City's mangroves ravaged by moths

MUMBAI: All along Mumbai''s coastline, mangroves that should be flushed lush green with rain have withered into dry brown, as if some unnatural pestilence has struck them.
A plague has indeed descended on these wetlands, not of locusts but another equally destructive insect—amoth known as the teak defoliator has been seasonally ravaging Mumbai''s mangroves for the past decade.
This moth, familiar to teak plantation owners as the most devastating of pests, breeds prolifically when the rains have been delayed or staggered, as they were this year.
The caterpillars devour the mangrove leaves, cocoon themselves in the shrivelled remains and emerge later in wings of brown felt, sometimes swarming across the suburbs between mid-September and October.
"It can be quite dangerous driving on the roads if there aremany of them," says Vivek Kulkarni, who works with the Godrej mangrove project in Vikhroli. He adds that the caterpillars also sometimes get into houses, causing much itching among residents.
This year, the Bombay Natural History Society (BNHS) has been receiving calls from residents from Borivli to Vashi, expressing concern about the sudden dessication of their local mangrove patches.
Some, like Michael Fernandes, who lives opposite the vast swathe of mangroves in Dahisar, thought that slumlords had sprayed some poisonous chemical to kill the trees.
"We keep explaining that it is a natural phenomenon and the leaves will grow back soon," says Isaac Kehimkar of the BNHS.
Little is known about when or why this moth began feeding on the city''s mangroves, but local botanists first noticed the phenomenon in the early 1990s.
In 1995, amassive moth population caused such destruction and panic that scientists called in the navy to aerially survey the damage to mangroves, while swarms of moths clustered around the floodlights of Navratri mandals and caused five plants in the Vikhroli Godrej premises to be shut down for a few days.
While Kulkarni believes that the appearance of the moth is due to the late-''80s surge in teak plantations in neighbouring coastal districts, others, like Naresh Chaturvedi, an entomologist with the BNHS, say that this species of mangroves is also one of the insect''s natural hosts.
"I would say it has always been there, but it is not clear why it started appearing in large numbers," he says, adding that it is possible that the moths have shifted their feeding habits more fully to the mangroves over the years.
Adds K S S Nair, the retired director of the Kerala Forest Research Institute and an expert on the teak defoliator, "The moth is known to feed on about 45 plant species, including several species of mangroves. Anew flush of leaves is necessary to elicit egg laying. I presume that Avicennia Marina (the mangrove species) in Mumbai must be holding a bounty of tender leaves now," he says.
Despite the fact that this phenomenon has been occurring for the last ten years, there has been no real study of the subject, regrets Kulkarni. Luckily, there does not seem to have been any serious damage so far.
"But we have heard about some long-term studies in other countries which show that the quality of the mangroves suffer, with the leaves getting thinner," says Chaturvedi.
There is an unpleasant side-effect though. The moth larvae attract hundreds of crows which destroy the nests of other birds in the mangroves.
"Mangroves host a huge variety of bird life, so it creates quite a problem and upsets the ecological balance," says Kulkarni. "We really don''t know the consequences of this, whether the system is going to take care of the problem or whether it will have long-term effects."