Nuclear receptor FTZ-F1 is required for larval-pupal molting by regulating ecdysteroidogenesis and chitin metabolism in Lasioderma serricorne

Fushi tarazu factor 1 (FTZ-F1) is a typical nuclear receptor transcription factor that plays crucial roles during the molting process in insects. However, the role of FTZ-F1 in Lasioderma serricorne, an important stored insect pest, remains unclear. In this study, the FTZ-F1 gene from L. serricorne was identified and cloned. The role of FTZ-F1 in regulating ecdysteroidogenesis and chitin metabolism was analyzed by RNA interference (RNAi) during larval–pupal transition of L. serricorne. The expression of LsFTZ-F1 varied during development and peaked in the final stage of fourth-instar larvae. The LsFTZ-F1 was mainly expressed in larval epidermis. The expression of LsFTZ-F1 was induced by 20-hydroxyecdysone (20E), but it was suppressed by silencing of ecdysone receptor genes LsEcR and LsUSP. RNAi-mediated knockdown of LsFTZ-F1 in the fourth-instar larvae significantly decreased 20E titers and the expression of 20E synthesis and signaling pathway genes. Suppression of LsFTZ-F1 disturbed the larval–pupal transition and resulted in 100% death, which could be rescued by supplementary 20E. The chitin contents of L. serricorne larvae treated with dsLsFTZ-F1 were decreased, as was the expression of chitin synthesis and degrading genes. Hematoxylin and eosin staining analysis indicated that LsFTZ-F1 depletion prevented the larval–pupal molt by inhibiting the synthesis of new cuticle. These results indicate that LsFTZ-F1 is critical for chitin metabolism and ecdysone synthesis during the larva to pupa molt, and that it is a promising RNAi target for L. serricorne control.