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Identification of the aggregation-sex pheromone produced by male Monochamus saltuarius, a major insect vector of the pine wood nematode
The pine tree is the most popular tree in Korea. It is one of the most numerous trees in Korea, and it best symbolizes our mindset and spirit, which is why it has long been loved by Koreans. Unfortunately, a silent disease caused by the pine wood nematode, called the pine wilt disease, has begun to kill off our beloved pine trees.
The pine wood nematode is a phytotrophic nematode approximately 1 mm in size that grows by eating plant tissues or microorganisms in pine trees. It infiltrates pine trees and attacks their cells, causing abnormalities in their vessels called tracheids, which inhibit water from traveling upwards and cause the pine trees to wilt. The pine wood nematode is native species in North America and is presumed to have entered Japan around 1905 and traveled to Korea in 1988. It spread rapidly to pine trees in Japan, China, Korea, Portugal, and Spain and has become a global problem.
The most important aspect of blocking the spread of pine wilt disease is controlling the vector. This is because the pine wood nematode cannot move between the trees independently. In Korea, Japanese pine sawyers (Monochamus alternatus) and pine sawyers (Monochamus saltuarius) have been the vectors spreading the pine wood nematode. The trees affected by the pine wood nematodes wilt and die. Female beetles oviposited eggs on the dead pine trees, and long-horned beetle larvae grow in trees infected by the pine wood nematode. When larvae become adult, pine wood nematode enter into the tracheal system of beetle. Adult beetles emerge from infected trees, and they start to eat twigs of healthy pine tree for sexual maturation. Pine wood nematode can invade health pine trees through the injury caused by adult beetles. To stop the spread of pine tree nematode disease, it is important to control insect vector.
Currently, ground and aerial spray of insecticides have been used in Korea to control long-horned beetles. However, chemical insecticides have caused many side effects including environmental pollution, toxic to non-target organisms, residue and resistance. Professor Park, Il-Kwon said, "Due to the necessity of an eco-friendly method that can control long-horned beetles, we have begun research on a method that attracts long-horned beetles using pheromones.”
Insects such as long-horned beetles and bark beetles attack a tree in groups in order to break through its resistance. During this process, an aggregation pheromone is secreted to attract further individuals from the same species. Professor Park analyzed this pheromone in Monochamus saltuarius, and found that the pheromone is secreted by the males. After testing this pheromone in the field, the research team confirmed that the pheromone attracted insects of the same species and concluded that this pheromone could be used to control the long-horned beetles.
The research team also discovered that while the pheromone attracts both sexes, it attracts females much more than males. Most insect pheromones are sex pheromones used to attract the opposite sex for mating, unlike the aggregation pheromone that is necessary to attract both males and females of the same species. According to this study, the pheromone from the Monochamus saltuarius is an aggregation-sex pheromone, which not only attracts male and female individuals of this species but also attracts three times more females than males, suggesting a role in the mating process. Professor Park stated that, "If this pheromone is used, more females can be caught, which is very important in order to reduce the population of the next generation."
This study is meaningful in that it has laid the foundation for eco-friendly pine wilt disease control technology. Instead of using conventional pest control methods, it has become possible to lure long-horned beetles, which are a vector for pine wood nematodes, into traps using the aggregation-sex pheromone without using organic synthetic pesticides. In addition, because using the aggregation-sex pheromone attracts more females than males, this technique has a significant effect on reducing the population of the vector insect. Professor Park’s team spoke of their anticipation "If the aggregation-sex pheromone pest control method is used in conjunction with other existing methods in areas with particularly severe damage, a strong population reduction effect will be seen in the next generation." The results of this study can be actively utilized to make predictions regarding long-horned beetles, such as the distribution and eclosion period of the mediating pests for each region and the mediating pest population by elevation.
Professor Park said, "Research on pest control for long-horned beetles will continue in the future.” Studies will be conducted to find a cooperative agent that can synergize with pheromones to lure long-horned beetles and to uncover how Japanese pine sawyers and pine sawyers distinguish each other as different species despite secreting the same pheromone. He is also developing a plan for manufacturing and industrializing pheromone traps in cooperation with KIP, and a plan for controlling other vector pests using ecologically friendly pheromones. We hope that pheromone-based vector control methods will become commercialized through Professor Park’s research and eradicate the pine wilt disease and that further eco-friendly pest control methods will increase the protection of forests.
Student Reporter Song, Iee-re / Kim, Su-yeon
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