natural-products-in-plant-pest-management

Global Scenario and Natural Products 7Neem products also function as insect growth regulators (IGRs). Thetreated insects are usually prevented from moulting to develop into the nextlife stage and they die. The treatment may also deter egg laying. Generally,chewing insects are affected more than sucking insects. Insects that undergocomplete metamorphosis are also generally affected more than those that donot undergo metamorphosis.Neem seeds are a rich storehouse of over 100 tetranortriterpenoids anddiverse non-isoprenoids (Devkumar and Sukhdev, 1993). The neem tree containsmore than 100 different limonoids in its different tissues (Isman et al., 1996).Many of these are biologically active against insects as antifeedants. Themost touted biologically active constituent of neem has been highlyoxygenated azadirachtin and some of its natural analogues and derivatives.Azadirachtin (molecular formula: C 35H 44O 16, chemical structure shown inFig. 1.2), a highly oxidized triterpenoid, is the most widely publicized bioactivemolecule in neem. It is systemic in nature, absorbed into the plant andcarried throughout the tissues, being ingested by insects when they feed onthe plant. This may make it effective against certain foliage-feeders thatcannot be reached with spray applications. Azadirachtin is more effectivewhen formulated in a neem oil medium together with the other naturalproducts of neem. Hence, it is preferable to use neem oil enriched withazadirachtin as a stable feed stock for making pesticide formulations.Neem as a harmless and safe pesticide fits into integrated pest managementand organic farming. In toxicological studies carried out in the USAand Germany, different neem products were neither mutagenic nor carcinogenic,and they did not produce any skin irritations or organic alterations inmice and rats, even at high concentrations. Azadirachtin is considerednon-toxic to mammals, having a low mammalian toxicity with an LD 50of>5000 mg/kg for rat (oral acute) (Raizada et al., 2001), fish (Wan et al., 1996)and pollinators (Naumann and Isman, 1996). Hence it is classified by theHCH 3 CH 3 CCOCH 3CH 3CH 3OOO CCC O OOHCH 3H H 3 C OHOOHOOHHOO C OOFig. 1.2. Azadirachtin.