Pesticides pyrethrin

Pyrethroid pesticides were developed as synthetic versions of the naturally occurring pesticide pyrethrin, which is found in chrysanthemums. Most pyrethroids are safer than the organochlorines, organophosphates, and carbamates, although some synthetic pyrethroids are toxic to the nervous system. Pyrethroids have been modified to increase their stability in the environment, and many different pyrethroids are being used today. 

Useful tor detectir some neim toxicants chlorin ed pesticides, pyrethrins, sodium, mercury)... 

Uses Emulsifer for agric. spray oils, pesticides (pyrethrin formulations)... 

Permethrin, a pyrethrin pesticide, decreased the inhibition of brain cholinesterase activity by methyl parathion, but methyl parathion decreased the LD50 of permethrin when the two pesticides were simultaneously administered to rats (Ortiz et al. 1995). The potentiation of permethrin lethality may be due to the inhibition by methyl parathion of carboxylesterase, which metabolizes permethrin. 

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 R/S ratios for permethrin and phenothrin in Table 3 are 204 and 283, respectively. The Hiroyama strain showed high cross-resistance to permethrin and phenothrin, whereas the R/S ratio for natural pyrethrins was only 7. Moreover, the R/S ratio for racemic allethrin was 97, indicating the slow development of resistance compared with permethrin and phenothrin. These results agree well with the findings of Sawicki et al. [49], who reported that pyrethroids with the cyclopentenolone ring showed only a slight resistance at the International Congress of Pesticide Chemistry in Ottawa in 1986. 

One approach to the discovery of new insecticides which fulfill the criteria of efficacy, safety, selectivity, etc., is through the study of the natural chemical defenses of plants. Extracts of plants have been used as Insecticides by humans since before the time of the ancient Romans, a practice that continues today with many of the 2000 species of plants known to have insecticidal properties (4-5). The use of insecticidal" plants is especially prevalent among subsistence farmers since plants grown locally are cheaper, and sometimes more accessible, than synthetic chemical pesticides. Commercially, however, only a few of these plants. Including those containing pyrethrins, rotenoids, and alkaloids, have been used to any extent in the United States as sources of insecticides (6-8). 

Pyrethrins are naturally occurring pesticides derived from chrysanthemum plants. They are active against many insects and mites. Over-the-counter liquid and gel preparations of pyrethrins with piperonyl butoxide are available for the treatment of pediculosis (piperonyl butoxide inhibits the hydrolytic enzymes that metabolize the pyrethrins in the arthropod). A synthetic pyre-throid, permethrin (Elimite), is available by prescription. A lower concentration of permethrin (Nix) is available without prescription. Pyrethrins and permethrin are quite safe. 

Organic sprays and dusts There are several natural sprays, dusts, or baits that repel or poison pests. You can make some types yourself from garden and kitchen ingredients. Vbu can buy products including botanical pesticides such as neem or pyrethrin. 

Many botanical insecticides, including pyrethrin, are broad-spectrum pesticides that kill a wide range of insects. Beneficials are often included among the dead. Also, spraying recklessly for one pest may result in the development of secondary pests. When you spray a broad-spectrum pesticide that also kills off many beneficials, some pest that survives the spraying and is now unchecked by a natural... 

Organically acceptable sprays such as horticultural oils make pest habitats inhospitable they also coat and suffocate scales. Soap sprays kill soft-bodied pests, as well as many beneficials, but are safer for the gardener than botanical pesticides such as pyrethrin. Gentle, nonpesticidal controls such as homemade herbal or baking soda sprays are much less toxic than botanical pesticides . select them first when you seek sprays or dusts to remedy pest problems. 

Many organically acceptable controls are known by more than one name. For e.xample. highly refined horticultural oils used to kill a variety of pests are also called supreme, summer, or superior oils. And some gardeners refer to spraying pyrethrin. while others call that botanical pesticide pyrethrum. 

Piperonyl butoxide, also called PBO, is a common synergist used with botanical insecticides such as pyrethrin and citrus oils. PBO is sufficiently toxic that it was recently recognized as a pesticide itself. When used frequently at high concentrations, PBO may affect the human nervous system. For this reason, many organic certification programs prohibit the use of pesticides that contain PBO... 

All manner of pollutants are considered under the discipline of terrestrial ecotoxicology including pesticides, persistent organic pollutants, other organic substances, and metals and metalloids (e.g., selenium and arsenic). Naturally occurring toxins such as those produced by poisonous plants, snakes, or invertebrates generally are not included unless people intentionally apply them for pest control. For example, the pyrethroid pesticides are derived from the naturally occurring pyrethrin toxin that is found in chrysanthemum. 

Environmental residues of pyrethroids and pyrethr-ins are degraded by hydrolysis, and pyrethrins by photolysis, and so do not accumulate in most ecosystems. The main environmental hazard associated with pyrethroid use is contamination of freshwater by acute run-off after use as an agricultural pesticide or ectoparisitide near to water, which can lead to death of aquatic invertebrates or fish (which have very limited pyrethroid detoxification capacity). 

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