Moths behind Mumbai mangrove browning

Anil Singh, The Times of India 15 Oct 10;

MUMBAI: Those worried about large swathes of mangroves drying up as soon as the monsoon receded can rest easy. Botanists and entomologists say there is no link between the recent oil spill and the browning of mangroves in the creeks of Mumbai and Thane.

"It is a moth attack but there is nothing to worry as the mangroves will turn green in a month," said Deepak Apte, assistant director of Bombay Natural History Society, who studied the effect of the recent oil spill on the mangroves. The moth attack, he said, has almost become an annual feature now.

According to entomologists, the moth in question is the Hyblaea puera, better known as the teak defoliator. Native to South-East Asia, its caterpillar feeds on teak and 45 other plant species, including several kinds of mangroves. A flush of new, tender leaves are necessary to elicit egg laying.

According to Avinash Kubal, deputy director of the Maharashtra Nature Park, the moth breeds when rains have been delayed or sporadic. Up to 1,000 eggs can be laid by one female on the undersurface of the leaf and the larvae hatch in two days. The caterpillars devour the mangrove leaves, cocoon themselves in the shriveled remains and emerge a week later in brown wings.

The adult moths are relatively small, with a wing span of 3-4 cm, and have a characteristic resting posture that conceals the black and orange-yellow hind wings under the grayish-brown fore-wings.

These moths hover around street lights and at railway stations in September and early October. They normally fly at night using moonlight for direction, but get confused by artificial lights.

Although, these moths have been appearing in Mumbai's mangroves since the past 15 years, no serious study has been done on them. In 1995, a massive moth population caused such defoliation in mangroves that the navy was called in to aerially survey the damage. Navratri mandals faced the nuisance of thousands of moths swarming around their floodlights.

According to Apte, a rapid assessment two months after the spill has revealed out that the mangroves are now showing signs of regeneration, especially the ones at Uran. Elephanta is the worst affected area with no signs of regeneration.

"In Uran, there are stunted mangroves which are three to four feet tall and it is an open canopy but in Vashi the mangroves are 10 feet high and it's a dense, closed canopy. So Vashi might take time to recoup," said Apte. According to him, the washing away of the oil with the tide and rain is the best way to deal with the problem.