Introduction to Conventional Pesticides for Insect Pests and Disease Management

1. Definition and Overview

What are Conventional Pesticides? Conventional pesticides are chemical substances used to kill, repel, or control pests, including insects, diseases, weeds, rodents, and other organisms that affect agricultural crops. They include a wide range of synthetic chemicals formulated for target-specific action against pests and diseases.

Purpose and Importance They are used to protect crops from insects, pathogens, weeds, and other pests that can cause significant damage. Conventional pesticides increase agricultural productivity by reducing pest-induced losses, thus ensuring food security.

Historical Background The use of pesticides dates back to ancient civilizations, with the Chinese using sulfur compounds as insecticides over 2000 years ago. Synthetic pesticides gained popularity in the 20th century with the discovery of DDT by Paul Müller in 1939, which was used extensively during World War II. Post-World War II saw the rapid development of various chemical classes of pesticides, including organochlorines, organophosphates, and carbamates.

Objectives of Using Conventional Pesticides

1. Protection of Crops: Safeguard crops from insect pests, fungal diseases, weeds, nematodes, and rodents. Maintain crop health and productivity.
2. Increase in Agricultural Yield: Minimize crop losses due to pest attacks, ensuring higher yield and quality.
3. Economic Benefits: Enhance profitability for farmers by reducing pest damage and improving marketable produce.
4. Public Health and Hygiene: Control vector-borne diseases by targeting disease-carrying insects like mosquitoes and flies. Ensure safe storage of food grains by controlling storage pests.

Mechanism of Action Conventional pesticides work through various mechanisms depending on their chemical nature and target pest:

• Contact Action Pesticides that kill pests upon direct contact. Absorbed through the pest’s cuticle or outer body surface. Example: Contact insecticides like Cypermethrin and Deltamethrin.
• Stomach Action Ingested by the pest through feeding on treated plant surfaces. Absorbed in the digestive tract, leading to poisoning and death. Example: Carbaryl and Malathion.
• Systemic Action Absorbed by the plant through roots or foliage and translocated within the plant system. Pests feeding on the treated plant parts ingest the pesticide, leading to death. Example: Imidacloprid and Acephate.
• Fumigant Action Vaporize to form toxic gases that penetrate pest respiratory systems. Effective against storage pests and soil-borne pests. Example: Aluminum phosphide and Methyl bromide.
• Growth Regulators Disrupt the normal development of insects by interfering with molting or metamorphosis. Example: Methoprene and Diflubenzuron.

Classification of Conventional Pesticides

Conventional pesticides are classified based on their chemical composition, mode of action, target pest, and application method. These classifications help in selecting the appropriate pesticide for specific pest problems while considering environmental safety and human health.

Based on Chemical Composition This classification is based on the chemical structure of the active ingredients used in pesticides.

1. Organochlorines These are synthetic organic compounds containing carbon, hydrogen, and chlorine atoms. Known for their high persistence in the environment, they are fat-soluble and bioaccumulative. Due to their long residual effects, they were widely used in the mid-20th century but later faced restrictions due to environmental concerns.

Mode of Action:

• • They affect the nervous system by disrupting the normal function of sodium channels in nerve cells, causing repetitive nerve impulses, paralysis, and death. Examples:
  • DDT (Dichlorodiphenyltrichloroethane): Used historically for mosquito control but banned due to its environmental persistence.
  • Endosulfan: Formerly used on crops like cotton and vegetables but banned in many countries due to health hazards.
  • Lindane: Used in agriculture and public health but restricted due to toxic residues.

Environmental and Health Concerns:

• • Highly persistent and remain in soil and water for years, leading to bioaccumulation in the food chain.
  • Toxic to wildlife, particularly birds and aquatic organisms.
  • Long-term exposure linked to cancer, endocrine disruption, and neurotoxic effects in humans.
• Current Status: Banned or restricted in many countries under international conventions like Stockholm Convention on Persistent Organic Pollutants (POPs).

2. Organophosphates: These are esters of phosphoric acid and are more biodegradable compared to organochlorines. Widely used due to their broad-spectrum activity against insects.

• Mode of Action:
  • Inhibit the enzyme acetylcholinesterase at nerve synapses, leading to the accumulation of acetylcholine, causing continuous nerve impulses, paralysis, and death. Examples:
  • Malathion: Used in agriculture and public health for mosquito control.
  • Chlorpyrifos: Broad-spectrum insecticide for crops like cotton, maize, and fruits but facing restrictions due to health concerns.
  • Dimethoate: Systemic insecticide effective against sucking insects like aphids and mites.

Environmental and Health Concerns:

• • High acute toxicity to mammals, including humans.
  • Symptoms of poisoning include nausea, vomiting, muscle twitching, respiratory distress, and neurological disorders.
  • Less persistent than organochlorines but can contaminate water sources. Current Status:
  • Restricted or banned in several countries due to their neurotoxic effects on humans, particularly on children.

3. Carbamates These are derivatives of carbamic acid and have a similar mode of action to organophosphates but are generally less persistent.

• Mode of Action:
  • Inhibit acetylcholinesterase enzyme temporarily, affecting the nervous system but with reversible inhibition compared to organophosphates. Examples:
  • Carbaryl: Broad-spectrum insecticide for fruits, vegetables, and ornamental plants.
  • Propoxur: Used in agriculture and for controlling household pests like cockroaches and ants.
  • Aldicarb: Highly toxic systemic insecticide for soil-borne pests but restricted due to human health risks.
• Environmental and Health Concerns:
  • High acute toxicity to humans and non-target species, including beneficial insects and aquatic organisms.
  • Exposure can lead to headaches, nausea, muscle weakness, and respiratory problems.
  • Moderate persistence in the environment but potential for groundwater contamination.
• Current Status:
  • Use is regulated due to toxicity concerns, and some carbamates are banned or restricted.

4. Pyrethroids Synthetic analogs of pyrethrins, which are natural insecticides derived from chrysanthemum flowers. Known for their fast knockdown effect, they are widely used in agriculture and public health.

• Mode of Action: Affect the sodium channels in the nerve cells, causing prolonged nerve excitation, paralysis, and death.
• Examples:
  • Cypermethrin: Broad-spectrum insecticide used for cereals, vegetables, and cotton.
  • Permethrin: Used in agriculture and public health, including mosquito nets.
  • Deltamethrin: Effective against a wide range of insects and used in agriculture, homes, and public health.
• Environmental and Health Concerns:
  • Low mammalian toxicity but highly toxic to aquatic organisms and bees.
  • Non-persistent but can bioaccumulate in aquatic ecosystems.
  • Irritant to skin and eyes in humans.
• Current Status: Widely used with some regulatory restrictions to protect pollinators and aquatic life.

5. Neonicotinoids

• Description: Systemic insecticides that are absorbed by the plant and translocated to all plant parts, providing long-term protection. They mimic nicotine and target the insect nervous system.
• Mode of Action: Bind to nicotinic acetylcholine receptors in the insect nervous system, causing paralysis and death.
• Examples: Imidacloprid: Effective against sucking insects like aphids and whiteflies. Thiamethoxam: Used as seed treatment, soil drench, and foliar spray.
• Environmental and Health Concerns:
  • High systemic activity leads to contamination of pollen and nectar, impacting pollinators.
  • Concerns over pollinator decline, particularly bees and butterflies.
  • Low mammalian toxicity but potential for groundwater contamination.
• Current Status: Banned or restricted in several countries, including the European Union, due to their impact on pollinators.

Based on Mode of Action

1. Contact Insecticides: Direct contact with the insect’s body.
2. Stomach Insecticides: Ingestion by feeding insects.
3. Systemic Insecticides: Absorbed and translocated within plants.
4. Fumigants: Inhaled as toxic vapors by insects.
5. Growth Regulators: Disrupt normal insect growth and development.

Based on Target Pest

1. Insecticides: Control insect pests.
2. Fungicides: Control fungal diseases.
3. Herbicides: Control weeds.
4. Rodenticides: Control rodents.
5. Nematicides: Control nematodes.

Advantages of Conventional Pesticides

• Rapid and Effective Control: Fast action against a broad range of pests.
• Increased Agricultural Productivity: Protects crops from pests, ensuring higher yields.
• Cost-Effective: Readily available and easy to apply.
• Flexibility in Application: Can be used as sprays, dusts, granules, or fumigants.
• Adaptability: Effective in diverse agricultural systems and climates.

Challenges and Limitations

• Environmental Pollution: Contamination of soil, water, and air.
• Non-Target Effects: Harmful to beneficial insects, pollinators, and wildlife.
• Human Health Hazards: Acute and chronic health effects on farmers and consumers.
• Pest Resistance: Overuse leads to resistance development, requiring stronger alternatives.
• Regulatory Restrictions: Several pesticides are banned or restricted globally.