Resistance to chlorpyrifos-methyl, pirimiphos-methyl, and malathion in Brazilian and U.S. populations of Rhyzopertha dominica (Coleoptera: Bostrichidae).
1996
Guedes R.N.C. | Dover B.A. | Kambhampati S.
Resistance to chlorpyriphos-methyl, pirimiphos-methyl, and malathion was detected in lesser grain borer, Rhyzopertha dominica (F.), collected from 8 sites in the states of Minas Gerais and Sao Paulo in Brazil and from 7 sites in northeast Kansas. These populations were screened for resistance by a discriminating concentration technique, which used vials impregnated with dried insecticide residues. Concentration-mortality regression lines were estimated to compare the resistance ratios for each insecticide and population. Malathion resistance ratios ranged from 2.1- to 12.2-fold at LC50; pirimiphos-methyl resistance ratios ranged from 2.4- to 9.2-fold: and chlorpyrifos-methyl resistance ratios ranged from 5.6- to 167.9-fold. Such high resistance levels to chlorpyrifos-methyl in lesser grain borer have never been reported before either in the United States or in Brazil. Because chlorpyrifos-methyl is not used against stored grain pests in Brazil, we conclude that chlorpyrifos resistance has evolved as a result of selection to other organophosphorus insecticides in Brazil.
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