Breeding habitat and nest‐site selection by an obligatory “nest‐cleptoparasite”, the Amur Falcon Falco amurensis

The selection of a nest site is crucial for successful reproduction of birds. Animals which re‐use or occupy nest sites constructed by other species often have limited choice. Little is known about the criteria of nest‐stealing species to choose suitable nesting sites and habitats. Here, we analyze breeding‐site selection of an obligatory “nest‐cleptoparasite”, the Amur Falcon Falco amurensis. We collected data on nest sites at Muraviovka Park in the Russian Far East, where the species breeds exclusively in nests of the Eurasian Magpie Pica pica. We sampled 117 Eurasian Magpie nests, 38 of which were occupied by Amur Falcons. Nest‐specific variables were assessed, and a recently developed habitat classification map was used to derive landscape metrics. We found that Amur Falcons chose a wide range of nesting sites, but significantly preferred nests with a domed roof. Breeding pairs of Eurasian Hobby Falco subbuteo and Eurasian Magpie were often found to breed near the nest in about the same distance as neighboring Amur Falcon pairs. Additionally, the occurrence of the species was positively associated with bare soil cover, forest cover, and shrub patches within their home range and negatively with the distance to wetlands. Areas of wetlands and fallow land might be used for foraging since Amur Falcons mostly depend on an insect diet. Additionally, we found that rarely burned habitats were preferred. Overall, the effect of landscape variables on the choice of actual nest sites appeared to be rather small. We used different classification methods to predict the probability of occurrence, of which the Random forest method showed the highest accuracy. The areas determined as suitable habitat showed a high concordance with the actual nest locations. We conclude that Amur Falcons prefer to occupy newly built (domed) nests to ensure high nest quality, as well as nests surrounded by available feeding habitats.     

Bumble bee abundance and richness improves honey bee pollination behaviour in sweet cherry

Pollination service in agricultural crops increases significantly with pollinator diversity and wild pollinator abundance. Differences in the foraging behaviour of pollinating insects are one of the reasons why pollinator diversity and abundance enhances crop pollination. Here, we focused on the foraging behaviour of honey bees and bumble bees in sweet cherry orchards. In addition, we studied the influence of bee diversity and abundance on the foraging behaviour of honey bees and bumble bees. Honey bees were found to visit fewer flowers than bumble bees. Bumble bees also showed a higher probability of changing trees between rows than honey bees. Both visitation rate and probability of row changes of honey bees increased with bumble bee diversity and with bumble bee abundance. We also found that the probability of row changes of honey bees increased with increasing bumble bee abundance. These effects of bumble bee richness and abundance on the pollination behaviour of honey bees can improve the pollination performance of honey bees in crops that depend on cross pollination. Our results highlight the higher pollination performance of bumble bees and the facilitative effect of wild pollinators to crop pollination.     

Bumble bee olfactory information flow and contact-based foraging activation

Nestmate foraging activation and interspecific variation in foraging activation is poorly understood in bumble bees, as compared to honey bees and stingless bees. We therefore investigated olfactory information flow and foraging activation in the New World bumble bee species, Bombus impatiens. We (1) tested the ability of foragers to associate forager-deposited odor marks with rewarding food, (2) determined whether potential foragers will seek out the food odor brought back by a successful forager, and (3) examined the role of intranidal tactile contacts in foraging activation. Bees learned to associate forager-deposited odor marks with rewarding food. They were significantly more attracted to an empty previously rewarding feeder presented at a random position within an array of eight previously non-rewarding feeders. However, foragers did not exhibit overall odor specificity for short-term, daily floral shifts. For two out of three tested scents, activated foragers did not significantly prefer the feeder providing the same scent as that brought back by a successful forager. Finally, bees contacted by the successful forager inside the nest were significantly more likely to leave the nest to forage (38.6% increase in attempts to feed from empty feeders) than were non-contacted bees. This is the first demonstration that tactile contact, a hypothesized evolutionary basal communication mechanism in the social corbiculate bees, is involved in bumble bee foraging activation. Received 4 September 2007; revised 30 May 2008; accepted 15 July 2008.     

What Currency Do Bumble Bees Maximize?

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.     

Pollination efficiency and foraging behaviour of honey bees and non‐Apis bees to sweet cherry

1. Crop pollination generally increases with pollinator diversity and wild pollinator visitation. To optimize crop pollination, it is necessary to investigate the pollination contribution of different pollinator species. In the present study, we examined this contribution of honey bees and non‐Apis bees (bumble bees, mason bees and other solitary bees) in sweet cherry.
2. We assessed the pollination efficiency (fruit set of flowers receiving only one visit) and foraging behaviour (flower visitation rate, probability of tree change, probability of row change and contact with the stigma) of honey bees and different types of non‐Apis bees.
3. Single visit pollination efficiency on sweet cherry was higher for both mason bees and solitary bees compared with bumble bees and honey bees. The different measures of foraging behaviour were variable among non‐Apis bees and honey bees. Adding to their high single visit efficiency, mason bees also visited significantly more flower per minute, and they had a high probability of tree change and a high probability to contact the stigma.
4. The results of the present study highlight the higher pollination performance of solitary bees and especially mason bees compared with bumble bees and honey bees. Management to support species with high pollination efficiency and effective foraging behaviour will promote crop pollination.

     

Effects of recent experience on foraging decisions by bumble bees

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

Spatial ecology of a range‐expanding bumble bee pollinator

Molecular methods have greatly increased our understanding of the previously cryptic spatial ecology of bumble bees (Bombus spp.), with knowledge of the spatial ecology of these bees being central to conserving their essential pollination services. Bombus hypnorum, the Tree Bumble Bee, is unusual in that it has recently rapidly expanded its range, having colonized much of the UK mainland since 2001. However, the spatial ecology of B. hypnorum has not previously been investigated. To address this issue, and to investigate whether specific features of the spatial ecology of B. hypnorum are associated with its rapid range expansion, we used 14 microsatellite markers to estimate worker foraging distance, nest density, between‐year lineage survival rate and isolation by distance in a representative UK B. hypnorum population. After assigning workers to colonies based on full or half sibship, we estimated the mean colony‐specific worker foraging distance as 103.6 m, considerably less than values reported from most other bumble bee populations. Estimated nest density was notably high (2.56 and 0.72 colonies ha^?1 in 2014 and 2015, respectively), estimated between‐year lineage survival rate was 0.07, and there was no evidence of fine‐scale isolation by distance. In addition, genotyping stored sperm dissected from sampled queens confirmed polyandry in this population (mean minimum mating frequency of 1.7 males per queen). Overall, our findings establish critical spatial ecological parameters and the mating system of this unusual bumble bee population and suggest that short worker foraging distances and high nest densities are associated with its rapid range expansion.     

Ecological meta‐networks integrate spatial and temporal dynamics of plant–bumble bee interactions

Bumble bees can forage on a large number of wild plants and crops. The survival of a colony depends on the availability of suitable food resources within foraging range and throughout their forage season. We studied the spatial and temporal use of floral resources by bumble bees in a set of 30 local plant communities and used these data to model colony survival under different combinations of patch size and bumble bee flight distance. Floral resources vary spatially and temporally at the landscape level, and bumble bees track these resources across the landscape during the season. The simulation model showed that different patterns of resources availability could affect the survival and distribution of bumble bee nests across the landscape. This model can be used to generate hypotheses explaining bumble bee richness and abundance that can be tested in real landscapes. Integrating the spatial and temporal dynamics of the flower resources used by bumble bees provides a new perspective that can be used to inform bumble bee conservation, particularly in the context of their widespread decline in recent decades.     

Nest Entrance Marking with Colony Specific Odors by the Bumble Bee Bombus occidentalis (Hymenoptera: Apidae)

We investigated the ability of naturally foraging female bumble bees (Bombus occidentalis) to recognize their nest entrance in the field. In a blind binary-choice paradigm, females discriminated between nest entrances tipped with caps from their own nest entrances and entrances tipped with caps previously associated with foreign heterospecific or foreign conspecific colonies. Washing caps in organic solvents eliminated the manifestation of this nest-entrance recognition and significantly decreased the episodes of antennating caps. These results indicate that bees deposit colony-specific chemicals on nest entrances that are later perceived via contact chemoreception. Females treated foreign heterospecific and foreign conspecific caps similarly, suggesting that bees may not assess or respond to the degree of similarity between their own colony odor and a foreign colony odor.     

The Potential Influence of Bumble Bee Visitation on Foraging Behaviors and Assemblages of Honey Bees on Squash Flowers in Highland Agricultural Ecosystems

Bee species interactions can benefit plant pollination through synergistic effects and complementary effects, or can be of detriment to plant pollination through competition effects by reducing visitation by effective pollinators. Since specific bee interactions influence the foraging performance of bees on flowers, they also act as drivers to regulate the assemblage of flower visitors. We selected squash (Cucurbita pepo L.) and its pollinators as a model system to study the foraging response of honey bees to the occurrence of bumble bees at two types of sites surrounded by a high amount of natural habitats (≥ 58% of land cover) and a low amount of natural habitats (≤ 12% of land cover) in a highland agricultural ecosystem in China. At the individual level, we measured the elapsed time from the departure of prior pollinator(s) to the arrival of another pollinator, the selection of honey bees for flowers occupied by bumble bees, and the length of time used by honey bees to explore floral resources at the two types of sites. At the community level, we explored the effect of bumble bee visitation on the distribution patterns of honey bees on squash flowers. Conclusively, bumble bee visitation caused an increase in elapsed time before flowers were visited again by a honey bee, a behavioral avoidance by a newly-arriving honey bee to select flowers occupied by bumble bees, and a shortened length of time the honey bee takes to examine and collect floral resources. The number of overall bumble bees on squash flowers was the most important factor explaining the difference in the distribution patterns of honey bees at the community level. Furthermore, decline in the number of overall bumble bees on the squash flowers resulted in an increase in the number of overall honey bees. Therefore, our study suggests that bee interactions provide an opportunity to enhance the resilience of ecosystem pollination services against the decline in pollinator diversity.     

Economic motivation for plant species preferences of pollen-collecting bumble bees

1. Pollen is an essential resource for bees as it provides the proteins needed for larval development and growth. Bumble bees typically collect pollen from a limited subset of the available plant species, indicating that bees perceive qualitative and/or quantitative differences between species. Because bumble bees typically exhibit different foraging behaviours when collecting pollen than when collecting nectar, and often visit different plant species, the economics of pollen collection are subject to unique benefits and costs.
2. The influences of pollen standing crop, grain volume, protein content and foraging costs on the choice of plant species by pollen-collecting bumble bees were assessed. Pollen was collected from different plant species available to bees and these species were ranked according to eleven currencies that differentially incorporate these influences on foraging economics.
3. Comparison of observed preferences at three sites with species rankings based on foraging currencies revealed that bumble bees do not assess plant species based solely on intrafloral characteristics. Instead, pollen-foraging bumble bees are sensitive to protein availability at the site as a whole as well as foraging costs, and forage in a manner that maximizes the site-specific efficiency of protein collection (protein collected/energetic costs). Such behaviour would promote proper larval development while maximizing forager lifespan.     

Trapline foraging by bumble bees: IV. Optimization of route geometry in the absence of competition

Foraging on resources that are fixed in space but that replenishover time, such as floral nectar and pollen, presents animalswith the problem of selecting a foraging route. What can flowervisitors such as bees do to optimize their foraging routes,that is, reduce return time or route distance? Some repeatedlyvisit a set of plants in a significantly predictable sequence(so-called "trapline foraging"), which may also enhance theirforaging efficiency. A moderate level of optimization and repetitionof foraging routes can be reached by following simple movementrules for choosing the distances and turning angles of successiveflights, without the use of spatial memory. If pollinators canlearn the locations of patches and choose among possible foragingroutes or paths, however, even better performance may be achieved.We tested whether and how bumble bees can optimize and repeattheir foraging routes in laboratory experiments with artificialflowers that secreted nectar at a constant rate. With increasingexperience, foraging routes of bees became more repeatable andefficient than expected from a combination of simple movementrules between successive flowers. We suggest that trapline foragingis a more sophisticated pattern of spatial use than searchingand is based on memory. On the other hand, certain spatial configurationsof flowers hampered optimization by the bees; bees preferredto choose short distances over straight moves and showed littleplasticity in this regard. Developing an efficient trapline,therefore, may require prior selection of a set of plants withan appropriate spatial configuration.     

Population genetics of wild and managed pollinators: implications for crop pollination and the genetic integrity of wild bees

Loss of habitat and chemical use associated with agriculture can cause population declines of wild pollinators. Less is known about the evolutionary consequences of interactions between species used in commercial agriculture and wild pollinators. Given population declines of many wild bee species, it is crucial to understand if commercial queens become established in natural areas, if wild bees visit agricultural fields and have the potential to interact with commercial bees, and if gene flow occurs between commercial and wild bees. We drew on a long-term data set that documents commercial bumble bee (Bombus impatiens) use in New England, and we conducted genetic analyses of foraging B. impatiens from areas with varying intensities of commercial bee use. In agricultural areas with a history of commercial bee use we also sampled bees directly from commercial hives. We found significant genetic differences among foraging B. impatiens and B. impatiens sampled directly from hives (average pairwise F′_ST = 0.14), but not among samples of foraging bees from natural areas (average F′_ST among foraging bees?=?0.002). Furthermore, Bayesian analysis of population structure revealed that foraging bees caught in areas with a history of commercial bee use grouped with samples from natural areas. These results document an agricultural setting where there was no widespread introgression of alleles from commercial bumble bees to wild bumble bees, commercial bumble bees did not become established in natural areas, and wild bees were providing pollination services to crops.     

Estimating nest locations of bumblebee <Emphasis Type="Italic">Bombus ardens</Emphasis> from flower quality and distribution

The central-place forager in a social-insect colony, e.g., the bumblebee, has been expected to maximize its net rate of energy gain to increase the success of its colony. In addition to foraging behavior, the nest location is an important factor for the success of the colony. The bumblebee’s nest location would be affected by the spatial distribution of flowers and their food quality. In this study, we constructed a model to estimate bumblebee nest sites, using the net energy intake rate at available food sites for workers foraging from the nest site. We hypothesized that the probability of colony establishment at a site in coordinates (x, y) was high as the sum of the net energy intake rate I(x, y) increased. To obtain I(x, y), nectar standing crop, sugar concentration, and foraging time were measured for ten plant species in the study site covering 6.25 km². As available flowers changed seasonally, I(x, y) was calculated for three periods: the end of April, the beginning of May, and the middle of May. To verify our hypothesis, we compared the estimations in our model with the actual nest sites of Bombus ardens found in the beginning of May and June by means of tracking bumblebees. From the results, we considered that the net energy intake rate at mid-May might represent the probability of colony establishment, because it could affect colony persistence and reproductive success.     

Estimating colony locations of bumble bees with moving average model

It is very difficult to find natural colonies of bumble bees in the field. In this study, the yearly dynamics of floral resources and foraging bumble bee workers were investigated. The optimal colony locations were estimated from the data using moving average on the assumption that bumble bee queens and workers were omniscient. Fortunately, a colony of Bombus ardens was found, and the true location of the colony was evaluated with the estimated optimal locations. The true location was optimal at the latter half of the breeding season.An erratum to this article can be found at     

High-altitude multi-taskers: bumble bee food plant use broadens along an altitudinal productivity gradient

We use an extensive historical data set on bumble bee host choice collected almost 50 years ago by L. W. Macior (Melanderia 15:1–59, 1974) to examine how resource partitioning by bumble bees varies over a 2,700-m altitudinal gradient at four hierarchical scales: individual, colony, species and community. Bumble bee behavior, resource overlap between castes, and plant-bumble bee networks change with altitude in accordance with tightening temporal constraints on flowering and colony growth in alpine habitats. Individual bees were more likely to collect pollen from multiple sources at high altitude. Between-caste foraging niche overlap increased with altitude. Similarly, alpine forager networks were more highly nested than either subalpine or montane networks due to increased asymmetric specialization. However, interspecific resource partitioning showed a more complex spatial pattern with low niche overlap at intermediate altitude (subalpine) compared to montane (disturbed) and alpine (unproductive) sites. Results suggest that spatial variation in interspecific resource partitioning is driven by a shift in the behavior of long-tongued bumble bees. Long-tongued bumble bees specialized in the subalpine but generalized in montane and alpine zones. Our reanalysis of Macior’s data shows that bumble bee behavior varies substantially with altitude influencing plant-bumble bee interaction networks. Results imply that pollination services to alpine host plants will change dramatically as subalpine species with unique foraging strategies move upward under global warming.     

Ground-nesting bees determine the location of their nest relative to a landmark by other than angular size cues

Bees and wasps acquire a visual representation of their nest's environment and use it to locate their nest when they return from foraging trips. This representation contains among other features cues to the distance of near-by landmarks. We worked with two species of ground-nesting bees, Lasioglossum malachurum (Hymenoptera: Halictidae), Dasypoda hirtipes (Hymenoptera: Melittidae) and asked which cues to landmark distance they use during homing. Bees learned to associate a single cylindrical landmark with their nest's location. We subsequently tested returning bees with landmarks of different sizes and thus introduced large discrepancies between the angular size of the landmark as seen from the nest during training and its distance from the nest. The bees' search behaviour and their choice of dummy nest entrances show that both species of ground-nesting bees consistently search for their nest at the learned distance from landmarks. The influence of the apparent size of landmarks on the bees' search and choice behaviour is comparatively weak. We suggest that the bees exploit cues derived from the apparent speed of the landmark's image at their retina for distance evaluation.     

Foraging behavior affects pollen removal and deposition in Impatiens capensis (Balsaminaceae)

Flowers of most plant species are visited by a variety of animals. Some of these visitors are effective pollinators while others remove resources without transferring pollen. Studies comparing the effectiveness of different visitors as pollinators often compare taxa without considering variation in behavior within a taxon. Wilson and Thomson (Ecology 72: 1503-1507, 1991) documented the effects of honey bees and bumble bees on the pollination dynamics of Impatiens capensis. They found that pollen-collecting honey bees removed large numbers of pollen grains from anthers but deposited little of it on stigmas; bumble bees, which sought nectar, removed less pollen but deposited more of it on stigmas. It is unclear whether the low pollen transfer efficiencies of honey bees are explained by their morphology or by their pollen-collecting behavior. We repeated the work of Wilson and Thomson at a site where honey bees were foraging for nectar, not pollen. We measured the quantity of pollen remaining in anthers, the number of pollen grains deposited on stigmas, and seed production after single visits by honey bees and bumble bees. The differences between the taxa disappeared when they were foraging in a similar manner. Our results clearly demonstrate the importance of foraging behavior on the pollination effectiveness of floral visitors.     

Honey bee (Hymenoptera: Apidae) distribution and potential for supplementary pollination in commercial tomato greenhouses during winter

This study examined the use of honey bees, Apis mellifera L., to supplement bumble bee, Bombus spp., pollination in commercial tomato, Lycopersicon esculentum Miller, greenhouses in Western Canada. Honey bee colonies were brought into greenhouses already containing bumble bees and left for 1 wk to acclimatize. The following week, counts of honey and bumble bees foraging and flying throughout the greenhouse were conducted three times per day, and tomato flowers open during honey bee pollination were marked for later fruit harvest. The same counts and flower-marking also were done before and after the presence of honey bees to determine the background level of bumble bee pollination. Overall, tomato size was not affected by the addition of honey bees, but in one greenhouse significantly larger tomatoes were produced with honey bees present compared with bumble bees alone. In that greenhouse, honey bee foraging was greater than in the other greenhouses. Honey bees generally foraged within 100 m of their colony in all greenhouses. Our study invites further research to examine the use of honey bees with reduced levels of bumble bees, or as sole pollinators of greenhouse tomatoes. We also make specific recommendations for how honey bees can best be managed in greenhouses.     

Survey of bumble bee (Bombus) pathogens and parasites in Illinois and selected areas of northern California and southern Oregon

Pathogens have been implicated as potential factors in the recent decline of some North American bumble bee (Bombus) species, but little information has been reported about the natural enemy complex of bumble bees in the United States. We targeted bumble bee populations in a state-wide survey in Illinois and several sites in California and Oregon where declines have been reported to determine presence and prevalence of natural enemies. Based on our observations, most parasites and pathogens appear to be widespread generalists among bumble bee species, but susceptibility to some natural enemies appeared to vary.