Abstract:
Optimal concentrations for nectar drinking are limited by the steep increase in the viscosity of sugar solutions with concentration. However, nectar viscosity is inversely related to temperature, which suggests advantages to foraging from flowers that are warmer than the surrounding air. The honey bee (Apis mellifera L.) dips nectar by a hairy tongue. However, microscopic dynamics of the tongue while the bee ingests nectar of varying concentration, viscosity and temperature are unknown. In this study, we find that honey bees respond to variation of nectar properties by regulating dipping frequency. Through high-speed imaging, we discovered that the honey bee traps warmer sucrose solutions with a quicker tongue. The honey bee dips the warmest and most dilute solution (40°C and 25% w/w sucrose) 1.57 times as fast as the coldest and thickest solution (20°C and 45% w/w sucrose). When the viscosity of different sucrose concentrations was kept constant by adding the inert polysaccharide Tylose, honey bees dipped nectar at constant frequency. We propose a fluid mechanism model to elucidate potential effects on sucrose intake and show that higher dipping frequency can increase the volumetric and energetic intake rates by 125% and 15%, respectively. Our findings broaden insights into how honey bees adapt to foraging constraints from the perspective of tongue dynamics, and demonstrate that elevated intrafloral temperatures and lower nectar viscosity can improve the volumetric and energetic intake rates of pollinators.
