Potential Positive Effects of Pesticides Application on Sesamia inferens (Walker) (Lepidoptera: Insecta)

In China, the pink stem borer (PSB) Sesamia inferens (Walker) (Lepidoptera: Noctuidae) has become a rice pest in some rice-producing regions. The cause of this shift from secondary to major pest is unknown. The major purpose of this study was to examine the effect of five commonly used pesticides in rice fields on reproduction of PSB and on biochemical substances of rice plants. The results showed that the weight of pupae developed from 1st instar larvae treated with 2 mg/L triazophos and the number of eggs laid by emerged females from the treatment were significantly greater than those of the control, increasing by 26.2% and 47%, respectively. In addition, a nontarget insecticide, pymetrozine 100 mg/L, and a target insecticide, chlorantraniliprole 2 mg/L, stimulated reproduction of PSB. Biochemical measurement showed that foliar sprays of these pesticides resulted in significant reductions of contents of resistant substances, flavonoids and phenolic acids, in rice plants. For example, flavonoids and phenolic acids of rice plants treated with triazophos reduced by 48.5% and 22.4%, respectively, compared to the control. Therefore, we predicted that the application of some pesticides, eg triazophos and chlorantraniliprole, may be the cause of the increase in the population numbers of PSB in rice fields.