Bombus terrestris in a mass‐flowering pollinator‐dependent crop: A mutualistic relationship?

Bumblebees (Bombus spp.) rely on an abundant and diverse selection of floral resources to meet their nutritional requirements. In farmed landscapes, mass‐flowering crops can provide an important forage resource for bumblebees, with increased visitation from bumblebees into mass‐flowering crops having an additional benefit to growers who require pollination services. This study explores the mutualistic relationship between Bombus terrestris L. (buff‐tailed bumblebee), a common species in European farmland, and the mass‐flowering crop courgette (Cucurbita pepo L.) to see how effective B. terrestris is at pollinating courgette and in return how courgette may affect B. terrestris colony dynamics. By combining empirical data on nectar and pollen availability with model simulations using the novel bumblebee model Bumble‐BEEHAVE, we were able to quantify and simulate for the first time, the importance of courgette as a mass‐flowering forage resource for bumblebees. Courgette provides vast quantities of nectar to ensure a high visitation rate, which combined with abundant pollen grains, enables B. terrestris to have a high pollination potential. While B. terrestris showed a strong fidelity to courgette flowers for nectar, courgette pollen was not found in any pollen loads from returning foragers. Nonetheless, model simulations showed that early season courgette (nectar) increased the number of hibernating queens, colonies, and adult workers in the modeled landscapes. Synthesis and applications. Courgette has the potential to improve bumblebee population dynamics; however, the lack of evidence of the bees collecting courgette pollen in this study suggests that bees can only benefit from this transient nectar source if alternative floral resources, particularly pollen, are also available to fulfill bees’ nutritional requirements in space and time. Therefore, providing additional forage resources could simultaneously improve pollination services and bumblebee populations.     

Reconstructing demographic events from population genetic data: the introduction of bumblebees to New Zealand

Four British bumblebee species (Bombus terrestris, Bombus hortorum, Bombus ruderatus and Bombus subterraneus) became established in New Zealand following their introduction at the turn of the last century. Of these, two remain common in the United Kingdom (B. terrestris and B. hortorum), whilst two (B. ruderatus and B. subterraneus) have undergone marked declines, the latter being declared extinct in 2000. The presence of these bumblebees in New Zealand provides an unique system in which four related species have been isolated from their source population for over 100 years, providing a rare opportunity to examine the impacts of an initial bottleneck and introduction to a novel environment on their population genetics. We used microsatellite markers to compare modern populations of B. terrestris, B. hortorum and B. ruderatus in the United Kingdom and New Zealand and to compare museum specimens of British B. subterraneus with the current New Zealand population. We used approximate Bayesian computation to estimate demographic parameters of the introduction history, notably to estimate the number of founders involved in the initial introduction. Species-specific patterns derived from genetic analysis were consistent with the predictions based on the presumed history of these populations; demographic events have left a marked genetic signature on all four species. Approximate Bayesian analyses suggest that the New Zealand population of B. subterraneus may have been founded by as few as two individuals, giving rise to low genetic diversity and marked genetic divergence from the (now extinct) UK population.     

The Value of Uncropped Field Margins For Foraging Bumblebees

The intensification of agriculture has led to declines in species diversity and abundance within groups of certain flora and fauna. Bumblebees (Bombus spp.) are one group where a decline has been documented, and it is thought to be attributable to a decrease in forage resources and potential nest sites. As bumblebees play an important role in the pollination of many entomophilous crops, this decline could impact on agricultural productivity. We examined the role of naturally regenerated field margins in providing forage plants on land where nectar resources are otherwise impoverished. The following question was addressed – Are naturally regenerated unsprayed field margins more attractive to foraging bumblebees and honeybees than cropped field margins managed as conservation headlands? Significantly more bees visited naturally regenerated field margins than cropped field margins. Honeybees (Apis mellifera), Bombus terrestris, and Bombus lapidarius were the most commonly observed bee species. Different wildflower species within the naturally regenerated margins varied greatly in relative number of visits received, and bumblebee species were found to prefer different flower species to honeybees. The potential role that naturally regenerated field margins could play in the conservation of bumblebee species, and the implications for other species of flora and fauna, are discussed.     

Worldwide migration of parasitic mites as a result of bumblebee commercialization

We investigated the status of infestation by a tracheal mite, Locustacarus buchneri, in natural populations of a Japanese native bumblebee species, Bombus hypocrita, collected on Hokkaido Island and in the Aomori prefecture between 1997 and 2001. We also investigated mite infestation in commercial colonies of the European bumblebee, Bombus terrestris, imported from the Netherlands and Belgium, and the Japanese native species, B. ignitus, imported from the Netherlands, between 1997 and 2001. We detected mites in natural populations of the two B. hypocrita subspecies and in the commercial colonies. Analysis of variations in 535 bp sequences of the mitochondrial cytochrome oxidase subunit 1 (CO1) gene showed that the mite haplotypes in the native populations and in the imported colonies did not overlap in 1997–1999, but in 2000–2001 some mites possessing European CO1 haplotypes were detected in the natural populations of Japanese native bumblebees. In addition, many mites possessing Japanese haplotypes were detected in the imported commercial colonies from Europe. Considering the fact that the Japanese native bumblebees, B. hypocrita, were once exported to Europe for commercialization, these results suggest that bumblebee commercialization has caused overseas migration and cross-infestation of parasitic mites among natural and commercial colonies. However, because the Japanese and European CO1 haplotypes were closely related, there was a possibility that the European haplotypes found in the mites in the Hokkaido Island revealed native variation. To clarify the status of mite invasion, further detailed analysis of genetic variation of the mite, using other genetic markers on additional samples, need to be performed.     

Bumblebees at an alpine site in northern Sweden: temporal development, population size, and plant utilization

The bumblebee community in an alpine valley in northern Sweden was studied for two seasons. Only two species of bumblebees, Bombus alpinus and B. hyperboreus. are common at the site. Bombus hyperhoreus is an obligate nest parasite on B. alpinus : the latter species is four times more abundant than the former. The number of captures on any given day was very low. However, the number of queens foraging in the area was estimated by a mark-reacapture method to ca 350 specimens, indicating that the queens forage over large areas. The dates for capturing queens carrying pollen in their corbiculae and the emergence of workers and males indicate that the queens only have time to produce one batch (or possibly two overlapping batches) of workers. The utilization of different plant species corresponds well with their flowering phenology at the site. The unspecialized flowers of Saxifraga oppositifolia are the main pollen and nectar source in the early part of the season. The bumblebees switch to Astragalus alpinus and Bartsia alpina as soon as they come into flower: these species show a typical bee pollination syndrome, the corbicular loads most commonly consisted of 91-100% of pollen from a single species. The change in flower utilization and the composition of the corbicular loads give no support for the hypothesis that aretie bumblebees should be more generalistic in their foraging than temperate species. The preference for Astragalus and Bartsia will probably have an effect on outcrossing in late-flowering specimens of Saxifraga oppositifolia , which has a very extended flowering period.     

Forage use and niche partitioning by non-native bumblebees in New Zealand: implications for the conservation of their populations of origin

Bumblebees were introduced into New Zealand from the UK approximately 120 years ago and four species became established. Two of these, Bombus terrestris and B. hortorum, are common in Europe whilst two, B. ruderatus and B. subterraneus, have experienced declines, and the latter is now extinct in the UK. The presence of these species in New Zealand presents an opportunity to study their ecology in a contrasting environment. Forage visits made by bumblebees in New Zealand were recorded across a season. Ninety-six percent of visits were to six non-native forage plants (Cirsium vulgare, Echium vulgare, Hypericum perforatum, Lotus corniculatus, Lupinus polyphyllus and Trifolium pratense). All but L. polyphyllus are European plant species, and three are noxious weeds in New Zealand. Several of these plants have decreased in abundance in the UK, providing a potential explanation for the declines of B. ruderatus and B. subterraneus in Britain. In contrast to studies conducted elsewhere, B. ruderatus, B. terrestris and B. hortorum did not differ in diet breadth and overlap in forage use was high, probably due to the reduced diversity of bumblebee forage plants present in New Zealand. Diel partitioning of forage use between the species was observed, with foraging activity of B. hortorum greatest in the morning and evening, B. ruderatus greatest in the middle of the day and B. terrestris intermediate between the two. These patterns correspond to the climatic preferences of each species as evidenced by their geographic ranges. Implications for bumblebee conservation in the UK are discussed.     

Foraging habitats and foraging distances of bumblebees, Bombus spp. (Hym., Apidae), in an agricultural landscape

Abstract: In selected foraging habitats of an agricultural landscape flower visits of bumblebees and community structure of foraging bumblebees were studied, with special regard to the role of crops as super-abundant resources. Most crops represent temporal foraging habitats with high abundance of bumblebees but mainly with low diversity in the bumblebee forage community, in contrast to permanent foraging habitats such as, for example, a hedgerow. The high numbers of bumblebees in the monoculture of crop plantations consisted mainly of short-tongued bumblebee species. The role of foraging distances for the visitation rate of foraging habitats was studied by performing capture–recapture experiments with natural nests of Bombus terrestris , Bombus lapidarius and Bombus muscorum . Differences were found on the species as well as the individual level. The foraging distances of B. muscorum were more restricted to the neighbourhood of the nesting habitat than the foraging activity of B. terrestris and B. lapidarius . High percentages of B. terrestris workers were recaptured while foraging on super-abundant resources in distances up to 1750 m from the nest. Isolated patches of highly rewarding forage crops, in agricultural landscapes, are probably only accessed by bumblebee species with large mean foraging distances, such as the short-tongued B. terrestris . Species like the rare, long-tongued B. muscorum depend on a close connection between nesting and foraging habitat. A restricted foraging radius might be one important factor of bumblebee species loss and potential pollinator limitation in modern agricultural landscapes. Furthermore, long-distance flights of bumblebee pollinators have to be considered in the present discussion on gene flow from transgenic plant species on a landscape scale.     

Flowers, Nectar and Insect Visits: Evaluating British Plant Species for Pollinator-friendly Gardens

Twenty-four plant species native or naturalized in Britain weregrown in the Cambridge University Botanic Garden, UK and evaluatedas potential resources for nectar-foraging bees, butterfliesand hoverflies. In ten plant species a series of measurementswere made, at regular intervals from dawn to dusk, of nectarsecretion rate and standing crop, and in all species insectvisits were monitored throughout daylight hours. The study revealeddifferences between plant species in the composition of theassemblage of insect visitors, and in the magnitude and temporaldistribution of the nectar reward. In some cases we found interestingcorrelations between temperature and secretion rates or patternsof insect visits. Species that received numerous insect visitsin our study are potentially valuable forage plants that mightbe planted by gardeners to support local pollinator populations.Deep flowers whose nectar is accessible to long-tongued bumblebees(Bombus hortorum, B. pascuorum) but not to honeybees may providelong-tongued pollinators with a resource refuge relatively freefrom honeybee competition. Features that make some of thoseplant species particularly interesting to observe in the gardeninclude robbing by short-tongued bumblebees inSaponaria,baseworkingby honeybees on closed flowers inMalva sylvestris, and apparentdisplacement of bumblebees by territorial behaviour of the solitarybeeAnthidium manicatumon species ofStachys.Copyright 1999 Annalsof Botany Company Wild flowers, gardens, nectar,Silene, Lychnis, Saponaria, Stachys, Malva, Dipsacus fullonum, Lythrum salicaria,pollinators, bumblebees,Bombus,honeybees,Apis,butterflies, Lepidoptera, hoverflies, Syrphidae,Anthidium manicatum, weeds.     

Pollination Ecology and Endemic Trends in Pedicularis bracteosa var. atrosanguinea Pennell & Thompson (Scrophulariaceae) in North America

Abstract Pedicularis bracteosa var. atrosanguinea occurs locally in association with P. racemosa or P. groenlandica in the Olympic Mountains in Washington. Other plant species, e.g., Polygonum bistortoides, Lupinus argenteus var. parviflorus and Valeriana sitchensis compete for space and bumblebee pollinators within the study area. Pollinator sharing, resulting from such competition, may increase the frequency of unvisited flowers of P. bracteosa var. atrosanguinea. P. bracteosa var. atrosanguinea , with blood purple nectariferous flowers, is presumed to lack intense reflections of blue spectral components from its corollas in attracting bumblebees compared to those of P. racemosa and P. groenlandica . Six species of bumblebees ( Bombus ) and cuckoo bees ( Psithyrus ) pollinate P. bracteosa var. atrosanguinea . Of these, Bombus mixtus and B. occidentalis occur in higher frequencies and are the major pollinators of P. bracteosa var. atrosanguinea . Queen and larger worker bumblebees pollinate nototribically as they probe for nectar, while smaller worker bumblebees pollinate sternotribically while scraping pollen from anthers deeply hidden in the dome-shaped galea. Corbicular pollen loads of bumblebees collected in the study area contain Pedicularis pollen alone/in combination of Polygonum, Valeriana, Lupinus, Erigeron and Bidens , or exclusively of Polygonum or Valeriana. P. bracteosa var. atrosanguinea does not suffer seriously from deficient pollination but seedlings resulting from pollinated flowers may be subjected to natural selection pressure exerted by colonial plant species for space. P. bracteosa var. atrosanguinea does not propagate asexually but resumes aerial growth seasonally from the self-same underground root stocks. If seedlings are under continuous selection pressure for lack of space, P. bracteosa var. atrosanguinea is presumed to regenerate primarily by perennial root stocks. This behavior may favor endemism in P. bracteosa var. atrosanguinea .     

草乌花蜜产量的梯度分布及熊蜂自下而上的访花行为

收益降低假说(declining reward hypothesis)认为熊蜂自下而上的访花顺序是对花蜜产量的直接响应,先访问下部花蜜产量高的花可以获得更多的收益;花开口方向假说认为自下而上访花是因为熊蜂更容易看见其上部的花朵。为了验证上述两个假说,我们于2008年8月在北京小龙门国家森林公园调查了红光熊蜂(Bombus ignitus)访问草乌(Aconitum kusnezoffii)直立和倒立顶生花序的访问顺序,测量了直立花序下部雌性阶段花和上部雄性阶段花花蜜的糖浓度、体积,计算了花蜜中的糖含量。结果表明,红光熊蜂在直立花序和倒立花序内均以向上运动为主,分别占总运动次数的62.77%和68.35%;直立花序下部雌性阶段花花蜜糖浓度比上部雄性阶段花低1.44%,但是花蜜体积和花蜜中的糖含量都显著高于雄性阶段的花。由于熊蜂访问倒立花序时先访问的是下部的低回报雄性阶段的花,然后再访问上部高回报的雌性阶段的花,这与收益降低假说矛盾,表明红光熊蜂自下而上访问草乌直立花序可能不是受到花蜜产量的调节。     

Does Aconitum septentrionale chemically protect floral rewards to the advantage of specialist bumblebees?

相似文献   

Targeted agri‐environment schemes significantly improve the population size of common farmland bumblebee species

Changes in agricultural practice across Europe and North America have been associated with range contractions and local extinction of bumblebees (Bombus spp.). A number of agri‐environment schemes have been implemented to halt and reverse these declines, predominantly revolving around the provision of additional forage plants. Although it has been demonstrated that these schemes can attract substantial numbers of foraging bumblebees, it remains unclear to what extent they actually increase bumblebee populations. We used standardized transect walks and molecular techniques to compare the size of bumblebee populations between Higher Level Stewardship (HLS) farms implementing pollinator‐friendly schemes and Entry Level Stewardship (ELS) control farms. Bumblebee abundance on the transect walks was significantly higher on HLS farms than ELS farms. Molecular analysis suggested maximum foraging ranges of 566 m for Bombus hortorum, 714 m for B. lapidarius, 363 m for B. pascuorum and 799 m for B. terrestris. Substantial differences in maximum foraging range were found within bumblebee species between farm types. Accounting for foraging range differences, B. hortorum (47 vs 13 nests/km²) and B. lapidarius (45 vs 22 nests/km²) were found to nest at significantly greater densities on HLS farms than ELS farms. There were no significant differences between farm type for B. terrestris (88 vs 38 nests/km²) and B. pascuorum (32 vs 39 nests/km²). Across all bumblebee species, HLS management had a significantly positive effect on bumblebee nest density. These results show that targeted agri‐environment schemes that increase the availability of suitable forage can significantly increase the size of wild bumblebee populations.     

Restoration and management of machair grassland for the conservation of bumblebees

Machair is a grassland habitat that supports nationally rare species including the bumblebee species Bombus distinguendus and Bombus muscorum. Changes in land management practices have resulted in a loss of floral diversity in some areas, reducing the availability of bumblebee foraging resources. In order to determine the most effective way of increasing forage plant availability on degraded machair, a restoration trial was established in western Scotland and comprised four seed mixes and a fallow treatment. Treatments were monitored over 3 years in order to compare the relative abundance of bumblebees and their forage plants. Two mixes contained wildflower species; one mix is currently used to create bird and bee foraging habitat on nature reserves and the fourth is a commercially available grass mix. There was little variation in inflorescence and bumblebee abundance between treatments early on but marked differences emerged later in the season in all 3 years. By the end of the monitoring period, the wildflower treatments contained between four and eighteen times more inflorescences than other treatment types. Similar trends were observed in bumblebee abundances. Some of the rarest bumblebee species exist primarily in areas that have largely escaped agricultural intensification. In these areas it is important that habitat management is specifically targeted and translated into appropriate agri-environment schemes. We suggest that the most effective method for restoring bumblebee forage plants on machair is to sow wildflower-rich seed mixes and this should be combined with late cutting and winter grazing practices to maintain sward diversity over time.     

Effects of three flower field types on bumblebees and their pollen diets

Agri-environment schemes, like flower fields, have been implemented in the EU to counteract the dramatic decline of farmland biodiversity. Farmers in Lower Saxony, Germany, may receive payments for three flower field types: annual, perennial (five years old), and mixed flower fields composed of yearly alternating annual and biannual parts. We assessed the effectiveness of these flower field types in providing bumblebee foraging habitat compared to control cereal fields. We sampled bumblebees with transect walks and assessed the richness of exploited pollen plants using DNA meta-barcoding and direct observations.All flower field types enhanced bumblebee abundance and species richness compared to control fields but attracted mostly three generalist species. Although we expected highest benefits from the more heterogeneous mixed flower fields, abundance was highest in annual, only intermediate in mixed, and lowest in perennial flower fields. Bumblebee species richness did not differ between flower field types.Overall, the proportion of sown plants in pollen loads was surprisingly low (< 50%). Bombus pascuorum, but not B. terrestris agg., exploited 10% of the sown plant species in perennial, 36% in annual and 45% in mixed flower fields, respectively. Compared to direct observations, pollen samples revealed 4.5 times more visited plant species and thus assessed floral resource use more reliably. Plant species richness in pollen loads decreased with local flowering plant species richness and increased with proportion of annual crops in the landscape, potentially due to the exploitation of more diverse and scattered resources, including flowering crops, in homogenized landscapes to fulfil dietary requirements.Our results indicate that under the current management, both annual and mixed flower fields provide the most attractive food resources, while perennial flower fields offered the poorest foraging habitats. Conclusively, flower fields seem important but resources from the surrounding landscape are still needed to sustain bumblebees in agricultural landscapes.     

Diet breadth,coexistence and rarity in bumblebees

Factors that determine the relative abundance of bumblebee species remain poorly understood, rendering management of rare and declining species difficult. Studies of bumblebee communities in the Americas suggest that there are strong competitive interactions between species with similar length tongues, and that this competition determines the relative abundance of species. In contrast, in Europe it is common to observe several short-tongued species coexisting with little or no evidence for competition shaping community structure. In this study we examine patterns of abundance and distribution in one of the most diverse bumblebee communities in Europe, found in the mountains of southern Poland. We quantify forage use when collecting nectar and pollen for 23 bumblebee species, and examine patterns of co-occurrence and niche overlap to determine whether there is evidence for inter-specific competition. We also test whether rarity can be explained by diet breadth. Up to 16 species were found coexisting within single sites, with species richness peaking in mountain pasture at ~1,000 m altitude. Results concur with previous studies indicating that the majority of pollen collected by bumblebees is from Fabaceae, but that some bee species (e.g. B. ruderatus) are much more heavily dependent on Fabaceae than others (e.g. B. lucorum). Those species that forage primarily on Fabaceae tended to have long tongues. In common with studies in the UK, diet breadth was correlated with abundance: rarer species tended to visit fewer flower species, after correcting for differences in sample size. No evidence was found for similarity in tongue length or dietary overlap influencing the likelihood of co-occurrence of species. However, the most abundant species (which co-occurred at most sites) occupied distinct dietary niche space. While species with tongues of similar length tended, overall, to have higher dietary niche overlap, among the group of abundant short-tongued species that commonly co-occurred there was marked dietary differentiation which may explain their coexistence.     

Habitat quality limits gene flow between populations of <Emphasis Type="Italic">Bombus ruderatus</Emphasis> in the South Island,New Zealand

One of the primary reasons for the decline of some bumblebee species has been habitat loss and fragmentation through land use change. Habitat fragmentation can limit connectivity between populations and gene flow between bumblebee populations can be limited by open water and human altered landscapes, however the influence of landscape features on gene flow has only been examined in non-declining species. The ruderal bumblebee, Bombus ruderatus, was successfully introduced to and is now relatively common in New Zealand, providing an opportunity to examine the biology of a species that is now rare in its native range in the UK. In this study, we examine the genetic structuring of B. ruderatus populations in the South Island of New Zealand and we demonstrate that a relatively simple classification of the landscape, into either good or poor foraging habitat at coarse resolution (800 m²), can predict levels of gene flow. We found populations of B. ruderatus as far apart as 160 km showing no significant genetic differentiation. However, this level of gene flow appears to be reliant upon continuous suitable habitat, as other populations <100 km apart were found to be significantly differentiated. These results suggest that corridors of continuous habitat are required to facilitate gene flow over large distances for this species.     

Diversity, flower visitation frequency and generalism of pollinators in temperate rain forests of Chiloé Island, Chile

Species richness and taxonomic composition of pollinator assemblages are documented for 26 plant species from temperate rain forests of northern Chiloé Island, southern Chile (42°30'S). We investigated the patterns of generalism and specialization among plants and animal pollinators by comparing the flower visit frequency by different pollen vectors during the spring and summer months of three consecutive years (2000–2002). Species studied exhibited a range of floral morphologies (radial vs. zygomorphic, open vs. tubular) and rewards (nectar and/or pollen). Overall, we recorded 172 pollinator species, with an average of 6.6 species of pollen vectors/plant species. Pollinators visited an average of 15.2 plant species/pollen vector. Pollinator assemblages were dominated by Coleoptera (75 species), Diptera (56 species) and Hymenoptera (30 species), but passerine birds and hummingbirds were also important. The most specialized plants were vines, including the bee-pollinated genus Luzuriaga (Philesiaceae) and two endemic species of hummingbird-pollinated Gesneriaceae. Hymenoptera contributed 41.2% of all visits, with the bumblebee Bombus dalhbomii accounting for 22.5% of these. Plants with unspecialized flower morphology supported a higher species richness of pollinators, but visiting rates did not differ from specialized flowers.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 147 , 399–416.     

Endangered by laws: potential consequences of regulations against thistles on bumblebee conservation

Many bumblebee (Bombus) species are undergoing a strong decline in Europe due to, amongst other things, a decrease of food resources. While leguminous plants (Fabaceae) are considered to be one of the main pollen sources of bumblebees, thistles (Asteraceae tribe Cardueae) have been suggested to be important for male diet. Yet, several European countries apply strict regulations against thistles since they are considered to be one of the principal weeds in agricultural landscapes. Such regulations could impact bumblebee conservation through disruption of male diet and ecology. Here, we assess the male-depending importance of thistles for bumblebee species based on field observations across countries where a legal regulation against thistles is in effect. We ultimately aim to evaluate the potential consequences of these regulations on bumblebee conservation. Our results confirm that most floral visit observations of males occur on thistles (mainly Cirsium spp. and Carduus spp.) and some species are almost exclusively observed on them. Thistle removal is thus most likely a threat for bumblebees. Therefore, we advocate repealing the thistle removal acts to make way for alternative thistle regulations which reconcile biodiversity conservation and agricultural requirements.     

Bumblebee colonies produce larger foragers in complex landscapes

The negative effect of agricultural intensification on bumblebee populations is thought to partly be caused by loss of food plants, for example because of increased field size and concomitant loss of non-crop field borders and their nectar and pollen plants. Earlier studies have focused on how loss of foraging resources affects colony growth and thereby abundance of workers and sexual reproduction. By comparing bumblebees in agricultural landscapes of different complexity in Southern Sweden, we here demonstrate that also the adult size of bumblebee foragers is significantly related to the availability of foraging resources. This effect was independent of both species identity and foraging habitat type. This suggests a shortage of flower resources in landscapes of lower complexity, which may also affect the reproductive success of colonies negatively.     

Population genetic structure of Bombus terrestris in Europe: Isolation and genetic differentiation of Irish and British populations

The genetic structure of the earth bumblebee (Bombus terrestris L.) was examined across 22 wild populations and two commercially reared populations using eight microsatellite loci and two mitochondrial genes. Our study included wild bumblebee samples from six populations in Ireland, one from the Isle of Man, four from Britain and 11 from mainland Europe. A further sample was acquired from New Zealand. Observed levels of genetic variability and heterozygosity were low in Ireland and the Isle of Man, but relatively high in continental Europe and among commercial populations. Estimates of F_st revealed significant genetic differentiation among populations. Bayesian cluster analysis indicated that Irish populations were highly differentiated from British and continental populations, the latter two showing higher levels of admixture. The data suggest that the Irish Sea and prevailing south westerly winds act as a considerable geographical barrier to gene flow between populations in Ireland and Britain; however, some immigration from the Isle of Man to Ireland was detected. The results are discussed in the context of the recent commercialization of bumblebees for the European horticultural industry.