Temperature is a critical factor of insect population abundance and distribution. Monochamus alternatus Hope (Coleoptera: Cerambycidae) is a significant concern since it is transmitted vector of the pinewood nematode posing enormous economic and environmental losses. This pest shows tolerance to heat stress, especially extremely high temperatures. Exposing for 6, 12, 24, 48, or 96 h, the 50% median lethal temperatures (Ltem 50) for fourth-instar larvae were 47.5, 45.5, 43.9, 43.4, and 42.3 • C, respectively. A total of 63,360 unigenes were obtained from complementary DNA libraries of M. alternatus fourth-instar larvae (kept at 25 • C and exposed to 40 • C for 3 h) and annotated with six databases. Five hundred sixty-one genes were significantly upregulated, and 245 genes were downregulated after heat stress. The Gene Ontology enrichment analysis showed that most different expression genes are categorized into "protein folding" and "unfold protein binding" terms. In addition, "Longevity regulating pathway-multiple species," "Antigen processing and presentation" as well as "MAPK signaling pathway" were significantly enriched Kyoto Encyclopedia of Genes and Genomes pathways. Further analysis of different expression genes showed that metabolism processes were suppressed, while ubiquitin proteolytic system, heat shock proteins, immune response, superoxide dismutase, cytochrome P450s, and aldehyde dehydrogenase were induced after heat shock. The stress signaling transduction pathways such as MAPK, Hippo, and JAK-STAT might be central convergence points in M. alternatus heat tolerance mechanism. The expression levels from quantitative realtime PCR of 13 randomly selected genes were consistent with the transcriptome results. These results showed that M. alternatus possessed strong heat tolerance and genes related to protein activity, immune response, and signal transduction composed of a complicated heat tolerance mechanism of M. alternatus. This research provided new insights into the mechanisms of thermal tolerance in other insects and aided in exploring the function of heat resistance-related genes.

Monochamus alternatus Hope (Coleoptera: Cerambycidae) warrants attention as a dominant transmission vector of the pinewood nematode, and it exhibits tolerance to high temperature. Heat shock protein 70 (HSP70) family members, including inducible HSP70 and heat shock cognate protein 70 (HSC70), are major contributors to the molecular chaperone networks of insects under heat stress. In this regard, we specifically cloned and characterized three MaltHSP70s and three MaltHSC70s. Bioinformatics analysis on the deduced amino acid sequences showed these genes, having close genetic relationships with HSP70s of Coleopteran species, collectively shared conserved signature structures and ATPase domains. Subcellular localization prediction revealed the HSP70s of M. alternatus were located not only in the cytoplasm and endoplasmic reticulum but also in the nucleus and mitochondria. The transcript levels of MaltHSP70s and MaltHSC70s in each state were significantly upregulated by exposure to 35–50°C for early 3 h, while MaltHSP70s reached a peak after exposure to 45°C for 2–3 h in contrast to less-upregulated MaltHSC70s. In terms of MaltHSP70s, the expression threshold in females was lower than that in males. Also, both fat bodies and Malpighian tubules were the tissues most sensitive to heat stress in M. alternatus larvae. Lastly, the ATPase activity of recombinant MaltHSP70-2 in vitro remained stable at 25–40°C, and this recombinant availably enhanced the thermotolerance of Escherichia coli. Overall, our findings unraveled HSP70s might be the intrinsic mediators of the strong heat tolerance of M. alternatus due to their stabilized structure and bioactivity.

Insect intestinal bacteria play an important role in resisting defensive substances of host plants. Pagiophloeus tsushimanus (Coleoptera: Curculionidae) feeds exclusively on camphor trees (Cinnamomum camphora, Laurales: Lauraceae) in China, causing substantial economic and ecological losses. It is unclear how the larvae of P. tsushimanus outcome the main secondary metabolites of C. camphora such as D-camphor, eucalyptol, and linalool. In this study, we isolated terpenoid-degrading bacteria from the gut of P. tsushimanus larvae by using selective culture medium. Maximum likelihood phylogenetic analyses were performed with 16S rDNA sequences to identify the bacteria, and results showed ten strains belonged to four genera, including Pseudomonas, Enterobacter, Serratia, and Corynebacterium. Then, gas chromatography was employed to determine the degradability of D-camphor, eucalyptol, and linalool by the isolated strains, results showed that Z5 strain (i.e., Corynebacterium variabile, Actinomycetales: Corynebacteriaceae), F1 strain (i.e., Pseudomonas aeruginosa, Pseudomonadales: Pseudomonaceae), and A3 strain (i.e., Serratia marcescens, Enterobacterales: Enterobacteriaceae) had the highest degradation rates of D-camphor, linalool, and eucalyptol, respectively. The intestinal bacteria were capable of terpenoid degradation in vitro, which suggested that these gut bacteria associated with P. tsushimanus play an important role in overcoming host plant secondary metabolite defense, thereby facilitating the host specialization of this pest.

A substantial increase in the occurrence of extremely high‐ or low‐temperature events caused by global climate change has imposed pressure on the survival and reproduction of invertebrates. Hyphantria cunea (H. cunea; Lepidoptera: Arctiidae) is a worldwide defoliator and has become a major forestry and agricultural pest during the past three decades in China. The thermal and cold tolerance has directly affected the population and geographical distribution of H. cunea, which remains poorly understood. Here, we examined the thermal tolerance of H. cunea larvae and discovered that they could endure extremely high temperatures, as demonstrated by median lethal times (Ltim50) of 103.3 hr at 37°C, 62.0 hr at 40°C and even 14.5 hr at 43°C. To further explore the molecular evidence of the physiological response to heat and cold, we cloned and characterized six small heat shock proteins (sHSPs). These proteins possessed the conserved α‐domain of the sHSP family at the C‐terminus and various N‐terminal domains. Phylogenetic analysis showed that the HCsHSPs presented a close evolutionary relationship with sHSP genes in noctuidae species. Four sHSPs in H. cunea were sensitive to heat stress, and only HCsHSP28.7 was induced by cold stress. The expression level of HCsHSPs peaked at 40°C and decreased in treatment at 45°C. HCsHSP20.0 transcripts were abundant in the cuticle after heat shock, and HCsHSP28.7 was most enriched in the fat body after cold shock. In addition, an equal molecular weight of the HCsHSP20.0 protein could completely protect malate dehydrogenase (MDH) from thermal aggregation. Recombinant HCsHSP28.7 E. coli cells exhibited tolerance to cold stress. Overall, our results demonstrate that HCsHSPs, especially HCsHSP20.0 and HCsHSP28.7, are vital genes in the adaptation of H. cunea larvae to extreme conditions in the context of global climate change.

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