Sublethal Indoxacarb Interferes with the Growth and Development of Silkworm by Damaging the Structure of Midgut Cells

As an important economic insect, Bombyx mori plays an essential role in the development of the agricultural economy. Indoxacarb, a novel sodium channel blocking insecticide, has been widely used for the control of various pests in agriculture and forestry, and its environmental pollution caused by flight control operations has seriously affected the safe production of sericulture in recent years. However, the lethal and sublethal effects of indoxacarb on silkworm remain largely unknown. In this study, the toxicity of indoxacarb on the 5th instar larvae of silkworm was determined, with an LC50 (72 h) of 2.07 mg/L. Short-term exposure (24 h) of sublethal indoxacarb (1/2 LC50) to silkworm larvae showed significantly reduced body weight and survival rate. In addition, sublethal indoxacarb also led to decreased cocoon weight and cocoon shell weight, but had no significant effect on pupation, adult eclosion, and oviposition. Histopathological and ultrastructural analysis indicated that sublethal indoxacarb could severely damage the structure of the midgut epithelial cells, and lead to physiological impairment of the midgut. A total of 3883 differentially expressed genes (DEGs) were identified by midgut transcriptome sequencing and functionally annotated using GO and KEGG. Furthermore, the transcription level and enzyme activity of the detoxification related genes were determined, and our results suggested that ESTs might play a major role in metabolism of indoxacarb in the midgut of B. mori. Future studies to examine the detoxification or biotransformation function of candidate genes will greatly enhance our understanding of indoxacarb metabolism in B. mori. The results of this study provide a theoretical basis for elucidating the mechanism of sublethal toxic effects of indoxacarb on silkworm by interfering with the normal physiological function of the midgut.