Transcriptome Analysis of the Japanese Pine Sawyer Beetle, Monochamus alternatus, Infected with the Entomopathogenic Fungus Metarhizium anisopliae JEF-197

The Japanese pine sawyer (JPS) beetle, Monochamus alternatus Hope (Coleoptera: Cerambycidae), damages pine trees and transmits the pine wilt nematode, Bursaphelenchus xylophilus Nickle. Chemical agents have been used to control JPS beetle, but due to various issues, efforts are being made to replace these chemical agents with entomopathogenic fungi. We investigated the expression of immune-related genes in JPS beetle in response to infection with JEF-197, a Metarhizium anisopliae isolate, using RNA-seq. RNA samples were obtained from JEF-197, JPS adults treated with JEF-197, and non-treated JPS adults on the 8th day after fungal treatment, and RNA-seq was performed using Illumina sequencing. JPS beetle transcriptome was assembled de novo and differentially expressed gene (DEG) analysis was performed. There were 719 and 1953 up- and downregulated unigenes upon JEF-197 infection, respectively. Upregulated contigs included genes involved in RNA transport, ribosome biogenesis in eukaryotes, spliceosome-related genes, and genes involved in immune-related signaling pathways such as the Toll and Imd pathways. Forty-two fungal DEGs related to energy and protein metabolism were upregulated, and genes involved in the stress response were also upregulated in the infected JPS beetles. Together, our results indicate that infection of JPS beetles by JEF-197 induces the expression of immune-related genes.

A new direction to understand the life cycle of the Japanese pine sawyer considering the selection strategy of instar pathways

The Japanese pine sawyer, Monochamus alternatus Hope (Coleoptera: Cerambycidae), transfers the pine wood nematode, Bursaphelenchus xylophilus (Steiner and Buhrer) that causes pine wilt disease (PWD), especially in Asian countries. The key for the control of PWD is primarily focused on vector management. Thus, understanding the exact life history of M. alternatus is required. Since the late 1980s, the life cycle of M. alternatus has been accepted under the assumption that the final larvae pass four instars in the field. This study is revising the previous error for the life cycle hypothesis of M. alternatus by finding various instar pathways, which pathway is defined as the number of instars that larvae pass through prior to pupation. We confirm experimentally that the overwintered fourth or fifth instar larvae directly pupate to emerge as adults, indicating the presence of four and five instar pathways, respectively. The selection of instar pathway might be determined primarily by habitat temperature. This information will be useful to explain the variation of life history in M. alternatus populations worldwide based on the thermal environments, and also can be served to predict the northern distribution limit by applying the threshold degree-days for the completion of four instar pathway.

Bidens pilosa Extract Effects on Pine Wilt: Causal Agents and Their Natural Enemies

We investigated the nematicidal and insecticidal activities of the aqueous extract from Bidens pilosa var. radiata on pine-wood nematode (Bursaphelenchus xylophilus) and Japanese pine sawyer (Monochamus alternatus) larvae and adults, the causal agent and vector of pine wilt, respectively. The aqueous extract killed the pine-wood nematode, adults, and larvae of the vector in vitro at all concentrations tested, and the effect decreased significantly with increasing extract dilution. Repellent activity was observed on the nematode and the vector adults as well, although the activity decreased with time in case of the vector. Furthermore, the aqueous extract of B. pilosa effectively promoted approximately 3.0–9.0 mm of hyphal growth in Beauveria spp., when compared with the control treatment. A minor insecticidal effect was also observed on two species of click beetle (Cryptalaus larvatus pini and Paracalais berus), which are natural predators of the Japanese pine-sawyer larvae. Pesticidal and repellent activities of the aqueous extract observed on several organisms related to pine wilt suggest that a multifactorial approach may effectively control this devastating disease.