Pesticides Azadirachtin

David Morgan is a member of the Chemical Ecology Group at Keele University. He was bom in Newfoundland and had his university education there, at Dalhousie University and University of King s College in Halifax, Nova Scotia, and at Oxford. His doctorate thesis was on the lipids of Mycobacterium tuberculosis. He later worked at the National Institute for Medical Research in London, and for Shell Chemical Company and Shell Research under the direction of Sir Robert Robinson, O.M., Nobel Laureate. From 1966 he has been at Keele in Staffordshire as lecturer, senior lecturer, reader, and professor. He discovered the natural pesticide azadirachtin and collaborated with S. V. Ley for its final structure elucidation. He is the author of over 300 papers and reviews, mostly on insect chemistry, editor, and contributor to several volumes and author of the book Biosynthesis in Insects. ... 

Plant derived pesticides Azadirachtin A and B (obtained from Azadirachta indica), Bacillus thuringiensis, Denis (rotenone), Neem oil (obtained from Azadirachta indica), nicotine, pyrethrum, Spinosad (a mixture of spinosyn A and spinosyn D) derived from soil bacterium Saccharopolyspora spinosa. 

A.J. Mordue, Actions of Azadirachtin, a Plant Allelochemical, against Insects , Pesticide Sci., 1997 (in press). 

Goktepe I, Plhak LC. 2002. Comparative toxicity of two azadirachtin-based neem pesticides to Daphniapulex. Environ Toxicol Chem 21 31-36. 

As if the words azadirachtin and dlatoma-ceous weren t tongue-twisting enough, you ll find even less familiar words in the fine print on pesticide labels. Here s an explanation of some common label lingo. 

Neem (also known as azadirachtin) is an insecticide extracted from the seeds of the neem tree (Azadirachta indica) common in most of Africa and India. It is closely related to the chinaberry tree (Melia azadarach), common in the southern and southeastern United States. Extracts of both trees have insecticidal properties. Neem is unique among pesticides since it has so many uses It acts as a broad-spectrum repellent, growth regulator, and insect poison. It discourages feeding by making plants unpalatable to insects if they still attack, it inhibits their ability to molt and lay eggs. 

Some of the metabolites of higher plants inhibit the feeding activity of insects. Poisons and antifeedants are the defense substances of higher plants against insects. Insect antifeedants have been studied as a part of our efforts to protect our crops against pest insects. A triterpene named azadirachtin (Figure 3.12) is practically used in several countries as a pesticide of natural origin. 

Pesticidal compositions containing CyDs to increase their solubility have also been patented [63]. Azadirachtin, a biopesticide of plant origin, highly unstable in aqueous media and extremely sensitive to sunlight, has been formulated using j5- and j5-methyl-CyD to enhance its solubility [64], avoiding the use of surfactants and organic solvents, which do not sufficiently enhance the shelf life of the formulations. 

To use a more sophisticated example, we can look to the products of the neem tree (Azadirzchta indica), a tropical plant that is known for its pesticidal properties. The seed of this tree is abundant with limonoids and simple terpenoids that are responsible for its biological activity. One particular limonoid found in the seed is Azadirachtin (2.134). The bioactivity of Azadirachtin potentially leads to a wide range of applications in herbal medicine and healthcare products for the treatment of malaria and tuberculosis and in anti-worm, clotting, and blood-detoxification preparations. These uses of Azadirachtin as a biopesticide or herbal medicine is limited due to solubility constraints in water and its instability as a result of its propensity to undergo complicated, irreversible rearrangements under acidic, basic and photolytic conditions. Consequently, there has been much research in the structural modification of Azadirachtin to overcome its solubility constraints to increase stability. This process normally involves many protection and deprotection synthetic steps and chromatographic separations. 

Advances in the chemistry of the neem tree Azadirachta indica A. Juss.) and other species of the Meliaceae have been rapid as a result of interest in the unique characteristics of their limonoids and other secondary metabolites. This is especially true for azadirachtin, the final compound in the biosynthetic scheme. The search for new, powerful, non-toxic insecticides has become a great priority for the pesticide industry, and azadirachtin is currently a leading candidate. Although recent reviews have been published 1-4), more precise information is rapidly being generated. In this chapter we will review present information on the chemical properties of neem compounds and specifically on the chemistry of azadirachtin and its use to control insect molt. 

---