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.

Pine wilt disease (PWD), caused by Bursaphelenchus xylophilus, poses a severe threat to coniferous forests worldwide, yet conventional control measures remain limited. Therefore, identifying resistance genes from resilient species such as Larix kaempferi has become crucial for developing genetic strategies to protect forests. The overexpression of LKF3H2 (LKF3H2-OE) from L. kaempferi in A. thaliana significantly enhanced both plant growth and resistance to B. xylophilu. Compared to wild-type (WT) plants, LKF3H2-OE transgenic lines exhibited a 61.4% increase in plant height, a 61.5% increase in silique number per plant, and accelerated bolting and flowering by 6 days and 5 days, respectively. Following nematode inoculation, the disease incidence in transgenic plants was 40%, significantly lower than that in WT plants (76%). This enhanced resistance was associated with the density- and time-dependent induction of LKF3H2 expression, which reached 2.04-fold under high inoculum pressure and 5.48-fold at 7 days post-inoculation. Furthermore, transgenic plants accumulated higher levels of defense-related metabolites, including flavonoids (up to 3.12 mg/g) and proline (up to 34.35 mg/g). These results demonstrate that LKF3H2 significantly improves nematode resistance by synergistically enhancing growth traits and activating disease-resistant metabolic pathways, highlighting its potential as a key genetic resource for breeding disease-resistant wood plants.