CHLORPYRIFOS RESISTANCE IN GREENBUGS (HOMOPTERA, APHIDIDAE) - CROSS-RESISTANCE AND SYNERGISM

Greenbugs, Schizaphis graminum (Rondani), with the pattern-2 resistanc e factor (enhanced metabolic degradation) were resistant to the three insecticides (carbofuran, chlorpyrifos, and malathion) evaluated in ou r research. Chlorpyrifos was mixed with selected insecticides and syne rgists in the laboratory to evaluate the potential of these mixtures f or overcoming resistance. The most effective mixture when the chemical s were applied simultaneously in vials was chlorpyrifos + carbofuran, which provided a 14-fold increase in toxicity compared with the chemic als applied individually. Malathion and the synergists piperonyl butox ide and DEF did not increase greenbug mortality when applied simultane ously with chlorpyrifos in vials. However, when aphids were exposed to the three chemicals Ih before they were placed in vials treated with chlorpyrifos, mortality increased 20.8-, 10.8-, and 4.5-fold for malat hion, piperonyl butoxide, and DEF, respectively. These results suggest that resistance to chlorpyrifos might be overcome if the chemical wer e combined with carbofuran or if the greenbugs were preexposed to inse cticide synergists before application of chlorpyrifos.