How bumblebees handle flowers of complex morphologies

Foraging bees expend considerable time and energy handling flowers that are morphologically complex whilst flowers with readily available rewards bloom simultaneously in their foraging environment. We studied Bombus terrestris workers in flight-room experiments to elucidate the behavioral mechanisms that allow their persistence on complex flowers. Firstly, using real flowers, we investigated how the bumblebees’ .foraging choices and success vary along a floral complexity gradient and with prior experience. Intact flowers of Tecoma x ‘Orange Jubilee’, Antirrhinum majus and Lupinus pilosus represented a gradient of increasing morphological complexity. We manipulated some flowers of each species to look simple with readily accessible food rewards, and allowed a single forager to choose between simplified and intact flowers of identical reward, color and odour. 60% of naïve foragers chose a complex flower on their first visit in all of the flower species. Experienced bees visited complex flower types in all three species, but their foraging efficiency decreased with increasing floral complexity. These results suggest that inexperienced foragers and unsuccessful feeding attempts increasingly contribute to floral pollination along the morphological complexity gradient. Next, using robotic flowers, we examined whether experience with a flower morphology (simple or complex) primes the bees’ preference for similar such additional morphologies. Priming on complex flowers, especially when they were highly rewarding, resulted in increased visitation to novel complex morphologies. From the plants’ eye view, this points out the potential of pollination facilitation between plants with similar floral morphologies.