Diversity of arthropod pollinators, foraging parameters of major bee species and the role of entomophily in sunflower (Helianthus annus L.) pollination

Abstract

Assessment of pollinator community, foraging behavior and pollination efficiency is essential for improving sunflower yield and optimizing crop and pollinator management. The experiment was carried out in a farmer’s field located at Bhayna village, West Bengal, India to study the pollinator community and its role in sunflower pollination. Field trials were conducted to study the abundance and diversity of pollinators. The foraging pattern was recorded at 08:00, 10:00, 12:00, 14:00, 16:00, and 18:00 h. The pollination efficiency index, a composite measure of pollinator abundance, visitation rate, flower handling time, and pollen load was assessed to understand the pollination effectiveness of individual bee pollinators. The effects of hand pollination, open pollination, combined hand and open pollination, and pollinator exclusion on sunflower yield were also assessed. Results showed that, among the insect pollinators, Apis dorsata was most abundant (27.46%) followed by Apis mellifera (24.99%), Halictus acrocephalus (11.94%) and Xylocopa fenestrata (7.04%). Maximum abundances of Apis dorsata (31.16%), Halictus acrocephalus (15.99%) and Xylocopa fenestrata (10.46%) were recorded at 10:00 h while maximum abundance of Apis mellifera (31.97%) was recorded at 16:00 h. Maximum pollinator diversity (Shannon Weiner index-2.41 and Simpson’s index-0.85) occurred at 10:00 h. Maximum foraging activity of Apis dorsata (2.33 bees/head/minute), Halictus acrocephalus (1.29) and Xylocopa fenestrata (1.00) were recorded at 10:00 h while maximum foraging activity of Apis mellifera recorded (1.97) at 16:00 h. Maximum foraging rate (flowers visited/minute) of the bees were recorded at 10:00 h, where, Apis mellifera showed maximum foraging rate (10.37) followed by Xylocopa fenestrata (8.34), Apis dorsata (6.46) and Halictus acrocephalous (3.38). Maximum time spent by Apis dorsata (36.68 s) followed by Apis mellifera (28.54 s), Xylocopa fenestrata (22.37 s) and Halictus acrocephalus (13.23 s) on the sunflower capitula. Each Xylocopa fenestrata bee carried the highest number of pollen grains (298,000), followed by Apis dorsata (182,000), Apis mellifera (153,000), and Halictus acrocephalus (138,000). Highest pollination efficiency index was recorded in Apis dorsata (42.57), followed by Apis mellifera (39.53), Xylocopa fenestrata (14.67), and Halictus acrocephalus (9.91). Maximum yield (14.25 q/ha), other yield attributing characters and germination (%) were recorded for hand and open pollination followed by open pollination and hand pollination only.