Caterpillars are devastating hundreds of hectares of pine forest in Nghe An province.
For about a month now, a caterpillar infestation has ravaged hundreds of hectares of pine forests in Nghi Loc district, stripping them of their leaves and putting them at risk of dying.
Risk of becoming an epidemic
In mid-August 2024, we followed officials from the Nghi Loc Protective Forest Management Board into the pine forest to trap caterpillars. This work had been carried out by the forest protection force for the past month, since the caterpillar infestation began to spread rapidly. Light traps are one of two solutions that the Nghi Loc Protective Forest Management Board has implemented to control this caterpillar species that is harming the pine trees.
According to forest protection officials, the pine caterpillar population in Nghi Loc district is experiencing a very complex situation, negatively impacting forest development. Currently, the third generation of caterpillars (2024) is present. In the eastern area, from National Highway 1A down to the communes of Nghi Yen, Nghi Tien, Nghi Quang, and Nghi Xa, the caterpillars are thriving. Specifically, up to 300 hectares of pine forest have been severely infested with a density of 350-400 caterpillars per tree, resulting in extensive damage and bare foliage. Additionally, 450 hectares of forest are less severely infested, with an average density of 150-200 caterpillars per tree.
In the pine forest areas of Nghi Dong and Nghi Hung communes, the caterpillar density is 20-30 caterpillars per tree, distributed locally and unevenly, mainly concentrated above the ridges…
Mr. Tran Van Truong, Deputy Head of the Nghi Loc Protective Forest Management Board, said that since the beginning of the year, warmer-than-average weather conditions have been favorable for the development of several pests, especially pine caterpillars. The complex nature of the pine caterpillar infestation poses a risk of outbreaks, so the unit has focused its human and financial resources on spraying for prevention and control. However, investigating and forecasting the development of different caterpillar generations is very difficult due to the large forest area, with a significant portion of the forest consisting of 5-6 year old pine trees with an average height of 20-25 meters, making it difficult to accurately determine the caterpillar density. Other factors such as climate and site conditions also affect the formation and development of different caterpillar generations. The spraying sites are located on high, steep, and precarious hills with dense bushes and vines, making prevention and control very challenging. To date, the unit has sprayed insecticides on an area of over 150 hectares.
Using lights to trap caterpillars.
Along with spraying pesticides, the Nghi Loc Protective Forest Management Board has recently implemented a solution to trap pine caterpillars using lights. According to Mr. Vo Hien Tuan, Head of the Science Department (Nghi Loc Protective Forest Management Board), like many other caterpillar species, adult pine caterpillars will enter cocoons, and after a short time, they will transform into butterflies and fly out to lay eggs, reproducing very quickly. "We call these butterflies adult caterpillars; they are very attracted to ultraviolet light. Therefore, trapping them with lights is also very effective," Mr. Tuan said.
To trap caterpillars, in recent days, every evening, four forest rangers, divided into two groups, laden with equipment, head towards the pine forests being ravaged by caterpillars. Their trapping equipment includes ultraviolet lights and tarpaulins to hold water beneath the lights. The traps must be placed in open spaces where the caterpillars in the pine forest can see the light. To power the lights, they carry hundreds of meters of electrical wire, connecting it to nearby houses. The trap locations must not only be open but also not too far from houses, allowing the wire to reach them. This light attracts caterpillars from a distance of about 1 kilometer.
At first glance, trapping caterpillars seems easy, but it's actually quite complex. The tarp, in addition to containing water, is also doused with a little oil to prevent adult caterpillars from flying back up once they fall in. After seeing the ultraviolet light, the adult caterpillars will fly down. The light is installed directly on the water-filled tarp, so the light reflects off it. "After flying down, the caterpillars see the reflected light in the water, mistake it for a real light, and rush towards it. That's how they get caught in the trap," Tuan explained.
Compared to spraying pesticides, trapping caterpillars with lights is not very strenuous. After setting up the traps, all they have to do is wait for the caterpillars to be lured in. However, for fear of losing the equipment, the forest rangers don't dare go home to sleep, and many nights they have to stay awake to guard them.
"These devices aren't expensive, but leaving them unattended all night is scary. Especially with hundreds of meters of electrical wire," Tuan said.
Every night, nearly 20 light traps are set up. Each trap can catch about 3 kg of adult caterpillars in a single night. There are countless caterpillars, and some people say that trapping them one by one like that isn't enough. But this is a fairly effective pest control method. Because if each adult caterpillar isn't caught, it will lay thousands of eggs a few days later, starting a new cycle.
In particular, according to these people, trapping caterpillars with lights is less strenuous and doesn't require traversing entire forests to spray pesticides. “Spraying pesticides isn't simple, because beforehand we have to research what age the caterpillars in this forest are before we can spray. We only spray when the caterpillars are at their peak feeding stage, because that's when they're most likely to absorb the pesticide clinging to the leaves. In addition, we have to pinpoint areas to spray promptly, because the caterpillars eat very quickly. Today the pine forest might still be green, but tomorrow it could be completely stripped bare. On days we go spraying pesticides, each person has to carry nearly 30 kg on their backs, and the terrain is mostly hilly and mountainous, so it's very tiring. Even with protective gear, there are so many caterpillars that they often crawl into our bodies. Each time that happens, it takes several days to recover from the poisoning,” added Mr. Vo Hien Tuan.
To spray pesticides more effectively and reduce the workload for staff, the Nghi Loc Protective Forest Management Board considered renting drones. They contacted several companies, but were quoted prices ranging from 800,000 to 1 million VND per hectare. With thousands of hectares of pine forest under their management, they lacked the funds to rent drones, so staff still had to venture deep into the forest to spray.
