Effects of spinosad on Helicoverpa armigera (Lepidoptera: Noctuidae) from China: tolerance status, synergism and enzymatic responses

BACKGROUND: Spinosad is increasingly used in pest management programmes, and resistance to it has been detected in recent years. However, there is no report on the susceptibilities of field populations of Helicoverpa armigera (Hübner) from China. Furthermore, the impact of spinosad on metabolic enzymes in this pest remains unknown. RESULTS: Four populations of H. armigera from different locations in China displayed less than 6.5-fold difference in LC(50) to spinosad, the highest being in the Xinjiang population, followed by Xiajin, Taian and Hubei populations, while there was no significant difference at LC(99) level among the four populations. The toxicity of spinosad could be synergised by piperonyl butoxide (PBO) and triphenylphosphate (TPP), but not by diethyl maleate (DEM). Spinosad exposure for 48 h significantly increased the activities of p-nitroanisole O-demethylase (ODM), while no significant changes in glutathione-S-transferase (GST) and carboxyl esterase (CarE) were observed. CONCLUSION: Field populations of H. armigera from China displayed marginally different susceptibilities to spinosad and had a relatively low LC(50). Cytochrome P450 monooxygenase might be involved in the metabolism of, and hence resistance to, spinosad in this pest in China.