Mechanics of nectar feeding in the orchid beeEuglossa imperialis: pressure, viscosity and flow

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.

Capillary Imbibition in a Diverging Flexible Channel

We study the imbibition of a wetting liquid between flexible sheets that are fixed at both ends. Assuming a narrow gap between the sheets, we solve the lubrication equation coupled with a slender body deformation. When the sheets are parallel, we find that the deformation initially speeds up the flow, as shown in previous studies, but only up to the middle of the channel. As the channel contracts, the hydrodynamic resistance increases and ultimately slows down the filling process. Below a threshold stiffness, the channel collapses and imbibition stops. We propose a scaling of the filling duration near this threshold. Next, we show that if the sheets are initially tilted with a minimal angle, the channel avoids collapse. The liquid front pulls the diverging sheets and spreads in a nearly parallel portion, which maintains the capillary propulsion and enhances the wicking. Therefore, while it is established that diverging rigid plates imbibe liquids slower than parallel ones do, we show that elasticity reverses this principle: diverging flexible sheets imbibe liquids faster than parallel ones. We find an optimal tilt angle that gives the shortest filling time.

Viscosity as a key factor in decision making of nectar feeding ants

It is well known that viscosity reduces the intake rates in nectar-feeding insects, such as nectivorous ants, though it remains unclear whether viscosity imposes a higher energy investment in these insects, and how this affects their feeding motivation. To address this issue, we studied feeding behavior, metabolism, and pharyngeal pump activity in the carpenter ant Camponotus mus during ingestion of ad libitum sucrose solutions. In some solutions tylose was added to modify viscosity without changing its sucrose concentration, in a way that allowed comparing: (1) two solutions with the same viscosity and different sucrose concentration (10 T and 50), and (2) two solutions with different viscosity and the same sucrose concentration (50 and 50 T). The viscosity increase was detrimental to the metabolic rate and energy balance. Ants feeding on a solution with high sucrose concentration and increased viscosity (50 T) spent extra-time until reaching a crop load similar to that reached by ingesting the solution without tylose (50). For all solutions offered, ants started feeding with the same pharyngeal pump frequencies, reflecting a similar motivation. Interesting, when ants fed on a low sucrose concentration and increased viscosity solution (10 T), their pump frequencies dropped rapidly respect to the pure-sucrose solution (50). On the contrary, pump frequencies for 50 and 50 T remained similar until the end of the intake. Since the pump frequency is strongly modulated by the ant motivation, an increase in viscosity with low sucrose content, demotivates the ants rapidly, suggesting a rapid integration of different kinds of information about the food value. Our results helped to understand how nectivorous ants could modulate their foraging decision-making.

How honey bees dip nectar: Dynamic spacing of tongue hairs facilitates to collect nectar of various viscosities

A honey bee can dip nectar of viscosity across two orders of magnitude, by viscous lapping technique using a segmental tongue covered with erectable hairs. The drinking technique suffers risks of leakage occurring between tongue hairs, and the amount of leakage is related to hair spacing as well as nectar viscosity. When lapping, tongue segments are elongated, which enlarges the hair spacing in longitudinal direction. Experimental observations show that the hair spacing of tongue increases with respect to sucrose solution concentration until it reaches the maximum extension when sucrose solution concentration is above 35%. Considering leakage occurring in the hairy tongue, we hypothesize that the dynamical extension of hair spacing may help honey bees minimize the effects of leakage to reach maximal nectar intake rate. A mathematical model is developed for determining the optimal hair spacing that can meet the demands of both augmenting the nectar intake rate and reducing the risk of leakage. Theoretical prediction and experimental measurements demonstrate honey bees are able to adjust the tongue to meet the optimal hair spacing when dipping nectar of concentration more dilute than 35% and maintain a maximum extension to improve the nectar intake rate when concentration is greater than 35%. We then give the prediction of concentration preferences of three bee species, and discuss effects of dipping frequency and gravity on the leakiness between tongue hairs. This work may not only gain insights into adaptive feeding strategy in insects, but inspire the design of adaptive microfluidic transport devices with dynamic brushy surfaces.

Drinking made easier: honey bee tongues dip faster into warmer and/or less viscous artificial nectar

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 there are advantages to foraging from flowers that are warmer than the surrounding air. The honey bee (Apis mellifera L.) dips nectar using a hairy tongue. However, the microscopic dynamics of the tongue while the bee ingests nectar of varying concentration, viscosity and temperature are unknown. In this study, we found that honey bees respond to the 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.

How do Caenorhabditis elegans worms survive in highly viscous habitats?

The nematode Caenorhabditis elegans is a filter feeder that lives in various viscous habitats such as soil, the intestines of slugs, and rotting materials such as fruits and stems. Caenorhabditis elegans draws in suspensions of bacteria and separates bacteria from water using the pharyngeal pump. Although these worms often live in highly viscous habitats, it is still unclear how they survive in these environments by eating bacteria. In this study, we investigated the effects of suspension viscosity on the survival rate of malnourished worms by combining live imaging and scaling analyses. We found that survival rate decreased with increases in viscosity because the high viscosity suppressed the amount of food ingested. The same tendency was found in two feeding-defective mutants, eat-6(ad467) and eat-6(ad997). We also found that the high viscosity weakened pump function, but the velocities in the pharynx were not zero, even in the most viscous suspensions. Finally, we estimated the amount of ingested food using scaling analyses, which provided a master curve of the experimental survival rates. These results illustrate that the survival rate of C. elegans worms is strongly dependent on the ingested bacteria per unit time associated with physical environments, such as the viscosity of food suspensions and the cell density of bacteria. The pump function of the C. elegans pharynx is not completely lost even in fluids that have 105 times higher viscosity than water, which may contribute to their ability to survive around the world in highly viscous environments.

The mechanics of nectar offloading in the bumblebee Bombus terrestris and implications for optimal concentrations during nectar foraging

Nectar is a common reward provided by plants for pollinators. More concentrated nectar is more rewarding, but also more viscous, and hence more time-consuming to drink. Consequently, theory predicts an optimum concentration for maximizing energy uptake rate, dependent on the mechanics of feeding. For social pollinators such as bumblebees, another important but little-studied aspect of foraging is nectar offloading upon return to the nest. Studying the bumblebee Bombus terrestris, we found that the relationship between viscosity (µ) and volumetric transfer rates (Q) of sucrose solutions differed between drinking and offloading. For drinking, Q ∝ µ^-0.180, in good agreement with previous work. Although offloading was quicker than drinking, offloading rate decreased faster with viscosity, with Q ∝ µ^-0.502, consistent with constraints imposed by fluid flow through a tube. The difference in mechanics between drinking and offloading nectar leads to a conflict in the optimum concentration for maximizing energy transfer rates. Building a model of foraging energetics, we show that including offloading lowers the maximum rate of energy return to the nest and reduces the concentration which maximizes this rate by around 3%. Using our model, we show that published values of preferred nectar sugar concentrations suggest that bumblebees maximize the overall energy return rather than the instantaneous energy uptake during drinking.

A Review of Native Wild Bee Nutritional Health

Declines in wild and managed bee species richness and abundances have been observed throughout Europe and North America in recent decades. These declines have led to questions regarding pollination of wild and cultivated plants. In response to these concerns, efforts towards the conservation of pollinators have been initiated. Part of this conservation effort should be to provide the basic nutritional needs for bees. Nutrition plays one of the most important roles in bee growth, development, and reproduction. There is a large body of information regarding honey bee nutrition, whereas we lack nutritional information on native wild bees. Our knowledge of bumble bee nutritional needs has increased since the introduction of commercial rearing and sale of certain bumble bee species; however, there is still a lack of basic nutritional guidelines such as minimum dietary needs of proteins, amino acids, lipids, and sterols. The large difference in physiology and life history between honey bees and North American wild bees suggests that their nutritional requirements could be quite different.

Drinking with a very long proboscis: Functional morphology of orchid bee mouthparts (Euglossini, Apidae, Hymenoptera)

Neotropical orchid bees (Euglossini) possess the longest proboscides among bees. In this study, we compared the feeding behavior and functional morphology of mouthparts in two similarly large-sized species of Euglossa that differ greatly in proboscis length. Feeding observations and experiments conducted under semi-natural conditions were combined with micro-morphological examination using LM, SEM and micro CT techniques. The morphometric comparison showed that only the components of the mouthparts that form the food tube differ in length, while the proximal components, which are responsible for proboscis movements, are similar in size. This study represents the first documentation of lapping behaviour in Euglossini. We demonstrate that Euglossa bees use a lapping-sucking mode of feeding to take up small amounts of fluid, and a purely suctorial technique for larger fluid quantities. The mouthpart movements are largely similar to that in other long-tongued bees, except that the postmentum in Euglossa can be extended, greatly enhancing the protraction of the glossa. This results in a maximal functional length that is about 50% longer than the length of the food canal composing parts of the proboscis. The nectar uptake and the sensory equipment of the proboscis are discussed in context to flower probing.

Quality versus quantity: Foraging decisions in the honeybee (Apis mellifera scutellata) feeding on wildflower nectar and fruit juice

Foraging animals must often decide among resources which vary in quality and quantity. Nectar is a resource that exists along a continuum of quality in terms of sugar concentration and is the primary energy source for bees. Alternative sugar sources exist, including fruit juice, which generally has lower energetic value than nectar. We observed many honeybees (Apis mellifera scutellata) foraging on juice from fallen guava (Psidium guajava) fruit near others foraging on nectar. To investigate whether fruit and nectar offered contrasting benefits of quality and quantity, we compared honeybee foraging performance on P. guajava fruit versus two wildflowers growing within 50 m, Richardia brasiliensis and Tridax procumbens. Bees gained weight significantly faster on fruit, 2.72 mg/min, than on either flower (0.17 and 0.12 mg/min, respectively). However, the crop sugar concentration of fruit foragers was significantly lower than for either flower (12.4% vs. 37.0% and 22.7%, respectively). Fruit foragers also spent the most time handling and the least time flying, suggesting that fruit juice was energetically inexpensive to collect. We interpret honeybee foraging decisions in the context of existing foraging models and consider how nest-patch distance may be a key factor for central place foragers choosing between resources of contrasting quality and quantity. We also discuss how dilute solutions, such as fruit juice, can help maintain colony sugar-water balance. These results show the benefits of feeding on resources with contrasting quality and quantity and that even low-quality resources have value.

Erection mechanism of glossal hairs during honeybee feeding

Many animals use their mouthparts or tongue to feed themselves rapidly and efficiently. Honeybees have evolved specialized tongues to collect nectar from flowers. Nectar-intake movements consist of rapid protraction and retraction of glossa from a tube formed by the maxillae and labial palps. We establish a physical model to reveal the driving mechanism of hair erection. Results indicate that the glossa of honeybees is similar to a compression spring. Experimental results show that hair erection is generated by the tension of hyaline rod and the elasticity of segmental sheath. The retractor muscle of hyaline rod is contracted at first, which compresses the sheath of pigmented rings and flattens the hairs. While the retractor muscle of hyaline rod relaxes, the elastic energy storage in the compressed glossal sheath will release to change the equivalent stiffness of glossal sheath and erect glossal hairs. These results explain the erection mechanism of glossal hairs during honeybee feeding.

Bee nutrition and floral resource restoration

Bee-population declines are linked to nutritional shortages caused by land-use intensification, which reduces diversity and abundance of host-plant species. Bees require nectar and pollen floral resources that provide necessary carbohydrates, proteins, lipids, and micronutrients for survival, reproduction, and resilience to stress. However, nectar and pollen nutritional quality varies widely among host-plant species, which in turn influences how bees forage to obtain their nutritionally appropriate diets. Unfortunately, we know little about the nutritional requirements of different bee species. Research must be conducted on bee species nutritional needs and host-plant species resource quality to develop diverse and nutritionally balanced plant communities. Restoring appropriate suites of plant species to landscapes can support diverse bee species populations and their associated pollination ecosystem services.

Paradox of the drinking-straw model of the butterfly proboscis

Fluid-feeding Lepidoptera use an elongated proboscis, conventionally modeled as a drinking straw, to feed from pools and films of liquid. Using the monarch butterfly, Danaus plexippus (Linnaeus), we show that the inherent structural features of the lepidopteran proboscis contradict the basic assumptions of the drinking-straw model. By experimentally characterizing permeability and flow in the proboscis, we show that tapering of the food canal in the drinking region increases resistance, significantly hindering the flow of fluid. The calculated pressure differential required for a suction pump to support flow along the entire proboscis is greater than 1 atm (~101 kPa) when the butterfly feeds from a pool of liquid. We suggest that behavioral strategies employed by butterflies and moths can resolve this paradoxical pressure anomaly. Butterflies can alter the taper, the interlegular spacing and the terminal opening of the food canal, thereby controlling fluid entry and flow, by splaying the galeal tips apart, sliding the galeae along one another, pulsing hemolymph into each galeal lumen, and pressing the proboscis against a substrate. Thus, although physical construction of the proboscis limits its mechanical capabilities, its functionality can be modified and enhanced by behavioral strategies.

Liquid-intake flow around the tip of butterfly proboscis

Butterflies drink liquid through a slender proboscis using a large pressure gradient induced by the systaltic operation of a muscular pump inside their head. Although the proboscis is a naturally well-designed coiled micro conduit for liquid uptake and deployment, it has been regarded as a simple straw connected to the muscular pump. There are few studies on the transport of liquid food in the proboscis of a liquid-feeding butterfly. To understand the liquid-feeding mechanism in the proboscis of butterflies, the intake flow around the tip of the proboscis was investigated in detail. In this study, the intake flow was quantitatively visualized using a micro-PIV (particle image velocimetry) velocity field measurement technique. As a result, the liquid-feeding process consists of an intake phase, an ejection phase and a rest phase. When butterflies drink pooled liquid, the liquid is not sucked into the apical tip of the proboscis, but into the dorsal linkage aligned longitudinally along the proboscis. To analyze main characteristics of the intake flow around a butterfly proboscis, a theoretical model was established by assuming that liquid is sucked into a line sink whose suction rate linearly decreases proximally. In addition, the intake flow around the tip of a female mosquito׳s proboscis which has a distinct terminal opening was also visualized and modeled for comparison. The present results would be helpful to understand the liquid-feeding mechanism of a butterfly.

Experimental analysis of the liquid-feeding mechanism of the butterfly Pieris rapae

The butterflies Pieirs rapae drink liquid by using a long proboscis. A high pressure gradient is induced in the proboscis when cibarial pump muscles contract. However, liquid feeding through the long proboscis poses a disadvantage of high flow resistance. Hence, butterflies may possess special features to compensate for this disadvantage and succeed in foraging. The main objective of this study is to analyze the liquid-feeding mechanism of butterflies. The systaltic motion of cibarial pump organ was visualized by using synchrotron X-ray imaging technique. In addition, an ellipsoidal pump model was established based on synchrotron X-ray micro-computed tomography. To determine the relationship between the cyclic variation of the pump volume and the liquid-feeding flow, velocity fields of the intake flow at the tip of the proboscis were measured using micro-particle image velocimetry. Reynolds and Womersley numbers of liquid-feeding flow in the proboscis were approximately 1.40 and 0.129, respectively. The liquid-feeding flow could be characterized as a quasi-steady state laminar flow. Considering these results, we analyzed the dimensions of the feeding apparatus on the basis of minimum energy consumption during liquid-feeding process. The relationship between the proboscis and the cibarial pump was determined when minimum energy consumption occurs. As a result, the volume of the cibarial pump is proportional to the cube of the radius of the proboscis. It seems that the liquid-feeding system of butterflies and other long-proboscid insects follow the cube relationship. The present results would provide insights into the feeding strategies of liquid-feeding butterflies.

Time management and nectar flow: flower handling and suction feeding in long-proboscid flies (Nemestrinidae: Prosoeca)

A well-developed suction pump in the head represents an important adaptation for nectar-feeding insects, such as Hymenoptera, Lepidoptera and Diptera. This pumping organ creates a pressure gradient along the proboscis, which is responsible for nectar uptake. The extremely elongated proboscis of the genus Prosoeca (Nemestrinidae) evolved as an adaptation to feeding from long, tubular flowers. According to the functional constraint hypothesis, nectar uptake through a disproportionately elongated, straw-like proboscis increases flower handling time and consequently lowers the energy intake rate. Due to the conspicuous length variation of the proboscis of Prosoeca, individuals with longer proboscides are hypothesised to have longer handling times. To test this hypothesis, we used field video analyses of flower-visiting behaviour, detailed examinations of the suction pump morphology and correlations of proboscis length with body length and suction pump dimensions. Using a biomechanical framework described for nectar-feeding Lepidoptera in relation to proboscis length and suction pump musculature, we describe and contrast the system in long-proboscid flies. Flies with longer proboscides spent significantly more time drinking from flowers. In addition, proboscis length and body length showed a positive allometric relationship. Furthermore, adaptations of the suction pump included an allometric relationship between proboscis length and suction pump muscle volume and a combination of two pumping organs. Overall, the study gives detailed insight into the adaptations required for long-proboscid nectar feeding, and comparisons with other nectar-sucking insects allow further considerations of the evolution of the suction pump in insects with sucking mouthparts.

Fearful foragers: honey bees tune colony and individual foraging to multi-predator presence and food quality

Fear can have strong ecosystem effects by giving predators a role disproportionate to their actual kill rates. In bees, fear is shown through foragers avoiding dangerous food sites, thereby reducing the fitness of pollinated plants. However, it remains unclear how fear affects pollinators in a complex natural scenario involving multiple predator species and different patch qualities. We studied hornets, Vespa velutina (smaller) and V. tropica (bigger) preying upon the Asian honey bee, Apis cerana in China. Hornets hunted bees on flowers and were attacked by bee colonies. Bees treated the bigger hornet species (which is 4 fold more massive) as more dangerous. It received 4.5 fold more attackers than the smaller hornet species. We tested bee responses to a three-feeder array with different hornet species and varying resource qualities. When all feeders offered 30% sucrose solution (w/w), colony foraging allocation, individual visits, and individual patch residence times were reduced according to the degree of danger. Predator presence reduced foraging visits by 55–79% and residence times by 17–33%. When feeders offered different reward levels (15%, 30%, or 45% sucrose), colony and individual foraging favored higher sugar concentrations. However, when balancing food quality against multiple threats (sweeter food corresponding to higher danger), colonies exhibited greater fear than individuals. Colonies decreased foraging at low and high danger patches. Individuals exhibited less fear and only decreased visits to the high danger patch. Contrasting individual with emergent colony-level effects of fear can thus illuminate how predators shape pollination by social bees.

Honeybees prefer warmer nectar and less viscous nectar, regardless of sugar concentration

The internal temperature of flowers may be higher than air temperature, and warmer nectar could offer energetic advantages for honeybee thermoregulation, as well as being easier to drink owing to its lower viscosity. We investigated the responses of Apis mellifera scutellata (10 colonies) to warmed 10% w/w sucrose solutions, maintained at 20-35°C, independent of low air temperatures, and to 20% w/w sucrose solutions with the viscosity increased by the addition of the inert polysaccharide Tylose (up to the equivalent of 34.5% sucrose). Honeybee crop loads increased with nectar temperature, as did the total consumption of sucrose solutions over 2 h by all bees visiting the feeders. In addition, the preference of marked honeybees shifted towards higher nectar temperatures with successive feeder visits. Crop loads were inversely proportional to the viscosity of the artificial nectar, as was the total consumption of sucrose solutions over 2 h. Marked honeybees avoided higher nectar viscosities with successive feeder visits. Bees thus showed strong preferences for both warmer and less viscous nectar, independent of changes in its sugar concentration. Bees may benefit from foraging on nectars that are warmer than air temperature for two reasons that are not mutually exclusive: reduced thermoregulatory costs and faster ingestion times due to the lower viscosity.

The effect of sugar solution type, sugar concentration and viscosity on the imbibition and energy intake rate of bumblebees

Nectar is an essential resource for bumblebees and many other flower-visiting insects. The main constituents of nectar are sugars, which vary in both composition and concentration between plant species. We assessed the influence of sugar concentration, sugar solution viscosity and sugar solution composition on the imbibition and energy intake rate of bumblebees, Bombus impatiens Cresson (Hymenoptera: Apidae). To do this, we measured their rate of solution intake for 49 different sugar solution treatments, which varied in both sugar composition and concentration. In general, the imbibition rates of bumblebees were found to increase with increasing sugar concentration, probably due to their preference for high sugar concentrations, up to a concentration of 27% (w/w), at which point solutions reached a threshold viscosity of approximately 1.5-1.6 mPa.s. Above this threshold, the increasing viscosity of the solutions physically inhibited the imbibition rates of bees, and imbibition rate began to decrease as the concentration increased. Nevertheless, bumblebee energy intake rate increased with increasing concentration up to about 42-56%. Although we found that sugar solution composition had an impact on both imbibition and energy intake rate, its effect was not as straightforward as that of sugar concentration and viscosity.

Nectar sugar composition of European Caryophylloideae (Caryophyllaceae) in relation to flower length, pollination biology and phylogeny

Floral nectar composition has been explained as an adaptation to factors that are either directly or indirectly related to pollinator attraction. However, it is often unclear whether the sugar composition is a direct adaptation to pollinator preferences. Firstly, the lower osmolality of sucrose solutions means that they evaporate more rapidly than hexose solutions, which might be one reason why sucrose-rich nectar is typically found in flowers with long tubes (adapted to long-tongued pollinators), where it is better protected from evaporation than in open or short-tubed flowers. Secondly, it can be assumed that temperature-dependent evaporation is generally lower during the night than during the day so that selection pressure to secrete nectar with high osmolality (i.e. hexose-rich solutions) is relaxed for night-active flowers pollinated at night. Thirdly, the breeding system may affect selection pressure on nectar traits; that is, for pollinator-independent, self-pollinated plants, a lower selective pressure on nectar traits can be assumed, leading to a higher variability of nectar sugar composition independent of pollinator preferences, nectar accessibility and nectar protection. To analyse the relations between flower tube length, day vs. night pollination and self-pollination, the nectar sugar composition was investigated in 78 European Caryophylloideae (Caryophyllaceae) with different pollination modes (diurnal, nocturnal, self-pollination) using high-performance liquid chromatography (HPLC). All Caryophylleae species (Dianthus and relatives) were found to have nectar with more than 50% sucrose, whereas the sugar composition of Sileneae species (Silene and relatives) ranged from 0% to 98.2%. In the genus Silene, a clear dichotomous distribution of sucrose- and hexose-dominant nectars is evident. We found a positive correlation between the flower tube length and sucrose content in Caryophylloideae, particularly in day-flowering species, using both conventional analyses and phylogenetically independent contrasts.

Suitability of a novel diet for a parasitic wasp, Cotesia plutellae

The braconid Cotesia plutellae (Kurdjumov) (Hymenoptera: Braconidae) is a major solitary, larval endoparasitoid of the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae). The impact of dietary protein was investigated in the laboratory by comparing performance of C. plutellae on honey, which is commonly used to rear the parasitoid, to that on a novel diet made of honey and protein-rich beebread. Cotesia plutellae was highly stimulated by honey and honey-beebread, with a feeding response exceeding 95%, a level that is comparable with its responses to fructose, glucose, and sucrose. The ability of honey-beebread to support host-parasitoid colonies was also comparable with that of honey. However, parasitoids raised on honey-beebread suppressed diamondback moths in rearing cages 3 weeks before the honey-fed wasps. The development time of C. plutellae reared on honey with or without beebread showed no significant difference, but adult wasps lived longer on honey-beebread. Mean developmental periods from oviposition to pupation and from pupation to adult emergence were 8 and 6 days, respectively. Adult wasps raised on honey-beebread outlived their conspecifics that were raised on honey by at least 4 days. Honey-beebread showed potential as a good food for rearing C. plutellae in the laboratory, and its benefit in parasitoid production is discussed.

The ecological basis for biogeographic classification: an example in orchid bees (Apidae: Euglossini)

Biogeography has been difficult to apply as a methodological approach because organismic biology is incomplete at levels where the process of formulating comparisons and analogies is complex. The study of insect biogeography became necessary because insects possess numerous evolutionary traits and play an important role as pollinators. Among insects, the euglossine bees, or orchid bees, attract interest because the study of their biology allows us to explain important steps in the evolution of social behavior and many other adaptive tradeoffs. We analyzed the distribution of morphological characteristics in Colombian orchid bees from an ecological perspective. The aim of this study was to observe the distribution of these attributes on a regional basis. Data corresponding to Colombian euglossine species were ordered with a correspondence analysis and with subsequent hierarchical clustering. Later, and based on community proprieties, we compared the resulting hierarchical model with the collection localities to seek to identify a biogeographic classification pattern. From this analysis, we derived a model that classifies the territory of Colombia into 11 biogeographic units or natural clusters. Ecological assumptions in concordance with the derived classification levels suggest that species characteristics associated with flight performance, nectar uptake, and social behavior are the factors that served to produce the current geographical structure.

The psychophysics of sugar concentration discrimination and contrast evaluation in bumblebees

The capacity to discriminate between choice options is crucial for a decision-maker to avoid unprofitable options. The physical properties of rewards are presumed to be represented on context-dependent, nonlinear cognitive scales that may systematically influence reward expectation and thus choice behavior. In this study, we investigated the discrimination performance of free-flying bumblebee workers (Bombus impatiens) in a choice between sucrose solutions with different concentrations. We conducted two-alternative free choice experiments on two B. impatiens colonies containing some electronically tagged bumblebees foraging at an array of computer-automated artificial flowers that recorded individual choices. We mimicked natural foraging conditions by allowing uncertainty in the probability of reward delivery while maintaining certainty in reward concentration. We used a Bayesian approach to fit psychometric functions, relating the strength of preference for the higher concentration option to the relative intensity of the presented stimuli. Psychometric analysis was performed on visitation data from individually marked bumblebees and pooled data from unmarked individuals. Bumblebees preferred the more concentrated sugar solutions at high stimulus intensities and showed no preference at low stimulus intensities. The obtained psychometric function is consistent with reward evaluation based on perceived concentration contrast between choices. We found no evidence that bumblebees reduce reward expectations upon experiencing non-rewarded visits. We compare psychometric function parameters between the bumblebee B. impatiens and the flower bat Glossophaga commissarisi and discuss the relevance of psychophysics for pollinator-exerted selection pressures on plants.

Effect of fluid viscosity on the liquid-feeding flow phenomena of a female mosquito

Liquid-sucking phenomena by the two-pump system of a female mosquito have been investigated experimentally to understand the feeding mechanism. In most previous experimental studies on liquid-feeding insects, the net increase of mass was divided by the feeding time and fluid density to evaluate the intake rate. However, this weighting method is not so precise for mosquitoes, because they are too lightweight to measure the gain of mass accurately. In this study, the intake rate of female mosquitoes feeding various sucrose solutions was estimated using a micro particle image velocimetry technique. As the sucrose concentration increases from 1% to 50%, the intake rate decreases from 17.3 nl/s to 5.8 nl/s. Furthermore, the temporal volume variations of the two-pump chambers were estimated based on the velocity and acceleration information of the flow at the center of food canal of the proboscis. One pumping period is divided into four elementary phases, which are related to the different operational modes of the two pumps. According to the hypothetical model established in this study, the phase shift (α) between the two-pump chambers increases from 14 ms to 28 ms and the percentage of reversal flow to forward flow in a pumping period decreases 7.6% to 1.7% with increasing viscosity. The developed analytic methodology is helpful to the study of an insect’s feeding mechanism.

Optimal concentrations in nectar feeding

Nectar drinkers must feed quickly and efficiently due to the threat of predation. While the sweetest nectar offers the greatest energetic rewards, the sharp increase of viscosity with sugar concentration makes it the most difficult to transport. We here demonstrate that the sugar concentration that optimizes energy transport depends exclusively on the drinking technique employed. We identify three nectar drinking techniques: active suction, capillary suction, and viscous dipping. For each, we deduce the dependence of the volume intake rate on the nectar viscosity and thus infer an optimal sugar concentration consistent with laboratory measurements. Our results provide the first rationale for why suction feeders typically pollinate flowers with lower sugar concentration nectar than their counterparts that use viscous dipping.

Experimental analysis of the blood-sucking mechanism of female mosquitoes

Pioneering studies have been conducted to reveal the functional characteristics of the two-pump system of the female mosquito. Mosquitoes are equipped with two pumping organs located in the head: the cibarial (CP) and the pharyngeal (PP) pumps. To analyze the functional relationship of these pumps during the blood-sucking process, micro-particle image velocimetry (PIV) and synchrotron X-ray micro-imaging were employed. The two pumps were found to be well coordinated with a phase shift (α) and time shift (β) but to have distinct functions in the liquid-sucking process. The first pump (CP) starts to expand first, and then the second pump (PP) expands in advance with a time shift (β) before the first pump (CP) begins to contract, playing a key role in improving pumping performance. The systaltic motion of the two pumps works systematically in a well-coordinated manner. In addition, the pumping performance of blood-sucking female mosquitoes is demonstrated to be superior to that of nectar-eating male mosquitoes. Intake flow rate is maximized by reducing the relaxation time of the CP and increasing the pumping frequency.

Dilute bird nectars: viscosity constrains food intake by licking in a sunbird

Floral nectars of bird-pollinated plants are relatively dilute. One hypothesis proposed to explain this concerns the difficulty for birds of drinking nectar of high viscosity. We examined the effects of viscosity, separately from those of sugar concentration, on feeding by captive whitebellied sunbirds (Cinnyris talatala). Viscosities of artificial nectar (sucrose solutions ranging in concentration from 0.25 to 1.5 mol/l) were altered with Tylose, an inert polysaccharide. Food consumption was measured over 3 h, and lick frequency and duration were recorded using photodetection devices on feeding apertures too small for the bill but large enough for the extended tongue. Volumetric intake rates (ml/s) were inversely proportional to nectar viscosity, and were similar over the range of sucrose concentrations when viscosity was held constant. Sucrose intake rates (mg/s) remained the same on pure sucrose solutions, but they decreased with increasing viscosity at a constant sucrose concentration. Lick frequencies and tongue loads were reduced at high viscosities, and lick duration increased, which confirms that sunbirds take longer to ingest viscous solutions. Licking behavior was remarkably similar in birds feeding on different sucrose concentrations if viscosity was held constant. Nectar ingestion rate is determined by viscosity; however, total food intake is mainly modulated by sugar concentration. Similar effects of food viscosity have been observed in insects that suck nectar.

Sucking pump activity in feeding behaviour regulation in carpenter ants

Modulation of liquid feeding-rate would allow insects to ingest more food in the same time when this was required. Ants can vary nectar intake rate by increasing sucking pump frequency according to colony requirements. We analysed electrical signals generated by sucking pump activity of ants during drinking solutions of different sucrose concentrations and under different carbohydrate-deprivation levels. Our aim was to define parameters that characterize the recordings and analyse their relationship with feeding behaviour. Signals showed that the initial and final frequencies of sucking pump activity, as well as the difference between them were higher in sugar-deprived ants. However, these parameters were not influenced by sucrose solution concentration, which affected the number of pump contractions and the volume per contraction. Unexpectedly, we found two different responses in feeding behaviour of starved and non-starved ants depending on concentration. Starved ants drank dilute solutions for the same length of time as non-starved ants but ingested higher volumes. While drinking the concentrated solutions, starved ants drank the same volume, but did so in a shorter time than the non-starved ones. Despite these differences, for each analysed concentration the total number of pump contractions remained constant independently of sugar-deprivation level. These results are discussed in the frame of feeding regulation and decision making in ant foraging behaviour.