Agriculture scientists warn that the killing spree by 'scale insects' — tiny red bugs — has assumed endemic proportions with one in 10 trees already infected or in the vulnerable zone. This will not only affect biodiversity, but also alter the micro-climate as the absence of so many shade-bearing trees will lead to an increase in temperature and decline in rainfall. In summers, the day-time temperature difference under the sun and below a rein (sirish) tree can be as high as 5 degrees Celsius in just 15 minutes.
"Lac insect, possibly Kerria lacca, has led to a large number of tree deaths in and around Kolkata. They have a voracious appetite and multiply to reach mammoth proportions in a few days," Santanu Jha of Bidhan Chandra Krishi Viswavidyalaya (BCKV) told TOI after studying samples of infected tree branches.
Plants used for avenue plantation like sirish, peepal, gulmohur, arjun and palash are vulnerable to lac attacks as they are natural hosts of these insects — much like pigs are to Japanese encephalitis virus. Jha suspects that rise in Kolkata's ambient temperature fuelled the attacks. There have been reports of similar insect attacks from other metros but none have killed so many.
According to Jha, the insects latch on to the stem and leaves, and begin sucking the sap. As the army of lac insects multiplies, it practically sucks out all the nutrients, leaving the tree dry and very ill. The insects also drop honey dew that encourages fungus and drives the infected tree to death. Sirish is the worst hit, accounting for nearly 60% of dead trees. These trees — Albizia saman — are the only species of rein alive in Kolkata. With the bug invasion growing more menacing, the entire rein tree population in the city and suburbs faces a wipeout. Most of the rein trees have disappeared from VIP Road, Bagmari, Rabindra Sarobar and Barasat. Other species like gulmohur and peepal are now under attack.
Can anything be done to stop the invasion? "Yes," says Samir Santra, a green activist from West Midnapore, who has saved several trees by using an unusual treatment protocol that involves cutting off the infected parts, spraying poison to prevent its spread and then applying vitamins to rejuvenate the uninfected section. "Management of plantations through scientific pruning, followed by application of granular insecticides in the soil, and, if required, through application of certain safer insecticides with fumigation may help," he said.
Then why hasn't Kolkata Municipal Corporation or any other civic body tried to stem the rot? Santra says vested interests have prevented an action plan that could have saved more than 1,000 trees. According to sources, KMC's reluctance is due to a powerful nexus at work to procure lac-infected trees to extract commercial lac. The going rate for each tree is Rs 1-1.5 lakh. Lac is the scarlet resinous secretion of a number of species of lac insects, of which the most commonly cultivated species is Kerria lacca.
Santra does not rule out the involvement of the 'lac mafia' in deliberately infecting trees to procure more lac. "All that one needs to do is get a stick (broodlac) that contains eggs ready to hatch and tie it to a healthy tree. Thousands of lac insects will colonize the branches of the host tree and secrete the resinous pigment that is processed to produce lac," he pointed out.
In recent times, the value of infected trees has shot up following a spurt in demand for Kerria lacca in cancer drug research. At Rabindra Sarobar, morning walker Debjani Ghosh recalled how several trees were hacked down by a contractor last year. "He showed us the Kolkata Improvement Trust order that he had bagged after paying Rs 4 lakh. Though only the infected branches were cut initially, the rest of the tree got affected and died as well," Ghosh said.
(With inputs from Saikat Ray & Ashis Poddar)
http://timesofindia.indiatimes.com/followceleb.cms?alias=scale insects,Samir Santra,Kolkata Municipal Corporation,Kolkata Improvement Trust,Kerria lacca
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