The ability of a honey bee to take nectar from various flowers depends on the length and diameter of the tongue hairs; this discovery could help local communities grow the right flowers to support this dwindling insect.
To produce one kilogram of honey, honey bees must visit an average of 2 million flowers. Honey bees must efficiently collect the nectar they need to produce the sweet, golden water because flying is labor-intensive. As scientists have long known, honeybees use their tongues covered with microscopic hairs to collect nectar. However, they were unaware of the methods honeybees use to increase their nectar consumption.
The effect of a bee's tongue retraction time on the rate of energy intake has now been investigated analytically and experimentally by Jianing Wu of Sun Yat-sen University in China and colleagues. The research team discovered that the length and diameter of the hairs covering a honeybee's tongue coincided with the ideal withdrawal time.
The long, thin, hairy tongue of honey bees is surrounded by a protective sheath. When the bee lands on a flower, this sheath opens and moves in and out to collect the nectar caught in the vertical slits between the tongue hairs. Nectar increases tongue diameter, which increases tongue drag. Therefore, tongue retraction takes longer to complete (when tongue is free of nectar and hairs are straight) than tongue retraction.
While the method of consuming honey bees is well understood, the effects of changes in the properties of various ingredients are unknown. Wu and colleagues created a fluid transport model that includes all components to explore this issue. They determined the best tongue retraction time (the shortest time the bees collect the most nectar) by varying the nectar concentration, tongue bristle opening time, and tongue length for six honeybee species with masses ranging from 12 to 256 mg.
The research team discovered that when a honey bee's body mass increases, the ideal retreat time is shortened. For example, the model predicts an ideal withdrawal time of 100 ms for the Western honeybee, which has an average mass of about 135 mg and is one of the most common honeybee species in the world. The ideal withdrawal time for the Southeast Asian Pearl Banded bee with a body mass of about 40 mg is roughly 200 ms.
The length of a honey bee's tongue and its length/diameter ratio are related to body mass. As a result, the withdrawal time is also related to the length/diameter ratio of the tongue hairs. For lower nectar concentrations, the model also predicts slower withdrawal times.
Experiments were conducted by Wu and colleagues to confirm these predictions. They set up a transparent device with honeybees to watch the bees drink water. The team sprayed sugar water between two glass slides and then used a high-speed camera attached to a microscope focused on the slides to record the movement of the bees' tongues. Wu and colleagues discovered that just like the model, the withdrawal time decreases with body mass.
Wu thinks his research will contribute to maintaining honeybee populations that have been in decline for some time. According to Wu, the survival of honeybees is vital to the health of our planet. “If honey bees go extinct, we lose 40% of our produce.” Fabian Brau, a physical chemist at the Free University of Brussels and researching how honey bees consume nectar, agrees with this view. According to Brau, communities can use the model developed by Wu and colleagues to decide which flowers to plant so that local honeybee species have access to flowers with the concentration of nectar they need to capture nectar most effectively.
Brau also points out that the predictions could change people's view of the behavioral difference between various honeybee species. According to Wu and colleagues' research, the rate at which honeybees of a particular species dip their tongues in and out of flowers varies. According to Brau, “We assumed that this frequency was constant for all bees.” Even if true for bees, it turned out that the bees were all roughly the same size.