Trade-off mechanism of honey bee sucking and lapping

Elastocapillary sequential fluid capture in hummingbird-inspired grooved sheets

Passive and effective fluid capture and transport at small scale is crucial for industrial and medical applications, especially for the realisation of point-of-care tests. Performing these tests involves several steps, including capturing biological fluid, aliquoting, reacting with reagents, and reading the results. Ideally, these tests must be fast and offer a large surface-to-volume ratio to achieve rapid and precise diagnostics with a reduced amount of fluid. Such constraints are often contradictory as a high surface-to-volume ratio implies a high hydraulic resistance and hence a decrease in the flow rate. Inspired by the feeding mechanism of hummingbirds, we propose a frugal fluid capture device that takes advantage of elastocapillary deformations to enable concomitant fast liquid transport, aliquoting, and high confinement in the deformed state. The hierarchical design of the device - that consists in vertical grooves stacked on an elastic sheet - enables a two-step sequential fluid capture. Each unit groove mimics the hummingbird's tongue and closes due to capillary forces when a wetting liquid penetrates, yielding the closure of the whole device in a tubular shape, in the core of which additional liquid is captured. Combining elasticity, capillarity, and viscous flow, we rationalise the fluid-structure interaction at play both when liquid is scarce and abundant. By functionalising the surface of the grooves, such a passive device can concomitantly achieve all the steps of point-of-care tests, opening the way for the design of optimal devices for fluid capture and transport in microfluidics.

Physiological and behavioral pharmacology of ethanol in honey bees

Ethanol has been consumed by humans since the dawn of civilization and, over the course of millennia, a wide variety of ethanol-rich drinks have been produced across cultures. Traditionally, it was believed that only humans voluntarily consume ethanol and become inebriated by it. However, a growing amount of evidence is showing that several non-human animal species spontaneously consume ethanol in nature. Among these, there is the honey bee (Apis mellifera), which can find ethanol in decaying fruits and in the fermented nectar of flowers. Importantly, honey bees represent a useful animal model of ethanol consumption as, like humans, they voluntarily consume ethanol, they show acute dose-dependent motor and postural signs of inebriation, they display ethanol-induced disruption of cognitive functions and social behavior, and they develop ethanol dependence. Moreover, they are small, easy to acquire and easy to maintain in the laboratory. Finally, we possess a vast database of information on their natural history, physiology, genetics and behavior, with their ethogram comprising a wide variety of basic to complex behaviors, including the capacity to self-administer large quantities of ethanol. The present article reviews what is currently known about the physiological and behavioral pharmacology of ethanol in honey bees. The topics covered include the effect of ethanol on gene expression, epigenetic changes of DNA, neuronal stress, posture, locomotion, learning (comprising classical and operant conditioning), communication, social feeding (trophallaxis), aggression and foraging-related decision-making in honey bees.

Adult rhinoceros beetles use a sweeping pattern to ingest high-viscosity fluid

More than half of all insect species utilize various natural liquids as primary diet. The concentrated liquids with energy-dense nutrition can provide highly favorable rewards, however, their high-viscosity poses challenges to the insect for ingesting. Here we show that rhinoceros beetles, Trypoxylus dichotomus (Coleoptera: Scarabaeidae), are capable of ingesting sugar solutions with viscosities spanning four orders of magnitude, exhibiting extraordinary adaptability to diverse natural liquid sources. We discovered a previously unidentified maxillae-sweeping motion that beetles preferentially adopt to consume highly viscous liquids, achieving a higher feeding rate than the more common direct sucking. By utilizing morphological characterizations, flow visualization, and fluid-structure coupling simulation, we revealed the underlying mechanisms of how this maxillary movement facilitates the transportation of viscous liquid. Our findings not only shed light on the multi-functionality of beetle mouthparts but also provide insights into the adaptability of generalized mouthparts to a broad range of fluid sources.

Honey bees switch mechanisms to drink deep nectar efficiently

The feeding mechanisms of animals constrain the spectrum of resources that they can exploit profitably. For floral nectar eaters, both corolla depth and nectar properties have marked influence on foraging choices. We report the multiple strategies used by honey bees to efficiently extract nectar at the range of sugar concentrations and corolla depths they face in nature. Honey bees can collect nectar by dipping their hairy tongues or capillary loading when lapping it, or they can attach the tongue to the wall of long corollas and directly suck the nectar along the tongue sides. The honey bee feeding apparatus is unveiled as a multifunctional tool that can switch between lapping and sucking nectar according to the instantaneous ingesting efficiency, which is determined by the interplay of nectar-mouth distance and sugar concentration. These versatile feeding mechanisms allow honey bees to extract nectar efficiently from a wider range of floral resources than previously appreciated and endow them with remarkable adaptability to diverse foraging environments.

Optimal kinematics of the bee tongue for viscous fluid transport

Honey bees can forage nectar from a large spectrum of nectariferous flowers using their rhythmically erectable tongue hairs in a viscous dipping fashion that involves a faster protraction stroke toward the nectar pool and a slower retraction stroke backward. Since honey bees are capable of using their hairy tongues to adapt to various feeding environments, the kinematic characteristics of the bee tongue, especially the retraction time, would likely represent evolutionary optimization. However, the phenomenon and mechanism remain elusive. In this combined experimental and theoretical study, we established a mathematical model to analyze the effects of tongue retraction time on the energy intake rate considering the unfolding dynamics of tongue hairs in the retraction phase. The theoretical optimal retraction time at which the energy intake rate reached the maximum was governed by the dimensions of tongue hairs, which matched well with the in vivo tests. This study may not only bridge the connection between the kinematics and geometry of the bee tongue but also shed light on a control strategy for micropumps equipped with dynamic surfaces.