Azadirachtin and three of its derivatives were injected orally into mature (fifth instar) larvae of Heliothis virescens (F.) (Noctuidae). At the lowest dose tested (0.5 µg) azadirachtin, 22,23-dihydroazadirachtin, and 2',3',22,23-tetrahydroazadirachtin, but not 3-deacetylazadirachtin, were significantly active. At a dose of 1.0 µg, all four compounds were effective in preventing pupation of the fifth instar and in causing larval mortality. At higher doses (2.0 and 4.0 µg), all four compounds were equally effective, causing 100% larval mortality. The same four compounds were exposed to ultraviolet radiation and analyzed for structural degradation and concomitant loss of biological activity. Of the four compounds tested, 2',3',22,23-tetrahydroazadirachtin was the most stable to ultraviolet radiation, remaining structurally unaltered and retaining full biological activity following 200 h of exposure. 2',3',22,23-tetrahydroazadirachtin photo degraded by 15% following 400 h of exposure, resulting in a significant decrease in biological activity. Although very little azadirachtin, 3-deacetylazadirachtin, and 22,23-dihydroazadirachtin remained intact following only 90 h of exposure to ultraviolet radiation, all three retained full biological activity. At least 200 h of exposure to ultraviolet radiation was necessary to significantly reduce the biological activity of azadirachtin, and at least 400 h of exposure was required to reduce the biological activities of 3-deacetylazadirachtin and 22,23-dihydroazadirachtin. These results suggest that one or more of the photodegradation products, likely involving the tigloyl moiety, are at least as biologically active as the native molecules.
Document Type: Research Article
Publication date: February 1, 1989
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Journal of Economic Entomology is published bimonthly in February, April, June, August, October, and December. The journal publishes articles on the economic significance of insects and is divided into the following sections: apiculture & social insects; arthropods in relation to plant disease; forum; insecticide resistance and resistance management; ecotoxicology; biological and microbial control; ecology and behavior; sampling and biostatistics; household and structural insects; medical entomology; molecular entomology; veterinary entomology; forest entomology; horticultural entomology; field and forage crops, and small grains; stored-product; commodity treatment and quarantine entomology; and plant resistance. In addition to research papers, Journal of Economic Entomology publishes Letters to the Editor, interpretive articles in a Forum section, Short Communications, Rapid Communications, and Book Reviews.