Annual assessment of mangrove defoliation by Hyblaea puera (Cramer, 1777) around Thane Creek, India using field observations and Sentinel-2 imagery from 2018 to 2022

Abstract

Mangroves are salt-tolerant trees thriving in coastal and brackish waters, adapting to harsh conditions with features like aerial roots and salt filtering. Out of 64 global mangrove species, 11 are endangered. In Maharashtra, mangroves are concentrated around Mumbai, with an estimated 54.5 square kilometers in Thane Creek, where Avicennia marina shows signs of infestation. This current research used Sentinel-2 data from 2018 to 2022 to assess defoliation caused by Hyblaea puera, the teak defoliator. Ground-truth observations from 2020 to 2022 confirmed the extent of defoliation and identified varying infestation levels categorized as very highly infested, highly infested, moderately infested, low infested, very low infested, and uninfested. NDVI analysis examined these levels in relation to meteorological factors such as rainfall, temperature, humidity, and wind speed. The analysis revealed an extended peak infestation both spatially and temporally, along with severe defoliation during the study period. Six categorical infestation hotspots were identified and compared with meteorological parameters, revealing that Hyblaea outbreaks were more common during low wind speeds and moderate temperatures, with peak infestations occurring after heavy rainfall and under moderate relative humidity. The study suggests further research to explore outbreak causes, insect preferences for specific mangrove species, and the broader implications of defoliation.