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Global warming is known to affect the growth, development and reproduction of insects. In this study, the larvae developmental process and endogenous hormone levels under high temperature (36 °C) stress were investigated in the lepidopteran model insect Bombyx mori (B. mori). After high temperature treatment, the duration of 5th instar larvae was shortened by 28 ± 2 h, the content of 20-hydroxyecdysone(20E) in hemolymph was significantly increased, and the transcription levels of the 20E response genes E93, Br–C, USP and E75 were up-regulated by 1.35-, 1.25-, 1.28-, and 1.27-fold, respectively. High temperature treatment also elevated the phosphorylation level of Akt and activated the downstream BmCncC/keap1 pathway, and the transcription levels of the 20E synthesis-related genes cyp302a1, cyp306a1, cyp314a1 and cyp315a1 were up-regulated by 1.12-, 1.51-, 2.17- and 1.23-fold, respectively. The transcription levels of cyp302a1 and cyp306a1 were significantly decreased in BmN cells after treatment with the double stranded RNA of BmCncC (dsBmCncC), whereas their transcription levels were significantly increased (2.15- and 1.31-fold, respectively) after treatment with the CncC agonist Curcumin. These results demonstrated that high temperature treatment promoted the metamorphosis and the BmCncC/keap1 pathway played a role in the metamorphosis of B. mori. Our results provided clues for understanding the CncC/keap1 pathway-mediated regulation of metamorphosis of Lepidopteran insects. • High temperature stress promotes the larvae development and changes endogenous hormone levels. • The activation of BmCncC/keap1 pathway is one of the reasons for the increase of 20E level. • BmCncC mediates ecdysone synthesis via Cyp302a1 and Cyp306a1. [ABSTRACT FROM AUTHOR]