Abstract: A fenvalerate resistant strain (Fen-R) of cotton bollworm, Heliothis armigera (Hiibner), was obtained by laboratory selection of a strain (YG) collected from Yanggu County, Shandong Province in 1990 after nine selections with fenvalerate during fifteen generations, and exhibited about 2463-fold resistance to this insecticide as compared with a susceptible strain collected from Dongtai County, Jiangsu Province in 1983. The LD₅₀ value (24.1412μg/larva) in F₁₅ generation after selection increased to l19.5-fold as compared with the LD₅₀ value (0.2020 [μg/larva) of F₁.A fenvalerate susceptible strain (Fen-S) was developed by selection of progenies that resulted from single-pair matings of cotton bollworm collected from Yanshi County,Henan Province, under conditions free of insecticides, and its LD₅₀ was 0.0116 μg/larva, close to that of Dongtai susceptible strain in 1983. Dose-mortality regressions were estimated for seven insecticides applied to Ygstrain before selection treatments and to Fen-R strain, respectively. A spectrum of cross-resistance was detected to deltamethrin [LD_{50(Fen-R)/LD50(YG).= 5.2X] andcypermethrin (2.5X), but no cross-resistance to cyhalothrin (0.66x), permethrin (0.87X), methomyl (0.74X), and monocrotophos (1.5x). The studies on synergism of fenvalerate+Pb in Fen-R strain showed that resistance was due principally to the metabolic (multiple function oxidase) mechanism. Toxicological data suggested that more than one factors (genes) were responsible for resistance to fenvalerate in Helio.Shis arrnigera (Hiibner).}

Key words: Heliothis armigera (Hiibner) selection for a resistant strain &mdash, &mdash, fenvalerate&mdash, &mdash, cross-resistance&mdash, &mdash, multiple function oxidase