Insect pollinators are important means for a stable ecosystem. The habitat types play a crucial role in the community composition, abundance, diversity, and species richness of the pollinators. The present study in Shivapuri-Nagarjun National Park explored the species richness and abundances of insect pollinators in four different habitats and different environmental variables in determining the community composition of the pollinators. Data were collected from 1500 m–2700 m using colour pan traps and hand sweeping methods. Non-metric multidimensional scaling (NMDS) and redundancy analysis (RDA) were conducted to show the association between insect pollinators and environmental variables. The results firmly demonstrated that species richness and abundances were higher in open trail compared to other habitats. The distribution of the pollinator species was more uniform in the open trail followed by the grassland. Similarly, a strong positive correlation between flower resources and pollinator's abundance was found. In conclusion, the open trail harbours rich insect pollinators in lower elevation. The community structure of the pollinators was strongly influenced by the presence of flowers in the trails.

Insect Pollinator sampling

The survey was performed in the spring and autumn seasons for the consecutive years 2018 and 2019. In each season, the pollinators were sampled for 3 consecutive days in sunny weather between 9 am to 4 pm (Pollard and Yates, 1994). The pollinators were collected by using hand sweeping and color pans. White, Yellow, and blue color pans were used for insect sampling. During each sampling day, a transect walk of 30 minutes was done along the 100 m of the trail in the open trail of the forest, forest trail, and trails of the managed habitat, while in grassland the transect walk was made in the edge and the middle (Stanley, 2013). The transect walk method was used to sample butterflies (Pollard & Yates, 1994), bumblebees (Fussell and Corbet, 1992), hoverflies, and other bees (Proesmans et al., 2019). During the walk, insect pollinators that were feeding on flowers within 2m of the observer were captured, identified, and released (Sutherland, 1996). In the case of the butterfly, they were observed and identified during flight and basking within the line transect. Unidentified insect pollinators were collected in separate vials, transferred in the icebox, and brought to the lab for identifications.

Pan traps were deployed in each transect. This method aided in simultaneous sampling multiple locations, coverage of a large number of sites, and is the efficient method of bee sampling (Westphal et al., 2008; Neilsen et al., 2011). The pans were plastic bowls of about 15 cm diameter and painted with non–toxic three different colors; white, yellow, and blue (LeBuhn et al., 2003). Each pan was attached to a post using a metal clamp adjusting bowl the rim. The pan was filled with about 400ml of detergent water. Three posts were deployed in 100 m distance and 20m apart from each other. The traps were visited for collecting the fallen insects after 24 hours and were transferred in labelled vials with 70% ethanol.

All the insect pollinators were identified to species level in the laboratory using relevant keys from adjacent regions. Bingham, 1897; Tadauchi & Matsumura, 2007; Williams et al., 2010; Imran et al., 2016; Aslam et al., 2017; Ngat et al., 2017, and Kumari et al., 2018 for bee specimens. Brunetti, 1923; Ghorpadé, 1994, 2016; Claussen & Weipert, 2003; Subhan, 2016; Sengupta et al., 2017; Hassan et al., 2019, 2020; Sankararaman et al., 2020 for hoverflies and Smith, 2011 for butterflies specimen’s identification.

Flower Survey

The flower survey was carried out in the spring and autumn season during the pollinator survey in the same transect. We made five quadrates of 10 m X 5 m in each sampling transect. For estimation of flower resource abundance, we scanned insect pollinating herbs and shrubs in each quadrate and identified genus and species levels. The cover of floral resources in each quadrate was ranked between 1– 6 (Szigeti et al., 2016). Rank 1 indicates very scarce, 2 for scarce, 3 for more or less scarce, 4 for more or less abundance, 5 for abundance, and 6 indicates extremely abundance. The flower resource abundance for each sampling transect was calculated as FLOWER= i=1 n t.taxon i ( t =mean of the rank of flowering plant of each transect).