Abstract: Animals collecting patchily distributed resources are faced withcomplexmulti-location routing problems. Rather than comparing all possible routes, they often find reasonably short solutions by simply moving to the nearest unvisited resources when foraging. Here, we report the travel optimization performance of bumble-bees (Bombus terrestris) foraging in a flight cage containing six artificial flowers arranged such that movements between nearest-neighbour locations would lead to a long suboptimal route. After extensive training (80 foraging bouts and at least 640 flower visits), bees reduced their flight distances and prioritized shortest possible routes,whilealmost never following nearest-neighbour solutions. We discuss possible strategies used during the establishment of stable multi-location routes (or traplines), and how these could allow bees and other animals to solve complex routing problems through experience, without necessarily requiring a sophisticated cognitive representation of space.
Abstract: 1. Animals exploiting renewable resource patches are faced with complex multi-location routing problems. In many species, individuals visit foraging patches in predictable sequences called traplines. However, whether and how they optimize their routes remains poorly understood.
2. In this study, we demonstrate that traplining bumblebees (Bombus terrestris) make a trade-off between minimizing travel distance and prioritizing the most rewarding feeding locations.
3. Individual bees trained to forage on five artificial flowers of equal reward value selected the shortest possible route as a trapline. After introducing a single highly rewarding flower to the array, they re-adjusted their routes visiting the most rewarding flower first provided the departure distance from the shortest possible route remained small (18%). When routes optimizing the initial rate of reward intake were much longer (42%), bees prioritized short travel distances.
4. Under natural conditions, in which individual flowers vary in nectar productivity and replenish continuously, it might pay bees to prioritize highly rewarding locations, both to minimize the overall number of flowers to visit and to beat competitors.
5. We discuss how combined memories of location and quality of resource patches could allow bees and other traplining animals to optimize their routing decisions in heterogeneous environments.
Abstract: It has been proposed that sympatric bumblebee species form mimicry rings to profit from learnt avoidance behaviour by predators. This hypothesis can be tested by comparing the predation rates of local bumblebees with those of imported nonnative bumblebees, whose coat colour is different from that of local bees, so that their coloration is unfamiliar to local predators. To test whether populations of non-native bumblebees suffer higher worker loss rates during foraging, we conducted transplant experiments in the UK, Germany and Sardinia. The loss rates of foraging workers of four Bombus terrestris populations (Bombus terrestris canariensis, Bombus terrestris terrestris, Bombus terrestris sassaricus and Bombus terrestris dalmatinus) were compared, evaluating data from 989 foragers, whose
flight times were monitored precisely (over 8258 h of foraging). While all of these workers display a bright UV-reflecting abdominal tip, the colours in other body parts differ strongly to the eyes of avian predators. The hypothesis that foragers from the non-native bumblebee populations, which differ in coloration from the local native population, would suffer higher predation risk was not upheld. In contrast, in one location (Sardinia) the native population had the highest loss rate. The consistent population rank order we found in terms of forager losses indicates that such losses are more prominently affected by factors other than the familiarity of local predators with aposematic colour patterns.
Abstract: Animals collecting resources that replenish over time often visit patches in predictable sequences called traplines. Despite the widespread nature of this strategy, we still know little about how spatial memory develops and guides individuals toward suitable routes. Here, we investigate whether flower visitation sequences by bumblebees Bombus terrestris simply reflect the order in which flowers were discovered or whether they result from more complex navigational strategies enabling bees to optimize their foraging routes. We analyzed bee flight movements in an array of four artificial flowers maximizing interfloral distances. Starting from a single patch, we sequentially added three new patches so that if bees visited them in the order in which they originally encountered flowers, they would follow a long (suboptimal) route. Bees’ tendency to visit patches in
their discovery order decreased with experience. Instead, they optimized their flight distances by rearranging flower visitation sequences. This resulted in the development of a primary route (trapline) and two or three less frequently used secondary routes. Bees consistently used these routes after overnight breaks while occasionally exploring novel possibilities. We discuss how maintaining some level of route flexibility could allow traplining animals to cope with dynamic routing problems, analogous to the well-known traveling salesman problem.
Abstract: 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 minutes. Repeated 20 minute exposures of a colony to recruitment pheromone, with at least 30 minute 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: The traditional emphasis when measuring performance in animal cognition has been overwhelmingly on accuracy, independent of decision time. However, more recently it became clear that tradeoffs exist between decision speed and accuracy in many ecologically relevant tasks, for example prey and predator detection and identification, pollinators choosing between flowers species, and spatial exploration strategies. Obtaining high quality information often increases sampling time, especially under noisy conditions. We discuss the mechanisms generating such speed-accuracy tradeoffs, their implications for animal decision making (including signalling, communication and mate choice) and the significance of differences in decision strategies among species, populations, and individuals. The ecological relevance of such tradeoffs can be better understood by considering the neuronal mechanisms underlying decision making processes.
Abstract: Studies of innate colour preference and learning ability have focused on differences at the species level, rather than variation among populations of a single species. Initial strength and persistence of colour preferences are likely to affect colour choices of naïve flower visitors. We therefore study the influence of both the strength and persistence of innate colour preference (for blue) on an operant learning task (associating food reward with yellow flowers) in two populations of the bumblebee Bombus terrestris. We found that both strength and persistence of blue preference differed significantly between populations: B. t. dalmatinus had a weaker and less persistent blue preference than B. t. audax. These differences in preference also influenced learning performance. Considering only landing behaviours, one-trial learning occurred in the majority (73%) of bees, and was achieved sooner in B. t. dalmatinus because of its weaker blue preference. However, compared to landing behaviours the relative frequency of approach flights to rewarding and unrewarding flower types changed more slowly with task experience in both populations. When considering both approaches and landings the rate of learning, following the first rewarded learning trial, was faster in B. t. audax than B. t. dalmatinus. However, the net effects of population differences in blue preference and learning dynamics result in similar final levels of task performance. Our results provide new evidence of behavioural differences among isolated populations within a single species, and raise intriguing questions about the ecological significance and adaptive nature of colour preference.
Abstract: The immune response affects learning and memory in insects. Given this and the known fitness costs of both the immune system and learning, does an evolutionary trade-off exist between these two systems? We tested this by measuring the learning ability of 12 bumble-bee (Bombus terrestris) colonies in a free-flying paradigm. We then tested their immune response using the zone of inhibition assay. We found a positive relationship between colony learning performance and immune response, that is, fast-learning colonies also show high levels of antimicrobial activity. We conclude that there is no a priori reason to demand an evolutionary relationship between two traits that are linked physiologically.
Abstract: A recent study has found that butterflies maintain behavioural plasticity useful to them in rare environments by reducing associated costs in common environments. Butterflies use innate sensory biases to locate common green hosts, but learn to modify these preferences to find rare, red host-plants.
Abstract: Although central to understanding life-history evolution, the relationship between lifetime reproductive success and longevity remains uncertain in many organisms. In social insects, no studies have reported estimates of queens' lifetime reproductive success and longevity within populations, despite the importance of understanding how sociality and associated within-group conflict affect life-history traits. To address this issue, we studied two samples of colonies of the annual bumblebee, Bombus terrestris audax, reared from wild-caught queens from a single population. In both samples, queens' lifetime reproductive success, measured as either queens' inclusive fitness or as total biomass of queen-produced sexuals (new queens and males), was significantly positively associated with queen longevity, measured from the day the first worker was produced. We suggest that a positive relationship between reproductive success and longevity was inherited from non-social ancestors showing parental care and maintained, at least in part, because the presence of workers buffers queens against extrinsic mortality.
Abstract: 1. Ants show complex interactions with plants, both facultative and mutualistic, ranging from grazers through seed predators and dispersers to herders of some herbivores and guards against others. But ants are rarely pollinators, and their visits to flowers may be detrimental to plant fitness.
2. Plants therefore have various strategies to control ant distributions, and restrict them to foliage rather than flowers. These ‘filters’ may involve physical barriers on or around flowers, or ‘decoys and bribes’ sited on the foliage (usually extrafloral nectaries - EFNs). Alternatively, volatile organic compounds (VOCs) are used as signals to control ant behaviour, attracting ants to leaves and / or deterring them from functional flowers. Some of the past evidence that flowers repel ants by VOCs has been equivocal and we describe the shortcomings of some experimental approaches, which involve behavioural tests in artificial conditions.
3. We review our previous study of myrmecophytic acacias, which used in situ experiments to show that volatiles derived from pollen can specifically and transiently deter ants during dehiscence, the effects being stronger in ant-guarded species and more effective on resident ants, both in African and Neotropical species. In these plants, repellence involves at least some volatiles that are known components of ant alarm pheromones, but are not repellent to beneficial bee visitors.
4. We also present new evidence of ant repellence by VOCs in temperate flowers, which is usually pollen-based and active on common European ants. We use these data to indicate that across a wide range of plants there is an apparent trade-off in ant-controlling filter strategies between the use of defensive floral volatiles and the alternatives of decoying EFNs or physical barriers.
Abstract: Geographic profiling (GP) was originally developed as a statistical tool to help police forces prioritize lists of suspects in investigations of serial crimes. GP uses the location of related crime sites to make inferences about where the offender is most likely to live, and has been extremely successful in criminology. Here, we show how GP is applicable to experimental studies of animal foraging, using the bumble-bee Bombus terrestris. GP techniques enable us to simplify complex patterns of spatial data down to a small number of parameters (2-3) for rigorous hypothesis testing. Combining computer model simulations and experimental observation of foraging bumble-bees, we demonstrate that GP can be used to discriminate between foraging patterns resulting from (i) different hypothetical foraging algorithms and (ii) different food item (flower) densities. We also demonstrate that combining experimental and simulated data can be used to elucidate animal foraging strategies: specifically that the foraging patterns of real bumble-bees can be reliably discriminated from three out of nine hypothetical foraging algorithms. We suggest that experimental systems, like foraging bees, could be used to test and refine GP model predictions, and that GP offers a useful technique to analyse spatial animal behaviour data in both the laboratory and field.
Abstract: Recruitment in social insects often involves not only inducing nestmates to leave the nest, but also communicating crucial information about finding profitable food sources. Although bumblebees transmit chemosensory information (floral scent), the transmission mechanism is unknown as mouth-to-mouth fluid transfer (as in honeybees) does not occur. Because recruiting bumblebees release a pheromone in the nest that triggers foraging in previously inactive workers, we tested whether this pheromone helps workers learn currently rewarding floral odours, as found in food social learning in rats. We exposed colonies to artificial recruitment pheromone, paired with anise scent. The pheromone did not facilitate learning of floral scent. However, we found that releasing floral scent in the air of the colony was sufficient to trigger learning and that learning performance was improved when the chemosensory cue was provided in the nectar in honeypots; probably because it guarantees a tighter link between scent and reward, and possibly because gustatory cues are involved in addition to olfaction. Scent learning was maximal when anise-scented nectar was brought into the nest by demonstrator foragers, suggesting that previously unidentified cues provided by successful foragers play an important role in nestmates learning new floral odours.
Abstract: Foraging activity in social insects should be regulated by colony nutritional status and food availability, such that both the emission of, and response to, recruitment
signals depend on current conditions. Using fully automatic radio-frequency identification (RFID) technology to follow the foraging activity of tagged bumblebees (Bombus terrestris) during 16,000 foraging bouts, we tested whether the cue provided by stored food (the number of full honeypots) could modulate the response of workers to the recruitment pheromone signal. Artificial foraging pheromones were applied to colonies with varied levels of food reserves. The response to recruitment pheromones was stronger in colonies with low food, resulting in more workers becoming active and more foraging bouts being performed. In addition to previous reports showing that in colonies with low food successful foragers perform more excited runs during which they release recruitment pheromone and inactive workers are more prone to leave the nest following nectar influx, our results indicate that evolution has shaped a third pathway that modulates bumblebee foraging activity, thus preventing needless energy expenditure and exposure to risk when food stores are already high. This new feedback loop is intriguing since it involves
context-dependent response to a signal. It highlights the integration of information from both forager-released pheromones (signal) and nutritional status (cue) that occurs within individual workers before making the decision to start foraging. Our results support the emerging view that responses to pheromones may be less hardwired than commonly acknowledged.
Abstract: Despite the widespread assumption that the learning abilities of animals are adapted to the particular environments in which they operate, the quantitative effects of learning performance on fitness remain virtually unknown. Here, we evaluate the learning performance of bumble-bees (Bombus terrestris) from multiple colonies in an ecologically relevant associative learning task under laboratory conditions, before testing the foraging performance of the same colonies under the field conditions. We demonstrate that variation in learning speed among bumble-bee colonies is directly correlated with the foraging performance, a robust fitness measure, under natural conditions. Colonies vary in learning speed by a factor of nearly five, with the slowest learning colonies collecting 40% less nectar than the fastest learning colonies. Such a steep fitness function is suggestive of strong selection for higher learning speed. Partial correlation analysis reveals that other factors such as forager body size or colour preference appear to be negligible in our study. Although our study does not directly prove causality of learning on foraging success, our approach of correlating natural within-species variation in these two factors represents a major advance over traditional between-species correlative analyses where comparability can be compromised by the fact that species vary along multiple dimensions.
Abstract: Despite the widespread assumption that the learning abilities of animals are adapted to the particular environments in which they operate, the quantitative effects of learning performance on fitness remain virtually unknown. Here we evaluate the learning performance of bumblebees (Bombus terrestris) from multiple colonies in an ecologically relevant associative learning task under laboratory conditions, before testing the foraging performance of the same colonies under the field conditions. We demonstrate that variation in learning speed among bumblebee colonies is directly correlated with foraging performance, a robust fitness measure, under natural conditions. Colonies vary in learning speed by a factor of nearly 5, with the slowest learning colonies collecting 40% less nectar than the fastest learning colonies. Such a steep fitness function suggests strong selection for higher learning speed in bumblebees. Demonstrating the adaptive value of differences in learning performance under the real conditions in which animals function represents a major step towards understanding how cognitive abilities of animals are tuned to their environment.
Abstract: Competition for pollination is thought to be an important factor structuring flowering in many plant communities, particularly among plant taxa with morphologically
similar and easily accessible flowers. We examined the potential for heterospecific pollen transfer (HPT) in a community of four Acacia species in a highly
seasonal tropical habitat in Mexico. Partitioning of pollen flow among sympatric species appears to be achieved, in part, through segregation of flowering in seasonal time, and interspecific differences in pollinator guilds. However, two coflowering species (Acacia macracantha and Acacia angustissima) shared multiple flower visitors, raising the possibility of HPT. Each of these coflowering species showed high intraspecific daily synchrony in pollen release, but dehisce at different times of day. Pollinators rapidly harvested available pollen from one species before abandoning it to visit the flowers of the second later in the day. The activity of shared pollinators, predominantly bees, is thus structured throughout the day, and potential for HPT reduced. Suggestive evidence in favour of a resource partitioning
explanation for this pattern is provided by the fact that A. macracantha showed significantly greater intraspecific synchrony when coflowering with a potential
competitor (A. angustissima) than when flowering alone. We discuss our results in light of previous work on coflowering acacia assemblages in Tanzania and Australia.
Abstract: To investigate how bumblebees (Bombus terrestris) learn the complex motor skills involved in pollen foraging, we observed naïve workers foraging on arrays of nectarless poppy flowers (Papaver rhoeas) in a greenhouse. Foraging skills were quantified by measuring the pollen load collected during each foraging bout and relating this to the number of flowers visited and bout duration on two consecutive days. The pollen standing crop (PSC) in each flower decreased drastically from 0530 to 0900 hours. Therefore, we related foraging performance to the changing levels of pollen available (per flower) and found that collection rate increased over the course of four consecutive foraging bouts (comprising between 277 and 354 individual flower visits), suggesting that learning to forage for pollen represents a substantial time investment for individual foragers. The pollen collection rate and size of pollen loads collected at the start of day 2 were markedly lower than at the end of day 1, suggesting that components of pollen foraging behaviour could be subject to imperfect overnight retention. Our results suggest that learning the necessary motor skills to collect pollen effectively from morphologically simple flowers takes three times as many visits as learning how to handle the most morphologically complex flowers to extract nectar, potentially explaining why bees are more specialised in their choice of pollen flowers.
Abstract: Innate sensory biases could play an important role in helping naïve animals to find food. As inexperienced bees are known to have strong innate colour biases we investigated whether bumblebee (Bombus terrestris) colonies with stronger biases for the most rewarding flower colour (violet) foraged more successfully in their local flora. To test the adaptive significance of variation in innate colour bias, we compared the performance of colour-naïve bees, from nine bumblebee colonies raised from local wild-caught queens, in a laboratory colour bias paradigm using violet (bee UV-blue) and blue (bee blue) artificial flowers. The foraging performance of the same colonies was assessed under field conditions. Colonies with a stronger innate bias for violet over blue flowers in the laboratory harvested more nectar per unit time under field conditions. In fact, the colony with the strongest bias for violet (over blue) brought in 41% more nectar than the colony with the least strong bias. As violet flowers in the local area produce more nectar than blue flowers (the next most rewarding flower colour), these data are consistent with the hypothesis that local variation in flower traits could drive selection for innate colour biases.
Abstract: Flower visitors of several taxa (including bees, butterflies and hoverflies) are known to move preferentially between flowers of the same species, while neglecting other equally rewarding flower species. Darwin proposed memory limitations as a potential mechanistic explanation for this flower constancy behaviour. This reanalysis of a previously published dataset, relating a real-time sequential analysis of bumblebee flower choices to the distance distribution between flowers in a natural meadow, shows that Darwin was right in an unexpected way. Bees (Bombus spp) can learn how to extract rewards from several flower species, and switching between flower species does not compromise their handling efficiency (i.e. flower handling times do not increase following a species switch). However,
bees do lose time fl ying between flowers. If a flower is encountered within a short time (0–2 secs) after the last flower visit, it is likely to be visited only if it is the same species. After longer intervals (3–6 secs), bees are more likely to switch to visiting different flower species. Thus, flower constancy is in part an effect based on comparing incoming stimuli (the flowers a bee detects in flight) with a transient form of short-term (working) memory, which holds the signal of the last visited flower. The relative weighting of working and reference memory changes as time passes following a flower visit. This results in a low probability of retrieving the memory for a different flower species (from that just visited) within a short time interval after the most recent flower visit (0–2 secs). This probability rises as the signal of the last visited flower fades from working memory (>2 secs).
Abstract: Our goal in this review is to determine whether particular behavioral traits represent actual adaptations in the context of foraging. Social bees are our chosen study system because they provide a convenient and tractable biological system with which to study the potential adaptiveness of a wide range of foraging traits, such as flower constancy, floral color preference, learning to associate floral color as a predictor of reward, traplining, and communication about food sources.
This variety of behavioral traits allows us to demonstrate the strengths, and weaknesses, of applying five approaches (four experimental and one theoretical) to the study of foraging at the species, population, and colony level. (1) The comparative approach allows us to contrast behavioral traits of extant species with those of their common ancestor. We correlated differences in floral color preference between closely related species (and populations), with a known phylogeny, with features in each bee's respective environment. (2) Reciprocal transplant experiments allowed us to test for local adaptation. We compared the relative foraging performance of distinct bee populations in both of their respective native environments. (3) Manipulating the foraging environment to eliminate specific behavioral traits permitted a direct comparison of animals' foraging performance in their normal and experimentally manipulated environment, allowing us to quantify the effect of the trait in question (traplining) on foraging performance. (4) Manipulating the foraging phenotype to eliminate specific behavioral traits is another valuable approach. Unless suitable behavioral mutants, knockouts, or molecular techniques to selectively block gene expression are available, creating such artificial foraging phenotypes is only possible for a very small number of specific traits, e.g. the honeybee dance language. (5) Integrating biologically realistic modeling with experimental studies allows us to test predictions about the adaptive significance of foraging related traits not amenable to experimental manipulation, and to identify the ranges over which these traits might affect fitness.
Do these approaches provide evidence that foraging behaviors are adaptive? In some cases, we show that forager behavior has indeed been tuned to function adaptively in a given niche: interestingly the adaptive benefits of such behavioral traits are often strongly context dependent. However in other cases, the observed patterns of behavior were more parsimoniously explained by chance evolutionary processes, or by the historical conditions under which bees operated in their evolutionary past.
Abstract: The flowers of angiosperm plants present us with a staggering diversity of signal designs, but how did this diversity evolve? Answering this question requires us to understand how pollinators analyze these signals with their visual and olfactory sense organs, and how the sensory systems work together with post-receptor neural wiring to produce a coherent percept of the world around them. Recent research on the dynamics with which bees store, manage and retrieve memories all have fundamental implications for how pollinators choose between flowers, and in turn for floral evolution. New findings regarding how attention, peak-shift phenomena, and speed-accuracy tradeoffs affect pollinator choice between flower species show that analyzing the evolutionary ecology of signal-receiver relationships can substantially benefit from knowledge about the neural mechanisms of visual and olfactory information processing.
Abstract: The first quantitative assessment of between-colony variation in learning ability within a natural bee population is presented here. Bumblebee (Bombus terrestris audax Harris 1776) colonies were raised in the laboratory, under identical conditions, from wild caught queens. 240 bumblebee workers from 16 colonies were individually tested in an ecologically relevant foraging situation in which they had to distinguish yellow, rewarding artificial flowers from blue, unrewarding ones under laboratory conditions. During the initial stages of the task, 15 colonies showed a very strong, unlearned preference for blue flowers (the other colony showed no strong colour preference). There was significant variation among the colonies tested in learning speed, task saturation performance, and the number of flower choices made prior to first feeding from a rewarding, yellow flower. Such intercolony variation in performance forms the raw material upon which any selection for learning ability might act. Overall, neither age nor size of bees were consistently correlated with learning performance, but older bees learned faster in one of the colonies, an effect that remained significant even after statistical correction for multiple comparisons.
Abstract: Recent research on ants shows that running in tandem might serve the function of teaching naïve ants about the path to a target. Although these new experiments represent perhaps the most highly controlled study of teaching in animals to date, the findings prompt the question of how teaching formally differs from other forms of communication.
Abstract: Honey bee males and queens mate in mid air and can fly many kilometres on their nuptial flights. The conservation of native honey bees, such as the European black bee (Apis mellifera mellifera), therefore, requires large isolated areas to prevent hybridisation with other subspecies, such as A. m. ligustica or A. m. carnica, which may have been introduced by beekeepers. This study used DNA microsatellite markers to determine the mating range of A. m. mellifera in two adjacent semi-isolated valleys (Edale and Hope Valley) in the Peak District National Park, England, in order to assess their suitability for native honey bee conservation and as isolated mating locations. Three apiaries were set up in each valley, each containing 12 colonies headed by a virgin queen and 2 queenright drone producing hives. The virgin queens were allowed to mate naturally with drones from the hives we had set up and with drones from hives owned by local beekeepers. After mating, samples of worker larvae were taken from the 41 queens that mated successfully and genotyped at 11 DNA microsatellite loci. Paternity analyses were then carried out to determine mating distances and isolation. An average of 10.2 fathers were detected among the 16 worker progeny. After correction for non-detection and non-sampling errors, the mean effective mating frequency of the test queens was estimated to be 17.2, which is a normal figure for honey bees. Ninety percent of the matings occurred within a distance of 7.5 km, and fifty percent within 2.5 km. The maximal mating distance recorded was 15 km. Queens and drones did occasionally
mate across the borders between the two valleys, showing that the dividing mountain ridge Losehill does not provide complete isolation. Nevertheless, in the most isolated part of Edale sixty percent of all matings were to drones from Edale hives. The large majority of observed mating distances fell within the range of Hope Valley, making this site a suitable location for the long term conservation of a breeding population of black bees.
Abstract: Commercial trade of bumblebees in Europe results in different subspecies of Bombus terrestris being shipped into regions where they are not native. Although previous studies have shown that these subspecies will interbreed, none have assessed mating preference of the different populations. This study examines the mating preferences between two geographically isolated populations of B. terrestris which have unnaturally been brought together through the commercial trade in bumblebees. Under controlled choice conditions, mating between commercially imported B. t. dalmatinus (from South-eastern Europe) and native British B. t. audax was non-random. Commercially imported gynes (unfertilised queens) preferred to mate with males from the same population (71% of matings). In light of the continued escape of imported gynes and males, these results indicate that there is a possibility of establishment of South Eastern European B. t. dalmatinus in Britain, and that hybrids will also occur. The ecological risks of such an establishment are discussed.
Abstract: The three bumblebee species Bombus terrestris (Linnaeus 1758), Bombus lapidarius (Linnaeus 1758), and Bombus pascuorum (Scopoli 1763) showed consistent differences in their respective levels of flower constancy when foraging on three different pairs of flower species. B. terrestris was always the most flower constant, followed by B. lapidarius, with B. pascuorum the least flower constant species. These interspecific differences in flower constancy were related to foraging performance under field conditions near Würzburg, Germany in 1999 and 2001. B. terrestris was more flower constant, and predominantly outperformed B. lapidarius at collecting nectar in both years. As B. terrestris is also the larger of these species, these data also support the idea that larger bees are more efficient at nectar foraging, i.e. they bring home more nectar per unit time. However B. pascuorum, the least flower constant of the three species tested, was the most efficient of them at collecting nectar, collecting 50% more nectar than B. terrestris per hour. Therefore flower constancy appears to be a relatively poor predictor of species foraging performance, which is likely to be influenced simultaneously by many other factors including worker body size, tongue length, and foraging range.
Abstract: Bumblebee (Bombus terrestris) colonies showed significant variation in their unlearned preference for violet (bee UV-blue) over blue (bee blue) flowers. Bumblebee colonies with a higher average innate preference for violet (over blue) in the laboratory harvested more nectar per unit time under field conditions. Although this correlation was strong (rs=0.82), it narrowly missed statistical significance at the 5% level (p=0.089), but was significant at the 10% level. This increase in foraging performance appears to make evolutionary sense because, on average, violet flower species contain around four times the amount of sugar (in nectar) as flowers of any other colour in the local area. Interestingly, although colonies with a stronger preference for violet were more effective at nectar foraging, this increase in colony food availability was not predictably translated into investment in fitness, quantified as gyne (new queen) production.
Abstract: We used a population biological approach to assist our understanding of the evolution of behaviour, with island bumblebees as our model system. The widespread European species Bombus terrestris occurs on all major Mediterranean, and some Atlantic islands. Bees from different populations differ in a variety of behavioural traits, including floral colour preferences, flower detection, and learning behaviour. We attempted to correlate these behavioural differences with each population’s environment, but could not find straightforward adaptive explanations. We also performed reciprocal transplant studies to compare nectar foraging performance of bees from three different populations, but found that non-native bees consistently outcompeted native bees. Thus, we consider genetic drift, exaptation, and pleiotropy as possible alternative explanations to a strictly adaptive explanation for between population behavioural differences in bumblebees.
Abstract: DNA sampling of insects frequently relies upon lethal or invasive methods. Because insect colonies contain numerous workers it is often possible to destructively sample workers for genetic analysis. However, this is not possible if queens or workers must remain alive after sampling. Neither is it possible to remove an entire leg, wing or other appendage as this will often hinder normal behaviour. This study investigates the possibility of genotyping queen honey bees Apis mellifera using DNA extracted from wing tips so that flight and other activities are unaffected. Our results show that wing tip samples (c. 1.3 mm2) provide good quality DNA which gives reliable genotypes when PCR amplified (94.3% success rate). Wing tip DNA sampling will permit a variety of novel research approaches, including genotyping of queens at emergence in breeding programs where certain patrilines or genotypes are preferred, and genotyping workers and queens which must behave normally following sampling.
Abstract: 1. The simultaneous occupation of a rare understorey ant-acacia Acacia mayana by its guarding ant Pseudomyrmex ferrugineus, and an apparent
opportunist parasite of the mutualism, the generalist ant Camponotus planatus is described. The two ant species occur together in 30.7% of the 26 mature
A. mayana plants [23.5% of all trees (n=34)] surveyed, but C. planatus is absent from saplings below 1m in height( n=8).
2. While P. ferrugineus shows behaviour compatible with effective host-tree defence, C. planatus does not attack phytophagous insects and appears ineffective
as an ant-guard. Camponotus planatus does, however, occupy swollen thorns (pseudogalls) on the host tree, and harvests nectar from extrafloral leaf nectaries.
Itis proposed that C. planatus is a parasite of the Acacia–Pseudomyrmex mutualism.
3. Camponotus planatus does not harvest the second trophic reward produced by the tree for its Pseudomyrmex ant-guards, protein-rich food (Beltian) bodies.
Camponotus planatus lack the specialised larval adaptations needed to use Beltian bodies as brood food, suggesting that this resource is potentially more resistant to exploitation by generalists than extrafloral nectar.
4. In competition for access to nectaries, C. planatus effectively displaced P. ferrugineus in 99.8%of encounters. These results suggest not only that C. planatus
is a parasite of this mutualism, but also that it is able to effectively counteract the aggression shown to other insects by the resident ant-guards.
Abstract: We review the pollination ecology of acacias worldwide, dicsussing (1) the rewards provided to flower visitors, (2) the temporal patterns of flowering and reward provision and (3) the taxonomic composition of flower visitor assemblages. The flowers of most acacias (including all members of the subgenus Phyllodinae) offer only pollen to flower visitors and floral nectar is limited to a minority of species in the subgenera Acacia and Aculeiferum. The most important pollinators of acacias are social and solitary bees, although other insects and nectar-feeding birds are important in specific cases. Acacias that secrete nectar attract far more species-rich assemblages of flower-visitors, although many of these are probably not important as pollinators. Most acacias in the subgenus Phyllodinae have long-lived protogynous flowers, without clear daily patterns in reward provision and visitation. In contrast, most members of the other two subgenera have flowers that last for a single day, appear to be protandrous and have clear daily patterning in reward provision and visitation. The generality of these patterns should not be assumed until the pollination ecology of many more phyllodinous acacias has been studied, particularly in arid environments. The accessibility of the floral rewards in acacia flowers makes them important examples of two general issues in plant communities - the partitioning of shared pollinators and the evolution of floral ant repellents.
Abstract: Ant-acacias represent a classic insect–plant mutualism: the ants defend the plant from attack by herbivores, and in return are provided with trophic rewards and living space within swollen thorns. A potential drawback of this and other ant–plant mutualisms is that ant-guards may drive away useful insects, particularly pollinators. We assess the potential for ant–pollinator conflict in a Mexican ant-acacia, Acacia hindsii. This Acacia is guarded by a highly aggressive ant (Pseudomyrmex veneficus), which resides entirely within the host plant canopy and is provided with extrafloral nectar and protein-rich Beltian bodies. Acacia hindsii flowers released their pollen from 0700 to 0830 hours, and were visited by pollinators from 0730 to 1300 hours. Over the same time period ants maintained high activity levels at extrafloral nectaries on young leaves. Although daily activity of ants and pollinators overlapped substantially in time, it was largely separated in space: resources exploited by the ants are predominantly concentrated within new growth, while inflorescences are present only on shoots from the previous year. Ants nevertheless visit extrafloral
nectaries on older leaves near inflorescences, and there is thus potential for ant–pollinator
conflict. Bioassays of ant behavior showed young A. hindsii inflorescences induce an avoidance
response in its ant-guards, which reinforces spatial segregation between ants and
pollinators. This effect is absent from buds or postreproductive flowers. Young flowers of
two non-myrmecophilous Acacia species also induced significant (though less potent) repellent
effects, suggesting a general role for ant-repellents in Acacia, with selective enhancement
in myrmecophilous species.
