Floral Characteristics Alter the Abundance and Richness of Bees Captured in Passive Traps

Bees are vital pollinators that maintain plant populations by transporting pollen among individuals; however, bees are declining, and information on how habitat characteristics alter the catch of bees in traps is needed to better assess monitoring. Few studies have measured how catch in passive traps may be altered by floral resources despite the well-known dependence of pollinators on forbs. We investigated the degree to which pollinating insects were attracted to vane traps and bee bowls placed at sites that varied in flower densities (0–800 flowers/m2). We also assessed if the catch of bees was better explained by flower characteristics directly around traps (subsite) or average flower characteristics at a site. Floral density, richness and surface area were measured in 1 m2 quadrats at each subsite. The surface area of flowers explained more variance in bees captured compared to the density or richness of flowers. Traps placed in areas with lower flower surface area captured the more bees and a more diverse sample. Floral resources at the subsite and site explained a similar amount of variance in the number of bees captured, suggesting that pollinators respond to flowers at both scales. We provide a method of correcting pollinator abundance by flower surface area to make catch in passive traps more comparable among areas. We can select sites that minimize or maximize the catch of bees by understanding how floral resources change the effectiveness of passive traps.