Abstract: The morphology of the 3rd instar larval cotton bollworm (Helicoverpaarmigera Hubner) ventral nerve and muscle was studied by scanning electron and light microscopes. The results of observation showed that all of the ventral longitudinal muscle cells are suitable for the electrophysiological intracellular recording. The nerve sensitivity to the corresponding pesticides of 3rd instar larval neuromuscular synapses of three strains of the cotton bollworm including the control, the cyhalothrin resistant (Cy-R, resistance ratio: 13.4) and the fenvalerate resistant (Fri-R, resistance ratio: 37.9)strains was studied by using the electrophysiological intracellular microelectrode recording technique. The results showed that when Cy-R was treated by 10^-6mol /L cyhalothrin, 60% individuals had the repetitive discharge within 30m in; however, the reaction time was 3.5 times as much as that of the control. And the other 40%individuals had no reaction. When Fn-R was treated by 10^-6mol /L fenvalerate, 53% individuals had the repetitive burst discharge within 30min, however, the reaction time was 4.2 times as much as that of the control. And the other 47% individuals had no reaction. It implies that the decreased nerve sensitivity is an important pyrethroid resistance mechanism of cotton bollworm.

Key words: Helicoverpa arrnigera, pyrethroid, resistance, nerve sensitivity