Insecticides synthetic

1 Organochlorines Historically these are the most important and controversial insecticides, and include the most widely known pesticide of all, DDT. 

Its great chemical stability is on the face of it very desirable, since this means the compound will remain unchanged and continue to exercise its insecticidal properties. Re-application will not be necessary and therefore the cost of treatment will be kept very low. Ironically, therefore, as we will see shortly, it was this very property which led to DDT s downfall. 

DDT first came to the general public s attention in 1943 during World War II, when it was used by the US Army in Naples to arrest, for the first time in history, a typhus epidemic. This one disease killed more than 2.5 million Russians during the same war. 

Once it had been recognized that DDT killed the mosquitoes which spread malaria, a worldwide malaria eradication programme was quickly put into 

These problems are a consequence of two properties of the DDT molecule—firstly, its solubility characteristics (virtually insoluble in water, 

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Furthermore, the share cf crops lost to Insects has nearly doubled during the last 40 years (Table 1), despite a more than 10-fold increase in both the amount and toxicity of synthetic insecticide used (17-19). Up to the present time the increased insect losses, in terms of yields per hectare, have been offset by increased crop yields obtained through the use of higher yielding varieties and greater use of fertilizers and other energy-based inputs (20, 21). 

Flubendiamide is an example of a new chemical class of insecticides that have been termed phthalic acid diamides (Nauen 2006, Copping and Duke 2007). They are related to the alkaloid ryanodine, which is extracted from Ryania species. Ryanodine affects muscles by binding to calcium channels of the sarcoplasmic reticulum. Ca + ions act as intracellular messengers, and their flux is modulated by calcium channels of this type. The toxic action of ryanodine and synthetic insecticides related to it is due to the disturbance of calcium flux. 

Pyrethroids Synthetic insecticides having a strong resemblance to pyrethrins. 

For the purpose of this review, the compounds considered are distributed among the following sections 1,1,l-trichloro-2,2-bis(p-fluorophenyl)-ethane, analogs of 1,1,1-trichloro-2,2-bis(p-fluorophenyl)-ethane, and miscellaneous organofluorine compounds. The chemistry, insecticidal activity, and toxicity of these groups of compounds are considered in the order given. Much of the work in synthetic insecticides, especially the biological portion, is necessarily of an exploratory character, and hence will have to be supported before appraisals become final. 

As Muller had prophesied and indeed hoped, DDT stimulated the discovery of more synthetic insecticides. DDT relatives included chlordane, toxaphene, aldrin, dieldrin, endrin, and heptachlor. Popular substitutes for DDT s family included organophosphates such as parathion, which is a powerful neurotoxin, and carbamates, which are also highly toxic to people. Unlike DDT, parathion and aldicarb have killed and injured many farm workers. Malathion was later developed to be several hundred times less toxic than parathion. 

The world had changed radically in the quarter century since Muller had begun his search for an effective synthetic insecticide. DDT and its chemical derivatives had been the most widely used insecticides for more than 20 years. Because insect resistance was weakening DDT s effectiveness, its use was beginning to decline. Since DDT-associated molecules have a half-life as long as 50 years, however, almost one billion pounds of DDT remained in the environment. 

Resistance to insecticides has drawn global attention since the Korean War in 1950 when the mass use of organic synthetic insecticides, such as DDT and BHC, against agricultural pests and sanitary pests became common. Organophosphorus compounds and carbamates were used thereafter, but invited problems of safety concerns and insect resistance. Synthetic pyrethroids were watched with keen interest as alternatives and have become used widely not only for sanitary pests but also agricultural pests. The development of resistance to synthetic pyrethroids is also not a rare phenomenon and has spread all over the world. 

Natural pyrethrins are a neurotoxin and repel, knock down, and kill by contact with insects at a low concentration. On the other hand, they have ideal features for household insecticides because of their quite low dermal and oral toxicides to warm-blooded animals. Neither plants other than pyrethrum nor synthetic insecticides have been reported to have such properties. Numerous synthetic pyrethroids have been developed by chemists since the complicated chemical structure of natural pyrethrins was elucidated in the middle of the twentieth century. Allethrin was the first synthetic pyrethroid put into practical use. 

Elliott M, Famham AW, Janes NF, Needham PH, Pulman DA (1974) Synthetic insecticides with a new order of activity. Nature 248 710-711... 

Pyrethroids are a class of synthetic insecticides designed and optimized based on the structure of the pyrethrins found in natural pyrethrum extracted from chrysanthemum flowers [1, 2], Pyrethroids are widely used to control insect pests in agriculture and public health because of their relative safety for humans and high insecticidal potency [3]. 

Way and van Emden state that appropriate conventional synthetic insecticides will remain as important IPM components in many crop systems for the foreseeable... 

Mirex and chlordecone are two separate synthetic insecticides that have similar chemical structures. They do not occur naturally in the environment. Mirex is a snow-white crystalline solid and chlordecone is a tan-white crystalline solid. Both compounds are odorless and neither burns easily. 

Fig. 13. Insecticidal compounds from the Piperaceae and the general structure of natural and synthetic insecticidal alkyl furans.

Insect resistance and environmental pollution due to the repeated application of persistent synthetic chemical insecticides have led to an Increased interest in the discovery of new chemicals with which to control Insect pests. Synthetic insecticides, including chlorinated hydrocarbons, organophosphorus esters, carbamates, and synthetic pyrethroids, will continue to contribute greatly to the increases in the world food production realized over the past few decades. The dollar benefit of these chemicals has been estimated at about 4 per 1 cost (JJ. Nevertheless, the repeated and continuous annual use in the United States of almost 400 million pounds of these chemicals, predominantly in the mass agricultural insecticide market (2), has become problematic. Many key species of insect pests have become resistant to these chemicals, while a number of secondary species now thrive due to the decimation of their natural enemies by these nonspecific neurotoxic insecticides. Additionally, these compounds sometimes persist in the environment as toxic residues, well beyond the time of their Intended use. New chemicals are therefore needed which are not only effective pest... 

Pyrethrins and pyrethroids are probably the best known and safest classes of natural or synthetic insecticides, widely used in domestic and agricultural applications (1-7). Pyrethrins are natural insecticides derived from the Chrysanthemum cineraria flowers the plant extract, called pyrethrum, is a mixture of six isomers (pyrethrin I and II, cinerin I and II, jasmolin I and II) which was first used in China in the century AD, during the Chou Dinasty. The world pyrethrum market is worth half a billion US dollars [main producers are East Africa highlands (Kenia, Tanzania and Rwanda) and Australia] however, its availability is subject to cyclical trends, due to rains and relations with farmers, who face high harvest costs also due to the fact that the flowers have to be... 

Plants that produce "specific toxins may be plagued by Insects that develop a tolerance to these toxins in much the same way as Insects develop tolerance to synthetic insecticides. Two examples from this chapter are the tobacco hornworm and the boll weevil which have developed a high tolerance to nicotine and gossypol, respectively. Some occurrence in the distant past may have placed sufficiently high selection pressure on these Insects that they developed tolerance to these compounds. Alternatively, the same effect could have occurred by a low selection pressure applied over a very long period time. Other plants protect themselves by employing general" toxins. 

Insects treated with such analogs, could rapidly become tolerant not only to the analog, but also to the natural allelochemlc. There are examples of cross-resistance in which an insect treated with one chemical was found to have resistance to a chemical with which it had never been treated. A strain of house-fly which had developed resistance to the synthetic Insecticide, DDT, was found to be resistant to the natural pyrethrln insecticides (286). 

M. Elliott, Synthetic Insecticides Related to Natural Pyrethrins , in Crop Protection Agents from Nature natural products and analogues , ed. L.G. Copping, Royal Society of Chemistry, Cambridge, UK, 1996, pp. 254-300. 

Synthetic chemical barrier preventive foliar sprays with synthetic insecticides, nematicides, acaricides, anticoagulants, fumigants, fungicides or bactericides botanical pesticides containing petroleum derivatives Absent Common... 

Chitin. Like cellulose synthase, fungal chitin synthases are present in the plasma membrane and extrude microfibrils of chitin to the outside.147 150 In the fungus Mucor the majority of the chitin synthesized later has its N-acetyl groups removed hydrolytically to form the deacetylated polymer chitosan.151152 Chitin is also a major component of insect exoskeletons. For this reason, chitin synthase is an appropriate target enzyme for design of synthetic insecticides.153... 

A recent example is given by the insecticidal properties of the neem tree (Stone). Neem seeds have chemicals that ward off more than 200 species of insects, while exhibiting less toxicity to humans than synthetic pesticides, and having little effect on predators of the insects. Neem seeds were valued at 300/ton in 1992. However, a lower pnce is needed if the extracts are to find widespiead use as insecticides. The economic potential for naturally derived insecticides is large considering that about 2 x 109 of synthetic insecticides are sold annually in the U.S, (Stone). 

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