Monitoring Insecticide Resistance in Field Populations of the Tarnished Plant Bug Using Biochemical and Molecular Approaches

Continuous and dominant use of chemical sprays has facilitated resistance development in the tarnished plant bug. Bioassay showed that esterase and glutathione S-transferase (GST) inhibitors significantly synergized toxicity of organophosphorous insecticide. Esterase and GST inhibitors also significantly suppressed esterase and GST enzyme activities in vitro. Field populations collected from Mississippi, Louisiana, and Arkansas were subjected to enzyme activity assay with α-naphthyl acetate (1-NA), β- naphthyl acetate (2-NA), ρ-nitrophenyl acetate (PNPA), 1-chloro-2,4,-dinitrobenzene, and acetylthiochroline. Results indicated that relatively big variations of esterase and GST activities and relatively low variation of acetylcholine esterase activity were detected among the different field populations. A total of 5 esterase cDNAs were cloned and sequenced by using cDNA library and RT-PCR. Real-time PCR examinations of esterase gene expressions revealed different esterase gene expression profiles in different field populations.