Chronic problem: Bugs in Mumbai's once-lush rain trees

  • Riddhi Doshi, Hindustan Times, Mumbai
  • Updated: Nov 09, 2014 18:15 IST

You’ve probably seen at least one or two casualties in your neighbourhood — giant beauties with their branches stretching to the sky, dry and leafless, the bark covered in clumps of white parasites.

Those parasites are mealybugs. Usually found on fruit-bearing trees, they are known to attack the weak, multiplying rapidly and sucking the sap till the once-lush canopy of the host is completely dry.

Over the past two-and-a-half years, the mealybugs have attacked 500 of Mumbai's 5,000 rain trees, killing 238, according to the Brihanmumbai Municipal Corporation.

Experts say that figure could be five times that.

“There are long stretches of road in areas across the city where clumps of 10 to 15 trees stand shrivelled and dead,” says D Stalin of Vanashakti, an NGO that is currently conducting a study of the mealybug infestation in rain trees in association with the botany department of Ramniranjan Jhunjhunwala College.

The odd thing is, mealybugs do not typically attack rain trees. So why has this become such a chronic problem in Mumbai?

Botanists and horticulturists attribute it to a combination of factors — including concretisation, changing climate and higher temperatures.

“There is just one previous instance of mealybug infestation in rain trees in the city, in the mid-1990s. It wasn’t severe and the rains that year washed out the bugs,” says horticulturist VK Ogale, former head of the Molecular Biology and Agriculture Division at the Bhabha Atomic Research Centre. “This time it’s quite serious. Unusually high temperatures after the rainy season revived the bugs. What’s worse, the bugs are preying on a rain tree population whose immunity has already been weakened, and the bugs are thriving.”

The trees’ immunity has been reduced over five to seven years by the concretisation of the areas around them, particularly their drip areas — the space directly beneath the canopy.

“Normally, water drips to the ground from the canopy and is taken in as food and nutrition by the tree’s roots. With the soil under these large tree replaced by layers of cement, tar, or paver blocks, the roots are not getting enough water and air. This hinders photosynthesis and weakens the tree,” says Ogale.

It was concerned residents and environmentalists that first raised the alarm about the shrivelling of their once-lush rain trees.

In 2010, the first instances were reported in Kandivli. “We then though it was a mild infestation,” said an official from the BMC garden’s department, speaking on condition of anonymity. By September 2013, when a healthy monsoon failed to wash away the bugs and many trees were found shrivelled and dead in the city, Vanashakti tied up with Jhunjhunwala college to study the issue and try to find a way to save the trees.

“We geotagged and studied 1,700 rain trees across the city and found that rain trees in gardens and areas with enough soil were unaffected by the mealybugs because they were healthy and able to fight the infestation,” says Stalin. Think of it like the recent cases of dengue, adds Ogale of the BARC. “Not everyone living in an area with dengue-carrying mosquitoes will suffer from the disease. It is the ones with weak immunity that will. It’s the same with the rain trees and mealybugs,” Ogale says.

In some cases, the mealybugs are also feasting on old trees that are weak because they are at the end of their life cycle, adds Avinash Kubal, an expert in forestry and deputy director of the Maharashtra Nature Park.

“However, the concretisation is quickening their death and allowing mealybugs to take root in the weakened, aged trees,” Kubal adds.

Fighting for their lives

It is not just the surviving rain trees but also trees of other species in the city that are under threat of being similarly ruined, says Usha Mukandan, head of the department of botany at Ramniranjan Jhunjhunwala College. “The good thing is that the damage caused, though grave, is reversible in some cases, although I fear that we have very little time.”

One way to reverse the damage is to strengthen the trees’ immunity by de-concretising a radius of 6 ft around the trunk, add layers of soil to it and water the area regularly until the monsoon. Meanwhile, experts such as Ogale say ladybug beetles can be used as an antidote, since they eat mealybugs. This is a slightly more expensive proposition, since the beetles must be procured from the National Bureau of Agricultural Insect Resources in Bangalore at a cost of Rs 2 each, and 100 to 200 of the bugs are required per tree.

For now, Vanashakti has procured an organic pesticide which the municipal corporation has sprayed on 15 infested rain trees in Khar to test its effectiveness.

“We are hoping that this spray will slow down or stall the mealybugs,” says Stalin. “But it will not solve the problem of how the growing concrete cover is weakening the trees.”

A people’s movement

Meanwhile, residents have launched their own initiatives to try and save their rain trees. Rishi Aggarwal, a fellow at urban planning thinktank Observer Research Foundation and a resident of Anushakti Nagar in Chembur, launched a people’s initiative titled Mumbai Trees on Facebook. It was on this platform, in fact, that the problem was highlighted in May 2011, when people began to post about the sudden disappearing green canopies outside their windows.

In December 2013, IT professional Kshitij Ashtekar, 30, a resident of Goregoan, designed a free app called Rain Tree to help people report rain tree causalities across the city. The app enabled everyone to see the exact location of all the reported trees and share details on the extent of the damage.

“The idea was to gauge the extent of the problem,” says Ashtekar. “It was used to plot 650 affected trees in Goregoan and Malad. I presented the app and the collected data to BMC authorities in January 2013 but never heard back. Of the 650 we reported, 500 are now dead.”

Around the same time, NGO Vanashakti approached the National Bureau of Agricultural Insect Resources (NBAIR) for help. “It was NBAIR that first suggested the ladybug beetles,” says Stalin. “We bought a total of 1,000 beetles, costing Rs 2 each, from our own NGO funds, and sprayed them on to 10 trees.”

Ashtekar also procured a few beetles and tried to spread them on trees himself. “I sought permission from flat owners to go to their balconies and spread the bugs. I also climbed bridges to do the same,” he says. “But I was fighting a losing battle. Only the BMC has the infrastructure and resources necessary for the task.”

Meanwhile, near the Andheri Sports Complex, a citizens’ group repeatedly petitioned the BMC to save their infested trees. “We finally gave up when they told us the trees were too close to the road and spraying ladybug beetles could cause problems to people,” says Vijay Kulkarni, 62, a retired engineer. “By May this year, 19 trees were dead. We have managed to get 10 saplings of native trees from the BMC. We are waiting for more.”

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