Organophosphorus pesticides are organic compounds containing organophosphorus pesticides, which are used to control plant diseases and insect pests. This kind of pesticide has many varieties, high efficacy, wide use and easy decomposition, and generally does not accumulate in human and livestock, so it is an extremely important compound in pesticides. However, many varieties have strong acute toxicity to people and animals, so special attention should be paid to safety when using them. In recent years, high-efficiency and low-toxicity varieties have developed rapidly, gradually replacing some high-toxicity varieties, making the use of organophosphorus pesticides safer and more effective.

In the past, most of the organophosphorus pesticides produced in China were pesticides, such as parathion, phosphorus absorption, malathion, dimethoate, trichlorfon and dichlorvos. In recent years, organophosphorus pesticides such as fungicides and rodenticides have been synthesized one after another. Organophosphorus pesticides are mostly phosphate or thiophosphate, and R 1 and R2 in the structural formula are mostly methoxy (CH3O-) or ethoxy (C2H5O-); Z is an oxygen (O) or sulfur (S) atom; X is alkoxy, aryloxy or other substituent. A variety of organophosphorus compounds can be synthesized.

Organophosphorus pesticides are mostly oily or crystalline, and industrial products are light yellow to brown. Except for trichlorfon and dichlorvos, most of them smell of garlic. Generally insoluble in water, soluble in organic solvents such as benzene, acetone, ether, nitrogen, methane and oil. It is stable to light, heat and oxygen, and easy to decompose and destroy when it meets alkali. Except trichlorfon, it is white crystal, soluble in water, and can be converted into highly toxic dichlorvos when it meets alkali. The dosage forms of organophosphorus pesticides sold in the market mainly include emulsifier, wettable powder, granule and powder. In recent years, mixtures and compounds have gradually increased.

Organophosphorus pesticides are mostly oily liquids, and a few are solid, which generally have a large smell and a slightly dark color. Most organophosphorus pesticides are insoluble or slightly soluble in water, but generally soluble in organic solvents. Some species, such as trichlorfon, dimethoate, methamidophos and ammonium phosphate, are soluble in water. Organophosphorus pesticides are easy to hydrolyze and decompose in water, and generally become nontoxic compounds after hydrolysis, and lose insecticidal activity; Alkaline conditions are conducive to hydrolysis reaction, and it is generally not suitable to mix with alkaline pesticides or alkaline substances. However, trichlorfon will become more toxic dichlorvos after hydrolysis.

Generally speaking, organophosphorus pesticides have a high control effect on insects and mites, and their toxicity to pests is second only to pyrethroid pesticides, and some varieties are higher than carbamate pesticides. There are various modes of action of organophosphorus pesticides, most of which have multiple effects, such as stomach toxicity and contact killing, but the same variety has different modes of action, such as contact killing of phoxim, stomach toxicity of trichlorfon and internal absorption of phosphorus.

Some varieties of organophosphorus pesticides are extremely toxic, but others are very toxic. The former is parathion and methamidophos, while the latter is malathion and cartap. It used to be thought that organophosphorus pesticides had no cumulative effect, but now it is considered that some varieties do not. The teratogenic and tumorigenic effects of some varieties such as trichlorfon and dichlorvos have also attracted people's attention.

The residue period of organophosphorus pesticides varies with varieties, and some varieties, such as trichlorfon and phoxim, completely decompose and fail after several hours to 2-3 days after application. The remaining period of some varieties is 1-2 months due to systematic action. The residual period is also related to the application technology and processing dosage form. For example, phoxim applied to soil can prolong the residual period, and methyl parathion microcapsules can also prolong the residual period. The use of organophosphorus pesticides should consider selecting varieties with different residue periods on different crops, such as vegetables, tea, tobacco, mulberry, trichlorfon, dichlorvos, phoxim, dimethoate and other varieties with short residue periods, and cotton, hemp and forest trees can choose varieties with long residue periods.

Carbamate insecticide English name: Carbamate insecticide Definition: Carbamate derivative synthesized with nitrogen as matrix. It can inhibit acetylcholinesterase in insects, block normal nerve conduction, and make insects die of poisoning.

Biomimetic synthetic pesticides are synthetic esters obtained by changing the chemical structure of natural pyrethrins. Natural pyrethrin is an ancient botanical insecticide and an effective component of pyrethrum flower. Its chemical structure was not confirmed until the 1940s, and then the synthesis of similar substances began. 1949, M.S. Schecter of the United States synthesized the first commercial analog allethrin. In 1950s and 1960s, some similar compounds were successfully developed, commonly known as pyrethroids. These early varieties, like natural pyrethrins, are easy to decompose and fail under light, and are only suitable for controlling pests indoors. Many scientists, including the team led by British chemist M Eliot, have conducted long-term research to find out the unstable parts of molecular structure that are easily decomposed by light. In the early 1970s, they made a breakthrough in structural changes and synthesized the first photostable variety permethrin suitable for controlling agricultural and forestry pests. Since then, many light-stable varieties have appeared, which are called the second generation pyrethroids, including fenvalerate without three-membered rings. Since 1980s, the research on structural changes has been deepened and new progress has been made. For example, varieties with fluorine atoms in their structures have acaricidal effect, and the toxicity to fish can be greatly reduced after ester bonds become ether bonds.

The insecticidal spectrum of this kind of insecticide is not as broad as that of organophosphorus, and it is generally impossible to control mites and scale insects. The structure of this kind of pesticide is closely related to its efficacy, and there are great differences in toxicity and control indexes among varieties with different structures.

Carbamate insecticides are generally safe to fish, but highly toxic to bees; The toxicity to humans and animals is relatively small, but some varieties, such as carbofuran, aldicarb and methomyl, are extremely toxic. The cumulative residue of these pesticides in the environment is very small.

Pyrethroids are a kind of broad-spectrum insecticides, which can control many kinds of pests. Their insecticidal toxicity is 10 ~ 100 times higher than that of the older generation insecticides such as organochlorine, organophosphorus and carbamate. Pyrethroids have a strong pyrethroid insecticide effect on insects.

Contact killing effect, some varieties have both stomach toxicity and fumigation effect, but no systemic effect. Its mechanism of action is to disturb the normal physiology of insect nerves and make them die from excitement, spasm to paralysis. Pyrethroids have low dosage and concentration, are safe for people and animals, and have little environmental pollution. Its main disadvantage is that it is toxic to fish and harmful to some beneficial insects, and it will also lead to drug resistance of pests after long-term repeated use.

Pyrethroid insecticides are a kind of broad-spectrum insecticides, which have strong contact activity, stomach toxicity, ovicidal, antifeedant and repellent effects, and have no systemic and fumigation effects. High efficacy, less dosage, less environmental pollution and moderate residual period.

Pyrethroid insecticides can be widely used in cotton, fruit trees, vegetables, tea, tobacco, corn, soybeans, wheat and other crops to control Lepidoptera, Homoptera, Hemiptera, Diptera and Coleoptera pests.

The insecticidal activity of pyrethroid insecticides is higher than that of organic phosphate insecticides, and the knock-down activity is also stronger. In addition, this kind of insecticide has high fat solubility, is resistant to rain erosion, and easily penetrates the body wall of pests after application, so the dosage is generally small.

Temperature has obvious influence on the insecticidal effect of this kind of insecticides. Generally, pyrethroid type I has high efficiency at low temperature, and type II has high efficiency at high temperature, but type III is related to the variety of drug efficacy, the species of pests and the temperature range.

Pyrethroids have a good killing effect on Spodoptera litura, alfalfa aphids, Laodelphax striatellus, and silk moth. At low temperature, but the killing effect on Plutella xylostella is not affected by temperature. The insecticidal effect of pyrethrins on armyworm, alfalfa aphid and library aphid is higher at high temperature than at low temperature. Permethrin has a good control effect on Spodoptera litura and Myzus persicae at low temperature. However, deltamethrin has stronger insecticidal effect on armyworm and Myzus persicae at high temperature than at low temperature.

Pyrethroid insecticides are easy to produce drug resistance when used alone. In recent years, many kinds of pests have developed different degrees of resistance to some varieties of these pesticides. Therefore, mixing these insecticides with organophosphorus insecticides and carbamate insecticides is beneficial to overcome or delay the emergence of insect resistance.

To sum up, I found the definitions and characteristics of these three categories for you. Part of the content comes from Baidu Library, and part of it comes from the newly written practical pesticide manual, especially the newly written agricultural manual. I typed it for you word for word. I don't know if it will help you.