Expression and inheritance of nerve insensitivity resistance in larvae ofHelicoverpa armigera(Lepidoptera: Noctuidae) from China

Nerve insensitivity resistance to synthetic pyrethroids was detected in a resistant field strain (JSFX-R) of the cotton bollworm, Helicoverpa armigera (Hübner), using a neurophysiological assay in which extracellular spontaneous neuronal activity was measured in response to cis-cypermethrin. The nerve insensitivity mechanism was selected using a combination of toxicological and neurophysiological methods. The third-instar larvae in selected strains of Family-37 and CTR strain expressed a very high resistance to fenvalerate (RF = 2060-fold and 805-fold, respectively) and high cross-resistance to DDT (RF = 1927-fold and 2384-fold, respectively) which was not affected by two metabolic synergists, PBO and DMC. The frequency of nerve-insensitive individuals detected in neurophysiological assays (54, 81 and 100% for JSFX-R strain, and the selected strains Family-43 and Family-37, respectively) was not only positively correlated (R2 = 0.968) with the frequency of non-PBO-synergisable resistant individuals detected in toxicological tests (37.5, 62.5 and 90% for JSFX-R strain, Family-43 and Family-37, respectively), but also positively correlated (R2 = 0.978) with the frequency of DDT-resistant individuals detected in toxicological tests (40, 67.5 and 93.3% for JSFX-R strain, Family-43 and Family-37, respectively). Analysis of dose–mortality lines to DDT and fenvalerate from F1 hybrids (R♀ × S♂) indicated that nerve insensitivity resistance to DDT and fenvalerate in the CTR strain was inherited in an incompletely recessive pattern. Degree of dominance (D) was estimated to be −0.66 (± 0.06) (DDT) and −0.26 (± 0.04) (fenvalerate). The dose–mortality curves to DDT in back-cross progeny were strongly suggested, by chi-square analysis, to be fitted with those expected of a one-gene model. Evidence for the co-existence of nerve insensitivity and oxidative metabolic resistance mechanisms within individual H armigera and the effects of their interaction on the expression of resistance to fenvalerate are discussed.