Nicotine insecticides

With the exception of nicotine, the agricultural chemicals derived from plants are probably among the least hazardous to man (6). Nicotine itself is one of the most efficient insecticides. Nicotine can cause serious poisoning or death if swallowed, inhaled, or absorbed through the skin. 

Several nerve toxins produced by plants are interesting because of their insecticidal properties. Insecticidal nicotine is extracted from tobacco. Rotenone (Figure 19.2) is synthesized by almost 70 legumes. This insecticidal compound is safe for most mammals, with the notable exception of swine. The most significant insecticidal plant derivatives, however, are the pyrethrins, discussed below. 

Dietary a-pinene causes southern armyworm larvae to become more tolerant to the botanical insecticide, nicotine. Enhanced tolerance to synthetic insecticides also has been demonstrated in phytophagous insects fed plants capable of inducing microsomal monooxygenase activity. Variegated cutworm larvae fed peppermint leaves are more tolerant of the insecticides carbaryl, acephate, methomyl, and malathion than larvae fed snap bean leaves. Increased tolerance for carbaryl and methomyl also has been observed in larvae of the cabbage looper and alfalfa looper (Autographa califomica) fed peppermint plants instead of their favored host plants, broccoli and alfalfa. 

In the seventeenth century the first naturally occurring insecticide, nicotine from extracts of tobacco leaves, was used to control the plum curcuUo and the lace bug. Hamburg (1705) proposed mercuric chloride as a wood preservative and a hundred years later Prevost described the inhibition of smut spores by copper sulfate. 

Nicotine is a highly poisonous alkaloid, extracted from special tobacco selected for its high nicotine content. When used as an insecticide, nicotine products are poisonous to most plant pests, including aphids, mealybugs, scales, and spider mites. However, nicotine is also highly toxic to mammals when taken internally or absorbed through the skin— more toxic, in fact, than many synthetic pesticides. It remains toxic on leaf surfaces for several weeks after an application. Also, nicotine products may contain the pathogen that causes tobacco mosaic virus in related... 

From a study of insecticidal nicotinic agents (114)imidacloprid (67) was reported to... 

The waste from tobacco Nicotiana tabacum production, family Solanacae, is used for the fabrication of raw nicotine, which also contains nor-nicotine and anabasine. Sulphates are made, and a solution is used as fumigant and insecticide. Nicotine must be handled with great care owing to the high toxicity (for humans) since 40 mg can be a lethal dose. 

The cholinergic synapse is the key target area for aU major insecticides. Nicotine and the neonicotinoids bind to the postsynaptic nicotinic acetylcholine receptor. 

Another biological target for many insecticides is the nervous system of the insect because this can result in selective toxicity. The neonicotinoids, in group 4, work by this mechanism and act on insect nicotinic acetylcholine receptors (nACtiR). Nicotine, the namesake of the nACtiR has been used for pest control since the century [33], However nicotine is hazardous to people and has limited effectiveness as an insecticide. Nicotine and its analog epibatidine, isolated from a tropical poisonous frog, exist mainly in the pro-tonated form at physiological pH. They are examples of the nicotinoid family and are toxic to mammals. 

For an account of the carbamate and organophosphorus insecticides, see Section 12.3 for nicotine. Section 13.6. These are the synapse-blocking insecticides. Nicotine is relatively little used. 

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