Regulation of nectar collection in relation to honey storage levels by honey bees, Apis mellifera

Honey bees collect distinct nutrient sources in the form ofnectar (energy) and pollen (nitrogen). We investigated the effectof varying energy stores on nectar and pollen foraging. We foundno significant changes in nectar foraging in response to changesin honey storage levels within colonies. Individual foragersdid not vary activity rates or nectar load sizes in responseto changes in honey stores, and colonies did not increase nectarintake rates when honey stores within the hive were decreased.This result contrasts with pollen foraging behavior, which isextremely sensitive to colony state. Our data show that individualforaging decisions during nectar collection and colony regulationof nectar intake are distincdy different from pollen foraging.The behavior of honey bees illustrates that foraging strategy(and therefore foraging models) can incorporate multiple currencies,including both energy and protein intake.[Behav Ecol 7: 286–291(1996)]     

The movement patterns of carpenter beesXylocopa micans and bumblebeesBombus pennsylvanicus onPontederia cordata inflorescences

The movement patterns of carpenter bees (Xylocopa micans) and bumblebees (Bombus pennsylvanicus) foraging for nectar on vertical inflorescences ofPontederia cordata were studied near Miami, Florida. The floral biology ofP. cordata is unique in several ways: (a) many short-lived flowers per inflorescence, (b) constant nectar production throughout the life span of each flower, and (c) abscence of vertical patterning of nectar and age of flowers. Inflorescences ranged between 3.5 and 15.8 cm long and had between 9 and 55 open flowers. Both carpenter bees and bumblebees arrived mostly on the bottom third of the inflorescence and left after visiting flowers on the top third of the inflorescence. The departure position from the inflorescence was higher up than observed in studies of other insect pollinators foraging on other speces of plants. This pattern of departure probably occurs in the absence of a vertical gradient of nectar or floral morphology.     

Risk‐averse inflorescence departure in hummingbirds and bumble bees: could plants benefit from variable nectar volumes?

Most hermaphroditic, many-flowered plants should suffer reduced fitness from within-plant selfing (geitonogamy). Large inflorescences are most attractive to pollinators, but also promote many flower visits during a single plant visit, which may increase selfing and decrease pollen export. A plant might avoid the negative consequences of attractiveness through modification of the floral display to promote fewer flower visits, while retaining attractiveness. This report shows that increasing only the variance in nectar volume per flower results in fewer flower visits per inflorescence by wild hummingbirds ( Selasphorus rufus ) and captive bumble bees ( Bombus flavifrons ) foraging on artificial inflorescences. Inflorescences were either constant (all flowers contained the same nectar volume) or variable (half the flowers were empty, the other half contained twice as much nectar as in the constant flowers). Both types of inflorescence were simultaneously available to foragers. Risk-averse foraging behaviour was expressed as a patch departure preference: birds and bees visited fewer flowers on variable inflorescences, and this preference was expressed when resource variability could be determined only by concurrent sampling. When variance treatments were clearly labelled with colour and offered to hummingbirds, the departure effect was maintained; however, when preference was measured by inflorescence choice, birds did not consistently prefer to visit constant inflorescences. The reduced visitation lengths on variable inflorescences by both birds and bees documented in this study imply that variance in nectar production rates within inflorescences may represent an adaptive trait to avoid the costs of geitonogamy.     

黄猄蚁对大蜜蜂的捕食行为及其潜在影响

捕食作用会对访花昆虫的种群、行为以及植物适合度产生影响,是植物与传粉者相互关系研究中常被忽视的因素.本文报道了黄猄蚁对大蜜蜂的捕食行为,并模拟捕食的关键环节研究了捕食过程对重要访花昆虫行为的影响.结果表明,黄猄蚁能够利用局部环境主动攻击猎物,利用群体合作捕获采集过程中的体型较大的大蜜蜂,捕食威胁是其影响植物-访花者关系的重要机制.大蜜蜂具有感知花上危险的能力,模拟处理的个体会逃离危险的花或植株并在花上留下标记,将危险信息传递给其它个体.其它拜访者对具有危险信号花的采集频次明显减少,采集时间缩短;模拟处理的影响会随时间推移而较快地消失.此外,该实验没有发现大蜜蜂在花上停留采集过程中具有明显的防御行为.     

How do bees choose flight direction while foraging?

ABSTRACT. Various authors have reported that nectar-collecting bees usually maintain an overall degree of directionality in their successive foraging flights. I here ask what kind of cues honeybees (Apis mellifera ) use to decide on departure direction from one inflorescence to the next. In a horizontally placed flower array, individual workers were experimentally rotated while imbibing sugar solution from an artificial flower mounted on a turntable. Rotation itself did not affect the subsequent departure direction. However, rotating the bees by 180° resulted in choices that were rotated by the same amount, as compared to the control treatment (i.e. no rotation). I suggest that flight directionality is determined in bees from the spatial orientation of their body before departure (e.g. by moving to the nearest flower they face).     

Incompletely informed shorebirds that face a digestive constraint maximize net energy gain when exploiting patches

Foragers that feed on hidden prey are uncertain about the intake rate they can achieve as they enter a patch. However, foraging success can inform them, especially if they have prior knowledge about the patch quality distribution in their environment. We experimentally tested whether and how red knots (Calidris canutus) use such information and whether their patch-leaving decisions maximized their long-term net energy intake rate. The results suggest that the birds combined patch sample information with prior knowledge by making use of the potential value assessment rule. We reject five alternative leaving rules. The potential encounter rate that the birds choose as their critical departure threshold maximized their foraging gain ratio (a modified form of efficiency) while foraging. The high experimental intake rates were constrained by rate of digestion. Under such conditions, maximization of the foraging gain ratio during foraging maximizes net intake rate during total time (foraging time plus digestive breaks). We conclude that molluscivore red knots, in the face of a digestive constraint, are able to combine prior environmental knowledge about patch quality with patch sample information to obtain the highest possible net intake over total time.     

Bumble bees (Bombus terrestris) store both food and information in honeypots

Social insect foragers often transmit information about foodsources to nest mates. In bumble bees (Bombus terrestris), forexample, successful foragers use excited motor displays anda pheromone as communication signals. In addition, bees couldmake use of an indirect pathway of information flow, via thehoney stores. We show here that, indeed, bees in the nest continuouslymonitor honeypots and sample their contents, thus obtaininginformation on supply and demand of nectar. When there is aninflux of nectar into the nest, the colony deploys more workersfor foraging. The number of new foragers depends on sugar concentration.Foragers returning with high-quality sugar solution displaymore "excited runs" on the nest structure. The recruits' response,however, does not depend on modulated behavior by foragers:more workers start to forage with high quality of incoming nectar,even when this nectar is brought by a pipette. Moreover, weshow that the readiness of bees to respond to recruitment signalsor incoming nectar also depends on colony demand. When colonynectar stores are full, the response of bees to equal amountsof nectar influx is smaller than when stores are empty. Whencolony nectar stores are depleted, foragers spend more timerunning excitedly and less time probing pots in the nest andrun with higher average speed, possibly to disperse the alertingpheromone more efficiently. However, more bees respond to nectarinflux to empty stores, whether or not this is accompanied byforager signals. Thus, honeypots serve to store informationas well as food.     

Habitat assessment by parasitoids: mechanisms for patch use behavior

Animals foraging for patchily distributed resources may optimizetheir foraging decisions concerning the patches they encounter,provided that they base these decisions on reliable informationabout the profitability of the habitat as a whole. Females ofthe parasitoid Lysiphlebus testaceipes exploit aphid hosts,which typically aggregate in discrete colonies. We show herehow between-colony travel time and the number of aphids in previouslyvisited colonies affect parasitoid foraging behavior. We firstassumed that parasitoids use travel time and previous colonysize to estimate a mean rate of fitness gain in the habitatand derived quantitative predictions concerning the effect ofthese two variables on patch residence time and patch-leavingrate of attack. We then tested these theoretical predictionsin laboratory experiments in which female parasitoids were allowedto visit two successive colonies. As predicted, the observedresidence time in the second colony increased with increasingtravel time and decreasing size of the first colony. Patch-leavingrate of attack decreased with increasing travel time but wasnot affected by previous colony size. These results suggestthat parasitoids use these two variables to assess habitat quality.However, discrepancies between the data obtained and quantitativepredictions show that the effect of travel time on patch usemay be more complex than assumed in our model.     

The effects of predation risk from crab spiders on bee foraging behavior

Recent studies have suggested that top–down effects ofpredation on plant–pollinator interactions may not be,as previously thought, rare and/or weak. In this paper, we explorethe effects of crab spiders (Araneae: Thomisidae) on the behaviorof 2 species of bee (Hymenoptera: Apidae) foraging for nectarand pollen on 3 different plant species in central Portugal.In 2 experiments, we found that the eusocial bee Apis melliferawas significantly less likely to inspect and accept a floweror inflorescence if it harbored a spider. In contrast, we foundno such effects of spiders on the behavior of the solitary beeEucera notata. Further experiments showed that the effects ofenvironmental cues associated with predators on flower visitationby A. mellifera were detectable even when no spider was presentat the moment a flower was encountered. Such indirect effectswere only identified, however, in bees foraging on 1 of 2 plantspecies studied. In a final experiment, A. mellifera was shownto respond negatively to the presence of the corpses of conspecificsglued to flowers. This suggests that prey corpses left exposedon petals or bracts by spiders provide an obvious cue that beescan use to avoid predators. These results add to a growing bodyof evidence that plant–pollinator interactions are notimmune to the effects of predation and suggest that the strengthof such effects vary both between and within species.     

Seasonal Variation in Parental Care Drives Sex-Specific Foraging by a Monomorphic Seabird

Evidence of sex-specific foraging in monomorphic seabirds is increasing though the underlying mechanisms remain poorly understood. We investigate differential parental care as a mechanism for sex-specific foraging in monomorphic Common Murres (Uria aalge), where the male parent alone provisions the chick after colony departure. Using a combination of geolocation-immersion loggers and stable isotopes, we assess two hypotheses: the reproductive role specialization hypothesis and the energetic constraint hypothesis. We compare the foraging behavior of females (n = 15) and males (n = 9) during bi-parental at the colony, post-fledging male-only parental care and winter when parental care is absent. As predicted by the reproductive role specialization hypothesis, we found evidence of sex-specific foraging during post-fledging only, the stage with the greatest divergence in parental care roles. Single-parenting males spent almost twice as much time diving per day and foraged at lower quality prey patches relative to independent females. This implies a potential energetic constraint for males during the estimated 62.8 ± 8.9 days of offspring dependence at sea. Contrary to the predictions of the energetic constraint hypothesis, we found no evidence of sex-specific foraging during biparental care, suggesting that male parents did not forage for their own benefit before colony departure in anticipation of post-fledging energy constraints. We hypothesize that unpredictable prey conditions at Newfoundland colonies in recent years may limit male parental ability to allocate additional time and energy to self-feeding during biparental care, without compromising chick survival. Our findings support differential parental care as a mechanism for sex-specific foraging in monomorphic murres, and highlight the need to consider ecological context in the interpretation of sex-specific foraging behavior.     

The use and misuse of public information by foraging red crossbills

Group foragers may assess patch quality more efficiently bypaying attention to the sampling behavior of group members foragingin the same patch (i.e., using "public information"). To determinewhether red crossbills (Loxia curvirostra) use public informationto aid their patch departure decisions, we conducted experimentsthat compared the sampling behavior of crossbills foraging ona two-patch system (one patch was always empty, one patch containingseeds) when alone, in pairs, and in flocks of three. When foragingalone, crossbills departed from empty patches in a way thatwas qualitatively consistent with energy maximization. We foundevidence for the use of public information when crossbills werepaired with two flock mates, but not when paired with one flockmate. When foraging with two flock mates, crossbills sampledapproximately half the number of cones on the empty patch beforedeparting as compared to when solitary. Furthermore, as expected ifpublic information is used, the variance in both the numberof cones and time spent on the empty patch decreased when crossbillsforaged with two flock mates as compared to when alone. Althoughhigh frequencies of scrounging reduce the availability of publicinformation, scrounging is usually uncommon in crossbills, apparentlybecause they exploit divisible patches. Consequently, publicinformation is likely to be important to crossbills in the wild.We also show that feeding performance is greatly diminishedwhen the feeding performances of flock mates differ. This providesa mechanism that will favor assortative grouping by phenotypewhen phenotypes affect feeding performance, which may in turnpromote speciation in some groups of animals.     

Carpenter Bee (Xylocopa micans) Risk Indifference and a Review of Nectarivore Risk-sensitivity Studies

This paper presents new results of risk-sensitive foraging studiesof the carpenter bee, Xylocopa micans, and reviews the workto date on risk sensitivity in nectarivores. In the field, nectarivoreschoose among alternative food sources (flowers) that differin the variabilities of their nectar rewards. In the lab, theforaging situation for carpenter bees was experimentally simplifiedby offering the bees a choice between either "low variance"or "high variance" artificial flowers. The two flower typesdiffered in their variabilities but offered the same expectedshortterm rates of net energy gain to test the predictions ofthe short-term rate maximization mechanism. Foragers were testedunder two energy budget conditions, hungry and well-fed, totest the predictions of the z-score model. Individual carpenterbees were indifferent to variability in both nectar volume andnectar sugar concentrations, and their risk-indifference wasunaffected by energy budget. These findings of risk indifferencesupport neither the variance discounting nor the z-score modelof risk sensitivity. Since the low and high variance flowertypes are equivalent for carpenter bees in short-term rate ofenergy gain, there can be no selection on carpenter bees tobe sensitive to variability based on differences in rate ofgain. Studies of risk sensitivity in honey bees and bumble beesusing variance in nectar concentration support this contention.These findings are compared with other nectarivore risk sensitivitystudies in order to highlight the most likely mechanisms underlyingaversion to variation in nectar rewards (short-term rate maximizing,the Weber-Fechner law of perception and learning non-empty flowers)and to suggest future research in the interplay of these threemechanisms.     

Honeybee (Apis mellifera ligustica) Response to Differences in Handling Time, Rewards and Flower Colours

Free flying honeybees were tested outdoors on blue–white and blue–yellow dimorphic artificial flower patches to examine the influence of reward difference, flower handling‐time difference and flower colour choice on foraging decisions. We employed different flower‐well depths to vary handling times (costs), and differences in sucrose molarity to vary reward quality. Tests were performed with 2 and 6 μl rewards to vary quantity. We show that when handling time is correlated with flower‐colour morphs on a pedicellate artificial flower patch, a honeybee's foraging behaviour is dependent on the flower colours used in the choice tests. This supports a honeybee foraging model where constraints are a significant factor in decision making. Bees visiting blue–yellow flower patches exhibited flower constancy to colour, where they restricted most visits to a single flower colour, some bees to blue and others to yellow, irrespective of handing time differences. When offered a choice of equally rewarding blue or white flowers, bees were not constrained by flower colour and chose to visit flowers with a lower handling time. When reward molarity varied with well depth between blue and white flowers, foragers chose shallow‐well flowers (short‐handling time) with a smaller net harvest rate over deep‐well flowers (long‐handling time) with a greater net harvest rate. Results using the blue–white dimorphic flower patch suggest that when foraging options simultaneously involve reward and handling‐time choices, honeybee forager behaviour is inconsistent with an absolute method of evaluating profit.     

Pollen foraging by bumblebees: Foraging patterns and efficiency on Lupinus polyphyllus

Summary Bumblebees foraging on vertical inflorescences start near the bottom and work upward, behavior commonly interpreted as a response to the greater amounts of nectar available in lower flowers. Lupinus polyphyllus, which produces no nectar, has more pollen available in upper flowers. Although bees are probably unable to detect this gradient, since pollen is hidden from their view, they still start low and forage upward. Therefore, we concluded that the bees' tendency to forage upward on vertical inflorescences is not tied to a reward gradient. In addition, bees use only about 15% of the flowers per inflorescence, although they could be much more efficient by visiting and revisiting every flower systematically. In general, revisits would not be penalized because most flowers contain enough pollen for several visits. Optimal foraging theory may not offer an adequate explanation for such gross inefficiency.     

Indirect cues in selecting a hunting site in a sit‐and‐wait predator

Sit‐and‐wait predators use relatively simple rules for their decisions to choose and leave a patch, such as using the direct presence of prey to select a hunting site. However, the direct presence of prey can only be used when there is a highly visited patch in the proximity of the predator. Therefore, it is plausible that sit‐and‐wait predators also exploit indirect cues of prey presence and, consequently, use associative learning to select a hunting site. The present study tests for the role of associative learning in a sit‐and‐wait predator species for which the ecology is well understood: Misumena vatia Clerck crab spiders. An ecologically relevant scenario is used by selecting flower colour as the conditioned stimulus and prey presence as the unconditioned stimulus. The results provide no evidence that M. vatia crab spiders use the association between flower colour and food presence for selecting a hunting site. After a training phase of being exposed to a colourful artificial flower highly visited by bees, spiders select a hunting site independently of its colour during the testing phase. Investigations of similar scope and ecological relevance are required with other sit‐and‐wait predators to identify the conditions promoting the use of associative learning for foraging site selection when animals face an unpredictable food supply.     

Departure rules used by bees foraging for nectar: A field test

Summary Departure rules used by solitary long-tongued bees (Anthophora spp. andEucera spp.) collecting nectar from flowers ofAnchusa strigosa (Boraginaceae) were studied. The amount of nectar a bee receives from an individual flower was estimated by measuring the time elapsed since the previous bee visit to that flower. Measurements of nectar accumulation in experimentally emptied flowers indicated that this time interval is an accurate predictor of nectar volumes in flowers. We found that nectar rewards influence the probability of departure from individual plants, as well as distances of movements within plants. The probability of departure from individual plants was negatively related to the amount of reward received at the two lastvisited flowers. This result indicates that the bees used a probabllistic departure rule, rather than a simple threshold departure rule, and that rewards from both the current and the previously visited flower were important in determining departure points. Distances of inter-flower movements within plants were negatively related to the amount of reward received at the current flower. The overall results suggest that the pollinators ofA. strigosa make two types of departure decisions-departures from the whole plant and departures from the neighbourhood of individual flowers-and that they use different departure rules for each scale. Factors influencing the decision-making processes of the observed foraging behaviour are discussed.     

Do cattle egrets gain information from conspecifics when foraging?

Summary We examined whether individual cattle egrets (Bubulcus ibis) base their decisions of where to forage, and how long to stay in a patch, on the behavior of other flock members. Cattle egrets commonly forage in flocks associated with cattle and capture prey at higher rates when they do not share a cow with another egret. Foraging egrets provide cues of the location of prey and their success in capturing prey. Therefore, there is the possibility of information transfer between egrets in a flock. We predicted that egrets should only move to occupied patches when the resident was capturing enough prey that it is profitable for the invader to share the patch or take over the patch. However, egrets did not seem to decide where to forage based on neighbors' rates of energy intake, but rather on the presence or absence of conspecifics in a patch. We also predicted that an egret should remain in a patch until its rate of energy intake dropped to or below the average rate for other egrets within the flock. However, egrets that were foraging more efficiently than the average rate for the flock switched patches sooner than less efficient foragers. Egrets did not appear to increase foraging success by gaining information on patch quality from neighbors.     

Testing predictions of foraging theory for a sit-and-wait forager, Anolis gingivinus

Research in foraging theory has been dominated by studies ofactive foragers choosing among patches and among prey withina patch. Studies of central-place foraging have mainly focusedon loading decisions of an animal provisioning a central place.The problem faced by a sit-and-wait forager that encountersprey at a distance has received little attention. In this studywe tested foraging theory predictions for such foragers, Anolisgingivinus females in the West Indies island of Anguilla. Wepresented lizards with antlion larvae at various distances.Experiment 1 showed that an individual's probability of pursuingprey decreases with the prey's distance and is best describedby a sigmoidal function (which may be as steep as a step function).This function's inflection point defines a cutoff distance.Experiment 3 tested how cutoff distance changes as a functionof prey size. Cutoff distances were greater for larger prey,as predicted for an energy-maximizing forager. Experiments 2and 4 tested how cutoff distance changes as a function of preyabundance. As predicted, cutoff distance were greater at a sitewhere prey abundance was lower. Furthermore, cutoff distancesdecreased immediately following prey augmentation and returnedto previous values within one day of ending augmentation. Thus,moles' foraging behavior is a dynamic process, consistent withthe qualitative predictions of foraging theory. We attributethe success of this study in supporting fundamental foragingtheory predictions to the lizards exhibiting natural behaviorunder field conditions and to particular advantages of studyingsit-and-wait foragers.     

Factors influencing seasonal absconding in colonies of the African honey bee,Apis mellifera scutellata

Summary This study investigated the effects of colony growth and development, food storage, foraging activity and weather on the migration behavior of African honey bees in the Okavango River Delta, Botswana. Four observation colonies were studied during the honey bee migration season (November–May), at which time the availability of blooming species was reduced. Two of the colonies (colonies 1 & 2) migrated during the study period, while the remaining two (colonies 3 & 4) did not. During the 4–6 weeks preceding the onset of migration preparations, colonies 1 & 2 exhibited increasing population sizes, high levels of brood production with low brood mortality, relatively large stores of food, and increasing mass. In contrast, the populations of colonies 3 & 4 did not increase, brood-rearing activity was erratic and lower, brood mortality was higher, food stores became depleted and colony mass declined. Both colonies 3 & 4 ceased rearing brood, and colony 3 died of starvation. Colony foraging activity was examined by monitoring waggle-dance activity 2–3 days each week. For 4–6 weeks before the onset of migration in colonies 1 & 2, daily foraging areas and mean daily foraging distances became increasingly large and variable. Colonies 3 & 4 exhibited foraging patterns similar to those observed for colonies 1 & 2 preceding migration. There was no clear association between 7 weather parameters examined and migration behavior. These data suggest that migration is influenced by an interaction of intra-colony demographics, food reserves and foraging patterns. Migration may be feasible only for those colonies that possess (1) a population of appropriate size and age structure to compensate for the natural attrition of older workers during the emigration process, and (2) sufficient food reserves for long-distance travel and the establishment of a new nest. Changing foraging patterns may reflect a deteriorating foraging environment, which may trigger the onset of migration preparations, provided that colony demographics and food reserves are conducive. Colonies that show decreased brood production, higher brood mortality and reduced food stores may be incapable of migrating, even when experiencing deteriorating foraging conditions. Rather, such colonies may have a greater chance of survival if they attempt to persist in a given area.     

Can honey bees change foraging patterns?

Abstract. 1. Foraging patterns were studied using honey bees on artificial flower patches to determine if given individuals could change behaviours under differing conditions.
2. Two types of flower patches were used; those simulating a population of flowers, dimorphic for colour, and grids simulating a single colour-dimorphic inflorescence.
3. In the simulated population of flowers bees were individually constant to colour over a range of reward volumes and flower patch sizes.
4. Each bee remained individually constant to a flower morph when visiting a population-type grid but changed to random visitation on the simulated inflorescence.
5. On the simulated inflorescence, with morphs providing unequal qualities of reward, most bees foraged on the higher molarity morph.
6. Most, but not all bees, failed to minimize uncertainty on the simulated inflorescence.
7. On the simulated inflorescence, bees failed to optimize when one morph provided a greater reward volume than did the other.
8. In the population of flowers bees flew from flower to flower, whereas, they walked on the simulated inflorescence.