Transcriptomic Analysis of Chilo suppressalis (Walker) (Lepidoptera: Pyralidae) Reveals Cold Tolerance Mechanisms Under Parasitism Stress

Parasitoids exhibit remarkable abilities to manipulate host physiology, ensuring offspring survival and development. This study investigated the molecular mechanisms underlying how the parasitoid <i>Cotesia chilonis</i> modulates cold tolerance in its host, the rice stem borer <i>Chilo suppressalis</i>, using transcriptome sequencing. We found that the host larvae's supercooling point was lowest at 3 days post-parasitism but increased significantly by day 4. Transcriptome analysis identified 507 differentially expressed genes (DEGs), including 235 up-regulated by parasitism. Functional enrichment revealed that these DEGs were primarily associated with ribosome biogenesis, protein processing in the endoplasmic reticulum (ER), and oxidative phosphorylation under parasitism stress. Notably, 24 DEGs linked to temperature tolerance were predominantly heat shock proteins (HSPs) and calcium signaling-related genes. The reliability of transcriptome data was confirmed via RT-qPCR for eight randomly selected DEGs. Functional assays demonstrated that parasitism stress significantly inhibited ER activity. However, HSP expression did not significantly affect ER activity or cytosolic Ca²⁺ concentration in the hemolymph cells of <i>C. suppressalis</i> larvae. This research provides insights into the complex physiological and molecular mechanisms through which <i>C. suppressalis</i> responds to parasitism stress, particularly concerning cold tolerance modulation.