Invasive red-necked longhorn beetles, an alien species, have been killing cherry, peach and other trees across Japan by eating them from the inside. A specialist warns cherry blossom viewing may not be possible in 20 or 30 years' time in the worst-case scenario.
The first case of damage done by the species -- called kubiakatsuya kamikiri in Japanese -- was reported in 2012 in Aichi Prefecture. Currently, 11 prefectures have been affected by the species, with many cherry trees in parks and schools, as well as peach trees in orchards, dying.
The red-necked longhorn was designated by the central government as an invasive alien species in 2018. The beetles are naturally found in China and Mongolia.
--Not effective
"No matter how many times we get rid of them, they just keep coming back," said the office manager of the prefectural Tatebayashi High School in Tatebayashi, Gunma Prefecture, in front a cherry tree with holes in its trunk made by the beetle. "We haven't been able to deal with their breeding speed."
There were originally 29 someiyoshino cherry trees, all about 40 years old, in front of the school gate. They were popular among students and local residents.
In July 2015, the trees started to die due to the damage caused by the beetle. The school took measures such as injecting chemicals into the bark and covering their trunks with nets to help keep the beetle and other insects away. However, a swarm of the beetles kept returning. The school's teaching and office staff took direct action against adult beetles, killing about 340 in August.
Of the 29 cherry trees, seven have already been cut down and six stand dead. The remaining 16 are blooming poorly. Sometimes, large branches suddenly fall off. Seeing this, the school has given up on preserving the trees and decided to cut them all down by as early as the end of next year.
--Strong breeders
Damage caused by the red-necked longhorn was first spotted in western Aichi Prefecture in 2012, according to the Environment Ministry. It was then seen in eight prefectures in 2017, before appearing in Ibaraki, Mie and Nara prefectures in 2019.
Specialists say the species may have been brought to Japan from overseas in wooden packing materials or similar objects that were shipped to Japan.
The problems are the insect's high fertility and its mobility. While a native Japanese long-horned beetle lays 100 eggs, at most, a red-necked longhorn can lay more than 500 eggs. Adults can travel more than two kilometers by riding the wind. They tend to breed in Japan partly because there are many peach and cherry trees, which are their favorite foods. The lack of natural enemies is thought to be another factor behind their active reproduction.
--Help needed
Afflicted local governments have been spraying pesticides and covering tree trunks with nets, for example. However, there is no specific method for complete eradication.
The Tatebayashi municipal government is asking its local residents to help kill off the species by offering to pay 50 yen per beetle killed. In fiscal 2020, 6,249 beetles have so far been killed by 91 people. However, the number of damaged trees rose to 1,323 from 1,272 in the previous fiscal year.
"If we don't act now, we may not be able to enjoy cherry blossom viewing as early as 20 to 30 years from now," said Ryutaro Iwata, a project professor specializing in forest science and forest entomology at Nihon University. "The central government must establish a system to forcibly cut down, burn and crush the damaged trees. They must transcend the boundaries of ministries and agencies, as well as local governments."
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