Abstract

The residual activity of actellic dust (pirimiphos-methyl) on Callosobruchus maculatus F. and the field-to-store bruchid richness of pigeon pea grains were studied at Nsukka, Nigeria. Results of the bruchid richness study showed that there was no emergence or infestation of bruchids from both the treated and untreated grains six months post harvest. Assessment of the residual activity of pirimiphos-methyl on C. maculatus six months post treatment revealed that although C. maculatus could not be controlled completely, its developmental potential and extent of grain damage were drastically reduced, which showed the continued activity of the pesticide six months post treatment. Incremental doses of actellic dust produced residual effects which significantly (P<0.05) reduced the number of F₁-emergence, adult bruchid emergence, total mortality count, grain weight loss and grain damage. Half-dose of pirimiphos methyl was not as effective as its full dose in controlling C. maculatus infestations under comparable residual level and grain post harvest storage period. Pigeon pea varieties differed significantly (P<0.05) in their grain susceptibilities to C. maculatus as assessed by the quantity of damaged grains, grain weight loss, mean developmental days of insects (MDD) and adult emergence of the pest; the characteristics which allowed the varieties be classified as moderately resistant to the bruchid attack. Residual effect of pirimiphos-methyl when combined with the varieties did not result in any significant effect on C. maculatus or grain damage by them.

Key words: Field-to-store pest, pirimiphos-methyl, bruchid richness, residual activity, pigeon pea.