Abstract
BackgroundIn many insect species, the larvae/nymphs are unable to disperse far from the oviposition site selected by adults. The Sakhalin pine sawyer Monochamus saltuarius (Gebler) is the newly discovered insect vector of the pine wood nematode (Bursaphelenchus xylophilus) in China. Adult M. saltuarius prefers to oviposit on the host plant Pinus koraiensis, rather than P. tabuliformis. However, the genetic basis of adaptation of the larvae of M. saltuarius with weaken dispersal ability to host environments selected by the adult is not well understood.ResultsIn this study, the free amino and fatty acid composition and content of the host plants of M. saltuarius larvae, i.e., P. koraiensis and P. tabuliformis were investigated. Compared with P. koraiensis, P. tabuliformis had a substantially higher content of various free amino acids, while the opposite trend was detected for fatty acid content. The transcriptional profiles of larval populations feeding on P. koraiensis and P. tabuliformis were compared using PacBio Sequel II sequencing combined with Illumina sequencing. The results showed that genes relating to digestion, fatty acid synthesis, detoxification, oxidation-reduction, and stress response, as well as nutrients and energy sensing ability, were differentially expressed, possibly reflecting adaptive changes of M. saltuarius in response to different host diets. Additionally, genes coding for cuticle structure were differentially expressed, indicating that cuticle may be a potential target for plant defense. Differential regulation of genes related to the antibacterial and immune response were also observed, suggesting that larvae of M. saltuarius may have evolved adaptations to cope with bacterial challenges in their host environments.ConclusionsThe present study provides comprehensive transcriptome resource of M. saltuarius relating to host plant adaptation. Results from this study help to illustrate the fundamental relationship between transcriptional plasticity and adaptation mechanisms of insect herbivores to host plants.
Highlights
In many insect species, the larvae/nymphs are unable to disperse far from the oviposition site selected by adults
Host plant free amino and fatty acid composition and content Eight free amino acids were found in P. koraiensis, including glutamic acid (Glu), aspartic acid (Asp), threonine (Thr), lysine (Lys), alanine (Ala), serine (Ser), valine (Val), and glycine (Gly)
We found that 11 Cytochrome P450 monooxygenases (P450), seven CE, and three UGT, and most of them were upregulated in the larvae feeding on P. tabuliformis compared with P. koraiensis
Summary
The larvae/nymphs are unable to disperse far from the oviposition site selected by adults. The Sakhalin pine sawyer Monochamus saltuarius (Gebler) is the newly discovered insect vector of the pine wood nematode (Bursaphelenchus xylophilus) in China. Adult M. saltuarius prefers to oviposit on the host plant Pinus koraiensis, rather than P. tabuliformis. The transfer of PWN between host trees is mediated by insect vectors, e.g., various species of Monochamus beetles [6, 7]. In Asia, PWN infection mainly occurs during feeding and oviposition of the Japanese pine sawyer Monochamus alternatus Hope [5]. Besides M. alternatus, the Sakhalin pine sawyer M. saltuarius (Gebler) (Coleoptera: Cerambycidae) is another important insect vector of PWN in Japan [8] and Korea [9]. Adults of M. saltuarius can be attracted by terpenes emitted from the host plant P. koraiensis for feeding and oviposition [19, 20]. The distribution pattern in the adults of M. saltuarius can be affected by host volatiles
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