Submitted to: Insect Biochemistry and Molecular Biology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/7/2004
Publication Date: 11/5/2004
Citation: Zhu, Y., Snodgrass, G.L., Chen, M. 2004. Enhanced esterase gene expression and activity in a malathion resistant strain of the tarnished plant bug, lygus lineolaris. Insect Biochemistry and Molecular Biology. Interpretive Summary: In this study, we examined esterase gene structure, gene expression levels, and enzymes activities between malathion-susceptible and -resistant strains of the tarnished plant bug. We also investigated how esterase inhibitors suppressed enzyme activities and synergized malathion toxicity to the tarnished plant bug. This study provides information on resistance gene regulation in malathion-resistant strains of the tarnished plant bug. Esterase-mediated metabolic resistance resulted in more than 10-fold higher esterase activity in a resistant strain conferring more than an 11-fold increase in resistance to malathion in a natural population. Increased esterase gene expression levels may be responsible for the resistance development. Two esterase inhibitors exhibited significant suppression to esterase activities, and synergism for malathion. Results from this study will facilitate further studies to investigate regulatory factors for gene overexpression, to develop molecular or biochemical markers for monitoring resistance in field populations, and to provide information for developing pest management strategies.
Technical Abstract: Extensive use of insecticides on cotton in the Mid-south has prompted resistance development in the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois). A field population of tarnished plant bugs in Mississippi with 11-fold higher resistance to malathion was used to examine how gene regulation conferred resistance to this organophosphate insecticide. In laboratory bioassays, synergism by the esterase inhibitors S,S,S,-tributylphosphorotrithioate (DEF) and triphenylphosphate (TPP) effectively abolished resistance and increased malathion toxicity by more than 80%. Esterase activities were compared in vitro between malathion susceptible and resistant (selected) strains. More than 6-, 3-, and 10-fold higher activities were obtained with the resistant strain using '-naphthyl acetate, ß-naphthyl acetate, p-nitrophenyl acetate, respectively. Up to 95% and 89% of the esterase activity in the susceptible and resistant strains, respectively, was inhibited by 1 mM DEF. Inhibition of esterase activity up to 0.03 mM TPP. Esterase activities in field populations increased by up to 5.4-fold during the fall season. The increase was synchronized with movement of the insect into cotton where exposure to pesticides occurred. Several esterase cDNA were cloned and sequenced from both malathion susceptible and resistant strains. The 1818-nucleotide cDNA contained a 1710-bp open reading frame coding a 570 amino acid protein which was similar to many insect esterases conferring organophosphate resistance. No amino acid substitution was observed between suseptible and resistant strains, indicating that esterase gene mutation was not involved in resistance development in the resistant strain in Mississippi. Further examination of esterase gene expression levels using quantitative RT-PCR revealed that resistant strain had a 5.1-fold higher level of esterase mRNA than the susceptible strain. The results of this study indicated that up-regulation of the esterase gene appeared to be related to the development of resistance in the tarnished plant bug.