Honey bee foraging density depends on plant size.

The spatial distribution of flowers has important impacts on pollinator movement and foraging decisions. For example, it is well established that bumble bees typically visit larger plants at a higher rate per plant, but the visit rate per flower typically declines as the number of flowers increases. However, much less is known about how honey bee foraging patterns are influenced by plant size and flower number, despite honey bees' importance as agricultural pollinators and their strong competitive impact on other bees. Using a combination of field observations and manipulative experiments with two different wild plant species, we confirmed that honey bees visit larger plants at a higher rate, not only per plant but also per inflorescence. This foraging pattern seems surprising, because it means that there is greater forager density and thus competition for resources on larger plants. We examine three hypotheses to explain why honey bees might nevertheless preferentially visit floral resources on larger plants: (1) larger plants are more salient, making them easier to find and advertise; (2) larger plants offer greater nectar rewards, making visits to them more worthwhile; (3) larger plants have more densely packed flowers, so they are less costly to navigate. We found that honey bee visit rates were indeed influenced by the costs and rewards of their local foraging experience, but the total number of flowers on the plant still positively affected visit rate even when controlling for those local factors. We suggest several ways that the collective foraging strategy of honey bees could lead to an aggregation of foragers on plants with more flowers and discuss the potential implications for agricultural pollination and wild bee conservation as well as foraging theory. • Honey bee visits/inflorescence were higher for large plants than for small plants. • Honey bees' focus on larger plants may stem from their collective foraging strategy. • Prior work has shown that bumble bee visits/flower typically decrease with plant size. • Variation in plant size may reduce competition between honey bees and native bees. [ABSTRACT FROM AUTHOR]