RESISTANCE TO DDT AND PYRETHROIDS IN BRAZILIAN POPULATIONS OF SITOPHILUS-ZEAMAIS MOTSCH (COLEOPTERA, CURCULIONIDAE)

Control failures of deltamethrin used against Sitophilus zeamais Motsch. in Brazil led to the investigation of the possible resistance of this pest to DDT, pirimiphos-methyl and the pyrethroids deltamethrin, cypermethrin and permethrin, synergized or not with piperonyl butoxide, DDT is not now approved for use in Brazil, but was widely used in the past against this pest. Pirimiphos-methyl and synergized deltamethrin are recommended for S. zeamais control, and cypermethrin and permethrin are not used despite their efficiency against this pest. Bioassay tests were carried out using the insecticide-impregnated filter paper method recommended by FAG, and the discriminating concentrations were established based in the LC(99.9) of each compound, synergized or not, for the standard susceptible population. With these tests, a cross-resistant spectrum to DDT and pyrethroids was verified in six populations of S. zeamais. One population showed resistance only to DDT and deltamethrin, while three other populations showed resistance only to DDT.