The Use of Polyacrylamide Gel Electrophoresis for the Investigation and Detection of Fenitrothion and Chlorpyrifos-Methyl Resistance in Oryzaephilus surinamensis (Coleoptera: Silvanidae)

Esterase activity in 16 strains of Oryzaephilus surinamensis (L.) with different degrees of resistance to chlorpyrifos-methyl and fenitrothion were investigated quantitatively and qualitatively. Chlorpyrifos-methyl resistance strongly and positively correlated with total esterase activity, whereas there was a moderate relationship between fenitrothion resistance and esterase activity. Polyacrylamide gel electrophoresis (PAGE) provided visual confirmation of these relationships and identified qualitative differences in esterase activity between the two highly chlorpyrifos-methyl strains. Both methods revealed that the elevated esterase activity was not acetylcholinesterase based. The involvement of elevated esterase activity in resistance was confirmed through its inhibition by chlorpyrifos and chlorpyrifos oxon. PAGE was identified as an effective too] for the simple and rapid detection of resistance due to the activity of esterases and is more powerful than quantitative total esterase assays due to its ability to identify both quantitative and qualitative differences.