Azadirachta indica, insecticidal

The seeds from the Indian neem tree, Azadirachta indica, are the source of two types of neem-derived botanical insecticides neem oil and medium polarity extracts. Neem seeds contain numerous azadirachtin (Fig. 9) analogs, but the major form is azadirachtin and the remaining minor analogs are likely to contribute little to the overall efficacy of the extracts. Typically, solvent partitions or other chemical processes are required to concentrate this active ingredient to the level of 10% to 50% seen in the technical grade material used to produce commercial products. 

Other naturally derived aflatoxin inhibitors obtained from the "neem" tree have been investigated in our laboratory (84), Azadirachta indica Juss. commonly known as "margosa" or "neem" is an ornamental tree of Asia and Africa that produces natural products having reputed value for their medicinal, antiviral, antibacterial, insecticidal, antifungal and antinematode properties (86, 87). Several active principles from different parts of the neem tree have been reported (88). Our investigation (84) examined the effects of these neem leaf components in neem leaves on aflatoxin biosynthesis by either Aspergillus parasiticus or A. flavus. 

The powerful antifeedant and insecticide azadirachtin (213), from the neem tree (Azadirachta indica, Meliaceae), is a highly oxidized limonoid with rings A, B, and D intact.2 It is used as a benchmark against which all other antifeedants can be compared (vide infra). The total synthesis of azadirachtin has recently been achieved in 64 steps.96 This is very unlikely to provide a synthetic source of the compound, but it does allow SAR studies to find maximum activity, and opens up the field to possible simpler synthetics modelled on it. As yet, even slight modifications of the structure tend to decrease activity. Azadirachtin (213) has been available commercially, particularly in the United States, but at present the cost of the seeds and the isolation procedure inhibit its wider use. 

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. 

Williams, L.A.D., Ajai Mansingh and Mansingh, A. (1996) The insecticidal and acaricidal actions of compounds from Azadirachta indica (A. Juss.) and their use in tropical pest management. Integrated Pest Management Reviews 1, 133-145. 

There can be no doubt that interest in the mahogany family (Meliaceae) was spurred by the development of natural insecticides from the Indian neem tree, Azadirachta indica A. Juss. This species and its commercial utility has been the subjeet of several international conferences, hundreds of research papers, and at least a dozen major volumes. This interest was manifest in the eollection and sereening of more than 100 species from the family for insect bioactivity, with particular emphasis on the genera Aglaia and Trichilia. Even before this, attention had turned to members of the genus most closely related to neem, Melia, namely the Asian chinaberry tree M. azedarach L. and the East African M volkensii Gurke. 

Insecticidal Constituents of Azadirachta indica and Melia azedarach (Meliaceae)... 

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. 

Certainly, in the case of the insecticides, past experience has shown this approach to be successful, with synthetic pyrethroids as the best example. Other commercially useful botanical pesticides include nicotine, pyrethrum, rotenone and several other alkaloids. Similarly, other natural compounds modifying feeding behavior or inhibiting the growth of insect larvae, are considered viable alternatives to acute toxins, for insect control (3). One of the most successful examples so far is Neem, extracted from the seeds of the tree Azadirachta indica. 

Azadirachtins. In the last 20 years a great deal of research effort by entomologists and phytochemists has been directed to the identification and biological evaluation of chemical constituents from the neem tree (Azadirachta indica) in relation to the recognized insecticidal properties of its fruits and leaves (Schmutterer, 1990). A large number of tetranortriterpenes have been isolated from this tree and other related members of the Meliaceae family. A recent review reports information about the chemistry of the melicane tetranortriterpenoids obtained from these plants (Kraus et al., 1993). 

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