LECTURE NOTES ON TYPES OF INSECTICIDES

CLASSIFICATION BASED ON MODE OF ENTRY: The way in which insecticides penetrate into an insect
From out side vary with the chemical nature of the insecticide.  Four major routes of entry in to an insect body have been recognized and accordingly insecticides are grouped under four major categories as follows.
1) CONTACT INSECTICIDES: These are highly toxic insecticides which have the ability to penetrate the body surface of insects on contact with it. After getting into the body of insects they interfere with its nervous system and kill it.
Eg:- DDT, HCH, Aldrin, Parathion, Nicotine.
2)STOMACH POISON:  These are chemicals which become toxic and fatal to the insect only when the insect ingests/eat them. From the gut they are absorbed to the tissues, interfere with the normal metabolism and kill the insect. They are basically compounds of Arsenic or fluorine.
3) FUMIGANTS: These are highly volatile insecticides, whose gases can produce a toxic cover around the insect. Fumigants are gases at normal temperature and pressure and hence they are stored in pressurized containers. They get into the insect body through spiracles. Fumigants are usually used to protect stored grains and other materials.
Eg:- Hydrogen cyanide, Methyl bromide, Ethylene dichloride, Ethylene dibromide, Lindane, Dichlorvos.
4) SYSTEMIC INSECTICIDES:  Systemic insecticide is a compound which can get absorbed to the sap stream of plants from stem, leaves, fruits and roots, generally it is through roots.  They move along the vascular system in an apical direction from the area of application. This may poison the insects that feed on the sap of these plants.
Eg:- Parathion,  Malathion, Diazinon, Lindane, Nicotine.   
The advantage of systemic insecticides are that (1) They need not be applied all over the plant body, (2)Action persists for long time,(3) No harmful effect on non-sap feeders and beneficial insects (4)They can be applied as direct foliar sprays or can be injected to the shoot system.         
CLASSIFICATION BASED ON APPLICATION: Based on the nature of their application, chemical pesticides can be grouped as the following categories.
1)ATTRACTANTS:  These are substances which can attract insects without contact. Synthetic chemical attractants are important in pest control. Both male and female insects will respond to them for feeding purpose, while only mature female insect will be attracted for egg-laying purpose.
2) REPELLENTS:  These are not successful in controlling plant pests, because a continuous emission is essential for effective protection. But chemical repellents are effective for personal protection from blood- sucking insects.
3)FEEDING DETERRENTS: These are chemicals which suppress the feeding instinct of insect pests. They influence the pests only after contacting them.
4) AUXILIARY SUBSTANCES:   These are substances that are mixed with insecticides to boost up its action.
CLASSIFICATION BASED ON CHEMICAL NATURE:
INORGANIC INSECTICIDES:  These are mainly made up of sulphur and mineral compounds. The common mineral compounds are the compounds of arsenic, copper, lead, mercury and fluorine. They are broad- spectrum poisons, which are highly toxic and essentially non-degradable. They can remain in the soil for log time and can cause permanent damage to most of the organisms.
Arsenic Compounds:- Lead arsenate, Calcium arsenate, White arsenic, Paris green.
Fluorine compounds:- These are primarily stomach poisons, and is soluble in the digestive juice of insects.               Eg:-Sodium fluoride, Sodium floroalumintate, Sodium fluorosilicate.
Sulphur:- Sulphur is mixed with