Chemical Control
(Importance of Chemical Control,
Classification of Insecticides)
BS VII
• Chemical control
• Management of insect pests by using chemical (insecticides,
pesticides) is termed as chemical control.
• Pesticides:
• Chemicals which are used to kill pests
• Insecticides:
• Chemicals which are used to kill insects
Importance of Chemical Control
• Chemical control have played key role in improvement of plant
suffering from abnormalities but have a negative perception in public
mind because pesticides are intrinsically toxic.
• In agricultural production, pesticides are a regular component of
most systems; their development has given rise to entirely new ways
of growing crops.
• The quantity and quality of our food and fiber production could not
be maintained without substantial pesticide inputs.
• They are highly effective, rapid in curative action, adoptable to most
situations, flexible in meeting changing agronomic and ecological
conditions and economical.
• Insecticides are the only tool for pest management that is reliable for
emergency action when insect pest populations approach or exceed the
economic threshold.
• It is difficult to imagine a technology that would produce the amount
of food and fiber and maintain the level of public health that we have
today, without pesticides.
• But their use presents a problem.
• The chemical insecticide came in limelight when DDT insecticidal
property discovered by Paul Muller of Switzerland in 1939.
• Paul Muller awarded Nobel Prize in 1948 for discovering insecticidal
property of DDT.
Advantages of Chemical Control
• 1. It is often the only means of combating pests.
• 2. It is curative in effect.
• 3. It is easy to apply/adopt.
• 4. Farmers can apply when and where required.
• 5. Large area can be covered in relatively short time.
• 6. Broad spectrum activity: A single or combination of two
insecticides in a single application may control the pest complex.
• 7. Depending upon crops, pests and nature of damage, a range of
insecticides is available to choose from.
• 8. Highly effective against pests than other methods of insect control.
• 9. It can be used in human health programme
• 10. It can protect animals from illness that can be caused by
parasites such as fleas.
• 11. Growers can get high returns on his investment in a short time.
• 12. It is economical and are easy to obtain and apply.
Disadvantages of Chemical Control
• 1. It is non selective: May harm natural enemies (Parasites and predators)
and pollinators.
• 2. It leads emergence of secondary pest outbreak.
• 3. Resistance often develops: Insects tend to become resistant to
insecticides after sometime, cannot be killed.
• 4. It pollutes air, water and land.
• 5. It may cause phytotoxicity.
• 6. Insecticides residues in food commodities and other components of
the environment affect wide variety of organisms in the food chain.
• 7. It upset the balance of nature, which may result in unexpected
problems
• 8. Noncompatible with biological control method.
• 9. Adverse effect on animals and man himself.
• 10. It is dangerous to consumers, workers during and after use.
Properties of an ideal insecticide or pesticide
• 1. It should be freely available in the market under different
formulations.
• 2. It should be toxic and kill the pest required to be controlled.
• 3. It should not be phytotoxic to the crops on which it is used.
• 4. It should not be toxic to non target species like animals, natural
enemies etc.
• 5. It should be less harmful to human beings and other animals.
• 6. It Should not leave residues in crops like vegetables.
• 7. It should have higher tolerance limits.
• 8. It Should possess quick knockdown effect.
• 11. It Should be stable on application.
• 12. It Should not possess tainting (pollute) effects and should be free
from offensive odor.
• 13. It Should be cheaper
Classifications of Insecticides
• Insecticides are classified in several ways taking into consideration
Their origin
Mode of entry
Mode of action
Based on toxicity
Based on generation
Based on stage specificity
I. Based on the origin and source of supply
• A. Inorganic insecticides:
• Comprise compounds of mineral origin and elemental Sulphur.
• This group includes arsenate and fluorine compounds as
insecticides.
• Sulphur as acaricides (kill ticks and mites) and zinc phosphide as
rodenticides (kill rodents).
• B. Organic Insecticides:
• 1. Insecticides of animal origin: Nereistoxin isolated from marine annelids,
fish oil rosin soap from fishes etc.
• 2. Plant Origin insecticides or Botanical insecticides: Nicotinoids,
pyrethroids, Rotenoids etc.
• 3. Synthetic organic insecticides: Organochlorines , Organophosphorous,
Carbamate insecticides etc.,
• 4. Hydrocarbon oils etc.
II. Based on the mode of entry
• (a) Stomach poison:-
• The insecticide applied on the leaves and other parts of plant when
ingested act on the digestive system of the insect and bring about
kill.
• This poison is used for chewing insects e.g. DDT, BHC, Aldrin,
Toxaphene dusts, Zinc phosphide, paris green synthetic pyrethyrium.
• (b) Contact poison:-
• The toxicant which brings about death of the pest species by means of
contact with the cuticle.
• e.g. quinolphos, Monocrotophos, dichlorvos, endrin, systemic pyrethruid.
• (c) Fumigant:-
• The toxicant which in its gaseous state penetrates insect body through the
tracheal system and kills the pests.
• e.g. Alluminium phosphide, ED\CT mixture.
III. Based on mode of action
• 1. Physical poisons:
• Bring about the kill of insects by exerting a physical effect.
• For example, Heavy oils, tar oils etc. which cause death by
asphyxiation (deprived of oxygen).
• Inert dusts effect loss of body moisture by their abrasiveness as in
aluminium oxide or absorb moisture from the body as in charcoal.
• 2. Protoplasmic poisons:
• A toxicant responsible for precipitation of cell protein especially
destruction of cellular protoplasm of midgut epithelium.
• e.g., Arsenical compounds.
• 3. Respiratory poison:
• A chemical which inhibit cellular respiration by blocking
cytochrome oxidase enzyme as with the fumigant like hydrogen
cyanide, carbon monoxide EDB, ED\CT etc. is said to be a respiratory
poison.
• 4. Nerve poisons:
• A chemical associated with solubility in tissue lipid and functions
activity by blocking acetylcholinesterase enzyme in insects and warm
blooded animals is called nerve poison
• e.g. organophosphate and carbamate insecticides, synthetic
pyrethroids.
• 5. Chitin inhibitors:
• Chitin inhibitors interfere with process of synthesis of chitin due to
which normal molting and development is disrupted.
• Examples, Novaluron, Diflubenzuran, Lufenuron, Buprofezin
• 6. General Poisons:
• Compounds which include neurotoxic symptoms after some period
and do not belong to the above categories.
• Examples, Chlordane, Toxaphene, aldrin
IV. Based on toxicity
Toxicological terminology
• LD50: Lethal dose required for killing 50% of insect and it is expressed
in terms of mg/kg body weight of insect.
• LC50: Lethal concentration required for killing 50% of insect and it is
expressed on terms of percentage.
• LC90: Lethal concentration required for killing 90% of insect and it is
measured in percentage.
• Thus higher the LC50 or LD90 values lesser the toxicity and vice
versa.
V. Based on stage specificity
• 1. Ovicides
• 2. Larvicides
• 3. Pupicides
• 4. Adulticides
VI. Generation wise
• First generation - Inorganics and Botanicals
• Second generation - Synthetic organics
• Third generation - Recent chemicals for reproductive control, IGRs
like MH & JH mimics
• Fourth generation - Synthetic pyrethroids
• Fifth generation - SPs, Neonicotinoids
