Nonconventional insecticidal effects of pesticides available from the Neem tree, <i>Azadirachta indica</i>

Abstract

Abstract Nonconventional insecticidal effects are exerted by preparations from the Neem tree, also called Indian lilac or Margosa tree ( Azadirachta indica A. Juss, syn. Melia azadirachta L. or Antelaea azadirachta L.) (Meliaceae). A closely related species, the chinaberry tree or Persian lilac ( Melia azedarch L.), is a source of substances with similar strctures and insecticidal activity. However, the seed kernels, whole fruits or leaves of many M. azedarch chemotypes contain tetranortriterpenoids and other principles highly toxic to mammals (meliatoxins). The most prominent insecticidal constituent of Neem seed kernels is the tetranortriterpenoid azadirachtin and related structures. Lesser concentrations of these active materials are found in the leaves and other parts of the tree. Third World farmers use crude Neem preparations, mainly seed kernel extracts or powders, as insecticides. An industrial Neem product, called Margosan‐O, is in commercial use in the USA. The nonconventional effects of preparations or compounds isolated from Neem may be classified as follows: (i) partial reduction or complete inhibition of fecundity and/or sometimes egg hatchability; (ii) reduction of the life span of adults; (iii) oviposition repellence against females; (iv) direct ovicidal effects; (v) antifeedant effects against larvae (and nymphs) and adults; (vi) formation of permanent larvae; (vii) insect growth regulator effects at molting between larval (or nymphal) instars and especially in the prepupal stage; and (viii) analogous lesions during the emergence of adults. Phenomena (vii) and (viii) give rise to characteristic larval‐pupal, nymphal‐pupal, nymphal‐adult and pupal‐adult intermediates, and to crippled adults. © 1993 Wiley‐Liss, Inc.