Usually, the OPIs are excreted in milk, urine and bile. The extent of absorption is more if these are applied in organic solvents. Dermal absorption is highly influenced by the solvent used. Mostly, OPIs are highly lipid-soluble except few like ecothiopate, and are rapidly absorbed practically by all routes including GIT, skin, mucus membrane and lungs. These events bring about an accumulation and, consequently, increase of ACh at the neuromuscular junction, which, in turn, respectively, excites muscle fibers and produces repetitive muscle contraction that causes tremors in the body muscles of the insect - and the insect finally dies of exhaustion. Ultimately the enzyme fails to recover quickly. The OP compounds phosphorylate the ChE and form a stable complex. At the enzyme site, they compete with ACh and bind with ChE, thus inhibiting its normal function. In its usual course of action, the ChE first gets acylated by losing one H + and then fast recovers by using one molecule of metabolic HOH.Īctually, the OP compounds are structurally similar to ACh. Very soon ACh is splitted by ChE present at the neuromuscular junction into choline and acetyl CoA.Īctually, splitting of ACh by ChE prevents its accumulation at the neuromuscular junction and thus assists in muscle relaxation after each contraction. The ACh excites muscle fibers and, consequently, muscle contractions take place. In other words, all OP compounds are anticholinesterase agents i.e., they inhibit the enzyme cholinesterase (ChE) at the neuromuscular junction.ĭuring normal muscle contraction, the cholinergic nerve fibers of autonomic system liberate acetylcholine (ACh) at the neuromuscular junction. In principle, OP compounds react with the active site of AChE (a serine hydroxyl group). The OPIs, in general, are less persistent than the organochlorines, a property due to which they are preferred to the organochlorines. Such compounds are absorbed into the sap of plants, remaining active and soluble for a reasonable period and are toxic to the plant pests but not to their predators e.g., mipafox, dimethoate, demethon schradan.
These organophosphorus insecticides exert their insecticidal action like the chlorinated hydrocarbon insecticides and are called contact poisons e.g., paraxon, parathion, Malathion, EPN, methyl parathion. According to the Manner in which OPIs Exert their Insecticidal Action: These insecticides undergo microbial conversion into metabolites which inhibit cholinesterase enzyme e.g.:Ģ.
These compounds act by directly inhibiting the cholinesterase enzyme, e.g., Fenchlorvos, Dichlorvos, Disopropyl fluorophosphate (DFP), Tabun, Serin, Soman, Tetraethylpyrophosphate (TEPP), Mevinphos, Disulfoton, Chlorothion, Triazophos, Chlorpyriphos, Bidrin and Anilophos. According to the manner in which OPIs exert their insecticidal action OPIs are classified into two broad groups on the following basis:Ģ.
Classification of Organophosphate Insecticides: Classification of Organophosphate Insecticides 2. In this article we will discuss about:- 1.
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