Naturally-occurring insecticides

Some pyrethroids have as many as eight different isomers, and there are several different types. Acute toxicity of a mixture of two isomers depends on the ratio of the amounts of isomers in the formulation. For example, the female rat s acute oral LD50 of permethrin increases from 224 mg/kg to 6,000 mg/kg as the proportion of transisomer increases from 20% to 80%. The route of exposure also is critical in assessing the acute toxicity of a synthetic pyrethroid. Like DDT and many other registered insecticides, naturally occurring pyrethrins and the synthetic pyrethroids are nerve poisons. 

Chiysanthemic acid (TM 355) is an important constituent of pyrethiins - naturally occurring insecticides which are virtually harmless to mammals. What feature of this molecule wiU dominate our strategic thinking ... 

Pyrethrms are a group of naturally occurring insecticidal substances found in the flowers of vanous plants of the chrysanthemum family The following is the structure of a typical pyrethnn cmerin I (exclusive of stereochemistry)... 

Synthetic Pyrethroid Insecticides. Elucidation of the chemical stmctures of the naturally occurring pyrethmm esters, their rapid and selective insecticidal action, and their high cost stimulated the search for effective synthetic derivatives (13,17,21). Since the 1940s, stmctural optimisation has produced an array of broad-spectmm insecticides with activity 10- to 20-fold greater than other types of insecticides, and with extended residual action. These synthetic pyrethroids have become one of the most important classes of insecticides with world aimual production estimated at 6000 t (21). 

Chlorinated Terpenes. A group of incompletely characterized insecticidal compounds has been produced by the chlorination of the naturally occurring terpenes. Toxaphene [8001-35-2] is prepared by the chlorination of the bicycHc terpene, camphene [79-92-5] to contain 67—69% chlorine and has the empirical formula C QH QClg. The technical product is a yellowish, semicrystalline gum (mp 65—90°C, d 1.64) and is a mixture of 175 polychloro... 

C. M. Ignoffo, ed.. Handbook of Naturally Occurring Pesticides Microbial Insecticides, CRC Press, Boca Raton, Fla., 1986. 

Chrysanthemum dicarboxylic acid or pyrethric acid may exist in eight stereoisomers, owing to the trans or cis configuration on the side chain of the double bond as well as that of the cyclopropane. The natural acid has been shown to be the trans-trans acid. As in the case of the chrysanthemum monocarboxylic acid, the naturally occurring configuration is more insecticidally active than the racemic form or any of the three isomers synthesized. 

STAHL, for instance, was able to demonstrate that on irradiation with long-wavelength UV light the naturally occurring contact insecticides pyrethrin I and II, cinerin I and II and jasmolin I and II present in Chrysanthemum cinerariifolium are converted to inactive pyrethrin oxides by the incorporation of oxygen [7]. 

The carbamate and OP insecticides and the organophosphorous nerve gases soman, sarin, and tabun all act as anticholinesterases, and most of their toxicity is attributed to this property. The naturally occurring carbamate physostigmine, which has been used in medicine, is also an anticholinesterase. Some OP compounds can cause relatively long-lasting inhibition of the enzyme because of the phenomenon of... 

Eldefrawi, M.E. and Eldefrawi, A.T. (1991). Nervous-System-Based Insecticides—Describes the mechanisms of action of a wide range of neurotoxic compounds, both human-made and naturally occurring. 

Natural pyrethrins, insecticidal ingredients occurring in the flowers of Tanacetum cinerariaefolium (also known as Chrysanthemum cinerariaefolium or Pyrethrum cinerariaefolium), have been modified for higher stability in the environment as well as better biological performance for more than 40 years, and consequently more than 30 synthetic pyrethroids have been marketed and used worldwide for controlling indoor and agricultural pest insects [1,2]. 

M. Jacobson and D.G. Crosby (1971). Naturally Occurring Insecticides , Marcel Dekker, INC., New York. 

Nonpoint source sampling occurs where the analyte of interest is dispersed over a large area such that a specific point of origin cannot be ascertained. The innate occurrence of analytes of interest would be an example of a nonpoint source. The occurrence of plant nutrients, either naturally occurring or from fertilization, is an example of a nonpoint source of agricultural analytes. Herbicides, insecticides, and pest-control agents are, once applied on a field scale, also potential nonpoint sources of analytes. It is common to think of crop... 

A second approach is to obtain (extract) water as it naturally occurs in soil pores. Typically, a porous ceramic cup (other materials are available) is placed in an unsaturated soil, either in the field or laboratory. A vacuum is applied (slightly more negative pressure than the water in the soil pores see also Chapter 5) to the ceramic cup via tubing to move water into a receiving container. This water can be analyzed for all its constituents. A reason for obtaining this type of soil water sample is to analyze it for one specific constituent such as a herbicide, insecticide, or pollutant. Water extracted in this way may also better represent the concentration of the analyte of interest to which plant roots are exposed. 

Alicyclic hydrocarbons are saturated carbon chains that form ring structures. Naturally occurring alicyclic hydrocarbons are common (Chap. 1). For example, alicyclic hydrocarbons are a major component of crude oil, comprising 20-67 vol.%. Other examples of complex, naturally occurring alicyclic hydrocarbons include camphor (a plant terpene) and cyclohexyl fatty acids (components of microbial lipids). Anthropogenic sources of alicyclic hydrocarbons to the environment include fossil-fuel processing and oil spills, as well as the use of such agrochemicals as the pyrethrin insecticides (Chap. 1, and references therein). 

Jacobson, M. "Naturally Occurring Insecticides" Jacobson, M. Crosby, D. G., Eds. Marcel Dekker, Inc. New York,... 

Fig. 12. Some naturally occurring insecticides against the fruit fly.

Alkyl furans are another class of naturally occurring compounds with insecticidal activity (Fig. 13)- This group of compounds, commonly referred to as avocado furans is present in avocados, Persea americana (Lau-raceae) and related plants. When tested against beet armyworm, Spodoptera... 

Many people think the ultimate pesticide should be developed from research now being done on certain insect attractants and juvenile hormones. Isolation of naturally occurring sex attractants (pheromones) and juvenile hormones has been accomplished. The attractants could be used to congregate large numbers of insects in one place for extermination by the already existing insecticides. Alternatively, juvenile hormones have been found that prevent maturation or cause sterility in many pests. 

The newest class of insecticide, pyrethroids, is loosely based upon the naturally occurring pyrethrum derived from chrysanthemum flowers. Synthetic pyrethroids were developed in the 1980s but the naturally occurring pyrethrum was first commercially used in the 1800s. The chemical structure of pyrethroids is quite different from organochlorines and organophosphates, but the primary site of... 

Below-grade bioremediation is an ex situ technology designed to treat soil, sludge, and sediment impacted with chlorinated cyclodiene insecticides such as chlordane and heptachlor. Naturally occurring fungi are added to pesticide-contaminated soil, which is then treated in a below-grade actively aerated bioremediation cell. 

In a recent literature survey of chromenes and benzofurans in flowering plants, we have documented that approximately 90% of the 200 compounds Isolated are present in the sunflower family (Asteraceae). These naturally occurring chemicals have recently received considerable attention because of their potent cytotoxic and insecticidal activity. Chemotaxonomlcally, not all tribes of the Asteraceae seem to produce chromenes or benzofurans, with the major tribes capable of synthesizing chromenes identified as the Eupatorleae, Hellantheae, Inuleae, Senecloneae and the Astereae (17). 

The salts of fatty acids (not naturally occurring) have long been known to have insecticidal properties. The most effective potassium salts center around oleate in the monounsaturated and saturated series, although potassium caprate (Cio) was especially active against Choristoneura occidentalis (Western spruce budworm) and Acleris gloverana (Western blackheaded budworm) (117). 

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