Spatial and temporal variation of floral visitors and their visitation pattern on Acanthus ilicifolius L.: A case study from the Indian Sundarbans

Abstract Acanthus ilicifolius is a spiny semi-woody evergreen shrub which is one of the most dominant mangrove associate species. Although its floral biology is well documented, there is not enough systematic study of floral visitors of this species. Successful plant reproduction is highly dependent on plant-pollinator interaction. The present study aims to understand the range of floral visitors of A. ilicifolius and their spatio-temporal variation in visitation pattern from the Indian Sundarbans. This study was conducted in five islands of Sundarbans Biosphere Reserve (SBR), namely, Bali, Gosaba, Satjelia, Gangasagar and Bakkhali during 2015 and 2016. Fifteen flower visitors under five taxonomic orders, i.e., Hymenoptera, Coleoptera, Diptera, Lepidoptera and Passeriformes were identified. Seven out of these fifteen species were reported for the first time as floral visitor of A. ilicifolius. Order Hymenoptera was the most frequent insect group, whereas Apis mellifera of this order was the predominant flower visitor. Although Gangasagar and Bakkhali being tourist spots, face greater anthropogenic interference, they had the highest abundance of floral visitors. A significant variation in floral visitor abundance was observed across different time of the day throughout the study period. Floral visitors were most abundant in the morning between 8 a.m. to 12 p.m. This study provides the first comprehensive report of diversity and abundance of the floral visitors and their visitation pattern on A. ilicifolius. Implications for insect conservation: Proper documentation of the ecology of insect pollinators would automatically help to conserve the plants along with the insects, and thus preserve the entire mangrove ecosystem of the Sundarbans as well as mangroves around the world.