Antifeedant and insecticide properties of a limonoid from Melia azedarach (Meliaceae) with potential use for pest management

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.