Abstract
Insecticide resistance in insects often is associated with elevated acetylcholin esterases and carboxylesterases. Three greenbug, Schizaphis graminum (Rondani), strains with different general esterase patterns were tested for differences in insecticide response. The standard strain had no noticeable elevated esterase activity. Pattern 1 and pattern 2 strains had different elevated esterase patterns. Toxicity of 5 organophosphorous (chlorpyrifos, dimethoate, disulfoton, malathion, and parathion) and 2 carbamate (carbofuran and methomyl) insecticides were tested using surface residue bioassays. Esterase pattern 1 greenbugs had significantly higher LC50s for each of the organophosphorous insecticides, but the LC50 for the 2 carbamate insecticides were not higher than the standard strain. Esterase pattern 2 greenbugs had significantly higher LC50s for 4 of the 5 organophosphorus insecticides (chlorpyrifos, dimethoate, disulfoton, and parathion) and the 2 carbamate insecticides, but the LC50 for malathion was not higher than the standard strain. Pattern 2 greenbugs had significantly higher tolerance to disulfoton than did pattern 1 greenbugs. This indicates that certain strains of the greenbug are cross resistant to many of the organophosphorous and carbamate insecticides currently labeled for greenbug control in wheat and sorghum. There is an urgent need to find alternative control measures.
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