An entire mangrove patch in Airoli was visibly dry on Saturday owing to an attack by the teak defoliator moth — Hyblaea puera. Every year, evergreen mangrove forests in the Mumbai Metropolitan Region (MMR), which should ideally flourish during post-monsoon months, wear a dry, skeletal look owing to certain defoliating pests feeding on leaves and barks. This year, however, Rthe phenomenon has happened unusually early. The state mangrove cell is investigating the reasons for this.

Scientists have discovered a direct correlation between the depth of rainfall over the town and annual pest assaults on mangroves, whereas indicating that the infestation was highest at mangrove forests within the Mumbai Metropolitan Region (MMR), for any coastal space.

The Institute of Wood Sciences and Technology (IWST), Bengaluru, submitted its ultimate report suggesting options for the annual invasion to the state mangrove cell final week after finding out the phenomenon for the previous three years.

“We found the intensity of the infestation varies every year and depends directly on the amount of rainfall received by the city during monsoon. Heavier the rains, worse the infestation,” stated R Raja Rishi, principal investigator of the venture, IWST.

The examine documented that the town obtained 2,239.6mm rain in 2018, lesser than the annual common, which noticed remoted incidents of the pest assault. In comparability, 3,670.4mm in 2019 (46% extra rain than the annual common) led to very excessive incidents of infestation.

“Pest attacks have been reported from mangrove forests across the Indian coastline, but the intensity and scale have been the highest in the MMR region. This is because the attack starts in the teak trees at Sanjay Gandhi National Park (SGNP) and surrounding territorial forests during summer and pre-monsoon, which is the primary host area. Whenever the climate is ideal [more rainfall], these pests move to mangrove forests within the region. By late October-November, they go back to the teak trees at SGNP, completing their lifecycle,” stated Rishi, including that availability of extra moisture and rain makes circumstances beneficial for his or her motion to mangrove timber. “However, a more in-depth study is needed to understand their movement vis-à-vis climate parameters,” he stated.

The report listed natural options in addition to a pesticide to make sure mangrove timber are rid of 5 main pests amongst 20, led by the Hyblaea Purea moth.

“We have suggested the use of a botanical bio-pesticide Hy-Act that has been successful in reducing infestation of the identified pests. It has been developed by the Institute of Forest Genetics and Tree Breeding in Coimbatore and is not commercially available. Other natural measures include using neem-based solutions [neem oil] to control these defoliating pests,” stated Rishi.

However, the examine concluded with a caveat that extra analysis was wanted, whether or not to regulate this annual pest outbreak or depart it as is. “Owing to several beneficial and positive impacts on the ecosystem through contribution to the nutrient cycle and food chain [enhance fishery resources or food source for birds], we must examine whether this natural process should be interfered with or conserved,” stated Rishi.

To get a greater concept about this phenomenon, the state mangrove cell in 2017 appointed IWST to check this phenomenon and counsel measures to regulate the infestation. With 25 discipline surveys carried out between 2017 and 2019, scientists collected samples of affected leaves, barks and the pest species from 4 mangrove forests in Airoli, Ghansoli, Gothivali, and Gorai. They carried out native experiments and assessed damages via laboratory research. In all, six species of caterpillars, 5 species of grasshoppers, two species every of semi loopers, snails and weevils, and one every of leaf miner, skeletonizer and bagworm had been recognized as defoliating pests affecting 5 completely different mangrove species. “Of these, the Hyblaea Purea moth was most threatening to mangrove trees, along with two similar moths and two snails,” stated Rishi.

The mangrove cell stated that some mangrove areas are already witnessing recent inexperienced cowl since rainfall lowered throughout the first week of October.

“Implementing the bio-pesticide on such a large scale is very difficult and may not be cost-effective at this moment,” stated Virendra Tiwari, extra principal chief conservator of forest (mangrove cell). “Even in the teak trees in forest areas in interior Maharashtra where Hyblaea Purea infestation is there, pesticide spraying is not done. To spray the entire mangrove forests is not practical,” he added.

However, Tiwari defined that if some mangroves confirmed extraordinarily poor survival charge or their immune system had weakened and pest assaults had been occurring too continuously, the cell could think about experimenting with this answer in small patches. “At least now we know this is happening and in most cases, mangroves mostly recover,” he stated.


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