Unidentified insect a threat to Sunderbans mangrove

Prithvijit Mitra, The Times of India 27 Nov 10;

KOLKATA: It's not just unauthorized chopping that threatens the Sunderbans mangroves. The forest could be faced with a new enemy that has been slowly eating into the trees on the edge of the water, reducing them to charred pulps of waste vegetation. Hundreds of black insects, shaped like caterpillars, have been raiding the mangroves for the last three months, causing serious damage to the plants. While experts haven't yet been able to identify the pest, a few specimens have been collected and sent to the Zoological Survey of India (ZSI).

A team of scientists from Jadavpur University's School of Oceanography chanced upon the insect during a visit last week. It was while surveying the mangroves that they noticed many with leaves that had been eaten up and looked as if they had been set on fire.

Initially, the experts suspected a human hand behind it but were soon corrected by the locals. "They led us to many more such damaged mangroves at places like Pakhiralaya, Sajnekhali, Lahiripur and Rangabelia. We were shocked to find hundreds of these insects crawling all over the mud on the banks. They were piling on to the mangroves in droves and feeding on the leaves. They were peeling off the leaves within minutes, reducing the mangroves to a skeleton of branches and twigs. Mysteriously, the leaves they were feeding on wore a charred look once the insects were gone. Neither the locals, nor any of us could identify them. We have collected a few specimen and sent them to ZSI," said Gautam Sen, a member of the oceanography team.

Such insects have never been known to exist in the Sunderbans. About an inch-and-half in length, they resemble caterpillars but without the hairy legs. The pests have so far only been raiding the bani trees (avicennia) that grow on the edge of the water. "No insect has ever been seen so close to the water, which is extremely saline. It needs to be found out if they have come from some other region or had so far restricted themselves to some other part of the forest," said Sen.

Climate change could have triggered the flight of these insects, it is being suspected. "The insects could have been dislodged from some island that's now submerged or was flooded after Cyclone Aila. What is worrying is that they have started moving towards the villages and have already raided some vegetable gardens. It would be disastrous if they raid the farmlands or move deep into the forests. Mangroves will be seriously affected unless we can stop the march of these mysterious insects," said Sarbaranjan Mondol, an NGO worker in the Sunderbans.

Member of the state biodiversity board, Silanjan Bhattacharya, said it was strange that a new insect specie has been spotted at the Sunderbans. "I was at the mangrove forest recently but didn't come across this new insect. There are insects which feed on mangrove leaves but locals are well acquainted with these. It might have floated in from some remote part of the mangrove forest along the waters in the post-Aila period. It is difficult to comment on this unless we have a look at the insect," said Bhattacharya, who is also the head of the department of zoology at West Bengal State University.