Reduced abundance and earlier collection of bumble bee workers under intensive cultivation of a mass‐flowering prairie crop

One of the most commonly seeded crops in Canada is canola, a cultivar of oilseed rape (Brassica napus). As a mass‐flowering crop grown intensively throughout the Canadian Prairies, canola has the potential to influence pollinator success across tens of thousands of square kilometers of cropland. Bumble bees (Bombus sp.) are efficient pollinators of many types of native and crop plants. We measured the influence of this mass‐flowering crop on the abundance and phenology of bumble bees, and on another species of social bee (a sweat bee; Halictus rubicundus), by continuously deploying traps at different levels of canola cultivation intensity, spanning the start and end of canola bloom. Queen bumble bees were more abundant in areas with more canola cover, indicating that this crop is attractive to queens. However, bumble bee workers were significantly fewer in these locations later in the season, suggesting reduced colony success. The median collection dates of workers of three bumble bee species were earlier near canola fields, suggesting a dynamic response of colonies to the increased floral resources. Different species experienced this shift to different extents. The sweat bee was not affected by canola cultivation intensity. Our findings suggest that mass‐flowering crops such as canola are attractive to bumble bee queens and therefore may lead to higher rates of colony establishment, but also that colonies established near this crop may be less successful. We propose that the effect on bumble bees can be mitigated by spacing the crop more evenly with respect to alternate floral resources.     

Bumble bee behavior and selection on flower size in the sky pilot,Polemonium viscosum

Summary In alpine Polemonium viscosum, plants having sweet-scented flowers are primarily pollinated by queens of the bumble bee species, Bombus kirbyellus. In this paper we ask whether two aspects of the pollination effectiveness of bumble bees, visitation rate and pollination efficiency, vary significantly with flower size in sweet-flowered P. viscosum.(i) Bumble bees visited plants with large flowers on 80–90% of encounters, but visited those with smaller flowers on only 49% of encounters. (ii) However, the gain in pollination that large-flowered plants obtained via increased visitation was countered in part because bumble bees deposited fewer outcross pollen grains per visit on stigmas of large flowers than on those of small ones. When both visitation rate and pollination efficiency are taken into account, the predicted value of a single bumble bee encounter declines from 1.06 seeds for flowers larger than 18 mm in diameter to 0.55 seeds for flowers smaller than 12 mm in diameter. Our results suggest that bumble bee pollinators of P. viscosum prefer flower morphologies that are poorly suited for precise pollination. Such behavioral complexities are likely to place constraints on the evolution of optimal floral design.     

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     

The pollination biology of Calypso bulbosa var. Americana (Orchidaceae): Initial deception of bumblebee visitors

Summary The orchid Calypso bulbosa var. americana has deceptive flowers that provide no rewards for visitors. Near Banff, Alberta, the flowering period of this species is synchronized with the emergence of its pollinators, large bumblebee queens, in late spring. Calypso flowers appear to rely on the initial attraction and deception of newly-emerged naive bumblebees for pollination. Indirect evidence suggests that individual bees subsequently learn to avoid these flowers and that avoidance is learned quite rapidly. Avoidance behavior by pollinators is obviously detrimental to sexual reproduction in Calypso. This negative effect appears to be offset by the large number of seeds produced in plants which are effectively pollinated. A test of the hypothesis that Calypso flowers mimic flowers of the shooting star, Dodecatheon radicatum (Primulaceae) failed to provide evidence for mimicry.     

Behavioral responses by bumble bees to variation in pollen availability

Summary Pollen-collecting bumble bees (Bombus spp.) detect differences between individual flowers in pollen availability and alter their behavior to capitalize on rewarding flowers. Specific responses by bees to increased pollen availability included: longer visits to flowers; visits to more flowers within an inflorescence, including an increased frequency of revisits; an increased likelihood of grooming while the bee flow between flowers within the inflorescence; and more protracted inter-flower flights, probably because of longer grooming bouts. The particular suite of responses that a bee adopted depended on the pollen-dispensing mechanism of the plant species involved. Bees buzzed previously-unvisited Dode-catheon flowers longer than empty flowers. In contrast, pollen availability did not significantly affect the duration of visits to Lupinus flowers, which control the amount of pollen that can be removed during a single visit. Simulation results indicate that the observed movement patterns of bumble bees on Lupinus inflorescences would return the most pollen per unit of expended energy. The increased foraging efficiency resulting from facultative responses by bees to variation in pollen availability, especially changes in the frequency and intensity of grooming, could correspondingly decrease pollen dispersal between plants.     

Pollen-Foraging Dynamics of Subalpine Bumblebees (Bombus Latr.)

Abstract A 23-year study on Mount Rainier of nectar-foraging hummingbirds and pollen-foraging bumblebees (Bom-bus Latr.) indicated a constant relative frequency of Bombus species in the area and a wide occurrence of insect species on flowers plus a wide range of flower species pollinated by a single insect. Early-blooming plants had a high queen/worker pollinator ratio, while workers predominated on later-blooming plants. No altitudinal difference in distribution of Bombus species occurred. Analysis of 955 corbicular pollen loads from 1158 bumblebees collected yielded 49.5% monolecty for queens and 34.5% for workers with a wider range for queens than for workers. Colors of corollas photographed in visible and ultraviolet light corresponded to the visual spectra of animal pollinators. In the stable plant-pollinator community investigated, pollinating insect activity appears phenologically controlled by floral anthesis and behaviorally related to floral form and function. Bumblebee tongue length, however. Is not a valid determinant for foraging niche separation except in Castilleja with a deep corolla tube accommodating long tongues of hummingbirds and bumblebees. It is concluded that in a biotic community well-coordinated with the physical environment, limited flower constancy of pollen-foraging pollinators appears to contribute a necessary degree of adaptive versatility through sharing of insect and floral resources. Flower constancy is primarily a function of the circumstance in which a pollinator operates and not simply a characteristic of the pollinator itself.     

Assessing the Threatened Status of Bumble Bee Species (Hymenoptera: Apidae) in Hungary,Central Europe

Decline in the populations of bumble bees and other pollinators stress the need for more knowledge about their conservation status. Only one of the 25 bumble bee species present in Hungary is included in the Hungarian Red List. We estimated the endangerment of the Hungarian bumble bee (Bombus Latr.) species using the available occurrence data from the last 50 years of the 20th century. Four of the 25 species were data deficient or extinct from Hungary. About 60% of species were considered rare or moderately rare. Changes in distribution and occurrence frequency indicated that 10 of the 21 native species showed a declining trend, while only three species increased in frequency of occurrence. According to the IUCN Red List categories, seven species (33% of the native fauna) should be labelled as critically endangered (CR) and 3 (14%) as endangered (EN). Our results stress an urgent need of protection plans for bumble bees in Hungary, and further underlines the validity of concern over bumble bees all over Europe.     

Mixed bumblebee and blowfly pollination of Cypripedium flavum (Orchidaceae) in Sichuan,China

Most Cypripedium species are specialized orchids pollinated by, in a broad sense, bees or flies. Here we present the first evidence that a slipper orchid, Cypripedium flavum, is pollinated by both bees and flies, i.e., bumblebees and blowflies. Artificial pollination experiments demonstrated that the flowers of C. flavum are self-compatible, but need pollen vectors for successful reproduction. Field observations detected 25 insects visiting the flowers, and 14 of these insects entered into the labellum of the flowers, but only female bumblebees, Bombus hypnorum, B. remotus, and the blowfly Calliphora vomitoria exited of the labellum with pollen smears of C. flavum. The floral functional morphology of C. flavum appears to be more suited to bumblebees than to blowflies. The bumblebees are more efficient pollinators of the orchid, but blowflies are more frequent visitors, so they pollinated more flowers despite being less efficient.     

AN EXPERIMENTAL STUDY OF THE FLORAL ECOLOGY OF DODECATHEON MEADIA

An established colony of Dodecatheon meadia on glacial drift in southeastern Wisconsin was observed for its insect pollination interrelationships. Twelve randomly distributed plants from which insects were excluded failed to produce seed, while plants exposed to insect visits set abundant seed. Female solitary bees of 2 species, viz., Augochloropsis metallica fulgida (Smith) and Lasioglossum forbesii (Robertson), and queens and workers of 7 species of Bombus were observed collecting pollen from the pendant anther cone by rapid wing vibration, while hanging inverted from the cone tip. This behavior—cinematographically recorded—was found fundamentally identical to that of females of the same species of solitary bees and of queens and workers of 5 species of Bombus on Solanum dulcamara, and of females of Lasioglossum forbesii (Robertson) and workers of 2 species of Bombus on Lycopersicum esculentum Mill. No other insects were found to pollinate these morphologically similar flowers in this manner, and crepuscular pollinators were not observed. Experimental modifications of form, function, and position of Dodecatheon flowers were offered to the pollinators, and behavioral changes of the insects were noted. Constituents of insect pollen loads were examined, and relationships of the pollinators to the flora of the region were noted. The detailed ecological study of insect pollen vector behavior as an aid in discovering biosystematic relationships of plant populations is suggested.     

THE POLLINATION ECOLOGY OF PEDICULARIS ON MOUNT RAINIER

Six native species of Pedicularis in Mount Rainier National Park in Washington State were studied for their reproductive relationships with animal pollinators. Cinematographic and stereophotographic records revealed pollination of the nectariferous P. bracteosa and P. rainierensis by upright, nectar-foraging queens and workers of five bumblebee (Bombus Latr.) species and by inverted workers scraping pollen from anthers concealed within the corolla galea. The nectarless, rostrate flowers of P. contorta, P. groenlandica, P. ornithorhyncha, and P. racemosa were pollinated by pollen-foraging workers and occasional queens virbrating pollen from concealed anthers. Insect exclosure methods revealed complete absence of fruiting in the absence of insects, and pollinator collections further indicate obligate dependence of the plants upon bumblebees for their sexual reproduction. Analysis of corbicular pollen loads from pollinators suggested that pollinator species are not monolectic but that individual pollinators range from monolectic to polylectic. Measurements indicated limited correlations between lengths of corolla tubes and tongues of nectar-foraging insects. Each nectarless Pedicularis species occupied a different, specific habitat, but P. bracteosa and the endemic P. rainierensis were sympatric in part. Each species had a unique spectral reflectance pattern from the corolla. Proximity of habitats and overlap of blooming periods of all Pedicularis species eliminate the possibility of contemporary geographic or phenological reproductive isolation. It is suggested that behavioral interactions of the plants and their insect pollinators may have been instrumental in the past in reproductively isolating these species, hybrids of which are unknown.     

Bumble bee colony dynamics: quantifying the importance of land use and floral resources for colony growth and queen production

Bumble bee (Bombus) species are ecologically and economically important pollinators, and many species are in decline. In this article, we develop a mechanistic model to analyse growth trajectories of Bombus vosnesenskii colonies in relation to floral resources and land use. Queen production increased with floral resources and was higher in semi‐natural areas than on conventional farms. However, the most important parameter for queen production was the colony growth rate per flower, as opposed to the average number of available flowers. This result indicates the importance of understanding mechanisms of colony growth, in order to predict queen production and enhance bumble bee population viability. Our work highlights the importance of interpreting bumble bee conservation efforts in the context of overall population dynamics and provides a framework for doing so.     

A new species of Psidium L. (Myrtaceae) from southern Brazil

Rewardless kettle‐trap flowers Cypripedium yunnanense and C. flavum were watched for pollinators during 73 and 101 man‐hours, respectively, in north‐west Yunnan at 3490–3590 m a.s.l. They differ from typical Cypripedium, such as C. calceolus, in having a broad infolded flap of the lip extending all around the entrance of the pouch (instead of being restricted to the vicinity of the staminode) and in the flap not being slippery. Cypripedium yunnanense is pollinated by Lasioglossum zonulum euronotum (Halictidae), and C. flavum is pollinated by Andrena orchidea and Andrena sp. (Andrenidae, two of nine new hymenopterans discovered at the sites). The bees do not inadvertently fall into the trap by slipping (as often occurs in other slipper orchids), but enter it by crawling down the flap in full control of their movements. No natural hybrids between the two orchids are known, although they occur in close‐by or mixed stands, are co‐flowering and size compatible with regard to their pollinators, and produce fruits following manual cross‐pollination in situ. Analyses of the (non‐Cypripedium) pollen carried indicate that: (1) the two andrenids are probably oligolectic; (2) the andrenids and the halictid do not share the same flower species; and (3) the halictid is polylectic. Points (1) and (2) are probable reasons for the lack of hybrids. The other reason why Lasioglossum zonulum euronotum does not visit C. flavum despite being polylectic may be the flower's odour; cases of discrimination of closely related flowers by polylectic Lasioglossum have been reported elsewhere. Blow flies Calliphora vomitoria and Calliphora pattoni (Calliphoridae) also enter the orchids, some smearing themselves with pollen, yet they are not pollinators. They are too large to leave by the exit and die imprisoned. However, they may be accidental pollinators of the rather larger C. tibeticum present at the sites. Such accidental pollinators probably play an important role in the evolution of new pollination syndromes. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 156 , 51–64.     

Correlates of reproductive success among field colonies of Bombus lucorum: the importance of growth and parasites

Abstract.

• 1 In natural populations, colonies of bumble bees vary in many important life history traits, such as colony size and age at maturity, or the number and sex of reproductives produced. We investigated how the presence of parasites in field populations of the bumble bee Bombus lucorum L. relates to variation in life history traits and reproductive performance. A total of thirty-six colonies was placed in accessible nest sites in the field and monitored at regular intervals throughout a season.
• 2 Among the life history correlates, early nest foundation was strongly associated with large maximum colony size, old age and large size at maturity, and this in turn with successful production of males and queens, as well as with the number of sexuals produced. Overall, reproductive success was highly skewed with only five colonies producing all the queens. Sixteen colonies failed to reproduce altogether.
• 3 The social parasite Psithyrus was abundant early in the Bombus colony cycle and preferentially invaded host nests with many first brood workers and thus disproportionately large size, i.e. those colonies that would otherwise be more likely to reproduce or produce (daughter) queens rather than males. To prevent nest loss, Psithyrus had to be removed soon after invasion. Therefore, the effects reported here can only be crude estimates.
• 4 Parasitoid conopid flies are likely to cause heavy worker mortality when sexuals are reared by the colonies. Their inferred effect was a reduction in biomass that could be invested in sexuals as well as a shift in the sex ratio at the population level resulting from failure to produce queens. We suggest to group the inferred correlates into ‘early events’ surrounding colony initiation and social parasitism, and ‘late events’ surrounding attained colony size in summer and parasitism by conopid flies. Our evidence thus provides a heuristic approach to understand the factors that affect reproductive success of Bombus colonies.

     

Increase of pollinator attraction by means of a visual signal in the sexually deceptive orchid, Ophrys heldreichii (Orchidaceae)

Orchids of the genus Ophrys are pollinated by males of solitary bees and wasps through sexual deception. Flowers mimic the odor of a receptive female and thus attract males that seek to copulate. Visual stimuli have been assumed so far to play only a minor role in male attraction. We investigated the role of the perigon as a potential visual signal in attracting pollinators in the orchid Ophrys heldreichii and its pollinator, the males of the long-horned bee Tetralonia berlandi (Apidae). In contrast to many other Ophrys species, O. heldreichii exhibits a large and bright pinkish perigon that appears visually conspicuous to a human observer. In a dual choice test we presented two flowers from a single plant and counted visitation rates. We then removed the perigon of one flower and retested the relative attractiveness of both flowers. For 292 male visits in ten trials we found a significant decrease of visitation rate for flowers with the perigon removed. In a second experiment we repeated the dual choice test using photos of the flowers. Males also significantly chose the picture of an intact flower over the picture of a modified flower where the perigon was digitally removed. From our data, we conclude that T. berlandi males respond to and are attracted by the bright pink perigon of the orchid in addition to other stimuli. A bright colorful perigon occurs almost only in the Ophrys holoserica-oestrifera group, a large sub-group of the genus. We hypothesize that this kind of visual signal is adaptive particularly in those Ophrys species where the targeted males patrol resourced-based encounter sites and strongly rely on their visual system while searching for their females.     

Annual flower strips support pollinators and potentially enhance red clover seed yield

Ecological intensification provides opportunity to increase agricultural productivity while minimizing negative environmental impacts, by supporting ecosystem services such as crop pollination and biological pest control. For this we need to develop targeted management solutions that provide critical resources to service‐providing organisms at the right time and place. We tested whether annual strips of early flowering phacelia Phacelia tanacetifolia support pollinators and natural enemies of seed weevils Protapion spp., by attracting and offering nectar and pollen before the crop flowers. This was expected to increase yield of red clover Trifolium pratense seed. We monitored insect pollinators, pests, natural enemies and seed yields in a total of 50 clover fields along a landscape heterogeneity gradient, over 2 years and across two regions in southern Sweden. About half of the fields were sown with flower strips of 125–2,000 m². The clover fields were pollinated by 60% bumble bees Bombus spp. and 40% honey bees Apis mellifera. The clover seed yield was negatively associated with weevil density, but was unrelated to bee species richness and density. Flower strips enhanced bumble bees species richness in the clover fields, with the strongest influence in heterogeneous landscapes. There were few detectable differences between crop fields with and without flower strips. However, long‐tongued bumble bees were redistributed toward field interiors and during phacelia bloom honey bees toward field edges. Clover seed yield also increased with increasing size of the flower strip. We conclude that annual flower strips of early flower resources can support bumble bee species richness and, if sufficiently large, possibly also increase crop yields. However, clover seed yield was mainly limited by weevil infestation, which was not influenced by the annual flower strips. A future goal should be to design targeted measures for pest control.     

Oriole pollination ofErythrina breviflora (Leguminosae): Evidence for a polytypic view of ornithophily

Erythrina breviflora is visited by large numbers of passerine birds of which orioles (Icterus: Icteridae) are the primary pollinators. The flowers produce large quantities of nectar but they are rarely visited by hummingbirds. Inflorescence and floral morphology, and low levels of sucrose in the nectar probably explain the rarity of foraging hummingbirds. A comparison of Old WorldErythrina and their pollinators with New World species pollinated by orioles and hummingbirds suggests that parallel evolution has occurred. When the comparison is expanded to include other species pollinated by orioles, it is clear that various New WorldIcteridae, Thraupidae, etc. are ecological equivalents of Old WorldOriolidae, Pycnonotidae, Sturnidae, etc. and that flowers pollinated by these birds have similar characteristics.     

Local bumble bee decline linked to recovery of honey bees,drought effects on floral resources

Time series of abundances are critical for understanding how abiotic factors and species interactions affect population dynamics, but are rarely linked with experiments and also scarce for bee pollinators. This gap is important given concerns about declines in some bee species. I monitored honey bee (Apis mellifera) and bumble bee (Bombus spp.) foragers in coastal California from 1999, when feral A. mellifera populations were low due to Varroa destructor, until 2014. Apis mellifera increased substantially, except between 2006 and 2011, coinciding with declines in managed populations. Increases in A. mellifera strongly correlated with declines in Bombus and reduced diet overlap between them, suggesting resource competition consistent with past experimental results. Lower Bombus numbers also correlated with diminished floral resources. Declines in floral abundances were associated with drought and reduced spring rainfall. These results illustrate how competition with an introduced species may interact with climate to drive local decline of native pollinators.     

Plant interactions for pollinator visits: a test of the magnet species effect

Summary From 1985–1987, patterns of fruit and seed set were studied in a population of mayapple (Podophyllum peltatum), a clonal, self-incompatible herb found in deciduous woods in eastern North America. Mayapple flowers do not produce nectar, but depend on infrequent visits by nectar-seeking queen bumble bees for pollination. In all years female reproductive success in mayapple colonies was influenced by colony size (number of flowers), by the distance to neighbouring colonies and by proximity to lousewort plants (Pedicularis canadensis), a prolific nectar producer heavily visited by bumble bees. In all years fruit and seed set were greater in mayapple colonies <25 m from lousewort flowers than in matched colonies which were >50 m from lousewort. In 1985 and 1987 the frequency of queen bumble bee visits to flowers in colonies close to lousewort was about four times greater than to distant colonies. In 1986 I removed about 80% of lousewort flowers to test whether the enhanced fruit and seed set in mayapples close to lousewort was pollinator mediated. Mayapple colonies close to flowerless lousewort patches did not differ in fruit or seed set from matched colonies >50 m from lousewort. In contrast, mayapples close to flowering lousewort patches had greater fruit and seed set compared with distant colonies. Over all years, a larger proportion of mayapples close to flowering lousewort patches had enhanced fruit and seed set compared with colonies close to louseworts without flowers. Though rarely documented, this type of facilitative interaction between plants that are highly attractive to pollinators (magnet species), and co-flowering species that are rarely visited by pollinators, may be widespread in plant communities.     

Moth pollination of woody species in the Cerrados of Central Brazil: a case of so much owed to so few?

We present a survey of moth pollination in woody species of the Cerrado of Central Brazil. Although with the exception of Roupala montana (which has simple polysepalous flowers arranged in dense cymes) all moth pollinated species in this community have tubular flowers, or a pseudo-tube formed from a single folded petal in Qualea grandiflora, settling moth flowers (tube less than 15 mm) vs. hawkmoth flowers (tube more than 50 mm) are markedly different in size. Moths visit some 20 woody Cerrado species, but they are probably effective pollinators of only 13 species or ca.14% of the woody taxa studied, and even in these latter species they are often very sparse visitors. Nevertheless, it is notable that moths are pollinators for 21% of the 38 most commonly distributed woody Cerrado species. Moreover, the reproductive efficacy of the studied moth pollinated species was similar to that of species pollinated by other kind of vectors.     

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.