Abstract: 【Aim】 In order to develop more effective methods for molecular detection of insecticide resistance, the molecular mechanisms of resistance to methoxyfenozide related to glutathione S-transferases (GSTs) in Helicoverpa armigera (Hübner) were studied. 【Methods】 The early 3rd instar larvae of the methoxyfenozide-resistant (R-methoxyfenozide) and the homologous control (S-methoxyfenozide) populations of H. armigera were treated with LC₄₀ of methoxyfenozide, and the specific activities of GST and the expression of five GST genes were measured before and after treatment. The coding sequence of one delta GST gene (GSTd1) was compared in the two populations. 【Results】 The coding sequences of GSTd1 in the R-methoxyfenozide and S-methoxyfenozide populations of H. armigera were identical, suggesting that no structural change occurrs in the isozyme. The GST activity in R-methoxyfenozide population of H. armigera was higher than that in the S-methoxyfenozide population before treatment. After treatment, the GST activity decreased in both populations, but fast recovered in the R-methoxyfenozide population. Except GSTe2, GST genes had a higher expression in the R-methoxyfenozide population than in the S-methoxyfenozide population before treatment. Effects generated by methoxyfenozide treatment on the expression of GST genes were quite different in the two populations. After treatment, the expression of GST genes, except GSTs1, initially decreased in the S-methoxyfenozide population, and then the expression of GSTd2 and GSTe2 recovered gradually. The expression of GSTs1 showed no obvious change within 36 h and increased at 48 h after treatment. But in the R-methoxyfenozide population, the expression of the five GST genes after treatment decreased initially, and then fast recovered. Except GSTe2, the initial and final expression of GST genes in the R-methoxyfenozide population were remarkably higher than that in the S-methoxyfenozide population. 【Conclusion】 The results suggest that resistance to methoxyfenozide in H. armigera is related to enhanced GST activities which are rooted from the over-expression of GST genes.

Key words: Helicoverpa armigera, methoxyfenozide, glutathione S-transferase, enzyme activity, gene expression, qRT-PCR