Synthetic pyrethrin

Verschoyle RD, Barnes JM (1972) Toxicity of natural and synthetic pyrethrins to rats. Pestic Biochem Physiol 2 308-311... 

Gerig VL (1979) The toxicity of synthetic pyrethrines to foraging bees. Schweiz Bienen Z 101 228-236... 

Bioallethrin is a synthetic pyrethrin insecticide. Piperonylbutoxide, a weak insecticide itself, has synergistic activity. The same holds true for the combination of pyrethrum extract with piperonylbutoxide. These combinations have the same efficacy as permethrin. Local irritation occurs frequently effect and contact with mucous membranes and the eyes must be avoided. 

Early insecticides were often inorganic arsenic, copper, lead, and sulfur compounds.6 An example is Bordeaux mixture, which contains copper sulfate and calcium hydroxide. Copper chromium arsenate is used today as a wood preservative. Organic natural products, such as pyrethrin and rotenone (11.1) have also been used. Rotenone is used today for killing undesirable fish, such as carp, before restocking ponds with game fish. Many synthetic pyrethrins are used today because of their relative safety to humans. However, both rotenone and pyrethrin7... 

Since most of the studies have been carried out on Aedes and Culex mosquitoes, it is interesting that a-terthienyl has also been tested as a potential larvicidal agent against a malaria vector with fourth-instar Anopheles gambiae in Tanzania (4). Little information on the experimental conditions was provided, but the activity of the chemical was found to be somewhat higher than that recorded with Aedes mosquitoes in Canada (3). These results were believed to compare favorably with those obtained with synthetic pyrethrins. 

Pyrethrins Natural insecticide originally extracted from chrysanthemums and used for insect control in households and storage facilities. Among insecticides, pyrethrins are known to have the least toxic effects for humans. There are synthetic pyrethrins with a similar structure to natural pyrethrins. 

This is interesting when one considers the effect of synergists on the synthetics. All of the synthetics mentioned above are based on chrysanthemum monocarboxylic acid and in the case of allethrin, cyclethrin, and furethrin on the alcohol moiety there is only one double bond. When checked against the standard synergists, these synthetics do not show the degree of synergism shown by pyrethrins and this may be because of the fact that there is only one double bond for epoxidation, compared with two in the pyrethrolone radical, and therefore the synergist would not block this epoxidation step as effectively. 

Many pesticides are not as novel as they may seem. Some, such as the pyre-throid and neonicotinoid insecticides, are modeled on natural insecticides. Synthetic pyrethroids are related to the natural pyrethrins (see Chapter 12), whereas the neo-nicotinoids share structural features with nicotine. In both cases, the synthetic compounds have the same mode of action as the natural products they resemble. Also, the synthetic pyrethroids are subject to similar mechanisms of metabolic detoxication as natural pyrethrins (Chapter 12). More widely, many detoxication mechanisms are relatively nonspecific, operating against a wide range of compounds that... 

The compounds featured in Table 1.1 are considered briefly here. Pyrethrins are lipophilic esters that occur in Chrysanthemum spp. Extracts of flower heads of Chrysanthemum spp. contain six different pyrethrins and have been used for insect control (Chapter 12). Pyrethrins act upon sodium channels in a manner similar to p,p -DDT. The highly successful synthetic pyrethroid insecticides were modeled on natural pyrethrins. 

Pyrethroids Synthetic insecticides having a strong resemblance to pyrethrins. 

In continuing efforts toward the development of other nontoxic insecticides, many new products are being synthesized and tested. The direction of the synthetic work is guided by the theory that the insecticidal activity of a given substance is due to the combined influence of a toxic nucleus and modifying auxiliary groups. To illustrate the theory, this paper presents information on six materials related to piperonyl butoxide, when tested in combination with pyrethrins. 

These synthetic pyrethroids mimic natural counterparts, of which the most important is pyrethrin 1 (10.265). Unfortunately, the natural products lack the photochemical and hydrolytic stability necessary for use as wool insect-resist agents. The synthetic products have the required stability, yet retain the low mammalian toxicity and low environmental retention of the natural products. Permethrin, however, is toxic to aquatic life and is therefore subject to increasingly severe discharge limits. There is some evidence that permethrin is less effective against larvae of a certain beetle. This can be compensated for by using a combination of permethrin with the hexahydropyrimidine derivative 10.264. Some possible alternative pyrethroids have been mentioned [517] as development products (10.266-10.269). 

Keywords Cross resistance Natural pyrethrins Safety Synthetic pyrethroid... 

As described in the section on Cross-resistance in this chapter, it was found that some insect species showed extremely low cross-resistance to three ingredients, pyrethrins as well as d-allethrin and prallethrin, although they developed resistance to photostable synthetic pyrethroids. The latter two compounds of d-allethrin and prallethrin have quite similar chemical structures and the same configuration as cinerin I (an ingredient of pyrethrins). It is considered preferable to develop pyrethroids retaining the characteristics of natural pyrethrins and household insecticides containing them in the perspectives of safety and low cross-resistance. 

Pyrethrum became the main source of household insecticides in sprays in the USA (1919) and mosquito coils (1895) as well as oil-based preparations (1924) in Japan. Thereafter, the insecticidal ingredients shifted from pyrethrins to various synthetic pyrethroids, but mosquito coils have been used worldwide for more than 110 years without changing in shape. 

After World War II, the production of pyrethrum in Japan fell markedly and declined to only 1,000 tons in terms of dried flowers in 1965. At present, pyrethrum is not cultivated in Japan and the main producers are Kenya, Tanzania, Tasmania, and China, with worldwide production in 2010 amounting to around 10,000 tons of dried flowers. Dried flowers are extracted and purified at pyrethrum-extracting factories on the spot, producing 25-50% pyrethrin extracts. While pyrethrum extracts have been replaced with various synthetic pyrethroids, they are still used in houses, food factories, gardens, and organic farms, all of which emphasize the importance of safety. Katsuda [1] reported that natural pyrethrins showed a low development of resistance by flies and mosquitoes compared with many synthetic pyrethroids, against which a high development of cross-resistance was observed. 

For the absolute configuration of the acid moieties, that of chrysanthemic acid was elucidated by Crombie et al. [13] in 1954 and that of chrysanthemum acid was determined by Inoue et al. [14] in 1955, respectively. The absolute configuration of the alcohol moiety was found by Katsuda et al. [15] in 1958. The complete elucidation of the absolute configuration of natural pyrethrins (Fig. 6) has led to the development of new useful synthetic products based on this model. 

Although pyrethroids consist of natural pyrethrins and many photostable synthetic pyrethroids, they must be discriminated when discussing cross-resistance. 

Cross-resistance to pyrethroids for outdoor use has developed markedly in M. domestica, mosquitoes, cockroaches, and so on however, it has also been found that natural pyrethrins as well as d-allethrin and prallethrin (ETOC ), which have very similar chemical structures and the same configuration as natural pyrethrins, show an extremely low degree of cross-resistance development by these highly-resis-tant sanitary pests compared to photostable pyrethroids. Many novel synthetic pyrethroids recently developed as household insecticides have tended to pursue efficacy improvements in terms of rapid knock-down effects, residual efficacy or volatility. 

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. 

Gersdorff WA, Piquett PG (1961) The relative effectiveness of two synthetic pyrethroids more toxic to houseflies than pyrethrins in kerosene sprays. J Econ Entomol 54 1250-1252... 

Begley MJ, Crombie L, Simmonds DJ et al (1974) X-ray analysis of synthetic (45)-2-(prop-2 -enyl)rethronyl (lJ )(3J )-chrysantemate 6-bromo-2,4-dinitrophenylhydrazone and (31 ) chiroptical correlation with the six natural pyrethrin esters. J Chem Soc Perkin Trans 1 879-913... 

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