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Unrewarding artificial flowers that trapped approaching bumblebees were used here for the first time to assess the effects of several floral characteristics on floral attractiveness to bumblebees that never obtained food from flowers. Floral size and floral scent had no discernable effect. In a comparison between two colors (white and blue) and two shapes (radial and square), choice proportions for blue radial flowers were significantly greater than chance. Our proposed method is an alternative to prior training, with food associated either with visual or olfactory stimuli, which is unnecessary to obtain floral preferences by free-flying bumblebees exploring potential food sources. [ABSTRACT FROM AUTHOR]

Plants often attract pollinators with floral displays composed of visual, olfactory, tactile and gustatory stimuli. Since pollinators' responses to each of these stimuli are usually studied independently, the question of why plants produce multi-component floral displays remains relatively unexplored. Here we used signal detection theory to test the hypothesis that complex displays reduce a pollinator's uncertainty about the floral signal. Specifically, we asked whether one component of the floral display, scent, improved a bee's certainty about the value of another component, color hue. We first trained two groups of bumble bees (Bombus impatiens Cresson) to discriminate between rewarding and unrewarding artificial flowers of slightly different hues in the presence vs absence of scent. In a test phase, we presented these bees with a gradient of floral hues and assessed their ability to identify the hue rewarded during training. We interpreted the extent to which bees' preferences were biased away from the unrewarding hue (`peak shift') as an indicator of uncertainty in color discrimination. Our data show that the presence of an olfactory signal reduces uncertainty regarding color: not only was color learning facilitated on scented flowers but also bees showed a lower amount of peak shift in the presence of scent. We explore potential mechanisms by which scent might reduce uncertainty about color, and discuss the broader significance of our results for our understanding of signal evolution. [ABSTRACT FROM AUTHOR]

Preference for certain types of flowers in bee species may be an adaptation for efficient foraging, and they often prefer flowers whose shape fits their mouthparts. However, it is unclear whether such flowers are truly beneficial for them. We address this issue by experimentally measuring foraging efficiency of bumblebees, the volume of sucrose solution consumed over handling time (µL/second), using long-tongued Bombus diversus Smith and short-tongued B. honshuensis Tkalcu that visit Clematis stans Siebold et Zuccarini. The corolla tube length of C. stans decreases during a flowering period, and male flowers are longer than female flowers. Long- and short-tongued bumblebees frequently visited longer and shorter flowers, respectively. Based on these preferences, we hypothesized that bumblebee foraging efficiency is higher when visiting flowers that show a good morphological fit between the proboscis and the corolla tube. Foraging efficiency of bumblebees was estimated using flowers for which nectar quality and quantity were controlled, in an experimental enclosure. We show that 1) the foraging efficiency of B. diversus was enhanced when visiting younger, longer flowers, and that 2) the foraging efficiency of B. honshuensis was higher when visiting shorter female flowers. This suggests that morphological correspondence between insects and flowers is important for insect foraging efficiency. However, in contradiction to our prediction, 3) short-tongued bumblebees B. honshuensis sucked nectar more efficiently when visiting younger, longer flowers, and 4) there was no significant difference in the foraging efficiency of B. diversus between flower sexes. These results suggest that morphological fit between the proboscis and the corolla tube is not a sole determinant of foraging efficiency. Bumblebees may adjust their sucking behavior in response to available rewards, and competition over rewards between bumblebee species might change visitation patterns in the wild. Thus, the determinants of foraging efficiency and visitation frequency for bee pollinators may be more complex than previously thought. [ABSTRACT FROM AUTHOR]

It is now recognized that many vertebrates and a few invertebrates show individual-specific consistency in their behaviour across time and context, sometimes in ways that can be paralleled with human personality. Our work aimed at assessing behavioural consistency in a social insect: the bumblebee Bombus terrestris. We focused on a behavioural dimension commonly used in personality studies: the response of an individual to novelty (neophilia/neophobia spectrum). We used a foraging paradigm to quantify individual bees’ response to novel flower colours and to assess the repeatability of this response over time. As for vertebrates, most individual bumblebees responded to a novel stimulus by increasing the time they spent investigating it compared to known stimuli. Using a new statistical approach, the consistency model, we found that individual bees tended to be consistent in their response to novelty over a few hours but were not consistent in their behaviour over 3 days. We conclude that for the neophilia/neophobia paradigm used here, bumblebee foragers do not fulfil the criteria for animal personality in the common sense of the term. Instead their behavioural response to novelty appears to be plastic, varying on a day to day basis. [ABSTRACT FROM AUTHOR]

In modelling bumble bee foraging, net rate of energetic intake has been suggested as the appropriate currency. The foraging behaviour of honey bees is better predicted by using efficiency, the ratio of energetic gain to expenditure, as the currency. We re-analyse several studies of bumble bee foraging and show that efficiency is as good a currency as net rate in terms of predicting behaviour. We suggest that future studies of the foraging of bumble bees should be designed to distinguish between net rate and efficiency maximizing behaviour in an attempt to discover which is the more appropriate currency. [ABSTRACT FROM AUTHOR]

Circadian clocks enable organisms to anticipate changes of environmental conditions. In social insects, the colony as a superorganism has a foraging rhythm aligned to the diurnal patterns of resource availability. Within this colony rhythm, the diurnal patterns of individuals are embedded, and various tasks within the colony are performed at different times by different individuals to best serve the colony as a whole. Recent studies have shown that social cues influence the traits of the circadian clock in social insects, but keeping track of the activity of individual workers is not an easy task. Here the authors use fully automatic radio-frequency identification (RFID) to analyze the circadian rhythms of bumblebee foragers (Bombus terrestris) in the normal social context of their nest. They monitored their foraging patterns under different light conditions in the laboratory, including light:dark cycles (LD) as well as constant darkness (DD) and constant light conditions (LL). Their results show that the majority of bumblebee foragers exhibit robust circadian rhythms in LD under laboratory conditions, while they show free-running rhythms both in DD and LL, with free-running periods being significantly shorter in LL conditions. The authors also found that bumblebee workers show an increased level of arrhythmic activity ("death dance") in the hours or days before their death. [ABSTRACT FROM AUTHOR]

Using scanning electron microscope, eight types of sensilla were found on the antennae of all castes in eight Bombus species (Hymenoptera: Apidae) collected in Jilin Province, China. The numbers of various types of antennal sensilla were analyzed by rough set data analysis method to determine which sensillum type might be useful in species and caste discrimination. The results showed that the number of sensilla basiconica A, B (s. t. a, s. t. b), sensilla trichodea A, B, C/ D (s. t. a, s. t. b, s. t. c/ d) and sensilla placodea (s. p) can be used in species discrimination, whereas only types s. t. a, s. t. b, and s. t. b are relevant in caste discrimination. Other types of sensilla had a lower taxonomic value for species and caste discrimination. This study provides a mathematic reference for the function research of antennal sensilla of Bombus determined by single-cell recording at both peripheral and antennal lobe (central nervous system) levels. [ABSTRACT FROM AUTHOR]

Brain plasticity is a common phenomenon across animals and in many cases it is associated with behavioral transitions. In social insects, such as bees, wasps and ants, plasticity in a particular brain compartment involved in multisensory integration (the mushroom body) has been associated with transitions between tasks differing in cognitive demands. However, in most of these cases, transitions between tasks are age-related, requiring the experimental manipulation of the age structure in the studied colonies to distinguish age and experience-dependent effects. To better understand the interplay between brain plasticity and behavioral performance it would therefore be advantageous to study species whose division of labor is not age-dependent. Here, we focus on brain plasticity in the bumblebee Bombus occidentalis, in which division of labor is strongly affected by the individual’s body size instead of age. We show that, like in vertebrates, body size strongly correlates with brain size. We also show that foraging experience, but not age, significantly correlates with the increase in the size of the mushroom body, and in particular one of its components, the medial calyx. Our results support previous findings from other social insects suggesting that the mushroom body plays a key role in experience-based decision making. We also discuss the use of bumblebees as models to analyze neural plasticity and the association between brain size and behavioral performance. Copyright © 2010 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Insects use visual estimates of flight speed for a variety of behaviors, including visual navigation, odometry, grazing landings and flight speed control, but the neuronal mechanisms underlying speed detection remain unknown. Although many models and theories have been proposed for how the brain extracts the angular speed of the retinal image, termed optic flow, we lack the detailed electrophysiological and behavioral data necessary to conclusively support any one model. One key property by which different models of motion detection can be differentiated is their spatiotemporal frequency tuning. Numerous studies have suggested that optic-flow-dependent behaviors are largely insensitive to the spatial frequency of a visual stimulus, but they have sampled only a narrow range of spatial frequencies, have not always used narrowband stimuli, and have yielded slightly different results between studies based on the behaviors being investigated. In this study, we present a detailed analysis of the spatial frequency dependence of the centering response in the bumblebee Bombus impatiens using sinusoidal and square wave patterns. [ABSTRACT FROM AUTHOR]

It has been argued that trichromatic bees with photoreceptor spectral sensitivity peaks in the ultraviolet (UV), blue and green areas of the spectrum are blind to long wavelengths (red to humans). South American temperate forests (SATF) contain a large number of human red-looking flowers that are reported to be visited by the bumblebee Bombus dahibomli. In the present study, B. dahlbomii's spectral sensitivity was measured through electroretinogram (ERG) recordings. No extended sensitivity to long wavelengths was found in B. dahlbomii. The spectral reflectance curves from eight plant species with red flowers were measured. The color loci occupied by these flowers in the bee color space was evaluated using the receptor noise-limited model. Four of the plant species have pure red flowers with low levels of chromatic contrast but high levels of negative L-receptor contrast. Finally, training experiments were performed in order to assess the role of achromatic cues in the detection and discrimination of red targets by B. dahlbomii. The results of the training experiments suggest that the bumblebee relies on achromatic contrast provided by the L-receptor to detect and discriminate red targets. These findings are discussed in the context of the evolutionary background under which the relationship between SATF species and their flower visitors may have evolved. [ABSTRACT FROM AUTHOR]

I present an increment-decay model for the mechanism of bumble bees’ decision to depart from inflorescences. The probability of departure is the consequence of a dynamic threshold level of stimuli necessary to elicit a stereotyped landing reaction. Reception of floral nectar lowers this threshold, making the bee less likely to depart. Concurrently the threshold increases, making departure from the inflorescence more probable. Increments to the probability of landing are an increasing, decelerating function of nectar volume, and are worth less, in sequence, for the same amount of nectar. The model is contrasted to threshold departure rules, which predict that bees will depart from inflorescences if the amount of nectar in the last one or two flowers visited is below a given level. Field tests comparing the two models were performed with monkshood (Aconitum columbianum). Treated flowers contained a descending series of nectar volumes (6 to 0 μL of 30%sucrose solution). The more nectar that bees encountered in the treated flowers, the more likely they were to remain within the inflorescence after subsequently visiting one to three empty flowers. I discuss the differences between rules and mechanisms in regard to cognitive models of foraging behavior. [ABSTRACT FROM AUTHOR]

Social insect societies are considered to be composed of many extremely cooperative individuals. While workers are traditionally believed to behave altruistically, recent studies have revealed behaviors that are more selfish. One such example is intraspecific social parasitism, where workers invade conspecific colonies and produce male offspring that are reared by unrelated host workers. Such intraspecific parasitism has been reported in honeybees ( Apis cerana, and A. florea) and “semi-wild” bumblebee colonies of Bombus terrestris. Here we report on intraspecific social parasitism by workers in “wild” colonies of the bumblebee B. deuteronymus. Three of the 11 B. deuteronymus colonies studied were invaded by non-natal workers, of which 75% became reproductive and produced 19% of the adult males. The invading non-natal workers produced significantly more males than resident natal workers and the non-natal brood was not discriminated against by the natal workers. [ABSTRACT FROM AUTHOR]

Inbreeding frequently has a costly impact on fitness, thus selection has favoured the evolution of kin recognition and inbreeding avoidance behaviour in many species. As haplodiploid Hymenoptera, bumblebees are susceptible to additional costs of inbreeding due to their single-locus complementary sex determination (sl-CSD) system, which means that incest can result in the production of costly diploid males. Here we test whether Bombus terrestris reproductives are able to discriminate between kin and non-kin and whether their willingness to mate is adjusted accordingly. We found that B. terrestris reproductives took significantly longer to mate with siblings compared to non-relatives. This indicates that this species exhibits kin recognition and uses this information to determine mating behaviour. [ABSTRACT FROM AUTHOR]

Commercial bumblebee colonies are important crop pollinators. Here we assess whether application of artificial foraging recruitment pheromone can increase foraging activity in Bombus terrestris colonies on a relevant timescale for commercial pollination. We measured bee traffic from the nest to a foraging arena, which is correlated with foraging activity under natural recruitment conditions. During continuous pheromone exposure bee traffic increased by 1.5 to 3.6 times, and this increase lasted up to 105?minute. Repeated 20 minute exposures of a colony to recruitment pheromone, with at least 30 minutes intermissions, triggered consistent traffic increases over a four week period. We conclude that artificial recruitment pheromone can reliably boost bee traffic leaving previously inactive colonies. This method could improve foraging activity and pollination in greenhouse colonies, especially young colonies reluctant to start foraging after introduction to the crop. [ABSTRACT FROM AUTHOR]

Many bees and wasps learn about the immediate surroundings of their nest during learning flights, in which they look back towards the nest and acquire visual information that guides their subsequent returns. Visual guidance to the nest is simplified by the insects' tendency to adopt similar viewing directions during learning and return flights. To understand better the factors determining the particular viewing directions that insects choose, we have recorded the learning and return flights of a groundnesting bumblebee in two visual environments an enclosed garden with a partly open view between north and west, and a flat roof with a more open panorama. In both places, bees left and returned to an inconspicuous nest hole in the centre of a tabletop, with the hole marked by one or more nearby cylinders. In all experiments, bees adopted similar preferred orientations on their learning and return flights. Bees faced predominantly either north or south, suggesting the existence of two attractors. The bees' selection between attractors seems to be influenced both by the distribution of light, as determined by the shape of the skyline, and by the direction of wind. In the partly enclosed garden with little or no wind, bees tended to face north throughout the day, i.e. towards the pole in the brighter half of their surroundings. When white curtains, which distributed skylight more evenly, were placed around the table, bees faced both north and south. The bees on the roof tended to face south or north when the wind came from a wide arc of directions from the south or north, respectively. We suggest that bees switch facing orientation between north and south as a compromise between maintaining a single viewing direction for efficient view-based navigation and responding to the distribution of light for the easier detection of landmarks seen against the ground or to the direction of the wind for exploiting olfactory cues. [ABSTRACT FROM AUTHOR]

Iridescence, the change in hue of a surface with varying observation angles, is used by insects, birds, fish, and reptiles for species recognition and mate selection. We identified iridescence in flowers of Hibiscus trionum and Tulipa species and demonstrated that iridescence is generated through diffraction gratings that might be widespread among flowering plants. Although iridescence might be expected to increase attractiveness, it might also compromise target identification because the object's appearance with vary depending on the viewer's perspective. We found that bumblebees (Bombus terrestris) learn to disentangle flower iridescence from color and correctly identify iridescent flowers despite their continuously changing appearance. This ability is retained in the absence of cues from polarized light or ultraviolet reflectance associated with diffraction gratings. [ABSTRACT FROM AUTHOR]

Pollinators are confronted with spatial heterogeneity in floral resources. Acquiring information about their environment enables pollinators to exploit floral resources optimally, and hence strongly affects their fitness. Despite their evolutionary importance, spatial resource distribution and social information use have never been addressed in a plant–pollinator framework. We experimentally tested the effects of inadvertent social information (ISI) use (without or with an experienced demonstrator) in relation to spatial flower distribution (random or patchy) in foraging Bombus terrestris. We studied naïve bees'' associative learning when confronted with rewarding and nonrewarding flowers that differed slightly in colour, reproducing the natural mimicry of deceptive species. Naïve bees were more efficient foragers with than without a demonstrator in the patchy flower distribution, suggesting that they used ISI from conspecifics, probably in the form of social attraction at the patch scale. In the random flower distribution, however, ISI did not improve performance of naïve bees, and could not replace individual sampling. Analyses of nonrewarding intraspecific transitions indicate that the efficiency of naïve bees in deceptive species pollination was lowered when rewarding and nonrewarding inflorescences were patchily distributed and especially when bees relied on ISI. Thus, spatial flower distribution and ISI availability interact in determining pollinator behaviour, which has important consequences for plant community pollination. This suggests that bumblebees are adapted to exploit patchily distributed resources socially, a characteristic that might be exploited by deceptive plant species. By coupling behavioural and community ecology, this study offers promising perspectives for cognitive ecology studies in plant–pollinator interactions. [Copyright &y& Elsevier]

We lack a mechanism that links wing wear with mortality in foraging social insects. This study tests the hypothesis that wing wear strongly degrades foraging flight performance, thereby providing a biomechanical explanation for the wing wear - mortality relationship. We examine the effect of simulated wing wear - wing area reduction and asymmetry - on the flight behaviour of bumble bee (Bombus flavifrons Cresson, 1863) workers moving between vertically oriented flowers spaced 30 cm apart and arranged in a two-dimensional horizontal grid. Flight behaviour was measured in three dimensions as total flying distance, mean velocity, variability of velocity, maximum acceleration, maximum deceleration, percentage of time spent accelerating, and displacement from a straight line path between flowers. Loss of wing area had surprisingly little effect on flight behaviour. Viewed multivariately, bees with low asymmetry and low loss of mean area, or with high asymmetry and high loss of mean area, differed from the other three treatment groups. When bees were burdened with both high asymmetry and high loss of wing area, their between-flower flight path was less direct. Overall, flight behaviour of bumble bees was highly resilient to major changes in wing area and asymmetry in this simple foraging environment. The wing wear-associated causes of increased mortality remain elusive. Il n’existe pas de mécanisme pour relier l’usure des ailes à la mortalité chez les insectes sociaux qui font des quêtes alimentaires. Notre étude teste l’hypothèse selon laquelle l’usure des ailes réduit considérablement la performance des vols de recherche de nourriture, ce qui fournit une explication biomécanique de la relation entre l’usure des ailes et la mortalité. Nous examinons l’effet d’une usure simulée des ailes - par réduction de la taille et asymétrie des ailes - sur le comportement de vol d’ouvrières de bourdon (Bombus flavifrons Cresson, 1863) qui se déplacent entre des fleurs à orientation verticale placées à 30 cm les unes des autres selon une grille horizontale bidimensionnelle. Le comportement vol a été évalué en trois dimensions d’après les variables suivantes: distance totale de vol, vitesse moyenne, variabilité de la vitesse, accélération maximale, décélération maximale, % du temps passé à l’accélération et déviation du trajet de la ligne droite entre les fleurs. La perte de surface alaire a étonnamment peu d’effet sur le comportement de vol. Dans une perspective multidimensionnelle, les abeilles qui possèdent une asymétrie et une perte de surface moyenne faibles et celles qui ont une asymétrie et une perte de surface moyenne fortes diffèrent des trois autres groupes expérimentaux. Lorsque les abeilles sont affligées à la fois par une forte asymétrie et une perte importante de surface alaire, leur trajet de vol entre les fleurs est moins direct. En somme, le comportement de vol des bourdons est très résilient aux changements importants de surface alaire et d’asymétrie dans cet environnement simple de recherche de nourriture. Les causes de mortalité accrue reliées à l’usure des ailes restent toujours difficiles à cerner. [ABSTRACT FROM AUTHOR]

A major determinant of bumblebees pollination efficiency is the distance of pollen dispersal, which depends on the foraging distance of workers. We employ a transect setting, controlling for both forage and nest location, to assess the foraging distance of Bombus terrestris workers and the influence of environmental factors on foraging frequency over distance. The mean foraging distance of B.?terrestris workers was 267.2?m???180.3?m (max. 800?m). Nearly 40% of the workers foraged within 100?m around the nest. B. terrestris workers have thus rather moderate foraging ranges if rewarding forage is available within vicinity of the nests. We found the spatial distribution and the quality of forage plots to be the major determinants for the bees foraging decision-making, explaining over 80% of the foraging frequency. This low foraging range has implications for using B.?terrestris colonies as pollinators in agriculture. [ABSTRACT FROM AUTHOR]

Bumblebees were trained to discriminate between two patterns, one rewarding (S+) and another unrewarding (S-) consisting of four orthogonal bars. Training and testing conditions were manipulated in a 2 X 2 between groups design. The training patterns differed only in the positioning of the bars in the inferior or the superior portion. The same was true of the testing patterns, both of which were unrewarding. A significant interaction between training and testing conditions was obtained on preference for one pattern, the diamond, which was present at testing for all four conditions. For the groups that were trained with the patterns that differed only in the inferior portion, when tested with patterns that differed in (1) the inferior portion: the diamond, for which the inferior portion matched that of the S+, was chosen at a level significantly above chance (2) the superior portion: the preference for the diamond disappeared--no discrimination was found, even though the alternative to the diamond was the same as the S+. For the groups that were trained with the patterns that differed only in the superior portion, the opposite effect of testing conditions was found: when tested with patterns that differed in (1) the inferior portion: the bees avoided the very same diamond that was preferred by the bees trained differently, and favoured the alternative, which was the same as the S+ (2) the superior portion: no pattern discrimination was found (i.e. the avoidance of the diamond disappeared). Two predictions were disconfirmed: that during testing bees would only (1) approach the pattern that was the same as the S+, or (2) discriminate between patterns that differed in the same area (inferior or superior) as did the training patterns. The data were in line with the interpretation that during differential conditioning the visual field used in future pattern discriminations is expanded to include not only the inferior portion of the pattern but more of the superior portion as well. [ABSTRACT FROM AUTHOR]

1. In social insects, reproductive success and survival of the colony critically depend on the colony's ability to efficiently allocate workers to the various tasks which need to be performed. In bumblebees, workers show a large variation of body size within a colony. Large workers tend to leave the nest and forage for nectar and pollen, whereas small workers stay inside the nest and fulfill nest duties. It was speculated that size-related differences of the sensory system might contribute to alloethism found in bumblebee colonies. 2. In the first part, we investigated how body size determines eye morphology. We measured several eye parameters of Bombus terrestris workers and drones. In both, workers and drones, larger individuals had larger eyes with larger facet diameters, more ommatidia and larger ocelli. At similar body size, drones exhibited larger eyes and ocelli compared to workers. Due to theoretical considerations, we predict that large individuals with large eyes should be better able to operate in illumination conditions of lower intensity than small individuals, since ommatidial sensitivity is proportional to the square of facet diameter. 3. In the second part, we tested this prediction. In a behavioural experiment, we first caught bumblebees of various sizes in the field and then determined the lowest light intensity level at which they are just able to fly under controlled laboratory conditions. We tested workers of B. terrestris and B. pascuorum, and workers and drones of B. lapidarius. Large bumblebees were able to fly under lower light levels compared to small bees, with light intensity thresholds ranging from 1·1 to 5·5 lux. 4. Our results indicate that the increased light sensitivity of the visual system of large bumblebees allows them to fly under poor light conditions, for example, very early in the morning or late at dusk. This is of potential benefit to the survival of a bumblebee colony since flowers that open early in the morning usually have accumulated a relatively high amount of nectar and pollen throughout the night, and large bumblebees can utilize these resources earlier than most other bees. Thus, our findings have important implications for the understanding of the functional significance and evolution of alloethism in bumblebee colonies. [ABSTRACT FROM AUTHOR]

In socially living animals, individuals interact through complex networks of contact that may influence the spread of disease. Whereas traditional epidemiological models typically assume no social structure, network theory suggests that an individual’s location in the network determines its risk of infection. Empirical, especially experimental, studies of disease spread on networks are lacking, however, largely due to a shortage of amenable study systems. We used automated video-tracking to quantify networks of physical contact among individuals within colonies of the social bumble bee Bombus impatiens. We explored the effects of network structure on pathogen transmission in naturally and artificially infected hives. We show for the first time that contact network structure determines the spread of a contagious pathogen ( Crithidia bombi) in social insect colonies. Differences in rates of infection among colonies resulted largely from differences in network density among hives. Within colonies, a bee’s rate of contact with infected nestmates emerged as the only significant predictor of infection risk. The activity of bees, in terms of their movement rates and division of labour (e.g., brood care, nest care, foraging), did not influence risk of infection. Our results suggest that contact networks may have an important influence on the transmission of pathogens in social insects and, possibly, other social animals. [ABSTRACT FROM AUTHOR]

Seed production may be limited because flowers do not get enough suitable pollen or because plants lack the resources to make seeds. We used replicated plantings to test factors that influence effects of bumblebee behavior on pollen limitation, as measured by the difference in seed set between hand- and naturally pollinated flowers, of Penstemon digitalis in patches of four to 41 flowering individuals. Seed set per flower was 376% higher in the largest as compared with the smallest Penstemon patches. This positive density dependence reflects activity of long-tongued bees, which (1) have higher effective density as patch size increases, (2) visit greater proportions of plants as patch size increases, and (3) visit smaller proportions of flowers per visited plant as patch size increases. Our results suggest that economics of flight and maneuverability of large, long-tongued bumblebees lead them to transfer more pollen between than within Penstemon plants in large patches. Density of smaller, short-tongued bumblebees was not positively associated with Penstemon seed set, but these bees may be important pollinators at low plant densities. Our experimental system indicates a clear positive relationship between activity of effective pollinators and seed set in a species capable of pollinating itself. [ABSTRACT FROM AUTHOR]

An exotic bumblebee species, Bombus terrestris, has colonized in Japan and becomes dominant in some local communities. We examined the effects of land use and bumblebee abundance on the number and body size of bumblebees collected using window traps in a lowland area in the southern Ishikari district, Hokkaido. In 2004, we collected 922 bumblebees of six species using 70 traps at 17 sites. A statistical model fitted to the data demonstrated that dispersion from commercial B. terrestris colonies used in greenhouses positively affected the number of B. terrestris caught by each trap. This exotic species was abundant in sites where paddy fields were prevalent, but three native species, B. hypocrita, B. ardens, and B. diversus, were abundant in sites where farms and woodlands were widespread. The local abundance of B. terrestris was not associated negatively with the number and body size of native bumblebees. Thus, we did not find any competitive interactions between exotic and native bumblebees although habitat conditions seem to be common determinants of the bumblebee populations. A morphological analysis showed that B. terrestris had intermediate tongue length between B. hypocrita and B. ardens. [ABSTRACT FROM AUTHOR]

1. Most pollination biologists have used the collective pollinator visits to a plant as the measure of its pollinator attraction. However, we know very little about how many returns by the same individuals compose these visits, and how far each visitor travels after leaving the plant. Such behavioural aspects of individual pollinators are essential to understand the patterns of pollen flow among plants. 2. We observed plant visits by tagged bumble bees Bombus diversus in a field population of Cirsium purpuratum. By dissecting the collective visitation data into visits made by individual foragers, we addressed how ‘visitor density’ (number of individuals that visited a plant per 2 h) and ‘individual visitation rate’ (number of visits made by each individual per 2 h) are related to floral display size (number of flowering heads on a plant) and local flower density (number of flowering heads on neighbouring plants). We also tracked individual bees to determine how display size and local flower density of a plant influences its relative position in a bee's foraging area. 3. Plants attracted both regular visitors (bees that visited a plant more than three times per 2 h) and occasional visitors (bees that visited a plant fewer than four times per 2 h). Densities of both types of visitors increased with floral display size, whereas only occasional visitor's density increased with local flower density. 4. Individual bees preferred to visit central plants within their own foraging areas, plants with larger displays, and plants with lower local flower density. However, these preferences were independent from one another. Plants with large displays were not necessarily chosen by a bee as the centre of its own foraging area. On the other hand, plants with high local flower density were often located near the centre of a bee's foraging area. 5. The observed pollinator movements have implications for pollen flow in the plant population. Plants with larger displays probably experience greater mate diversity by attracting more occasional visitors, but they also assure matings with particular plants by increasing returns from regular visitors. [ABSTRACT FROM AUTHOR]

An environmental study of pollinator effectiveness of Bumblebees in Agapanthus compared to other insects in the region of Tasmania is presented. White and blue naturalized flowers (Agapanthus) of the area with pollen loads of 9-10 specimens for each of Bumblebees and other pollinator insects were considered for the study. From the product of the number of flower visits, the percentage of visits that involved stigmatic contact, and the mean number of Agapanthus pollen grains per insect type, the pollinator effectiveness score was calculated for each insect type. The study concluded Bumblebee workers/drones were the most common visitors to flowers of Agapanthus, followed by honeybees and other insects.

We presented bumblebees a spatial memory task similar to that used with other species (e.g., cats, dogs, and pigeons). In some conditions we allowed for presence of scent marks in addition to placing local and global spatial cues in conflict. Bumblebees ( Bombus impatiens) were presented an array of artificial flowers within a flight cage, one flower offering reward (S+), while the others were empty (S−). Bees were tested with empty flowers. In Experiment 1, flowers were either moved at the time of testing or not. Bees returned to the flower in the same absolute position of the S+ (the flower-array-independent (FAI) position), even if it was in the wrong position relative to the S− and even when new flower covers prevented the use of possible scent marks. New flower covers (i.e., without possible scent marks) had the effect of lowering the frequency of probing behavior. In Experiment 2, the colony was moved between training and testing. Again, bees chose the flower in the FAI position of the S+, and not the flower that would be chosen using strictly memory for a flight vector. Together, these experiments show that to locate the S+ bees did not rely on scent marks nor the positions of the S−, though the S− were prominent objects close to the goal. Also, bees selected environmental features to remember the position of the S+ instead of relying upon a purely egocentric point of view. Similarities with honeybees and vertebrates are discussed, as well as possible encoding mechanisms. [ABSTRACT FROM AUTHOR]

1. Little is known about the pollinators of rare plants, which is cause for concern given that pollination is essential for the long-term survival of most plant species. The aim of this study was to determine the probable pollinators of three species of rare arable weed: red hemp-nettle Galeopsis angustifolia, small-flowered catchfly Silene gallica and spreading hedge-parsley Torilis arvensis. Species of arable weed are among those suffering the greatest declines in the UK. 2. Five field sites were chosen, two of which were sampled in 2 years. Visitation and pollen transport webs were constructed for the entire plant–pollinator community at each site. Visitation webs described the frequency with which each insect species visited each plant species. Pollen transport webs quantified which insect species transported the pollen of which plant species. 3. A wide range of insect species visited the three plant species. A pollinator importance index was calculated that combined information on both the relative abundance of each insect carrying the pollen of the rare plant and its pollen fidelity. Using this method Galeopsis angustifolia was most likely to be pollinated by Bombus pascuorum at one site and Sphaerophoria scripta at another. Silene gallica was also likely be pollinated by Sphaerophoria scripta. 4. The pollinator fauna of the three plant species varied considerably across their geographical range, but less from one year to the next. 5. Synthesis and applications. All three species of rare plant were linked to other plant species in the community by shared pollinators. In many cases these other plant species constituted the primary food sources for the shared pollinators. Therefore, the long-term survival of rare plant populations is likely to depend on the more common plant species in the community. We recommend that management of the rare plants studied here should also include the protection and management of populations of some of the more common plant species in their respective communities. [ABSTRACT FROM AUTHOR]

Individual bumblebees were tested on a task of walking along a test tunnel to collect sucrose solution in an initial training illumination condition that simulated natural daylight, and in two spectrally different illumination conditions. Compared to the training condition the bees took a significantly longer time to complete the task in conditions that simulated either an ultraviolet negative illumination environment, or an illumination environment that represented blue skylight. In a control condition, bees did not derive this cue from spectral information reflected from the dark background material. This result shows that bees can directly perceive spectral changes in illumination conditions, even in the context of a task that does not require colour processing. This potentially enables the visual system of bees to have prior knowledge about the spectral quality of illumination conditions in which they may forage. The findings are discussed in relation to both theoretical models and empirical evidence of colour constancy, and it is concluded that bees can use multiple mechanisms to solve the dilemma posed by having to find colour targets in the spectrally different illumination conditions that exist for insects visiting flowers. [ABSTRACT FROM AUTHOR]

Investigating how differential gene expression underlies caste determination in the social Hymenoptera is central to understanding how variation in gene expression underlies adaptive phenotypic diversity. We investigated for the first time the association between differential gene expression and queen–worker caste determination in the bumble-bee Bombus terrestris. Using suppression subtractive hybridization we isolated 12 genes that were differentially expressed in queen- and worker-destined larvae. We found that the sets of genes underlying caste differences in larvae and adults failed to overlap greatly. We also found that B. terrestris shares some of the genes whose differential expression is associated with caste determination in the honeybee, Apis mellifera, but their expression patterns were not identical. Instead, we found B. terrestris to exhibit a novel pattern, whereby most genes upregulated (i.e. showing relatively higher levels of expression) in queen-destined larvae early in development were upregulated in worker-destined larvae late in development. Overall, our results suggest that caste determination in B. terrestris involves a difference not so much in the identity of genes expressed by queen- and worker-destined larvae, but primarily in the relative timing of their expression. This conclusion is of potential importance in the further study of phenotypic diversification via differential gene expression. [ABSTRACT FROM AUTHOR]

Learning difficult tasks requires an extended period of experience. It is unclear, however, what level of experience is exhibited by individuals in natural populations. If many individuals are rather inexperienced at any given time, they may not possess subtle information concerning, for example, local distributions of reward and danger, which may require long acquisition periods. To quantify individual experience in field settings, we conducted a field study involving extensive marking of individual honey bees (Apis mellifera L., 1758) and bumble bees (Bombus vagans Smith, 1854 and Bombus terricola Kirby, 1837) visiting milkweed (Asclepias syriaca L.) patches that harbored crab spiders (Misumena vatia (Clerck, 1757)), which prey on bees. The vast majority of bees either were fully inexperienced or had little experience with the specific flower patch that they were visiting. It is likely that such inexperienced bees do not possess subtle local information involving either reward or danger. Contrary to our prediction, even the most experienced bees did not avoid experimental patches harboring crab spiders, perhaps because even these bees did not possess sufficient experience. Our results indicate that conclusions from controlled laboratory experiments may not readily generalize to natural field settings. Thus, we must gather additional data on the long-term behavior of individually marked bees in natural conditions to better understand the interactions among flowers, bees, and bees' predators. ..LAN-FR L'apprentissage des tâches difficiles requiert une longue période d'expérience. Il n'est pas clair, cependant, quel niveau d'expérience possèdent les individus dans les populations naturelles. Si plusieurs individus sont relativement inexpérimentés à un moment donné, ils peuvent ne pas posséder l'information détaillée concernant, par exemple, la répartition locale des bénéfices et des dangers, ce qui peut demander de longues périodes d'acquisition. Afin d'évaluer l'expérience individuelle dans des conditions de terrain, nous avons marqué un à un en nature un grand nombre d'abeilles domestiques (Apis mellifera L., 1758) et de bourdons (Bombus vagans Smith, 1854 et Bombus terricola Kirby, 1837) butinant des bouquets d'asclépiades (Asclepias syriaca L.) qui portaient des araignées crabes (Misumena vatia (Clerck, 1757)), des prédateurs des abeilles. La grande majorité des abeilles avaient peu ou pas d'expérience du bouquet particulier de fleurs qu'elles visitaient. Il est peu probable que de telles abeilles inexpérimentées possèdent la connaissance locale détaillée des bénéfices et des dangers. Contrairement à notre prédiction, même les abeilles les plus expérimentées n'évitent pas les bouquets expérimentaux contenant des araignées crabes et peut-être même ces abeilles n'ont pas suffisamment d'expérience. Nos résultats indiquent que les conclusions obtenues dans des expériences de laboratoire contrôlées ne peuvent pas être élargies facilement aux conditions naturelles de terrain. Il nous faut donc accumuler plus de données sur le comportement à long terme en conditions naturelles d'abeilles marquées individuellement pour mieux comprendre les interactions entre les fleurs, les abeilles, et les prédateurs des abeilles.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

We examined the effects of floral reward level and spatial arrangement on the propensity of bumble bees to exhibit flower constancy. In three separate experiments, we compared the flower constancy of bees on dimorphic arrays of blue and yellow flowers that differed either in reward concentration, reward volume, or inter-flower distance. Overall, flower choice patterns varied among bees, ranging from random selection to complete constancy. When flowers contained greater reward volumes and were spaced farther apart, bees showed less flower constancy and more moves to closely neighbouring flowers. Changes in reward concentration had no effect on flower constancy; however, more dilute rewards produced shorter flight times between flowers. In addition, there was a strong positive relationship between degree of flower constancy and net rate of energy gain when flowers were spaced farther apart, indicating that constant bees were more economic foragers than inconstant bees. Together, these results support the view that the flower constancy of pollinators reflects an economic foraging decision. [ABSTRACT FROM AUTHOR]

Behavioural interactions are often analysed in terms of their costs and benefits to the actors [Hamilton, (1964) J. Theor. Biol. 7 1–16; Gadagkar, (1993) Trends Ecol. Evol. 8 232–234; Foster et al., (2001) Ann. Zool. Fenn. 38 229–238]. Using the bumblebee Bombus terrestris, we wish to distinguish between two possible determinants of interaction behaviour between conspecifics, namely kindirected behaviour that reflects genetic distance between individuals, or, alternatively, interactions guided by a functional distance between individuals, specifically, with respect to disease susceptibility. We find no relationship between contact rate of individuals and the genetic distance of their respective colonies. Interestingly, we do find a significant negative correlation between contact rate and the distance between the two colonies in susceptibility to a spectrum of parasite strains. This cannot be explained by either of the a priori alternatives so we propose two further testable hypotheses to explain our results. [ABSTRACT FROM AUTHOR]

Interindividual variability in response to environmental stimuli is believed to have a major impact on collective behaviors in social insects. The present study presents a detailed investigation of the variability in individual fanning behavior underlying the collective control of nest climate in bumblebee (Bombus terrestris) colonies. Four colonies were repeatedly exposed to increasing temperature and CO2 levels. The response threshold of each worker (defined as the mean stimulus intensity at which a worker responded by fanning) was determined. Temperature response thresholds of 118 workers and CO2 response thresholds of 88 workers were analyzed. Workers differed in their response thresholds. Some consistently responded to low stimulus intensities, others consistently responded to high stimulus intensities. No consistent correlation between temperature and CO2 thresholds was found within individuals. Response thresholds of fanning bees decreased over successive trials, providing empirical support for the idea of specialization through individual threshold reinforcement. In addition to variability in individual response thresholds, workers of a colony differed in two other parameters of responsiveness: response probability (the probability of responding to a stimulus once it exceeded an individual's response threshold) and response duration (the persistency with which fanning was performed once an individual responded). The results of the present study suggest that response threshold, response probability and response duration are important independent parameters of individual responsiveness in the collective control of nest climate in bumblebee colonies. [ABSTRACT FROM AUTHOR]

Bumble bees were trained to discriminate between two visual patterns, one of which was rewarding (S+) and one of which was unrewarding (S−). Subsequently, they were tested for discrimination between two non-rewarding patterns: the top halves of the training patterns, the bottom halves or the side halves. Three conditions were tested: (1) When the S+ was a star and the S− was a circle, all halves of the star were chosen above chance level, which may reflect an unlearned preference for radial patterns. (2) When the S+ and S− were reversed, the bottom half and the side half of the circle were chosen above chance level, but not the top half. (3) In the last condition, the S+ was again a circle, but the feeder tube was placed below the training pattern rather than above, and again the bottom halves were discriminated but neither the top nor the side halves were. In learning pattern discriminations, the ventral portion of the pattern is weighted more strongly than the dorsal portion, which enables recognition of incomplete patterns, and the weighting depends little on angle of approach. [Copyright &y& Elsevier]

Large flowers often contain larger nectar rewards, and receive more pollinator visits, than small flowers. We studied possible behavioral mechanisms underlying the formation of flower size preferences in bumblebees, using a two-phase laboratory experiment. Experimentally naive Bombus terrestris (L.) foraged on artificial flowers that bore either a large (3.8 cm diameter) or a small (2.7 cm diameter) display of a uniform color. Only flowers of one display size contained nectar rewards. We changed the display color and the locations of large and small flowers in the second experimental phase. We recorded the bees' choices in both phases. Almost half of the bees (41%) made their first visit to a small flower. The bees learned to associate display size with food reward, and chose rewarding flowers with >85% accuracy by the end of each experimental phase. Some learning occurred within the bees' first three flower visits. Learning of the size–reward association was equally good for large and small displays in the first experimental phase, but better for small displays in the second phase. Formation of size–reward associations followed a similar course in both phases. This suggests that the bees did not apply their experience from the first learning phase to the new situation of the second phase. Rather, they treated each phase of the experiment as an independent learning task. Our results suggest that associative learning is involved in the formation of preferences for large displays by bees. Moreover, bees that had learned to prefer large displays in one foraging situation may not transfer this preference to a novel situation that is sufficiently different. We propose that this feature of the bees' behavior can select for honest advertising in flowers. [ABSTRACT FROM AUTHOR]

Most highly social insects exhibit a distinct size dimorphism between the female castes: queens being larger than workers. Nutritional factors are known to influence caste specific development to a great extent, but little is known about this in bumblebees. Totest whether size differentiation in Bombus terrestris results from differences in food intake and fat body metabolism, as was suggested in earlier research, we compared the weight gain of the midgut and the fat body, as well as its general composition for last instar queen and worker larvae. The present results show that the relative growth rates and the general composition of the fat body in queen and worker larvae are similar, indicating that caste specific size dimorphism is not owing to differences in fat body metabolism. The timing of the onset of defecation appeared to have a pronounced effect on the determination of midgut weight and body mass, and it is discussed that this might have complicated the correct interpretation of earlier results. [ABSTRACT FROM AUTHOR]

Determines the importance of female status and courtship behavior in predicting copulation in the bumblebee, Bombus terrestris. Ground and flight activity of the queen; Contributing factors that determine the copulation interaction between males and females; Effect of female repulse behavior on chance of copulation.

Abstract The flower in Aconitum has five violet sepals. Its morphology is unique and thought to be adapted for pollination by bumblebees. To assess the adaptive significance of Aconitum flower morphology, we examined the function of the five sepals in bumblebee-pollination. We manipulated the flower by removing the sepals and then observed and measured bumblebee pollination efficiency in a single visit. Bumblebee behavior differed somewhat on the manipulated flowers. Manipulation of the two lower sepals led to a pollination efficiency that was the same as no manipulation. Pollination efficiency was lowered significantly after lateral sepal manipulation, and this was caused by the absence of the arch structure normally formed by two lateral sepals changing the posture of the pollinator. Therefore, it was postulated that the arch structure formed by the lateral sepals functions to ensure correct pollination. [ABSTRACT FROM AUTHOR]

Presents a study which determined whether multiple mating by females reduce parasitism in bumblebee Bombus terrestris. Review of related literature; Materials and methods used; Results and discussion.

Regulation of nest temperature is important to the fitness of eusocial insect colonies. To maintain appropriate conditions for the developing brood, workers must exhibit thermoregulatory responses to ambient temperature. Because nest-mate workers differ in task performance, thermoregulatory behavior provides an opportunity to test threshold of response models for the regulation of division of labor. We found that worker bumble bees (Bombus bifarius nearcticus) responded to changes in ambient temperature by altering their rates of performing two tasks – wing fanning and brood cell incubation. At the colony level, the rate of incubating decreased, and the rate of fanning increased, with increasing temperature. Changes in the number of workers performing these tasks were more important to the colony response than changes in workers’ task performance rates. At the individual level, workers’ lifetime rates of incubation and fanning were positively correlated, and most individuals did not specialize exclusively on either of these temperature-sensitive tasks. However, workers differed in the maximum temperature at which they incubated and in the minimum temperature at which they fanned. More individuals fanned at high and incubated at low temperatures. Most of the workers that began incubating at higher temperatures continued performing this task at lower temperatures, when additional nest-mates became active. The converse was true for fanning behavior. These data are consistent with a threshold of response model for thermoregulatory behavior of B. bifarius workers. [ABSTRACT FROM AUTHOR]

Evaluates the flight behavior of bumblebees, Bombus terrestis, searching for artificial flowers of various sizes and colors. Floral color properties and detectability; Detection area and color recognition area; Flower size and flight behavior.

We studied pollinator visitation rates and movement patterns in experimental arrays of irises at two sites within a Louisiana iris hybrid zone. Arrays contained single-flowered stems of red-flowered Iris fulva, blue-flowered I. hexagona, and purple-flowered F1 hybrids. At one site, where I. hexagona was the only wild-growing iris, queen bumble bees were the most common pollinator, and the rank order of pollinator visit rates was I. hexagona > F1 < I. fulva. At a second site, where I. fulva predominated in the wild, hummingbirds were the most common pollinators, and this order was reversed: I. hexagona < F1 > I. fulva. Thus, at both sites, the naturally occurring iris was visited most frequently and F1 flowers were visited more frequently than the non-native species. Pollinators used both long-distance and short-distance cues to discriminate among flowers, and differences in visit rates seemed to be based on differences in the ease of access to pollen and nectar rewards on flowers of different size. Analysis of movement patterns between flowers showed that pollinators were more likely to make parental-F1 transitions than heterospecific transitions. These data suggest that pollinator behavior acts as a partial barrier to initial hybridization, although this barrier largely breaks down after F1 formation. Our results help to explain the existence of many introgressed populations of Louisiana iris, despite the fact that F1s are extremely rare in the wild.. [ABSTRACT FROM AUTHOR]

Pollinators collect resources that are patchy, since flowers are usually aggregated on several spatial scales. Empirical studies have established that pollinators almost invariably visit a smaller proportion of flowers as patch size increases. This has not been adequately explained. Here I present data on the payoff curve achieved by bumblebees, Bombus lapidarius, when visiting patches containing different numbers of inflorescences, and use the marginal value theorem to predict the optimum duration of stay within patches. The data demonstrate that visiting a declining proportion of inflorescences as patch size increases is an optimal strategy, if we assume that bees are attempting to maximise their rate of reward acquisition. I argue that this occurs because searching for the remaining unvisited inflorescences is easier in a small patch. On large patches, bees visited more inflorescences per patch than predicted (although still visiting a declining proportion). I suggest that this may occur because bees are using simple departure rules which result in near-optimal behaviour. I show that a departure rule based on two successive encounters with empty inflorescences closely predicts observed behaviour. [ABSTRACT FROM AUTHOR]

ABSTRACT.--We examined the roles of floral scent and color in attracting bumblebees (Bombus spp.) to snapdragon flowers (Antirrhinum, Sonnet cultivar). Corolla color differences covaried with differences in floral scent emissions in two inbred lines of snapdragon. White-flowered plants emitted methyl cinnamate, a scent compound not produced by yellow flowered plants, but lacked methyl benzoate, one of the major floral volatiles of the yellow-flowered line. Qualitative scent differences between the two lines were eliminated by applying the complementary scent compounds to filter paper wicks placed within the corollas. Laboratory analyses were performed using gas chromatography-mass spectrometry to verify appropriate modification of floral scents by this method. Two randomized arrays of control and scent-augmented flowers were visited by freely-foraging bumblebees in subalpine meadows in Colorado. Overall, yellow-flowered plants received more pollinator visits and had more flowers foraged per plant visit than did white-flowered plants. The addition of sweet-smelling methyl benzoate or spicy methyl cinnamate neither stimulated nor deterred bumblebee visits to either flower color. [ABSTRACT FROM AUTHOR]

Studies the sperm transfer and potential competition between males over mating opportunities in bumblebees. Measurement of the duration of copulation; Deposition of `mating plug' into females; Implications of male selfishness to the ability of females to seek other mates.

AbstractBehavioral field studies were conducted to determine if bumble bees (Bombus terrestris L.) can use pollen odor to assess pollen availability in flowers of Rosa rugosa (Rosaceae), a nectarless species with a distinctive pollen odor. Pollen volatiles were added singly and in mixtures to newly opened flowers from which anthers were removed and were offered to free-flying bumble bees in an array that included intact flowers as controls. The addition of 2-tridecanone and geranyl acetate reduced landing responses, but the addition of tetradecyl acetate and especially eugenol significantly increased landing frequency as well as the display of vibratile pollen-collecting behavior, suggesting that they are key chemicals in a bee’s assessment of pollen availability in individual flowers. Bee responses to flowers in which androecia were exchanged between first-day flowers (with pollen reward) and second-day flowers (without pollen reward) provide evidence that bee discrimination between flowers is based mainly on stimuli from the anthers. Overall, the findings show that bumble bees foraging on R. rugosa use primarily pollen odor in concert with visual stimuli from the androecium and secondarily petals odors and colors in selecting rewarding flowers. Controlled pollination and bagging studies indicate that R. rugosa requires cross-pollination by insects, pointing to the selective advantage that pollen odor provides by increases plant fitness through the enhanced foraging efficiency of bumble bee pollinators. [ABSTRACT FROM AUTHOR]

Presents abstracts of several research on animal behavior. 'Foraging Path Selection in Bumblebees: Hindsight or Foresight?'; 'Contrasts in the Songs of Two Sympatric Chaffinch Species'; 'Predictions From the Ranging Hypothesis for the Evolution of Long Distance Signals in Birds.'