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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. [ABSTRACT FROM AUTHOR]

Background: Pagiophloeus tsushimanus (Coleoptera: Curculionidae), an emerging forest pest exclusively infesting camphor trees, has recently caused severe ecological and economic damage in localized areas in China. Its population outbreak depends largely on the capacity to overcome the pressure of terpenoid-derived metabolites (e.g. linalool) from camphor trees. At present, the molecular basis of physiological adaptation of P. tsushimanus to dietary linalool is poorly understood, and there is no available reference genome or transcriptome. Results: Herein, we constructed the transcriptome profiling of P. tsushimanus larvae reared on linalool-infused diets using RNA sequencing and single-molecule real-time sequencing. A total of 20,325 high-quality full-length transcripts were identified as a reference transcriptome, of which 14,492 protein-coding transcripts including 130 transcription factors (TFs), and 5561 long non-coding RNAs (lncRNAs) were detected. Also, 30 alternative splicing events and 8049 simple sequence repeats were captured. Gene ontology enrichment of differential expressed transcripts revealed that overall up-regulation of both cytochrome P450s (CYP450s) and cuticular proteins (CPs), was the primary response characteristic against dietary linalool. Other physiological effects possibly caused by linalool exposure, such as increase in Reactive Oxygen Species (ROS) and hormetic stimulation, were compensated by a handful of induced genes encoding antioxidases, heat shock proteins (HSPs), juvenile hormone (JH) epoxide hydrolases, and digestive enzymes. Additionally, based on co-expression networks analysis, a diverse array of hub lncRNAs and TFs co-expressed with CYP450s and CPs were screened as the potential gene regulators. Temporal expression of candidate transcripts determined by quantitative real-time PCR also indicated a cooperative relationship between the inductions of CYP450s and CPs upon exposure to linalool. Conclusions: Our present study provides an important transcriptome resource of P. tsushimanus, and lays a valuable foundation for understanding how this specialist pest copes with chemical challenges in its specific host environments. [ABSTRACT FROM AUTHOR]

Camphor oil (EO) and its main component (i.e. d-camphor) form specific terpenoid defences in camphor trees, Cinnamomum camphora. However, an emerging insect pest, Pagiophloeus tsushimanus (Coleoptera: Curculionidae) has recently caused serious damage to this intractable plant species, which is largely elusive. To investigate the mechanism underlying the tolerance of this weevil to host-specific terpenoid defences, we carried out the bioassays, RNA-seq, and RT-qPCR analysis based on a simulated diet environment with EO or d-camphor exposure. First, a hormetic response (a highly generalized dose–response phenomenon in toxicology) in the larval overall performance was observed in terpenoid-feeding individuals. Then, genes encoding cytochrome P450 (CYP450) and cuticular protein (CP) were induced by both EO and d-camphor exposures using comparative transcriptome, suggesting that this weevil could deploy the dual mechanism (i.e. CYP450-mediated metabolic resistance and CP-mediated cuticular resistance) to counter host terpenoid defences. Furthermore, temporal expression of CYP450 and CP genes under a low dose of d-camphor exposure indicated that there was a trade-off relationship between the inductions of CYP450 and CP genes. We speculate that the dual mechanism of terpenoid tolerance in this specialist is an essential precondition for the hormetic response in larval growth and development, ultimately contributing to its successful colonization on camphor trees. Additionally, we found a few genes related to glucose transport, juvenile hormone, and odorant binding were fine-tuned under terpenoid exposures. Taken together, our study will open new avenues for understanding insect-plant coevolutionary adaptation and developing durable control strategies for this insect pest. [ABSTRACT FROM AUTHOR]

Camphor, Cinnamomum camphora (L.) Presl, is used for mothproofing material due to its content of secondary metabolites. However, the phloem‐feeding weevil, Pagiophloeus tsushimanus (Coleoptera: Curculionidae), has been observed to feed exclusively on this plant without incurring apparent fitness costs. This phenomenon remains to be elucidated.Gas chromatography–mass spectrometry analysis of essential oil extracted from the phloem of camphor tree was performed. The top three components, all monoterpenoids, were eucalyptol (31.9%), D‐camphor (19.2%) and linalool (10.2%), respectively.In headspace bioassays, both eggs and larvae showed the greatest sensitivity to eucalyptol, and there was a bell‐shaped relationship between the concentrations used and developmental time for eggs when exposed to D‐camphor volatile.Exposure to essential oil mixture and D‐camphor notably increased the activity of glutathione S‐transferase in the weevil. A corresponding short‐term induction of gene expression was also observed according to quantitative real‐time polymerase chain reaction analysis.In general, P. tsushimanus possessed various levels of tolerance to different host monoterpenoids. Over‐expression of glutathione S‐transferase in vivo probably relates to detoxification metabolism of these monoterpenoids. Our findings provide a valuable clue to understanding the mechanism underlying resistance to host‐specific chemical defences in this weevil pest. [ABSTRACT FROM AUTHOR]

The landscape plant, Cinnamomum camphora, is a broad-spectrum insect-repelling tree species, mainly due to a diversity of terpenoids, such as camphor. Despite its formidable chemical defenses, C. camphora is easily attacked and invaded by a monophagous weevil pest, Pagiophloeus tsushimanus. Deciphering the key olfactory signal components regulating host preference could facilitate monitoring and control strategies for this pest. Herein, two host volatiles, camphor and ocimene, induced GC-EAD/EAG reactions in both male and female adult antennae. Correspondingly, Y-tube olfactometer assays showed that the two compounds were attractive to both male and female adults. In field assays, a self-made trap device baited with 5 mg dose d(+)-camphor captured significantly more P. tsushimanus adults than isopropanol solvent controls without sexual bias. The trunk gluing trap device baited with bait can capture adults, but the number was significantly less than that of the self-made trap device and adults often fell after struggling. The cross baffle trap device never trapped adults. Neither ocimene nor isopropanol solvent control captured adults. When used in combination, ocimene did not enhance the attraction of d(+)-camphor to both female and male adults. These results indicate that d(+)-camphor is a key active compound of P. tsushimanus adults for host location. The combination of the host-volatile lure based on d(+)-camphor and the self-made trapping device is promising to monitor and provide an eco-friendly control strategy for this novel pest P. tsushimanus in C. camphora plantations. [ABSTRACT FROM AUTHOR]