This study had the objective of evaluating the degradation/ persistence of the residues of the organophosphate insecticide pirimiphos-methyl on/in corn and popcorn grains, in some of their processed products, and its residual action on corn weevils, Sitophilus spp. The grains were treated with the recommended dose of 12 mg.kg-1 (ppm) of a.i. pirimiphos-methyl for the control of the weevils. Samples were taken at zero, 15, 30, 60, 120 and 240 days after treatment (three replications). Processed products analysed were: corn: grain, bran, hominy and corn flour; popcorn: grain and popcorn. The analytical method consisted of extraction of residues with acetone, clean-up by partition with acetonitrile/hexane, followed by silica gel column chromatography (spe) eluted with a mixture of hexane/acetone. Quantitative measurements were made by gas chromatography, by using a flame photometric detector. For pirimiphos-methyl residual action studies, samples of both types were taken at 15, 30 days after treatment and subsequently at monthly intervals up to one year. Forty grams of treated and non-treated (control) grains were infested with 40 weevil adults (5 replications). Mortality was checked 15 days after exposure. Pirimiphos-methyl residues were not persistent on/in both grains, in corn bran and popcorn (5-6 times losses during the sampling period). In hominy and corn flour they were more persistent, but the contamination levels were low. The insecticide remained effective against the pest over the entire period of observation (1 year) for both type of grains.
Species 1: Coleoptera Curculionidae Sitophilus (corn weevils)
Keywords: pirimiphos-methyl residues
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