Expansion of the conservation toolkit: using seed provenance diversity to support durability of bumble bee (Bombus spp.) resources

Bumble bees (Bombus spp.) are valuable pollinators of wild and cultivated plants. Many bumble bee species have been in decline in recent decades, threatening this ecosystem service. Conservation efforts commonly focus on mitigating habitat loss by creating and enhancing native plantings. Typically, a two-dimensional approach of increasing flower species diversity and quantity is used to bolster the supply of nectar and pollen resources available to bumble bees. In this study, we explore a third dimension of resources: plant provenance. Seeds from 6 native flower species were collected from northern, central, and southern Missouri and planted in a common garden in central Missouri. We examined the effects of seed source on the timing and availability of nectar and pollen resources in addition to bumble bee visitation to flowers weekly during the summer months. We found that provenance affected peak blooming times of some species; for example, peak bloom for swamp milkweed (Asclepias incarnata) plants grown from seed collected in southern MO was 3-4 weeks earlier than with seed collected from central or northern MO. Bumble bee visitation of flowers tracked bloom phenology and peaked at different times depending on the provenance. These results suggest that increasing provenance diversity provides an extended bloom period and more stable nectar and pollen resources for bumble bees than any one provenance alone. The findings point toward the possibility of leaning into this three-dimensional approach of diversity, provenance, and quantity to strengthen ongoing conservation efforts and further stabilize resources for bumble bees in the summer season.