However, experts are calm and said it was normal
The second outbreak of Chirpine defoliator in some parts of Wangdue and Punakha have left the communities there in much worry as the Chirpine trees, botanically known as Pinus roxburghii are left without the pine needles.
The mountains and valleys, which earlier remained adorned with beautiful and towering green Chirpine trees now wear an ugly look, with Chirpine in patches, shedding their leaves, leaving only its trunk and leafless branches standing. It wears look of a mountain freshly burnt with its bare ground visible from far away.
The people residing around the contaminated areas wonder if it is a natural process, as many trees shed their leaves with the changing season. The pine trees which belong to the evergreen category are shedding their leaves and drying up.
Curious as to what is behind all the drama, but more concerned, a group of forestry officials have visited the areas such as Omtekha, Phangyuel, Gumkarmo, Dorongthang, Rinchengang and below Khujula where extent of Chirpine death are more visible. The site visits to study the cause and pinpoint the culprit was identified and confirmed on July 29 this year.
Upon their field visits and on carefully studying the area, the officials have found that the cause of Chirpine mass suicide is the Chirpine defoliator. Chirpine defoliator is described as larvae of a certain moth species often seen bare with no hair and slender body with the sucker feet, usually dull black to brown in colour with diamond-shaped markings on their backs. It is known to look like dry twigs. But the colour changes as the larvae mature and transform into moths. Those who have seen the caterpillar say that it curves its body as it moves around in the forest in vertical loops. Hence, the insect is also known as a looper or an inch worm.
In addition, people living in the affected areas have seen the larvae produce silken threads, and they say that the larvae normally travel from one tree to another when blown away by wind while still hanging on its silken threads. Others say that it uses the silken threads to quickly climb down the tree once it has finished defoliating and move to another healthy tree.
Upon investigation, the forest officials found the defoliators are ravaging the forests as it moves along. This was evident since the initial defoliation occurred in an area opposite to Khuruthang town in Punakha, no insects were found in the areas which presumably have moved to other areas.
The team has also studied the larvae specimen in laboratories and confirmed the defoliator as Lambdina sp.
Although the stretch of forests under attack of the larvae looks completely obliterated, the good news, according to experts is that there is nothing to worry about. Foresters say the Chirpine is a hardy species that can withstand any injury by pests. Researches conducted in the past have confirmed that the trees will recuperate from such damages by growing new needles. “Chirpine is resistant to defoliation and the defoliation will have a small effect on its annual increment or growth,” said one of the forest officials.
Even during recent site visit, the team found out that infected trees have already begun to recover from the attack. New and fresh needles were seen already sprouting on the trees that were rendered bare by the defoliator.
Records show that this is not the first such outbreak of Chirpine defoliation in the area. Similar outbreak was reported from Kamichu area in Wangdue in 1984 to 1986. Few years later, the incidence of defoliation also occurred Serichu areas in Mongar in mid 90s. The same Chirpine tree where the defoliation is on-going was also observed severe defoliation in mid 1990s, making this outbreak a second one.
In the past, the caterpillar damage in trees assessed in some localities was found to be extensive, but those trees had recovered the following year. This is primary because the caterpillar seems to feed only on pine needles and do not damage the stem or the main tree trunk. Hence, albeit the extensive outbreak, the damage done is insignificant as trees recover fast, usually within a year.
An expert opinion is that such an outbreak occurs intermittently. An entomologist said that it has some relation with prevailing seasonal conditions. “Normally, caterpillar outbreak is associated with dry weather conditions,” said the entomologist. He explained that it is similar to paddy and maize nurseries outbreak of caterpillar which is not a new phenomenon, and it normally occurs during dry spring conditions.
Hence, authorities remain optimistic that such attacks are not detrimental to the environment as a whole and the Chirpine trees in particular. “Control measure is not advisable because of vast infected area and also due to the reason that Chirpine trees are not going to die because of defoliation,” assured the entomologist.
Unlike in the past, this year the local communities claim that the caterpillar is striking back with overwhelming population. This is because the pine needles in trees in the affected areas are completely chewed up.
However, the officials said the rainfall reduces the population of defoliators and little or no rain, particularly during March or April will enhance high survival percentage of newly hatched larva. The larval stage has lasts till August and with monsoon rain already here, it will certainly help in reducing the population of the defoliator.