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)]     

Effects of recent experience on foraging decisions by bumble bees

The temporal and spatial scales employed by foraging bees in sampling their environment and making foraging decisions should depend both on the limits of bumble bee memory and on the spatial and temporal pattern of rewards in the habitat. We analyzed data from previous experiments to determine how recent foraging experience by bumble bees affects their flight distances to subsequent flowers. A single visit to a flower as sufficient to affect the flight distance to the next flower. However, longer sequences of two or three visits had an additional effect on the subsequent flight distance of individual foragers. This suggests that bumble bees can integrate information from at least three flowers for making a subsequent foraging decision. The existence of memory for floral characteristics at least at this scale may have significance for floral selection in natural environments.     

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.     

Colour learning when foraging for nectar and pollen: bees learn two colours at once

Bees are model organisms for the study of learning and memory, yet nearly all such research to date has used a single reward, nectar. Many bees collect both nectar (carbohydrates) and pollen (protein) on a single foraging bout, sometimes from different plant species. We tested whether individual bumblebees could learn colour associations with nectar and pollen rewards simultaneously in a foraging scenario where one floral type offered only nectar and the other only pollen. We found that bees readily learned multiple reward–colour associations, and when presented with novel floral targets generalized to colours similar to those trained for each reward type. These results expand the ecological significance of work on bee learning and raise new questions regarding the cognitive ecology of pollination.     

Choice of flowers by foraging honey bees (Apis mellifera): possible morphological cues

Abstract.

• 1 Honey bees foraging for nectar on lavender (Lavandula stoechas) chose inflorescences with more of their flowers open. The number of open flowers predicted whether an inflorescence was visited by bees, inspected but rejected, or ignored. Inflorescences chosen arbitrarily by observers had numbers of open flowers intermediate between those of visited and ignored inflorescences.
• 2 Differences in morphological characters between types of inflorescence correlated with nectar volume and sugar weight per flower so that visited inflorescences had a disproportionately greater volume of nectar and weight of sugar per flower and greater variance in nectar volume.
• 3 Although there were significant associations between nectar content and the morphological characters of inflorescences, discriminant function analysis revealed discrimination on the basis of morphology rather than nectar content.
• 4 Visited inflorescences tended to have smaller than average flowers but bees tended to probe the largest flowers on visited inflorescences.
• 5 Choice of flowers within inflorescences is explicable in terms of the relationship between flower size and nectar content.

     

Heritable allometric variation in bumble bees: opportunities for colony-level selection of foraging ability

Different characters of an organism may be correlated if genes control the allometric relationship between them. If genetic variation exists for such genes then the allometric relation itself is potentially subject to change by selection. In social insects allometric relations represent colony-level characters. If colonies differ in these relations and this variation leads to differential productivity among colonies, then selection on allometric relations can operate at the level of the colony. We assessed the extent of heritable, between-colony variation for the allometric coefficients relating proboscis ( = glossa) length to wing length for two bumble bee species (Bombus huntii and B. occidentalis). We found that in both species colonies did not differ significantly in slope (b) but did differ significantly in intercept (a) of the regression of glossa length on wing length. Within-colony variation of the intercept was estimated by randomly constituting groups of five workers from each colony and calculating the regression for each group. The intraclass correlation was then calculated from the between- and within-colony mean squares. We found significant intraclass correlations in both species, giving heritabilities of 0.5 ± 0.3 in B. hunti and 0.7 ± 0.3 in B. occidentalis. If this allometric relation affects colony foraging success and foraging environments vary geographically, then the intercept should exhibit corresponding geographic variation. We tested this prediction by comparing intercepts calculated using wild-caught B. vagans workers from Alberta, Ontario and Maine. We found that the intercepts did differ significantly between sites, with the bees from Alberta having a significantly smaller intercept than the bees from eastern North America. Our results illustrate the opportunity for selection on an allometric relation that directly affects the foraging success of individual bumble bee colonies.     

Light intensity limits foraging activity in nocturnal and crepuscular bees

A crepuscular or nocturnal lifestyle has evolved in bees severaltimes independently, probably to explore rewarding pollen sourceswithout competition and to minimize predation and nest parasites.Despite these obvious advantages, only few bee species are nocturnal.Here we show that the sensitivity of the bee apposition eyeis a major factor limiting the ability to forage in dim light.We present data on eye size, foraging times, and light levelsfor Megalopta genalis (Augochlorini, Halictidae) in Panama,and Lasioglossum (Sphecodogastra) sp. (Halictini, Halictidae)in Utah, USA. M. genalis females forage exclusively during twilight,but as a result of dim light levels in the rain forest, theyare adapted to extremely low intensities. The likely factorlimiting their foraging activity is finding their nest entranceon return from a foraging trip. The lowest light intensity atwhich they can do this, both in the morning and the evening,is 0.0001 cd m^–2. Therefore, they leave the nest at dimmerlight levels in the morning than in the evening. Lasioglossum(Sphecodogastra) foraging is limited by light intensity in theevening, but probably by temperature in the morning in the temperateclimate of Utah. We propose that the evolution of nocturnalityin bees was favored by the large variance in the size of females.     

Foraging strategies of insects for gathering nectar and pollen, and implications for plant ecology and evolution

The majority of species of flowering plants rely on pollination by insects, so that their reproductive success and in part their population structure are determined by insect behaviour. The foraging behaviour of insect pollinators is flexible and complex, because efficient collection of nectar or pollen is no simple matter. Each flower provides a variable but generally small reward that is often hidden, flowers are patchily distributed in time and space, and are erratically depleted of rewards by other foragers. Insects that specialise in visiting flowers have evolved an array of foraging strategies that act to improve their efficiency, which in turn determine the reproductive success of the plants that they visit. This review attempts a synthesis of the recent literature on selectivity in pollinator foraging behaviour, in terms of the species, patch and individual flowers that they choose to visit.

The variable nature of floral resources necessitate foraging behaviour based upon flexible learning, so that foragers can respond to the pattern of rewards that they encounter. Fidelity to particular species allows foragers to learn appropriate handling skills and so reduce handling times, but may also be favoured by use of a search image to detect flowers. The rewards received are also used to determine the spatial patterns of searches; distance and direction of flights are adjusted so that foragers tend to remain within rewarding patches and depart swiftly from unrewarding ones. The distribution of foragers among patchy resources generally conforms to the expectations of two simple optimal foraging models, the ideal free distribution and the marginal value theorem.

Insects are able to learn to discriminate among flowers of their preferred species on the basis of subtle differences in floral morphology. They may discriminate upon the basis of flower size, age, sex or symmetry and so choose the more rewarding flowers. Some insects are also able to distinguish and reject depleted flowers on the basis of ephemeral odours left by previous visitors. These odours have recently been implicated as a mechanism involved in interspecific interactions between foragers.

From the point of view of a plant reliant upon insect pollination, the behaviour of its pollinators (and hence its reproductive success) is likely to vary according to the rewards offered, the size and complexity of floral displays used to advertise their location, the distribution of conspecific and of rewards offered by other plant species, and the abundance and behaviour of other flower visitors.     

Morphological correlates of nectar production used by honeybees

Abstract.  1. Honeybees foraging on lavender have been shown to choose inflorescences that are larger and have more flowers. If they are selecting optimally then these inflorescences should yield higher net rates of energy gain. The number and distribution of flowers within inflorescences is a complex function of age, however, which might itself influence nectar quality and availability.
2. Sampling of the overnight nectar secretion of visited and unvisited inflorescences showed that younger inflorescences with more flowers produced more sugar per flower and had fewer unproductive flowers than other inflorescences, but the size of the inflorescence had no effects.
3. Overall display size attracted bees to inspect inflorescences, as inflorescences that were inspected but rejected were larger and/or had larger or more bracts than those that were ignored. Bees, however, accepted more productive inflorescences based on different cues: inflorescence age and number of flowers.
4. Inflorescence choice thus appeared to reflect a two-stage decision process based on different morphological criteria at each stage.     

Spatial adaptations for plant foraging: women excel and calories count

We present evidence for an evolved sexually dimorphic adaptation that activates spatial memory and navigation skills in response to fruits, vegetables and other traditionally gatherable sessile food resources. In spite of extensive evidence for a male advantage on a wide variety of navigational tasks, we demonstrate that a simple but ecologically important shift in content can reverse this sex difference. This effect is predicted by and consistent with the theory that a sexual division in ancestral foraging labour selected for gathering-specific spatial mechanisms, some of which are sexually differentiated. The hypothesis that gathering-specific spatial adaptations exist in the human mind is further supported by our finding that spatial memory is preferentially engaged for resources with higher nutritional quality (e.g. caloric density). This result strongly suggests that the underlying mechanisms evolved in part as adaptations for efficient foraging. Together, these results demonstrate that human spatial cognition is content sensitive, domain specific and designed by natural selection to mesh with important regularities of the ancestral world.     

Seasonality of salt foraging in honey bees (Apis mellifera)

1. Honey bees (Apis mellifera) prefer foraging at compound‐rich, ‘dirty’, water sources over clean water sources. As a honey bee's main floral diet only contains trace amounts of micronutrients – likely not enough to sustain an entire colony – it was hypothesised that honey bees forage in dirty water for physiologically essential minerals that their floral diet, and thus the colony, may lack. 2. While there are many studies regarding macronutrient requirements of honey bees, few investigate micronutrient needs. For this study, from 2013 to 2015, a series of preference assays were conducted in both summer and autumn. 3. During all field seasons, honey bees exhibited a strong preference for sodium in comparison to deionised water. There was, however, a notable switch in preferences for other minerals between seasons. 4. Calcium, magnesium, and potassium – three minerals most commonly found in pollen – were preferred in autumn when pollen was scarce, but were avoided in summer when pollen was abundant. Thus, as floral resources change in distribution and abundance, honey bees similarly change their water‐foraging preferences. 5. Our data suggest that, although they are generalists with relatively few gustatory receptor genes, honey bee foragers are fine‐tuned to search for micronutrients. This ability likely helps the foragers in their search for a balanced diet for the colony as a whole.     

Temporal resource partitioning and climatological influences on colony flight and foraging of stingless bees (Apidae; Meliponini) in Ugandan tropical forests

We studied the flight activity of two stingless bee species (Meliponula ferruginea and Meliponula nebulata) and the environmental factors influencing their flight. Two morphs of M. ferruginea were studied: M. ferruginea (brown) in Budongo forest and M. ferruginea (black) in Bwindi Park. The two bee species exited their nests in characteristically distinct foraging bouts suggesting that the recruitment methods used may be direct leading or ‘piloting’. The number of individuals in a returning bout was less than that in an exiting bout suggesting recruits do not follow experienced foragers the whole distance to food source, a phenomenon referred to as ‘partial piloting’. Flight period of M. ferruginea (black) and M. nebulata in Bwindi was restricted to a few hours each day. Meliponula nebulata foraged in the drizzle; a survival strategy, which could promote its reproductive fitness. Nectar and pollen foraging took place throughout the day while the removal of debris was greater in the late hours of the morning. Increased temperature resulted in significant increase in number of exiting bees. There was increase in number of exiting bees with decrease in humidity up to an optimal of 78% thereafter, increase in humidity resulted in reduced number of exiting bees.     

Disentangling olfactory and visual information used by field foraging birds

Foraging strategies of birds can influence trophic plant–insect networks with impacts on primary plant production. Recent experiments show that some forest insectivorous birds can use herbivore‐induced plant volatiles (HIPVs) to locate herbivore‐infested trees, but it is unclear how birds combine or prioritize visual and olfactory information when making foraging decisions. Here, we investigated attraction of ground‐foraging birds to HIPVs and visible prey in short vegetation on farmland in a series of foraging choice experiments. Birds showed an initial preference for HIPVs when visual information was the same for all choice options (i.e., one experimental setup had all options with visible prey, another setup with hidden prey). However, if the alternatives within an experimental setup included visible prey (without HIPV) in competition with HIPV‐only, then birds preferred the visual option over HIPVs. Our results show that olfactory cues can play an important role in birds’ foraging choices when visual information contains little variation; however, visual cues are preferred when variation is present. This suggests certain aspects of bird foraging decisions in agricultural habitats are mediated by olfactory interaction mechanisms between birds and plants. We also found that birds from variety of dietary food guilds were attracted to HIPVs; hence, the ability of birds to use plant cues is probably more general than previously thought, and may influence the biological pest control potential of birds on farmland.     

The evolution of floral sonication,a pollen foraging behavior used by bees (Anthophila)

Over 22,000 species of biotically pollinated flowering plants, including some major agricultural crops, depend primarily on bees capable of floral sonication for pollination services. The ability to sonicate (“buzz”) flowers is widespread in bees but not ubiquitous. Despite the prevalence of this pollinator behavior and its importance to natural and agricultural systems, the evolutionary history of floral sonication in bees has not been previously studied. Here, we reconstruct the evolutionary history of floral sonication in bees by generating a time‐calibrated phylogeny and reconstructing ancestral states for this pollen extraction behavior. We also test the hypothesis that the ability to sonicate flowers and thereby efficiently access pollen from a diverse assemblage of plant species, led to increased diversification among sonicating bee taxa. We find that floral sonication evolved on average 45 times within bees, possibly first during the Early Cretaceous (100–145 million years ago) in the common ancestor of bees. We find that sonicating lineages are significantly more species rich than nonsonicating sister lineages when comparing sister clades, but a probabilistic structured rate permutation on phylogenies approach failed to support the hypothesis that floral sonication is a key driver of bee diversification. This study provides the evolutionary framework needed to further study how floral sonication by bees may have facilitated the spread and common evolution of angiosperm species with poricidal floral morphology.     

Actual vs perceived profitability: A study of floral choice of honey bees

The relationship between actual and perceived profitability was investigated by quantifying choice behavior of foraging honey bees (Apis mellifera).Rate of net energy gain was used as a measure of profitability. Individual bees repeatedly chose between a yellow and a blue tubular artificial flower which had different associated profitabilities. Handling costs were manipulated by using flowers of different depth;energy gains were manipulated by using different volumes of a 20% (w/w) sucrose solution. Bees' discrimination between the two flowers increased as the absolute difference in profitabilities increased and discrimination decreased as profitabilities of both flowers increased. Therefore, discrimination depended on the relative difference in profitability between flowers, and therefore, perception was a nonlinear function of actual rates of net energy gain. The results also suggested that motivation to choose between flowers depended on the level of profitability. We suggest that nonlinear perceptual scales and motivation should be incorporated into models of food choice as constraints and should be considered in the design of experiments used to test predictions of models and in the interpretation of experimental results.     

Caste-specific patterns of flower visitation in bumble bees (Bombus kirbyellus) collecting nectar from Polemonium viscosum

ABSTRACT.

• 1 Foraging routes of worker and queen bumble bees (Bombus kirbyellus Curtis) collecting nectar from flowers of the alpine sky pilot, Polemonium viscosum Nutt., were followed and the corolla tube length, corolla diameter, floral scent, and number of flowers on plants visited or bypassed by bees were monitored. Additionally, the number and proportion of flowers visited per inflorescence and distance flown from each to the next were recorded. Queens and workers differed significantly in choice of flowers. However, intra-inflorescence visitation rates and departure distances were similar between castes. Castes differed in the extent to which visitation reflected patch quality versus individual floral traits.
• 2 Both queens and workers failed to visit skunky-flowered plants more often than they failed to visit sweet-flowered ones, and preferred large over small inflorescences. However, queens visited large-flowered plants more often than small-flowered ones, while workers preferred flowers with shorter corolla tubes, regardless of their diameter. Although a number of studies have documented caste specialization on alternate species of host plants, ours is one of the first to show that morphological preferences promote comparable foraging differences between castes on monospecific plant resources.
• 3 Queens, once on a plant, responded to floral traits by probing more flowers on large inflorescences, as well as on those with broader floral form. Workers did not alter intra-inflorescence visitation rate in response to floral traits.
• 4 For workers, no significant relationship was demonstrated between the likelihood of passing by a plant and the number of flowers probed on the previous inflorescence visited. Thus, workers appeared to accept or reject each plant of P. viscosum independently. However, queens passed by fewer plants when leaving rich inflorescences than poor ones. These results suggest that workers use only individual plant acceptability in choosing which plants to visit, whereas queens base plant choice on patch and individual attributes. Such differences between castes in foraging rules when exploiting the same floral resource have received little attention, and provide insights into the heterogeneity of harvestable reward distributions from the perspective of the forager population.

     

Using niche construction theory to generate testable foraging hypotheses at Liang Bua

Niche construction theory (NCT) has emerged as a promising theoretical tool for interpreting zooarchaeological material. However, its juxtaposition against more established frameworks like optimal foraging theory (OFT) has raised important criticism around the testability of NCT for interpreting hominin foraging behavior. Here, we present an optimization foraging model with NCT features designed to consider the destructive realities of the archaeological record after providing a brief review of OFT and NCT. Our model was designed to consider a foragers decision to exploit an environment given predation risk, mortality, and payoff ratios between different ecologies, like more‐open or more‐forested environments. We then discuss how the model can be used with zooarchaeological data for inferring environmental exploitation by a primitive hominin, Homo floresiensis, from the island of Flores in Southeast Asia. Our example demonstrates that NCT can be used in combination with OFT principles to generate testable foraging hypotheses suitable for zooarchaeological research.