INSECTICIDES - Mechanism of action, Structure, Biochemical action

Insecticides can be classified according to
– Mode of action
– Structure
– Biochemical action

MODE OF ACTION

Systemic insecticides

The chemical enters the plant either by the roots or leaves and they travel through the xylem or phloem and kill the insect feeding on it.

Fumigants

These are compounds with high vapor pressure. They enter the insect through the respiratory system.

Contact insecticides

Chemical is deposited on the surface of the plant and the insect is killed when it comes in contact with the deposited insecticide. They usually penetrate the cuticle of the insect.

STRUCTURE

Botanical insecticides
Azadirachitin from neem

Microorganisms
Bacillus thurengiensis

Insect derived
Natural pheramones, Growth regulators, Juvenile hormones

Synthetic insecticides

• Inorganic insecticides: arsenates, Fluorides, Borates, Cu(CH3CO2)2 , Cu(AsO2)2 NaF , Na2SiF6
• Organic insecticides - Organochlorines, Organophosphates, Carbamates, Pyrethroids, Synthetic pheromones
• Organometallic insecticides - Tin, Mercury compounds

BIOCHEMICAL ACTION

1) Insecticides can act on the following target sites within the nervous system.
a) Nicotine cholinergic receptor: Nocotine

b) Octopamine receptor: Amitraz

 c) Sodium channels: DDT, Pyrethroids

 d) Acetylcholinesterase: Organophosphates, Carbamates

e) Chloride ion channels: Chlorocyclodienes, Avermectins

2) Inhibitors of oxidative phosphorylation.
    Rotenone, Pyrimidifen, Diafenthiuron

3) Muscle contraction: Ryanodine

4) Growth regulators
    a) Chitin biosynthesis: diflubenzuron
    b) Juvenile hormone: methoprene
    c) Sex pheromone: gossyplure