Downregulation of HSC70 in Haemaphysalis flava: effect on its reproduction and oviposition

Heat shock cognate protein 70 (HSC70), a member of the heat shock protein 70 (HSP70) family, is highly expressed in the salivary glands, midgut, and ovaries of the Haemaphysalis flava ticks, and is known to participate in vital physiological processes such as blood feeding and blood meal digestion. However, whether HSC70 is also involved in the reproductive and oviposition processes of H. flava and the underlying molecular mechanisms remains unclear. In this study, RNA interference (RNAi) was employed to knock down the expression of HSC70 in H. flava , and its effects on oviposition efficiency, the rate of egg morphological abnormality, and hatchability were examined. Additionally, full-length transcriptome sequencing technology was conducted to analyze differentially expressed genes (DEGs) and their associated signaling pathways following HSC70 knockdown. The results showed that silencing HSC70 significantly reduced female oviposition efficiency, increased the rate of egg morphological abnormality, and decreased the hatchability. Comparative transcriptomic analysis revealed that knocking down HSC70 in H. flava significantly downregulates genes involved in the metabolism of amino sugar and chitin, which may affect symbiont interactions and the integrity of the midgut peritrophic matrix (PM). Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis showed that two critical genes in the insect hormone biosynthesis pathway, Novelgene3177 (encoding juvenile hormone acid methyltransferase) and HaeL11405 (annotated as cytochrome P450), were markedly downregulated. These two genes are involved in the biosynthesis of juvenile hormone and 20-hydroxyecdysone, respectively, which regulate vitellogenesis and vitellogenin (Vg) synthesis, ultimately influencing tick reproduction and oviposition. Furthermore, HSC70 silencing alters the innate immune pathway, highlighting its role in tick immunity. These findings suggest that HSC70 may play a critical role in the reproduction and oviposition of H. flava by affecting peritrophic membrane structure, hormonal signaling, and innate immunity.