Nectar sources of stingless bees (<i>Tetragonula pagdeni</i> Schwarz) in southern West Bengal, India assessed through pollen analysis of honey and field surveys

Understanding nectar sources is essential for sustainable meliponiculture involving Tetragonula pagdeni; yet, information on the nectariferous plants utilised by this stingless bee species remains limited. We conducted pollen analysis of honey samples (n = 54) in conjunction with direct field surveys (n = 864) to identify the nectar sources of Tetragonula pagdeni in West Bengal, India. Quantitative pollen analysis revealed that the honey contained 59,821.04 ± 40,698 pollen grains per 10 g of honey, most of which belonged to class II, containing 20,000–100,000 pollen grains per 10 g of honey. Qualitative analysis identified 96 pollen types (94 at the species level), mostly from nectariferous plants (n = 87) and only a few (here, n = 7) from non-nectariferous plants. The most represented plant families were Asteraceae, Anacardiaceae, Cucurbitaceae, Euphorbiaceae, Fabaceae, Lamiaceae, Malvaceae, Myrtaceae, and Rutaceae. Among the analysed honey samples, 10 (18.52%) had predominant pollen types (i.e. unifloral). The predominant pollen types in the honey samples were Borassus flabellifer, Brassica juncea, Cocos nucifera, Coriandrum sativum, Eucalyptus tereticornis, and Lannea coromandelica. Other frequently occurring pollen types included Acacia auriculiformis, Alangium salviifolium, Allium cepa, Momordica charantia, Moringa oleifera, Mikania micrantha, Phoenix sylvestris, Spondias pinnata, and Ziziphus mauritiana. The diversity of pollen types varied seasonally, with higher values during summer and monsoon, but relatively lower in late autumn. Additionally, field observations identified eight more nectariferous plant species that the bees visited. Based on the characteristics of bee-visited plants, Tetragonula pagdeni was characterised as a generalist forager, collecting nectar from a wide variety of floral types. This study shows that combining melissopalynology with field surveys is more effective than using either method alone for accurately identifying bee nectar sources, and it provides important insights for sustainable meliponiculture and the conservation of this stingless bee species.