषाक्त) | 50-500 | 200-2000 |
| Blue (नीला) | Moderately Toxic (मध्यम विषाक्त) | 500-5000 | 2000-20000 |
| Green (हरा) | Less Toxic (कम विषाक्त) | >5000 | >20000 |
TIP
Remember the sequence: R-Y-B-G (Red-Yellow-Blue-Green) from most toxic to least toxic. A lower LD50 value means the substance is MORE toxic (it takes a smaller dose to kill).
Key Toxicity Concepts
| Term | Definition |
|---|---|
| LD50 (Median Lethal Dose) | The dose (in mg per kg of body weight) that kills 50% of test organisms. This is the standard measure of acute toxicity. |
| LC50 (Median Lethal Concentration) | The concentration (in ppm or %) that kills 50% of test organisms — used when exposure is through air or water |
| LT50 (Median Lethal Time) | The time taken to kill 50% of test organisms at a given dose/concentration |
Classification of Insecticides
I. Based on Mode of Entry (कीट के शरीर में प्रवेश)
This classification describes how the insecticide enters the insect's body:
| Type | Mechanism | Examples |
|---|---|---|
| Contact Poison (संस्पर्श विष) | Kills on contact/touch by penetrating through the cuticle (body wall) | Pyrethrum, Malathion, Carbaryl, DDVP |
| Stomach Poison (जठर विष) | Enters through the mouth when the insect feeds; kills upon ingestion and digestion | Monocrotophos, Lindane, Arsenic compounds, Metasystox |
| Fumigants (धूमक) | Enters through the tracheal system (spiracles); blocks respiration by replacing oxygen | Hydrogen cyanide (HCN), Methyl bromide, Aluminium phosphide, Ethylene dibromide |
II. Based on Mode of Action (क्रियाविधि)
This classification describes how the insecticide kills at the physiological level:
| Type | Mechanism | Examples |
|---|---|---|
| Physical Poison | Kills by dehydration — absorbs the waxy layer of the cuticle, causing water loss (not a chemical poison in the strict sense) | Aluminium oxide |
| Protoplasmic Poison | Precipitates cell proteins, disrupting normal cell function | Arsenic, Nicotine, Nitrophenol, Copper, Barium |
| Respiratory Poison | Blocks the respiratory system — prevents oxygen utilisation at the cellular level | HCN, Aluminium phosphide, Ethylene dibromide |
| Nerve Poison | Inhibits acetylcholinesterase (AChE) enzyme of the nervous system, causing continuous nerve stimulation, convulsions, paralysis, and death | Organophosphates, Carbamates |
NOTE
Most modern insecticides (OPs and carbamates) are nerve poisons. They work by preventing the breakdown of the neurotransmitter acetylcholine at nerve junctions, causing uncontrolled nerve firing that leads to paralysis and death.
III. Based on Chemical Nature
A. Inorganic Insecticides (अकार्बनिक कीटनाशी)
These are the oldest insecticides, made from mineral compounds:
| Group | Examples |
|---|---|
| Arsenicals (यौगिक) | Lead arsenate, Calcium arsenate, Sodium arsenate, Paris Green, Arsenic oxide, Arsenic acid |
| Fluorine compounds (फ्लुओरीन) | Sodium fluorosilicate, Sodium fluoride, Barium fluorosilicate, Cryolite |
| Sulphur compounds | Sulphur dust, Lime sulphur; also has fungicidal + acaricidal properties; e.g., Gandhak dhuli (sulphur dust), Chuna gandhak (lime sulphur) |
| Phosphorus compounds | Zinc phosphide (used primarily as a rodenticide for rats) |
B. Organic Insecticides (कार्बनिक कीटनाशी)
1. Animal Origin
- Nereistoxin — obtained from the marine annelid worm Lumbriconereis heteropoda; the commercial product derived from it is Cartap Hydrochloride, which is used against rice stem borers
2. Botanical Insecticides (वानस्पतिक कीटनाशी)
These are derived from plants and are generally considered safer for the environment:
| Botanical | Source | Details |
|---|---|---|
| Pyrethrum | Chrysanthemum cinerarifolium and C. coccineum flowers | Contains 1-1.5% pyrethrins (ester compounds); provides rapid knockdown effect on flying insects |
| Neem (Azadirachtin) | Azadirachta indica | Active compounds: Azadirachtin (most important), Nimbidin, Meliantriol; Products: Achook, Nimigold, Nimayel, Nimmark, Nimilin; applied as NSKE @ 5% or Neem oil @ 3% |
Neem Tree (Azadirachta indica) — source of azadirachtin, the most important botanical insecticide — Source: Wikimedia Commons (CC)
| Ryania | Ryania speciosa stems | Contains the alkaloid Ryanodine, which disrupts muscle contraction | | Nicotine | Nicotiana tabacum & N. rustica | Contains 4-5% nicotine in tobacco leaves; commercial product: Black Leaf-40; acts as a nerve poison | | Sabadilla | Schoenocaulon officinale seeds (Liliaceae) | Known as "Ju Powder" in South America; effective against sucking pests | | Rotenone | Roots of Derris elliptica, D. malaccensis, Lonchocarpus utilis | Also a fish poison; widely used in organic farming | | Plumbagin | Plumbago europaea roots | Acts as an antifeedant; disrupts cell membranes |
3. Oils
- Concentration: 1-3% when diluted for application
- Types: Summertime oil (lighter, for active season), Dormant oil (heavier, for dormant season), Straw oil
- Oils work by suffocating insects, blocking their spiracles
4. Organic Thiocyanate
- Thanite, Lethane-60, Bethane-384 — contact poisons with quick knockdown
5. Sulphonate, Sulphide & Sulphone
- Primarily acaricidal (effective against mites)
- Examples: Tetrasol, Tetradifone, Aramite, Ovex, Fenitrothion, Sulphone
6. Dinitrophenol
- Effective against both insects and mites
- Examples: Binaprex, Dinocap
7. Chlorinated Hydrocarbons (Organochlorines)
Organochlorines were the first widely-used synthetic insecticides but are now largely banned or restricted due to their persistence in the environment and tendency to bioaccumulate in food chains.
- DDT: Dichloro Diphenyl Trichloroethane; first synthesized by O. Ziedler (1874); insecticidal property discovered by P.H. Muller (1939)
- BHC/HCH: 1,2,3,4,5,6-Hexachlorocyclohexane; first synthesized by M. Faraday (1825); insecticidal property discovered by Dupite, Raucourt & Slade (1942)
- Lindane: The gamma isomer of BHC (99% pure); isolated by V. Linden; more volatile than DDT and is the only insecticidally active isomer
- Others: Chlordane, Heptachlor, Aldrin, Dieldrin, Endrin, Endosulfan, Mirex, Isodrin
- Status: Most organochlorines are banned/restricted in India due to persistence and bioaccumulation
8. Organophosphate Insecticides (OP) — 45% of all insecticides
Organophosphates constitute the largest group of insecticides in use, making up about 45% of all insecticides globally. They work as contact and stomach poisons combined, and their mode of action is inhibition of the acetylcholinesterase enzyme.
- Examples: Malathion, Parathion, Methyl Parathion, Dimethoate, DDVP, Monocrotophos, Chlorpyrifos, Quinalphos, Profenofos, Ethion
- Schradan = the first organophosphate compound ever synthesized
- OPs are generally less persistent than organochlorines but more acutely toxic to mammals
9. Synthetic Pyrethroids
Synthetic pyrethroids are modelled after natural pyrethrum but are more stable and long-lasting:
- Examples: Fenvalerate, Cypermethrin, Permethrin, Deltamethrin, Lambda-cyhalothrin
- Advantages: Low mammalian toxicity, fast knockdown effect, effective at very low doses
- They are nerve poisons that act on sodium channels in nerve membranes
10. Carbamate Insecticides
Carbamates also inhibit acetylcholinesterase but their binding is reversible (unlike OPs where binding is irreversible), which is why the antidote differs:
- Examples: Carbaryl (Sevin), Carbofuran, Aldicarb, Carbosulfan, Methiocarb, Thiodicarb
11. Fumigants
| Fumigant | Details |
|---|---|
| EDB (Ethylene Dibromide) | Important for fruits and vegetables; Trade names: Minifume, Bromofume, Dowfume |
| Aluminium Phosphide (AlP/Celphos) | Releases phosphine gas; 3g tablet releases 1g PH3; market names: Phostoxin, Quickphos, Celphos |
| HCN | First used for San Jose Scale (1886) in California |
| Methyl Bromide (MB) | Widely used for quarantine treatment of export commodities |
Newer/Miscellaneous Insecticide Groups
These represent the latest advances in insecticide chemistry, often with improved selectivity and reduced environmental impact:
| Group | Details | Examples |
|---|---|---|
| Neonicotinoids | Act on nicotinic acetylcholine receptors; highly effective against sucking pests; systemic action | Imidacloprid, Acetamiprid |
| Phenyl Pyrazole | Blocks GABA-gated chloride channels in nerves | Fipronil |
| Spinosad | Derived from the actinomycete bacterium Saccharopolyspora spinosa; for cotton + other crops | Dose: 75-100 gm a.i./ha |
| Abamectin | Derived from Streptomyces avermitilis actinomycete; works as both insecticide + acaricide | — |
| Oxadiazine group | Effective against borers; blocks sodium channels | Indoxacarb |
| Tetronic acid | Disrupts lipid synthesis in mites | Spiromesifen |
| Tetramic acid | Similar lipid synthesis disruption | Spirotetramat |
| IGR (Insect Growth Regulators) | Benzyl Phenyl Urea compounds: Buprofezin, Novaluron, Lufenuron | Disrupt chitin synthesis, preventing moulting |
Antidotes for Insecticide Poisoning
Knowing the correct antidote for each insecticide class is critical for saving lives in cases of accidental poisoning:
| Insecticide Type | Antidote |
|---|---|
| Nicotine | Potassium Permanganate (पोटेशियम परमैगनेट) |
| Zinc Phosphide | Vitamin K (विटामिन-K) |
| Organophosphate | Atropine Sulphate + 2-PAM (एट्रोपिन सल्फेट व 2-PAM) |
| Carbamate | Atropine only (एट्रोपिन) — NOT 2-PAM (because carbamate binding is reversible; 2-PAM can actually worsen the condition) |
| Organochlorine | Phenobarbital (फिनो बारबिटोल) — a sedative that controls convulsions |
WARNING
For carbamate poisoning, never administer 2-PAM (Pralidoxime). Use Atropine only. This is a critical distinction from organophosphate poisoning where both Atropine and 2-PAM are used together.
Other Important Points
- In 1960, the insecticide of choice for pest and fish control was DDT
- Insects developing resistance is caused by indiscriminate/excessive use of the same insecticide repeatedly
- Mammals have the lowest resistance to insecticides compared to insects
- Malathion is the least toxic among commonly used OP insecticides (Blue label)
- Resistance to rat poison is produced by Zinc Phosphide through repeated sub-lethal exposure
Insecticide Spraying & Dusting Equipment
Classification of Sprayers
A. Hydraulic/Liquid Operated Sprayers
These use a pump to create pressure that forces liquid through a nozzle:
- Pump → Liquid → Pressure → Spray
- Examples: Bucket, Rocker, Foot/Pedal sprayer, Hydraulic sprayer, Hand sprayer, Stirrup sprayer
B. Hand Compression / Pneumatic Sprayer
These use compressed air to propel the liquid; no agitator is required since air pressure keeps the mixture uniform:
- Examples: Compression sprayer, Hand compression sprayer
C. Gaseous
- Hand atomizer (कणिज) — produces fine droplets for small-scale application
Knapsack Sprayer (नैपसैक स्प्रेअर)
The Knapsack sprayer is the most commonly used sprayer by Indian farmers for field application of pesticides.
- Capacity: Tank holds 10-30 litres; usually 10-16 litres
- Pressure: 3-5 kg/cm² (3-5 bar)
- Used for crops up to 2.5 metres height
- Can cover 1+ hectare per day
- Components: Tank, Agitator, Filter, Pump, Energy source, Pressure gauge, Valve, Hose, Lance (90 cm tube + nozzle), Spray cut-off device, Boom, Nozzle
Nozzle Types
Different nozzle types produce different spray patterns suited to specific applications:
| Type | Use |
|---|---|
| Hollow cone nozzle | Pest and disease management on plants — produces fine droplets that coat leaf surfaces |
| Solid cone nozzle | Soil application — produces a full cone of spray for even soil coverage |
| Flat fan nozzle | Herbicide application — produces a flat, even band of spray ideal for uniform ground coverage |
Hand Rotary Duster (हैण्डरोटेरी डस्टर)
- Also called fan duster or paddle duster
- Used for dusting low-height crops and vegetables with powder formulations
- Coverage: 1-1.5 hectares per day
- Best time for dusting: early morning (when dew is present on plant surfaces, helping the dust particles stick)
Droplet Size for Different Applications
The effectiveness of a spray depends greatly on droplet size — smaller droplets provide better coverage but drift more easily:
| Application | Droplet Size (microns) |
|---|---|
| Flying insects | 10-50 |
| Surface insects | 30-150 |
| Plant diseases | 30-150 |
| Weeds (herbicides) | 100-300 |
| Type of Spray | Droplet Size (microns) | Energy |
|---|---|---|
| Vapour | 0.001-0.01 | Thermal |
| Smoke | 0.01-1.0 | Thermal |
| Fog/Aerosol | 1.0-50 | Thermal |
| Mist | 51-100 | Gaseous |
| Fine spray | 101-200 | — |
| Medium spray | 201-400 | — |
| Coarse spray | >400 | — |
Semiochemicals & Innovative Approaches
I. Semiochemicals (सेमियोकेमिकल)
The term comes from the Greek word "semeion" meaning a mark or signal. Semiochemicals are chemicals that modify the behaviour of organisms. They are classified based on whether the interaction is within or between species.
(a) Pheromones (फीरोमोन) — Intraspecific (within same species)
Pheromones are chemicals released by an individual of a species that trigger a behavioural or physiological response in another individual of the same species.
- First described by Karlson & Luscher in 1959
- First pheromone ever identified (1959): Bombykol — isolated from the female silkworm moth (Bombyx mori)
- In the field, pheromone traps are placed at 5-7 per hectare, at 50 metre intervals, hung at crop canopy height
- Pheromone lures should be replaced every 20 days as the chemical gradually evaporates
| S.No. | Insect | Pheromone Name |
|---|---|---|
| 1. | Silkworm (Bombyx mori) | Bombykol |
| 2. | Cotton bollworm (Pectinophora gossypiella) | Gossyplure |
| 3. | Boll weevil (Anthonomus grandis) | Grandlure |
| 4. | Helicoverpa armigera | Helilure |
| 5. | Spodoptera litura | Litlure |
| 6. | Fruit fly | Luplure |
(b) Allelochemicals — Interspecific (between different species)
Allelochemicals mediate interactions between individuals of different species:
| Type | Benefit To |
|---|---|
| Allomone | Emitter (the organism releasing the chemical benefits) |
| Kairomone | Receiver (the organism detecting the chemical benefits) |
| Synomone | Both emitter and receiver benefit |
| Apneumone | Chemical from a non-living substance → beneficial for the receiver |
II. Insect Hormones (कीट हार्मोन)
Understanding insect hormones has led to the development of Insect Growth Regulators (IGRs) that mimic or disrupt natural hormones:
| Hormone | Function |
|---|---|
| Brain hormone (मस्तिक्क हार्मोन) | Initiates the moulting process by stimulating the prothoracic gland |
| Ecdysone (इक्डाइसोन) | The moulting hormone; triggers cuticle shedding and formation of new cuticle |
| Juvenile hormone (जूवेनाइल हार्मोन) | Maintains larval characters; prevents adult development; its levels must drop for metamorphosis to occur |
| Eclosion hormone (इक्लोसन हार्मोन) | Triggers adult emergence from the pupal case |
| Tanning hormone (टैनिंग हार्मोन) | Hardens and darkens the new cuticle after moulting (sclerotisation) |
III. Repellents (रिपैलेन्ट)
Substances that drive pests away without killing them:
- Citronella oil — widely used for mosquito repellency
- Naphthalene balls — used in wardrobes for cloth moth repellency
IV. Antifeedants (प्रति-पोषक)
Substances that inhibit feeding behaviour:
- Azadirachtin (from neem) — the most important antifeedant for phytophagous (plant-eating) insects. It disrupts feeding, growth, and reproduction simultaneously.
V. Attractants (आकर्षक)
Substances that lure pests to a specific location for monitoring or killing:
- Pheromones, Natural food lures, Oviposition lures, Poison baits
VI. Chemosterilants (किमोस्टेरीलेन्ट)
Chemical compounds that cause sterility in insects without killing them:
- Apholate, Aphomide, Aphoxide (TEPA), Thio TEPA, Meta TEPA
VII. Genetic Control (आनुवांशिक नियंत्रण)
- Sterile Insect Technique (SIT): Males are mass-reared in laboratories → sterilised by gamma radiation → released in large numbers into the field → they mate with wild females → eggs are infertile → population declines over time
- Hybrid sterility: Crossing different species or strains to produce sterile offspring
- Cytoplasmic incompatibility: Using Wolbachia bacteria to cause reproductive incompatibility
VIII. Push-Pull Technology
An innovative approach that combines repellent plants within the crop (push) and attractive trap plants around the border (pull) to manage pests:
| Component | Plants |
|---|---|
| Push (Repellent) | Molasses grass (M. minutiflora), Silverleaf desmodium (D. uncinatum), Greenleaf desmodium (D. intortum) — planted between crop rows to repel stem borers |
| Pull (Attractive trap) | Napier grass (Pennisetum purpureum), Sudan grass (Sorghum vulgare) — planted around the field border to attract stem borers away from the main crop |
Key Points for CUET
IMPORTANT
- DDT discovered 1939 (insecticidal property by P.H. Muller); first synthesized 1874 by Ziedler
- Silent Spring (1962) by Rachel Carson — warned about pesticide hazards
- Red label = Extremely toxic (LD50: 1-50); Green label = Least toxic (LD50: >5000)
- Aluminium Phosphide = Most common fumigant; releases phosphine gas
- OP antidote: Atropine + 2-PAM; Carbamate antidote: Atropine only (NOT 2-PAM)
- Neonicotinoids (Imidacloprid) = For sucking pests; systemic action
- Bombykol = First pheromone identified (1959); from silkworm moth
- Knapsack sprayer: most common; hollow cone nozzle for pests; flat fan for herbicides
- OPs make up 45% of all insecticides; Schradan = first OP synthesized
- Azadirachtin (neem) = Most important antifeedant and botanical insecticide
Summary Cheat Sheet
| Concept / Topic | Key Details / Explanation |
|---|---|
| DDT discovery | Synthesized by O. Ziedler (1874); insecticidal property by P.H. Muller (1939) — Nobel Prize |
| Silent Spring | Rachel Carson (1962) — warned about pesticide hazards; catalysed environmental movement |
| Pesticide types | Insecticides (insects), Acaricides (mites), Nematicides, Rodenticides (rats), Fungicides, Herbicides (weeds) |
| Dust formulation | AI 0.1-25%; applied 20-25 kg/ha; best in morning (dew helps adhesion) |
| Granules | Size 0.25-2.38 mm; AI 2-10%; e.g., Carbofuran 3G, Phorate 10G |
| EC (Emulsifiable Concentrate) | Oil + Emulsifier + Solvent; e.g., Chlorpyrifos 20 EC (20% AI) |
| Aluminium Phosphide (AlP) | Most common fumigant; releases phosphine gas (PH₃); 3 g tablet → 1 g PH₃; trade names: Celphos, Phostoxin |
| Toxicity colour code | Red (LD₅₀ 1-50, extremely toxic) → Yellow (50-500) → Blue (500-5000) → Green (>5000, least toxic) |
| LD₅₀ | Dose killing 50% of test organisms; lower LD₅₀ = MORE toxic |
| Mode of entry — Contact | Penetrates through cuticle; e.g., Pyrethrum, Malathion |
| Mode of entry — Stomach | Enters through mouth on ingestion; e.g., Monocrotophos |
| Mode of entry — Fumigant | Enters through spiracles/trachea; e.g., AlP, HCN |
| Mode of action — Nerve poison | Inhibits acetylcholinesterase (AChE); OPs & carbamates |
| Organochlorines | DDT, BHC/HCH, Lindane, Endosulfan; mostly banned — persistent, bioaccumulate |
| Lindane | Gamma isomer of BHC (99% pure); isolated by V. Linden |
| Organophosphates (OPs) | 45% of all insecticides; AChE inhibitors; first OP = Schradan |
| Synthetic pyrethroids | Modelled after pyrethrum; low mammalian toxicity; fast knockdown; act on sodium channels |
| Carbamates | AChE inhibitors but binding is reversible; e.g., Carbaryl (Sevin), Carbofuran |
| Antidote — OP poisoning | Atropine Sulphate + 2-PAM |
| Antidote — Carbamate poisoning | Atropine only (NOT 2-PAM) |
| Antidote — Organochlorine | Phenobarbital |
| Antidote — Zinc Phosphide | Vitamin K |
| Neonicotinoids | Act on nicotinic acetylcholine receptors; systemic; e.g., Imidacloprid, Acetamiprid |
| Neem / Azadirachtin | Most important antifeedant + botanical insecticide; NSKE @ 5% |
| Pyrethrum | From Chrysanthemum; rapid knockdown effect |
| Rotenone | From Derris roots; also a fish poison |
| IGR | Disrupt chitin synthesis; e.g., Buprofezin, Novaluron |
| Knapsack sprayer | Most commonly used sprayer; 10-30 L tank; covers 1+ ha/day |
| Hollow cone nozzle | For pest and disease management |
| Flat fan nozzle | For herbicide application |
| First pheromone | Bombykol (1959) — from silkworm moth; by Karlson & Luscher |
| Pheromone examples | Gossyplure (cotton bollworm), Helilure (H. armigera), Grandlure (boll weevil) |
| Allelochemicals | Allomone (benefits emitter), Kairomone (benefits receiver), Synomone (both benefit) |
| Insect hormones | Ecdysone (moulting), Juvenile hormone (maintains larval stage), Eclosion (adult emergence) |
| SIT | Sterile Insect Technique — sterilise males with gamma radiation then release |
| Push-Pull technology | Push (repellent: Desmodium) + Pull (attractive trap: Napier grass) |
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