Annual loss of agricultural produce by pests and pathogens alone is 30%. So use of pesticides has increased the yield from high yielding varieties of plants which are more easy victims of pests and parasites than their wild relatives. Flit, baygon and mosquito coils are pesticides. DDT (insecticide), 2-4-D (weedicide) are two synthetic pesticides introduced after world war -2. Bordeaux mixture is a fungicide used from a century ago. This mixture of copper sulphate and calcium hydroxide was discovered in Bordeaus University in France as an effective killer of fungus Plasmopara viticola, causing deadly downy mildew in vine.
The pesticides used in India can be classified into five on the basis of chemical nature.
1. ORGANOCHLORIDES :- These are organic compounds with several atoms of chlorine per molecule. DDT, BHC,ALDRIN,DIELDRIN and ENDRIN are organo chlorine pesticides. DDT is the oldest and most popular synthetic pesticide. BHC alone represent 50% of the total pesticide volume of pesticide. Aldrin is used in the foundation of buildings to prevent attack by termites. All these chemicals are lipophillc and get bioaccumulated in the fatty tissue of animals.
2. ORGANOPHOSPHATES :- MALATHIION (Flit) used in antimalarial programmes and PARATHION are esters of organic compounds with phosphoric acid. Fenitrethion, malathion and parathion are very effective on the nervous system.
3. CARBAMATES :- These are compounds having a chemical structure similar to acetylecholine. Carbofuran (furadon), propoxur (baygon) are carbamate pesticides.
4. PYRETHROIDS :- These are synthetic products from pyrethin, a plant chemical extracted from chrysanthemum cinerarifolium.
5. TRIAZINES :- These are compound like simazine, altrazine derived from urea. They are effective weedicides (herbicides) used against the weeds of tea, tobacco and cotton.
ACTION OF PESTICIDES
In animals, pesticides interferes with the functioning of nervous system. In plants, herbicides interferes with photosynthesis (photolysis of water is in photosystem-2) and translocation of food.
BENEFITS OF PESTICIDE
Green revolution and Grey revolution in plants White revolution and Blue revolution in animals was greatly facilitated by pesticides. DDT was used in the control of vector borne diseases in man like malaria, filaria, sleeping, sickness, dengue fever etc.
PROBLEM OF USING PESTICIDE
Pesticides cannot discriminate between harmful target pests are biologically controlled by non pest predators. When pesticides kill the sensitive predators, the resistant pests increase in numbers. In India, mosquitoes have become resistant to DDT, BHC, MALATHION,PARATHION, AND FENITROTHION. Framers have to use larger share of their capital produce for increasing use of pesticides to control pesticide resistant pests. Natural selection acting on pesticide resistant genes have increased the pesticide resistant pests and decreased the number of their natural predators.