Flower Nectar Sources of Leafcutter Bees (Megachile spp.; Megachilidae) in West Bengal, India: Patterns of Foraging Niche Overlap and Resource Partitioning

Leafcutter bees (Megachile spp.) are important pollinators, yet their nectar-foraging patterns and resource partitioning remain poorly understood in eastern India. This study investigated nectar sources, seasonal variation in floral resource use, foraging niche overlap, and resource partitioning among four leafcutter bee species, Megachile disjuncta, Megachile lanata, Megachile lerma, and Megachile umbripennis, in West Bengal, India. Across all species, 40 nectariferous plant species belonging to 16 families were recorded, with Fabaceae being the most important family, followed by Asteraceae and Cucurbitaceae. The principal nectar sources included Cajanus cajan, Crotalaria juncea, Luffa acutangula, Luffa aegyptiaca and Peltophorum pterocarpum. Nectar-resource diversity varied seasonally, with the greatest number and diversity of plants recorded during summer and monsoon and the lowest during late autumn. No significant interspecific differences were detected in the number, diversity, or evenness of nectar resources. Community-level nectar-foraging niche overlap varied significantly among seasons, with relatively high overlap from monsoon to winter and lower overlap in spring. Individual trait-level (viz., flower, inflorescence, and plant) foraging niche overlap remained lower than community-level assessment values. Niche overlap declined from the individual-plant to the inflorescence and flower levels, whereas resource partitioning increased at finer spatial scales (highest at the flower-level assessment). Foraging resource partitioning also varied plant species-wise. Temporal partitioning was comparatively weak. These findings indicate that the four Megachile species share a broad floral resource base but coexist primarily through fine-scale spatial differentiation in flower and inflorescence use. Maintaining diverse and seasonally continuous flowering vegetation is therefore important for conserving leafcutter bee communities in West Bengal.