Silicon-mediated multiple interactions: Simultaneous induction of rice defense and inhibition of larval performance and insecticide tolerance of Chilo suppressalis by sodium silicate

The rice striped stem borer (SSB, Chilo suppressalis) is one of the most destructive pests of rice plants. Si-mediated rice defense against various pests has been widely reported, and sodium silicate (SS) has been used as an effective source of silicon for application to plants. However, there is quite limited information about the direct effects of Si application on herbivorous insects. SSB larval performance and their insecticide tolerance were examined after they had been reared either on rice plants cultivated in nutrient solution containing 0.5 and 2.0 mM SS or on artificial diets with 0.1% and 0.5% SS. SS amendment in either rice culture medium or artificial diets significantly suppressed the enzymatic activities of acetylcholinesterase, glutathione S-transferases, and levels of cytochrome P450 protein in the midgut of C. suppressalis larvae. Larvae fed on diets containing SS showed lower insecticide tolerance. Additionally, RNA-seq analysis showed that SS-mediated larval insecticide tolerance was closely associated with fatty acid biosynthesis and pyruvate metabolism pathways. Our results suggest that Si not only enhances plant resistance against insect herbivore, but also impairs the insect's capacity to detoxify the insecticides. This should be considered as another important aspect in Si-mediated plant-insect interaction and may provide a novel approach of pest management.

Keywords: Chilo suppressalis; Oryza sativa; chlorpyrifos; detoxifying enzyme; insecticide resistance; plant defense; silicon.