Insecticidal efficacy of Azadirachta indica powders from sun- and shade-dried seeds against Sitophilus zeamais and Callosobruchus maculatus

Abstract

The Azadirachtin A contents of Azadirachta indica powders from sun-dried kernels, shade-dried kernels, sun-dried seeds and shade-dried seeds, were determined. Cowpea or maize grains were admixed with the powders at the rates 0, 5, 10, 20, 30 and 40 g/kg for the assessment of mortality over a 6-d (Callosobruchus maculatus) or 14-d period (Sitophilus zeamais), as well as for damage and persistence bioassay. Drying regime did not affect the Azadirachtin A amounts in the seeds. All A. indica powders caused a significant dose-dependent mortality to S. zeamais and C. maculatus, as well as completely suppressed progeny production and grain damage. S. zeamais was more susceptible to the powders than C. maculatus. That the bioactivity of powders from sun-dried A. indica seeds were generally similar to those of the shade-dried ones, could speed up processing of seeds by farmers and minimize attacks by fungi which may produce aflatoxins on treated grains.