Doctor of Philosophy (PhD)
Esterase-based metabolic resistance was studied using biochemical and biological assays with organophosphate (OP)- and pyrethroid (PYR)- resistant tobacco budworms, Heliothis virescens. In biochemical assays, results suggest that: (1) esterase activities toward all substrates used were enhanced in both resistant strains compared with the susceptible strain, suggesting that esterases were involved in resistance; (2) esterase profiles differed depending on the strain and substrate used, and these differences were visualized by using native polyacrylamide gel electrophoresis; 3) esterase activities toward some pyrethroid substrates were significantly higher (P ≤ 0.01) in the PYR-R strain than those in the OP-R strain. These results suggest that pyrethroid substrates may be useful indicators for detecting esterases associated with pyrethroid resistance. Finally, biochemical assays were modified for use on solid materials, and esterase substrates were tested in filter paper assays. Whereas some differences in color intensity were detected between susceptible and resistant strains, these differences were not dramatic. Thus, utility of these substrates in such assays appears limited at this time, but further research is warranted. In biological assays, two approaches were taken to improve the precision with which esterases associated with pyrethroid resistance were detected. First, bioassays were used to test effects of pyrethroid substrates and traditional synergists (e.g., piperonyl butoxide) on insecticide toxicity. Non-toxic pyrethroid esters enhanced pyrethroid toxicity to a greater extent than DEF, a compound widely used as an esterase inhibitor. In addition, synergism of profenofos and cypermethrin toxicity in both resistant strains by an oxidase inhibitor, 1, 2, 4-trichloro-3 (2-propynyloxy) benzene, suggests that P450 monooxygenases were also involved in resistance. The second method tested was to utilize bioactivated insecticides to detect esterases. Absence of negative cross-resistance to insecticides (i.e., acephate and indoxacarb) that are activated by esterases suggests that detoxication of these compounds in resistant insects proceeds more rapidly than their activation by esterases. Finally, levels of cross-resistance to tefluthrin and trans-fenfluthrin were lower than to permethrin and cypermethrin in both resistant strains, suggesting that resistance to insecticides in which sites for detoxifying enzymes (e.g., oxidases) are blocked develops more slowly than resistance to those in which metabolic sites are present.
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Huang, Huazhang, "Development of diagnostic tools for detecting expression of resistance-associated esterases in the tobacco budworm, Heliothis virescens (F.)" (2002). LSU Doctoral Dissertations. 3869.
James A. Ottea