The pine sawyer beetle (scientific name: Monochamus alternatus) is an insect belonging to the longhorn beetle family (Cerambycidae). They are commonly known as carriers of pine wilt disease because their larvae parasitize pine trees and can spread the disease.
Pine wilt disease is one of the most dangerous and destructive forest diseases globally, classified as a quarantine pest in over 50 countries. This disease is highly contagious and damaging, posing serious threats to pine trees, hence its metaphorical name “cancer of pine trees.” Pine wilt disease is highly pathogenic, affecting hosts rapidly and presenting significant challenges in management.
Picture: A pair of Monochamus alternatus specimens. This beetle is one of the vectors for pine wilt disease. Photo: Linda, taken at the National Museum of Animals. Photo by Linda Wong ©CBCGDF
As depicted, the Monochamus alternatus is a relatively large beetle, measuring about 15 to 30 millimeters in length. The adults are typically black or dark brown, slender-bodied, with long antennae. Their forewings are black or brown with white or pale yellow spots or stripes, which may vary slightly among individuals. Adults of Monochamus alternatus emerge between May and July, are diurnal, and exhibit phototaxis. Females lay eggs in bark crevices; upon hatching, larvae bore into the bark to feed, eventually pupating inside the tree trunk. Monochamus alternatus completes one generation per year.
Adults are active mainly from spring to summer, preferring to fly around trees or in forested areas. Females select suitable pine trees to lay eggs beneath the bark or in cracks. After hatching, the larvae tunnel inside pine wood, feeding on it. The primary hosts of Monochamus alternatus are pine trees, especially Japanese black pine and Yunnan pine.
Monochamus alternatus is primarily distributed in Eastern Asia, including China, Japan, North Korea, South Korea, and Russia. Their larvae bore into the bark and wood of coniferous trees, serving as the primary vectors of pine wilt disease.
Pine wilt disease was first discovered in Nanjing, Jiangsu Province, China, in 1982, and rapidly spread, causing significant ecological and economic losses to China’s pine forests and forestry ecosystems. Data from 2017 indicate that pine wilt disease affected a total area of 85,524 hectares in mainland China, resulting in economic losses of approximately 19.5 billion RMB, with direct losses amounting to 3.5 billion RMB and indirect losses of 16 billion RMB. Controlling the damage caused by Monochamus alternatus to pine trees is crucial for forest conservation and tree health management.
Over the past 30 years, this significant plant epidemic has led to direct economic losses and ecological service value losses of over a trillion RMB in China alone!
During a training session, I learned about the severe current damage caused by this tiny creature. According to the 2020 autumn census results and the latest reports from various regions, the national distribution of pine forests has been categorized into heavily affected areas, lightly affected areas, key prevention areas, and general prevention areas. Among these, there are 518 heavily affected areas, 206 lightly affected areas, 740 key prevention areas, and 1,127 general prevention areas.
Despite their attractive appearance as specimens, these insects are indeed hidden “killers” of forest health.
Image source: from a Lecture PPT by Prof Yu Haiying. She elaborated on the occurrence, field identification, and detection techniques of pine wilt disease.
【Another unknown source of transmission】
Further investigation reveals that besides the known natural and human factors contributing to the spread of pine wilt disease, there is another often overlooked factor—the impact of electrical infrastructure. Surprising, isn’t it?
When power companies install and maintain equipment in mountainous areas, they dismantle wooden packaging materials and cable reels containing live pine sawyers or carriers of pine wilt disease, potentially spreading the disease within healthy forest ecosystems. Undoubtedly, although mostly unintentional, such actions pose a threat to ecological security.
During a training session on “Theory and Practice of Pine Wilt Disease Prevention and Control,” speaker Zhang Xingyao also mentioned that areas around power lines, communication towers, railway lines, scenic areas, and construction sites are high-risk zones for pine wilt disease. In the construction of power transmission towers, packaging materials often contain insect carriers; after tower completion, these materials are discarded in mountainous areas, naturally spreading to other regions.
Image: Major natural hosts susceptible to diseases. Image source: Lecture PPT by Professor Yu Haiying. She detailed the occurrence, field identification, and detection techniques of pine wilt disease.
Currently, there are no specific laws or regulations in China addressing the risk of pine wilt disease associated with the construction of power and communication facilities. Prevention and control of pine wilt disease emphasize prevention rather than remedy. In a proposal draft for the two sessions in spring 2022, researchers from the China Biodiversity Conservation and Green Development Foundation (CBCGDF) highlighted the improper handling and disposal of packaging materials from power and communication equipment as a topic, urging attention from relevant departments. This policy proposal was subsequently submitted to relevant departments supported by Chinese lawmaker at the 2023 China’s Two Sessions (top political advisory bodies).
Original post in Chinese published on CBCGDF-OceanWetlands platform:
《“松树癌症”的背后：松墨天牛》
https://mp.weixin.qq.com/s/KunEtbUO047W7wDh5OjLbQ
Reporter: Linda Wong
Editor: Samantha
Contact: v10@cbcgdf.org; +8617319454776
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