Essential role of papillae flexibility in nectar capture by bees

Abstract

Many bees possess a tongue resembling a brush composed of a central rod (glossa) covered by elongated papillae, which is dipped periodically into nectar to collect this primary source of energy. In vivo measurements show that the amount of nectar collected per lap remains essentially constant for sugar concentrations lower than 50% but drops significantly for a concentration around 70%. To understand this variation of the ingestion rate with the sugar content of nectar, we investigate the dynamics of fluid capture by Bombus terrestris as a model system. During the dipping process, the papillae, which initially adhere to the glossa, unfold when immersed in the nectar. Combining in vivo investigations, macroscopic experiments with flexible rods, and an elastoviscous theoretical model, we show that the capture mechanism is governed by the relaxation dynamics of the bent papillae, driven by their elastic recoil slowed down through viscous dissipation. At low sugar concentrations, the papillae completely open before the tongue retracts out of nectar and thus, fully contribute to the fluid capture. In contrast, at larger concentrations corresponding to the drop of the ingestion rate, the viscous dissipation strongly hinders the papillae opening, reducing considerably the amount of nectar captured. This study shows the crucial role of flexible papillae, whose aspect ratio determines the optimal nectar concentration, to understand quantitatively the capture of nectar by bees and how physics can shed some light on the degree of adaptation of a specific morphological trait.

Climate Change–Induced Stress Reduce Quantity and Alter Composition of Nectar and Pollen From a Bee-Pollinated Species (Borago officinalis, Boraginaceae)

“…Decreased sugar quantity affect negatively flight performance of bees (Hendriksma et al, 2014). We also observed that sugar nectar concentration increased with temperature rise, from on average 50 • Brix at 21 • C to 60 • Brix at 24 and 27 • C. This increase might perhaps negatively impact nectar uptake by insects as it was recently shown that the opening of the papillae of bee tongue (Bombus terrestris) was maximized up to a sugar concentration in the nectar of 55% concentration (Lechantre et al, 2021). A reduced nectar volume per flower decreases also the amount of water that the insects collect through nectar which could influence their water balance, although bees seem less subject to desiccation than most terrestrial insects (Nicolson, 2009).…”

Relaxation dynamics of a flexible rod in a fluid

“…During the tongue protraction, the hairy structure, initially adhering to the tongue (glossa) by capillary forces [51,52], relaxes to a widely open brushlike shape when immersed in the nectar. During the retraction, this peculiar tongue's morphology allows the nectar to be trapped by viscous entrainment and capillary forces and finally driven to the bee's mouth [53][54][55][56][57][58][59][60][61][62][63]. The amount of nectar collected per laps is essentially constant at sufficiently low sugar concentration but drops sharply when the sugar content exceeds around 60% [62][63][64][65].…”

Nectar Feeding by a Honey Bee’s Hairy Tongue: Morphology, Dynamics, and Energy-Saving Strategies

“…The majority of flower-visiting insects, including bees, wasps [ 1 , 2 ], flies [ 3 ], butterflies [ 4 ], moths [ 5 ], and some beetles [ 6 , 7 ], obtain nutrition from floral nectar and pollen from flowering plants [ 8 ]. The honey bee ( Apis mellifera ligustica ) is a typical pollinator in the world [ 9 ].…”

“…Honey bees can feed on a range of viscous fluids at high efficiencies [ 8 ]. This behaviour is challenging because of the physical property of nectar, suggesting the nectar viscosity increases steeply with respect to the concentration, through which the glossa should have to resist high viscous drag [ 11 , 12 , 13 , 14 ].…”