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Insect defenders for water hyacinths

- Midnapore botanist’s study says spiders & ants protect plants that guard coasts

Water hyacinths that protect the coast but are being destroyed by rampant construction, or by animals who feed on them, have a set of tiny but fierce guards by nature.

Amal Kumar Mandal, who teaches botany at Midnapore’s Vidyasagar University, has worked for six years on insects that protect this plant.

His research is now being published in the country’s leading science journals. He has also received a grant of Rs 15 lakh from the UGC to continue the research.

A set of spiders, ants and some other insects form a protective shield for the water hyacinths (kochuripana in Bengali), says Mandal’s research. When cattle approach the plants, these insects charge at the animals in groups and the cows and goats have to backtrack.

The Journal of Geo-marine Science has a picture of water hyacinths on its cover that also features the friendly ants in its February issue. Amal Kumar Mandal was helped in the research by Sanjukta Mandal, head of department of biology, Lady Brabourne College, and Tamal Chakraborty who is a research student at Vidyasagar University.

“We have been conducting field studies in the coasts of Odisha and Bengal from 2008 to 2013,” says Amal Kumar Mandal. The plant Ipomoea pes-caprae pushes its roots down to 6ft below the earth and spreads them like a net. They act as a natural guard against soil erosion. That is why they are called sand-binding plants,” he adds.

“Mindless construction of houses and hotels is killing these plants. It is speeding soil erosion. These plants have practically disappeared from Digha and Shankarpur. The illegal construction at Mandarmani has also killed these plants,” says Amal Kumar Mandal.

“In addition, cattle try to eat these plants. The insects fight them. The secretions of these plants are food for them. The insects come in huge numbers together to have them at the time of the secretions. The secretions also take place when the plants are under attack from cattle. The insects attack them back. The cattle are forced to flee. This is called ‘defence mechanism mutualism’,” says the researcher.

“The secretion from these plants is known as extra-floral nectarines. These contain carbohydrates, amino acids and some more complexes, which attract the insects. No one has researched in our country the co-habitation of plants and ants and insects due to this,” says Amal Kumar Mandal.

In 2006, the then Digha-Shankarpur Development Authority chairperson, who had earlier been the Vidyasagar University vice-chancellor, Anandadeb Mukhopadhyay, had issued the same warning.

Mukhopadhyay, an oceanographer, had said that these plants were essential to the life of the coast. Three steps were taken under his guidance to stop the erosion of coastlines: placement of boulders between the coast and the water to lessen the intensity of the waves; protection of the ipomoea pes-caprae and plantation of jhau trees on the coast to cut down the force of the wind. But these measures were not followed up.

“Since 2006, the number of hotels in Mandarmai has increased by 60 per cent to 70 per cent. The number of tourists has gone up. So the ecology here is losing its balance increasingly. Business runs on the principle of who can build closest to the sea,” says Amal Kumar Mandal.

The February issue of the Indian Journal of Geo-Marine Science, a publication of the Council of Scientific and Industrial Research under the Union HRD ministry, had for its theme the impact of climate change in the Indian Ocean.

The team was informed of the UGC grant on March 5.

“Now we will intensify the research,” says Amal Kumar Mandal.

“We may come to know of more such mutually beneficial relationships between plants and insects. We can reach our findings to those who work on protecting the environment. We can find an easy, cheap and natural barrier against the erosion of the coast,” he adds.

Says vice-chancellor of Vidyasagar University Ranjan Chakravorty: “This research has made us proud and will benefit the entire country.”