“Bees without flowers: Before peak bloom, diverse native bees find insect-produced honeydew sugars”

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Joan M. Meiners, Terry L. Griswold, David J. Harris, and S. K. Morgan Ernest

What do bees do when they don't have flowers? Forty-two species of wild bees can find insect honeydew sugars on a stick!

Bees without flowers: How bees find honeydew sugars

Therese Lamperty (left) and Joan Meiners (right) sampling for bees at Pinnacles National Monument in 2012. Pinnacles became a National Monument in 1908 and a National Park in 2013.
(Credit: Pete Lamperty)

What do bees do when flowers are few? They find invisible honeydew. While studying bee biodiversity at California’s Pinnacles National Park, researchers from the University of Florida and the USDA at Utah State University discovered native, solitary bees foraging on sugars from insect-produced “honeydew” during the low-bloom early spring. Honeydew sugars, which are excreted by plant-feeding insects like aphids and scales, are similar in content and concentration to floral nectar but have no inherent scent or visual signal. Mutualistic relationships between honeydew producers and ants are well known. Use of honeydew across a native bee community, however, had never been evaluated despite its potential as an emergency food to tide over bees facing degraded habitats or delayed bloom.

Native bee (Andrena sp.) foraging on honeydew on a non-flowering Adenostoma fasciculatum shrub.
(Photo © Paul G. Johnson)

Bees foraging on honeydew is particularly interesting given that decades of research have focused on bee responses to the colors, scents, shapes, humidity, temperature, and even the electric fields of flowers, and their influence on floral evolution. How solitary bees find scentless, invisible sugars on flowerless plants, however, is a mystery.

Meiners and colleagues set up a field experiment to determine how many bee species use honeydew and how they find it on non-flowering shrubs. They used artificial honeydew, color signals, infrared thermometers, and scale insecticide to determine that forty-two species of mostly solitary bees can quickly find unadvertised sugars without relying on cues from the scale insects or host plants. To explain this ability, the team analyzed the visitation response curve and hypothesized that foraging strategies for native bees may include “interspecific eavesdropping,” or noticing the activity of other bee species that have stumbled upon a novel resource. This is important because, while honeybees communicate about resources via the waggle dance, solitary bees were assumed to forage independently and to focus on floral cues.

Scale insect (Parthenolecanium sp.) honeydew-producers on an A. fasciculatum branch.
(Photo © Paul G. Johnson)

Results of this study suggest that native bee foraging may be more opportunistic, dynamic, and interconnected across a diverse community than was previously understood. At a perilous time for bee populations, the use of nontraditional resources and interspecific cues may influence how diverse native bees cope with floral unpredictability and increasing environmental change. Read the Article