Attraction of Bees to Native and Introduced Willows (Salix spp.)

Introduced willows have mostly been employed as a renewable feedstock for bioenergy in the northeastern USA. The question of whether introduced willows provide the same biodiversity value and attractiveness as native willows has not yet been explored. The objective of this study was to compare the attractiveness of native and introduced willows to different subfamilies of bees. The common garden experiment planted at Storrs, CT, USA, included three native (S. eriocephala, S. sericea, S. lucida) and three introduced (S. 'SX64', S. 'Onondaga', S. 'S365') willows. Various willow taxa flowered at different times through spring, allowing pollinators to be collected over a 6-week period using colored bowl traps. As a result, 2430 bees were collected and identified to the subfamily level. Andreninae was the most prevalent pollinator visiting all taxa of willows, followed by Hylaeinae and Colletinae. There were no significant differences in the number of pollinators collected from either native or introduced taxa during the progressive willow flowering during mid-March-May of 2021 and 2022, suggesting their equal attractiveness to pollinators. Similarly, during the concurrent flowering of the two native and two introduced taxa, there were no significant differences in the number of pollinators associated with either group suggesting that when pollinators had foraging choices, they were similarly attracted to both native and introduced willows. The overall finding of this study suggested that plantings of either native or introduced willows to meet bioenergy goals offer similar benefits of floral resources for pollinators.