Biological activity of limonoids from the rutales

Natural Science Foundation of China[30000213, 30370160, 30670214]; National Basic Research Program of China (973 Program)[2009CB522300]; Chinese Academy of Sciences

Meliaceous limonoids: chemistry and biological activities.

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.

Nonconventional insecticidal effects of pesticides available from the Neem tree, Azadirachta indica

In the course of screening for novel naturally occurring insecticides from plants, the activity of the fruit extract of the Argentinian Melia azedarach L. (Meliaceae) and its recently described limonoid meliartenin were investigated. The antifeedant activity of the fruit extract was tested on a variety of herbivore and granivorous insects through choice tests. Sixteen of 17 species belonging to three orders consume significantly less food when treated with the extract. The bioactivity of the isolated active compound meliartenin and its interchangeable isomer 12-hydroxiamoorastatin (1) was further studied. In choice tests, compound 1 inhibited feeding of Epilachna paenulata Germ. (Coleoptera, Coccinellidae) larvae, with an ED(50) value of 0.80 microg/cm(2), comparable to that of azadirachtin (2) and lower than that of toosendanin (3) (0.72 and 3.69 microg/cm(2), respectively), both compounds used for comparison purposes. In no-choice tests, E. paenulata larvae reared on food treated with 1 or 2 ate less, gained less weight, and suffered greater mortality rates than control larvae. The activity of compound 1 was comparable to that of 2, with LD(50) values of 0.76 and 1.24 microg/cm(2), respectively, at 96 h. Shorter LT(50) values were recorded for 1 at 4 and 1 microg/cm(2) in comparison with 2. Thus, M. azedarach fruit extract and its active principle have interesting potential for use in pest control programs.

Michael W. Hill

Papers

Toxic tetranortriterpenes of the fruit of Melia azedarach