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棉 花 学 报 Cotton Science 2008，20(4)：249-255
Cross Resistance Patterns and Biochemical Mechanisms in a Chinese Helicoverpa armigera Strain Selected with an Organophosphate / Pyrethroid Mixture Abstract：Selection of a field strain of Helicoverpa armigera (HN) was undertaken by treatment with a mixture of an organophosphate (phoxim) + a pyrethroid (cyhalothrin) (25︰1,a.i.) for 33 generations. The resistance to phoxim of the selected strain (HN-R) increased to 17.4-fold and the resistance to cyhalothrin increased to 144.7-fold. High level cross-resistance to two pyrethroids was detected (86.2-fold to deltamethrin and 23.4-fold to fenvalerate) in the HN-R strain. In addition, the HN-R strain also possessed a moderate level of cross-resistance to monocrotophos (5.2-fold), a low level cross-resistance to methyl parathion(1.6-fold), profenofos (1.8-fold), and methomyl (2.4-fold). The esterase inhibitor S,S,S-tributylphosphorotrithioate (DEF) was very effective in reducing phoxim resistance of the HN-R strain (with a synergism ratio of 15.3-fold) but the mixed function oxidase (MFO) inhibitory synergist piperonyl butoxide (PBO) had no synergism to it at all. In contrast，PBO dramatically removed most of resistance to three pyrethroids with synergism ratios of 21.9-fold to cyhalothrin, 19.1-fold to deltamethrin, and 21.4-fold to fenvalerate, but DEF had no synergism to them. Both DEF and PBO can remove about half of the resistance to monocrotophos (with synergism ratio of 2.2- and 2.5-fold, respectively). Compared to the reference HN strain, the MFO activity of the resistant HN-R strain to p-nitroanisole (pNA) was 6.5-fold and total esterase activity to 1-naphthyl acetate (a-NA) was 1.6-fold. At least two metabolic resistance mechanisms are involved in this resistant HN-R strain: esteratic detoxification (to phoxim and monocrotophos) and oxidative metabolism by mixed function oxidases (to pyrethroids and monocrotophos). The results suggest the use of pyrethroid/organophosphate mixtures in the field is likely to lead the simultaneous selection of multiple metabolic mechanisms of resistance, and thus a broad cross-resistance spectrum.
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