Insecticidal Compounds from Animals

Animals often use toxins to immobilise their prey, often insects. Wasps, bees, spiders, mites, scorpions, snakes and other reptiles are all capable of producing potent toxins many of which are insect specific. There is much work in progress around the world examining the opportunities that exist to exploit these toxins to produce new insecticides. This is usually undertaken in two different ways. The first is to determine the mode of action of the natural toxin and to use this novel effect to find synthetic compounds with insecticidal activity in biochemical screens. The second is to attempt to synthesise compounds with the same structural features of the natural toxin and hence with the same mode of action but with better stability following application. The types of compounds that are known are discussed by Blagbrough and Moya13 but none has been commercialised to date. 

Some of these toxins are proteins and the genes for several insect-specific toxins have been isolated and used to transform both crops (Transgenic Crops, Section 6) and baculoviruses (Section 5.1). 

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In the field of organic phosphorus compounds there is a wealth of highly toxic compounds from which to pick a potential insecticide. The ultimate choice will be based not only on toxicity to a certain group of insect species, but on volatility, stability, safety in handling and applying, and freedom from plant injury, spray-residue and translocation hazards, and long-term toxicity to man and animals. 

It is also shown that organic-chlorine residues on alfalfa hay resulting from insecticide applications of toxaphene and the organic-chlorine content of beef fat from animals fed alfalfa hay containing toxaphene residues or sprayed with benzene hexachloride or DDT approximate a true measure of the amounts of these compounds present. 

There is sufficient evidence for the carcinogenicity of ETU in experimental animals. When administrated in the diet, ETU induced increased incidences of thyroid follicular cell carcinomas and papillary carcinomas with some metastases and liver hyperplastic nodules in rats of both sexes. There is inadequate evidence fw the carcinogenicity of ETU in humans [42]. ETU is used primarily as an accelerator for vulcanizing polychloropene and polyacrylate rubbers. The primary routes of potential human exposure to ETU are inhalation, ingestion and dermal contact. Potential occupational exposure also occurs during the manufacture of Cumulation and rqrplication of fungicides and insecticides prepmed from ETU. Residues of the compound have been found in 28 different commercial ethylenebisdithiocarbamates products [59]. 

Pyrethrins are a group of closely related, naturally occurring compounds that are the active insecticidal ingredient of pyrethmm and have been used for centuries. Pyrethmm, which has been used as a pesticide in commercial applications since the early nineteenth century, is extracted from the flowers of Chrysanthemum cinerariaefolium and Chrysanthemum cineum [1]. Most of the insecticides derived from plants traditionally have been considered safe for use on animals, and pyrethmm is an example of such material. There are six active insecticidal compounds that comprise the natural pyrethrins pyrethrin 1 and 11, cinerin 1 and 11, and... 

The effects of pollution can be direct, such as toxic emissions providing a fatal dose of toxicant to fish, animal life, and even human beings. The effects also can be indirect. Toxic materials which are nonbiodegradable, such as waste from the manufacture of insecticides and pesticides, if released to the environment, are absorbed by bacteria and enter the food chain. These compounds can remain in the environment for long periods of time, slowly being concentrated at each stage in the food chain until ultimately they prove fatal, generally to predators at the top of the food chain such as fish or birds. 

When DDT is fed to animals, even in small quantities, there is an accumulation of the compound in the tissues, particularly the fat. Telford and Guthrie (18), Orr and Mott (13), Woodward et al. (20, 21), and Laug and Fitzhugh (9) have demonstrated that DDT will accumulate in certain tissues and in milk fat of domestic and laboratory animals. Marsden and Bird (12) found that DDT was toxic to turkeys in concentrations above 0.075% of the diet, and that turkeys fed the insecticide for 7 to 8 weeks stored DDT in their fat at concentrations ranging from 4 to 8 times that in the diet. Rubin et al. (14) reported that hens fed 0.062% DDT in their diet for 12 weeks showed reduced egg production with lowered hatchability. At one half this concentration there was a detrimental effect on egg production, but hatchability was not seriously affected. The hens were killed by doses of 0.125% DDT. The insecticide was found in the eggs in quantities much smaller than in the body fat. Harris et al. (8) have shown that DDT will accumulate in considerable quantities in the fat of lambs fed DDT-treated hay. Small amounts of the insecticide were found in other tissues. 

Wegmann and Hofstee [43] have developed a capillary gas chromatographic method for the determination of organochlorine insecticides in river sediments. Bottom soils from rivers, collected in slow current areas may contain high concentrations of organochlorine insecticides and polychlorobiphenyls. When the current moves more rapidly or benthic animals become more active, these compounds are stirred into the water along with suspended particles and become accessible to organisms that live in the bottom layer. 

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