Search

Melanin has been recognized as a crucial factor in the evolution, polymorphisms, and environmental adaption of insects. Within the Coleoptera family, ladybird beetles exhibit remarkable phenotypic variation characterized by the number and size of black spots on their elytra. This distinctive characteristic makes ladybird as ideal models for studying melanin synthesis and its associated physiological effects. In this study, we focused on tyrosine hydroxylase (CsTH) and dopa decarboxylase (CsDDC), which participate in melanin biosynthesis in the monomorphic seven-spotted ladybird beetle, Coccinella septempunctata. Spatial expression profiles in adults revealed that CsTH was predominantly expressed in the elytra, while CsDDC was primarily expressed in elytra and ovaries. RNA interference (RNAi)-mediated silencing of these genes in fourth instar larvae led to reduced melanin on the cuticle, complete mortality shortly after eclosion, and disrupted eclosion processes. Furthermore, dopamine levels significantly decreased following the silencing of CsTH. Silencing CsTH during early pupal stages prevented eclosion, while later silencing permitted eclosion but resulted in melanin deficiency. In contrast, silencing CsDDC did not affect adult cuticle melanin synthesis. Our findings highlighted the vital roles of CsTH and CsDDC in melanin synthesis and metamorphosis in C. septempunctata, demonstrating that dopamine melanin is the primary component of cuticle melanin and underscoring the multifunctional effects of these genes on metamorphosis. The results highlight some mechanisms underneath insect melanization during cuticle formation and provide evidence of the multifunctional effects of essential genes in metamorphosis process in insects. [ABSTRACT FROM AUTHOR]