To elucidate the effect of cold stress on Dendroctonus valens larvae, a study was conducted under controlled laboratory conditions to examine the physiological and biochemical mechanisms associated with cold stress, coupled with transcriptome sequencing. Physiological and biochemical assessments indicated stable water content in larvae during cold stress initiation, with triglycerides and fats serving as primary energy reserves that decreased over cold stress progression. Glycogen and trehalose were identified as energy sources for larval energy metabolism, with their levels increasing as cold stress duration extended. Superoxide dismutase (SOD) activity exhibited an initial decline followed by an increase, while peroxidase (POD) activity initially rose before decreasing over induction time, and catalase (CAT) activity decreased during cold stress induction. Transcriptome sequencing at various time points revealed 4630 upregulated and 1554 downregulated genes, predominantly involved in metabolic pathways such as carbohydrate, amino acid, and lipid metabolism. Quantitative polymerase chain reaction (qPCR) results validated the transcriptome data accuracy. This investigation delineated the physiological, biochemical, and transcriptome alterations during cold stress, offering a theoretical framework for the rational prediction of Dendroctonus valens outbreaks.

The pine wood nematode (PWN) Bursaphelenchus xylophilus is a highly destructive forest quarantine pest and causal agent of pine wilt disease. The molecular response mechanism of Larix kaempferi (Japanese larch) to B. xylophilus infection remains unclear. This study aims to reveal the dynamic patterns of its defense response and screen key genes through time series transcriptomics. We found larch trees can proactively adjust their defense strategies to deal with the invasion of B. xylophilus. According to the Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, plant hormone signal transduction, MAPK signal pathway, and genes related to phenylpropane biosynthesis were more important. Through weighted gene coexpression network analysis (WGCNA), we identified two core modules that were rich in terpenoids, genes related to phenylpropane metabolism and cell wall strengthening, hormone signaling and defense regulation, and cytoskeleton and transport. Ultimately, we identified 20 core genes that were associated with several resistance-related processes, including the biosynthesis of resistance metabolites, post-translational regulation of protein homeostasis and defense signals, and transcriptional and translational reprogramming of gene expression. This study systematically depicted for the first time the continuous transcriptional regulatory network of L. kaempferi in response to pine wood nematodes. The key genes discovered provide important targets for subsequent functional verification and resistance breeding.