Pest attack on Mumbai’s mangrove forests unusually early this year: Forest department

Evergreen mangrove forests in the Mumbai Metropolitan Region (MMR) that normally flourish during the post-monsoon months have been wearing a dry, and skeletal look. Experts have blamed certain defoliating pests–snails, caterpillars, grasshoppers–among the reasons for it.

The pests during their larval stage feed mainly on leaves and sometimes mangrove tree barks. They consume chlorophyll, which is an essential pigment for photosynthesis, the process plants use to make food. This makes these trees appear dry. Experts said it will take a little over a week for these trees to replenish and the pests to move away from these forests.

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Deputy conservator of forest (Mangrove Cell) Neenu Somraj said they are noticing something unusual this year possibly because of changes in the weather patterns, moisture availability, and intense rainfall over the past two months. “…the teak defoliator moth Hyblaea puera, in its caterpillar form, has been observed along with other pests…[and] swarmed several mangrove forests much before the actual phase post-monsoon. We have asked all our forest officers to report changes in their respective jurisdictions to assess the impact so far this year.”

Environmentalist Nandkumar Pawar said a four-acre mangrove patch has dried up. “Mangrove trees in these areas have turned brown suddenly. We must investigate whether there is any foul play involved.”

Somraj said they are aware of the patches affected by the defoliator pests. “Similar examples have been witnessed along with the western suburb creek areas as well. These pests are targeting the Avicennia Marina or the grey mangrove–a fruiting plant with dark green leaves– the most dominant species along the Maharashtra coast,” she said. “We cannot spray pesticides because they might damage the trees permanently and also leak into the creek.”

The Mangrove Cell in 2018 roped in experts from Bengaluru’s Institute of Wood Science and Technology (IWST) to study this phenomenon and suggest measures to control the infestation. They studied mangrove forests in Airoli, Ghansoli, and along the Thane-Vashi creeks between 2018 and 2019.

According to their interim report released last year, six species of caterpillars, five species of grasshoppers, two species each of semi loopers, snails and weevils, and one each of leaf miner, skeletonizer, and bagworm were identified as defoliating pests affecting five different mangrove species. While the experts were supposed to submit their final report this year, the Mangrove Cell extended their scope of the study.

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“As of now, we have suggested only organic solutions. Owing to the Covid-19 pandemic, our research is slightly delayed but a detailed list of guidelines to address this will be shared, which can be implemented from 2021 onwards,” said an IWST scientist, requesting anonymity.

Similar infestations have been observed in mangrove forests in Honk Kong (1995), Rio de Janeiro, Brazil (2001), Ecuador (2008), and Indonesia (2019). They were either treated using pesticides or allowed natural regeneration.

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