Cinnamomum camphora (L.) J. Presl. (Laurales: Lauraceae) is widely cultivated as an important landscape tree species in many urban areas in South China, especially in Shanghai City. Pagiophloeus tsushimanus Morimoto has become a destructive insect pest of C. camphora plantations in Shanghai, but the biological and ecological traits of this pest remain largely unknown. In this study, we investigated the damage and life history and determined the larval instar of P. tsushimanus. The results indicated that P. tsushimanus is a monophagous weevil pest, and C. camphora is the unique host tree species. C. camphora plantations in all administrative districts of Shanghai have been seriously damaged by P. tsushimanus. Adults often aggregate for feeding on the tender bark of twigs and occasionally on newly emerged buds. After experiencing damage, the twigs shrink and crack and the buds will shrink. Adults tend to repeatedly mate and oviposit, and all females lay single eggs at a time. Eggs will be covered with a mixture of secretions and wood chips by female adults. Larvae (1st–2nd instar) feed on the phloem, while 3rd–5th instar can bore into the phloem and the cambium. Massive tunnels, including three shapes (inverted “L”, inverted “T”, and inverted “Z”), were observed in the trunk of each tree, and resulted in swelling of the outer bark. P. tsushimanus has one life cycle per year in Shanghai. Both adults and larvae (3rd–5th instar) overwinter from early November to early April. Adults overwinter in grooves on the underside of branches or at branch nodes, and larvae overwinter in tunnels. Five larval instars of P. tsushimanus were determined according to Dyar's and Crosby's rules. The biological traits and life history of P. tsushimanus have been identified and can provide guidance in terms of pest control and plantation management.

The weevil Pagiophloeus tsushimanus Morimoto (Coleoptera: Curculionidae), native to Eastern Asia, is a wood‐boring pest that causes severe damage to camphor trees (Cinnamomum sp.) in Shanghai, China. Other Lauraceae tree species that grew sympatrically with this pest in close proximity could face a potential threat. To assess the potential risks of host shift, we explored the phenotypic associations between preference and performance in P. tsushimanus reared on three Lauraceae tree species. In a no‐choice experiment offering branches of each plant as diet material and oviposition sites, we found that individuals reared on Cinnamomum camphora (L.) Presl (Laurales: Lauraceae) exhibited the strongest performance with shorter development time, higher survival and growth rate in the immature stage, longer longevity and greater fecundity in adults. In contrast, those on novel Lauraceae tree species (Cinnamomum chekiangensis Nakai and Phoebe chekiangensis Shang) had difficulty completing their whole life cycle due to significantly lower survival and reproduction. In a multiple‐choice experiment, C. camphora was established as the preferred host. However, we found that the larval experiences on the non‐preferred host plants contributed to an increased preference for that plant species. These results indicated that both the preference‐performance hypothesis and the Hopkins’ host selection principle are applicable in this weevil under experimental conditions. It is possible that although the weevil performed poorly on two novel Lauraceae tree species, under favourable conditions their surviving offspring could evolve into a new host‐specific population. Consequently, this weevil pest needs to be monitored on these novel Lauraceae tree species.

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.

Understanding the mechanism of insect resistance to toxic effects of phytochemicals can provide an insight into plant-herbivore interactions. Monochamus alternatus Hope, a main vector of pine wood nematode (Bursaphelenchus xylophilus), prefers to infest masson pine (Pinus massoniana Lamb) and causes huge economic and environmental losses. α-Pinene is the primary component of resin produced by masson pine and plays a crucial role in defending against herbivorous insects, but its defensive effects on M. alternatus larvae are barely known. Here, we explored the physiological metabolism in M. alternatus larvae that were fumigated with (+)α-pinene, (-)α-pinene, β-pinene, (R)-(+)-limonene, myrcene and (-)α-phellandrene. (+)α-Pinene showed the highest fumigant toxicity to M. alternatus larvae among these monoterpenes, and the fourth instar larvae possessed the highest resistance to this compound at the larval stage. Comparative transcriptome analysis detected 423 up-regulated and 311 downregulated genes in the larvae fumigated with (+)α-pinene, which were mainly related to detoxification, energy and protein metabolism. Among the differentially expressed genes encoding for detoxification enzymes, 14 P450s, 13 UGTs, 1GSTs and 3ABCs were dramatically up-regulated in the larvae fumigated with (+)α-pinene. Silencing of P450s via RNA interference led to an increased mortality in the larval fumigated with (+)α-pinene. Piperonyl butoxide exposure significantly increased the mortality and inhibited the expressions of P450s, UGTs and ABCs in the larvae fumigated with (+)α-pinene. These results suggested an important role of P450s in the resistance of M. alternatus larvae to (+)α-pinene fumigation, which may facilitate the understanding of terpenoid detoxification in M. alternatus larvae.

1. 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.2. 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.3. 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.4. 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. 5. 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 hostspecific chemical defences in this weevil pest.