Common Bumblebee Species Research Articles

Rearing of Native Bumblebee Species Bombus haemorrhoidalis for Greenhouse Pollination in Pakistan

Greenhouse tomato production is a growing business worldwide, and it is strongly promoted by bumblebee pollination. Although there are over 250 bumblebee species worldwide, very few species have been reared successfully for greenhouse tomato pollination. Those successfully managed species, especially Bombus terrestris, are shipped around the world for commercial use. However, managed bumblebees are known to escape greenhouse facilities, have established local populations, spread disease to local bumblebees, and are blamed for the declines of some indigenous bee species. An alternative to shipping exotic bumblebees around the world is to develop local species for greenhouse pollination. Such an approach has the dual benefits of creating a new industry of insect rearing while reducing threats to local bee communities. In this study, we successfully reared Bombus haemorrhoidalis, which is the most common bumblebee species in Northern Pakistan, in a laboratory and compared its effectiveness as a tomato pollinator with that of commercial B. terrestris in a greenhouse. We found that the effectiveness of B. haemorrhoidalis in tomato pollination in a greenhouse is very similar to that of B. terrestris when it comes to the fruit size, number of seeds, and fruit weight. Our study provides an example of how to rear a native bumblebee species to pollinate local crops, which is a method that could potentially substitute the importation of non-ingenious bumblebees.

High temperature sensitivity of bumblebee castes and the colony-level costs of thermoregulation in Bombus impatiens

Physiological thermal limits often reflect species distribution, but the role that ambient temperature (Ta) plays in limiting species within their thermal environment remains unclear. Climate change-linked declines in bumblebees, an important pollinator group, leave questions regarding which aspect of their physiology is hindered under high Ta. As a eusocial species, bumblebees utilize their ability to thermoregulate as a superorganism to maintain nest temperature (Tn) within a narrow thermal window to buffer developing larvae from developmental defects. Thermoregulatory behaviours, such as thermogenesis to warm up and fanning to cool down the nest, are energetically expensive and it is uncertain how successful large colonies are at maintaining Tn within its optimal range. Using a common bumblebee species, Bombus impatiens, our study first established the critical thermal limits (CTmax) of workers, queens, drones and larvae to determine which caste is most thermally sensitive to heat. We found that larvae had significantly lower heat tolerance than adults, highlighting the importance of colonial thermoregulation. We then measured the energy expenditure of large colonies under acute thermal stress (5–40 °C) using flow-through respirometry while simultaneously quantifying Tn. Colonies that experienced Ta at or below optimal Tn (≤30 °C) were successful at thermoregulation. At 35 °C and above, however, Tn increased despite high energetic costs to the colony. Together our results demonstrate that high Ta poses a risk to colonies that fail to buffer thermally sensitive larvae from changes in Tn.

How competition between overlapping generations can influence optimal egg-laying strategies in annual social insects.

Annual social insects are an integral functional group of organisms, particularly in temperate environments. An emblematic part of their annual cycle is the social phase, during which the colony-founding queen rears workers that later assist her in rearing sexual progeny (gynes and drones). In many annual social insects, such as species of bees, wasps, and other groups, developing larvae are provisioned gradually as they develop (progressive provisioning) leading to multiple larval generations being reared simultaneously. We present a model for how the queen in such cases should optimize her egg-laying rate throughout the social phase depending on number-size trade-offs, colony age-structure, and energy balance. Complementing previous theory on optimal allocation between workers vs. sexuals in annual social insects and on temporal egg-laying patterns in solitary insects, we elucidate how resource competition among overlapping larval generations can influence optimal egg-laying strategies. With model parameters informed by knowledge of a common bumblebee species, the optimal egg-laying schedule consists of two temporally separated early broods followed by a more continuous rearing phase, matching empirical observations. However, eggs should initiallybe laid continuously at a gradually increasing rate when resources are scarce or mortality risks high and in cases where larvae are fully supplied with resources at the egg-laying stage (mass-provisioning). These factors, alongside sexual:worker body size ratios, further determine the overall trend in egg-laying rates over the colony cycle. Our analysis provides an inroad to study and mechanistically understand variation in colony development strategies within andacross species of annual social insects.

Biodiversity measures providing food and nesting habitat increase the number of bumblebee (Bombus terrestris) colonies in modelled agricultural landscapes

Individual biodiversity measures in agricultural landscapes such as flower strips are reported to promote the diversity and abundance of pollinating insects. Those biodiversity measures can be important food sources increasing the amount and continuity of pollen and nectar supply besides sometimes also offering nesting and hibernation sites. Still little is known about combined effects of biodiversity measures at the landscape scale and their long-term impact on pollinator population development. We used the agent-based simulation model BumbleBEEHAVE to investigate, if biodiversity measures have a positive effect on bumblebee populations at landscape scale in terms of the number of colonies per hectare. For this purpose, we chose Bombus terrestris, the most common bumblebee species in Germany, as target species. We used three real landscapes located in different regions of Germany as landscape settings for the simulations. The landscapes had strongly different farming systems regarding crop diversity and rotations and, consequently, different spatial structure and areal proportions of land-use types and semi-natural habitats. Between 2017 and 2020, distinct combinations of biodiversity measures, such as flower strips, flowering headland and fallows, were established by farmers on different areal proportions of the three landscapes. The biodiversity measures differed in plant-seed mixtures and, thus, the pollen and nectar supply by plants. We simulated the development of bumblebee colonies in the landscapes with and without the implemented biodiversity measures over eight years (four years in a twice repetition). We found that the implementation of biodiversity measures had a significant positive effect on the number of colonies. Further analysis showed that the pollen and nectar supplied by biodiversity measures had positive effects in all three landscapes, while the effect of additional nesting habitat differed among landscapes. Mass-flowering crops had little to no significant effect on the number of bumblebee colonies, whereas semi-natural habitats had a markedly positive effect. Our study underlines that not only biodiversity measures are likely to affect the bumblebee population, but that the overall landscape composition, particularly proportion of semi-natural habitats, is also important. So, to achieve high effectiveness of biodiversity measures, landscape context may be taken into account.

Verges Along Forest Roads Promote Wild Bees

AbstractForests in Germany are occupied with roads, paths, and trails with a density of 5.03 km/km². Their construction and maintenance create a network of verges promoting flowering plants. Whether these verges are visited by bees, which factors are determining their abundance, diversity, and composition, and which flowering resources are used is unknown. We selected 13 verges in the Black Forest (Germany), sweep-netted wild bees along transects, calculated the flowering area of all herbs, and measured the area (hectares) of grassland within 1 km around the transects. To evaluate the resource use of a common bumblebee species, we analyzed the pollen load of common carder bees (Bombus pascuorum) using microscopes. The abundance and diversity of wild bees was positively related to flowering area. With an increasing area of grassland, the abundance of ubiquitous species increased. Wild bee community composition was driven by flowering area. Common carder bees collected pollen from several flower resources but mainly used few species, such as the common hemp nettle (Galeopsis tetrahit L.). As the flowering area influenced wild bee abundance, diversity, and composition, we suggest creating road verges that favor the occurrence of native flowering plants to support wild bees in forest ecosystems.Study Implications: Forest road verges generally have higher light availability than the forest interior and therefore have higher availability of flowering plants. Although the importance of verges for wild bee conservation in agricultural landscapes is known, forest road verges are understudied. Our study demonstrates that forest road verges are important habitats for many ubiquitous bees and that the flowering area on these verges is the key determinant for the abundance and diversity of wild bees. Therefore, creating road verges that favor the occurrence of native flowering plants is key to support bees on these verges.

Mass-flowering red clover crops have positive effects on bumblebee richness and diversity after bloom

Floral resource quantity in agricultural landscapes plays a key role in the persistence of wild pollinators. An equally important, but less investigated factor is how variation in floral resource availability over time, e.g. floral resource pulses, affects pollinator abundances and diversity. Despite the potential importance of late-season resource pulses for bumblebee reproduction, few studies have evaluated the effects of late-season mass-flowering crops on bumblebee abundances and diversity during and after crop bloom. We assessed how bumblebee abundances, diversity and traits associated with species rarity were affected by cultivation of late-season mass-flowering red clover grown for seed production. Bumblebees were surveyed in red clover fields and flower-rich field borders across 20 landscapes with or without a red clover field during and after crop bloom in southern Sweden. Bumblebee worker abundances were higher in clover fields compared to flower-rich borders in the surrounding landscape. There was no relationship between presence of clover fields and the abundance of males of social bumblebees, but more male cuckoo bumblebees were found in flower-rich borders in landscapes with clover following crop bloom. Mass-flowering red clover also had a positive effect on bumblebee species richness and diversity after crop bloom. Overall, clover had positive and lasting effects on less common bumblebees thereby sustaining higher bumblebee species richness after bloom. Cultivation of red clover has the potential, in combination with the management of flower-rich habitats, to benefit less common bumblebee species in temperate agroecosystems.

Urbanization is associated with shifts in bumblebee body size, with cascading effects on pollination.

Urbanization is a global phenomenon with major effects on species, the structure of community functional traits and ecological interactions. Body size is a key species trait linked to metabolism, life‐history and dispersal as well as a major determinant of ecological networks. Here, using a well‐replicated urban–rural sampling design in Central Europe, we investigate the direction of change of body size in response to urbanization in three common bumblebee species, Bombus lapidarius, Bombus pascuorum and Bombus terrestris, and potential knock‐on effects on pollination service provision. We found foragers of B. terrestris to be larger in cities and the body size of all species to be positively correlated with road density (albeit at different, species‐specific scales); these are expected consequences of habitat fragmentation resulting from urbanization. High ambient temperature at sampling was associated with both a small body size and an increase in variation of body size in all three species. At the community level, the community‐weighted mean body size and its variation increased with urbanization. Urbanization had an indirect positive effect on pollination services through its effects not only on flower visitation rate but also on community‐weighted mean body size and its variation. We discuss the eco‐evolutionary implications of the effect of urbanization on body size, and the relevance of these findings for the key ecosystem service of pollination.

Shift in size of bumblebee queens over the last century.

Species can respond differently when facing environmental changes, such as by shifting their geographical ranges or through plastic or adaptive modifications to new environmental conditions. Phenotypic modifications related to environmental factors have been mainly explored along latitudinal gradients, but they are relatively understudied through time despite their importance for key ecological interactions. Here we hypothesize that the average bumblebee queen body size has changed in Belgium during the last century. Based on historical and contemporary databases, we first tested if queen body sizes changed during the last century at the intraspecific level among four common bumblebee species and if it could be linked to global warming and/or habitat fragmentation as well as by the replacement by individuals from new populations. Then, we assessed body size changes at the community level, among 22 species, taking into account species population trends (i.e. increasing, stable or decreasing relative abundance). Our results show that the average queen body size of all four bumblebee species increased over the last century. This size increase was significantly correlated to global warming and habitat fragmentation, but not explained by changes in the population genetic structure (i.e. colonization). At the community level, species with stable or increasing relative abundance tend to be larger than declining species. Contrary to theoretical expectations from Bergmann's rule (i.e. increasing body size in colder climates), temperature does not seem to be the main driver of bumblebee body size during the last century as we observed the opposite body size trend. However, agricultural intensification and habitat fragmentation could be alternative mechanisms that shape body size clines. This study stresses the importance of considering alternative global change factors when assessing body size change.

What kind of flowering plants are attractive for bumblebees in urban green areas?

In the face of progressing impoverishment of bumblebee numbers and species richness it is important to recognize their diversified dietary needs. It is a crucial matter in the context of active protection of these insects and their habitats, including in urban spaces. During our surveys we analyzed the dietary preferrences of 17 species from the Bombus genus living in urban areas. We analyzed plants for their taxonomy, type and status in Central Europe, flower colours and shapes. We found out that the preferred plants for most bumblebee species are perennial and native plants, with violet/pink flowers with papilionaceous or bilabiate structure. We suggest that such plant species should be planted in ubran spaces in order to actively protect bumblebees. Moreover, it is important to consider less common bumblebee species, with a narrower specialization and different dietary requirements. For this group of bees we suggest flowers with longer corollas, especialy those from Fabaceae, Lamiaceae, Boraginaceae, Plantaginaceae and Ranunculaceae families.

Urban bumblebees are smaller and more phenotypically diverse than their rural counterparts.

With urbanization identified as being one of the key drivers of change in global land use, and the rapid expansion of urban areas world-wide, it is relevant to evaluate how novel ecological conditions in cities shape species functional traits, which are essential for how species interact with their environments and with each other. Despite the many comparative studies on organisms living in urban and non-urban areas, our knowledge on species responses to urban environments remains limited. For one, much of the ecological research has assumed that the environment changes in a linear fashion from the city core to the city edges, whereas in reality the environments within the cities are highly heterogeneous. Furthermore, studies on species responses to these highly variable ecosystems are often based on interspecific mean trait values, which ignore the potential for high levels of intraspecific variation among individuals in key functional traits. The current study investigated intraspecific functional trait differences for four functional traits associated with body size, mobility and resource selection among rural and urban populations of two common bumblebee species, Bombus pascuorum and Bombus lapidarius, in urban centres and adjacent rural areas in Switzerland. We document shifts in functional traits towards smaller individuals and higher multidimensional trait variation in urban populations compared to rural conspecifics of both species. This shows that urban individuals for both species are on average smaller sized but populations are distinctively different from rural population by increasing their trait richness and diversifying their trait combinations. In addition, we found bimodality in tongue length within urban B.pascuorum populations. Our results suggest that urban and rural populations possibly experience differential selection pressures resulting in trait differences across and among populations. We argue that variations in the respective foraging landscapes in cities leads to smaller sized but phenotypically more diverse populations, and drive functional trait divergence.

Pattern of population structuring between Belgian and Estonian bumblebees

Several population genetic studies investigated the extent of gene flow and population connectivity in bumblebees. In general, no restriction in gene flow is considered for mainland populations of common bumblebee species. Whether this assumption holds true for all species is not known. An assessment of bumblebee genetic structure in the context of their geographic distribution is needed to prioritize conservation and management needs. Here, we conducted a genetic study on seven bumblebee species occurring in Belgium and Estonia. Using 16 microsatellite markers, we investigated genetic diversity and population structuring in each species. This is the first study investigating population structuring of both declining and stable bumblebee species on both small and large geographic scales. Our results showed no or only low population structuring between the populations of the restricted and declining bumblebee species on both scales, while significant structuring was found for populations of the common species on the larger scale. The latter result, which may be due to human or environmental changes in the landscape, implies the need for the conservation of also widespread bumblebee species. Conservation strategies to improve gene flow and connectivity of populations could avoid the isolation and future losses of populations of these important species.

Seasonal Food Scarcity Prompts Long-Distance Foraging by a Wild Social Bee.

Foraging is an essential process for mobile animals, and its optimization serves as a foundational theory in ecology and evolution; however, drivers of foraging are rarely investigated across landscapes and seasons. Using a common bumblebee species from the western United States (Bombus vosnesenskii), we ask whether seasonal decreases in food resources prompt changes in foraging behavior and space use. We employ a unique integration of population genetic tools and spatially explicit foraging models to estimate foraging distances and rates of patch visitation for wild bumblebee colonies across three study regions and two seasons. By mapping the locations of 669 wild-caught individual foragers, we find substantial variation in colony-level foraging distances, often exhibiting a 60-fold difference within a study region. Our analysis of visitation rates indicates that foragers display a preference for destination patches with high floral cover and forage significantly farther for these patches, but only in the summer, when landscape-level resources are low. Overall, these results indicate that an increasing proportion of long-distance foraging bouts take place in the summer. Because wild bees are pollinators, their foraging dynamics are of urgent concern, given the potential impacts of global change on their movement and services. The behavioral shift toward long-distance foraging with seasonal declines in food resources suggests a novel, phenologically directed approach to landscape-level pollinator conservation and greater consideration of late-season floral resources in pollinator habitat management.

An updated understanding of Texas bumble bee (Hymenoptera: Apidae) species presence and potential distributions in Texas, USA.

Texas is the second largest state in the United States of America, and the largest state in the contiguous USA at nearly 700,000 sq. km. Several Texas bumble bee species have shown evidence of declines in portions of their continental ranges, and conservation initiatives targeting these species will be most effective if species distributions are well established. To date, statewide bumble bee distributions for Texas have been inferred primarily from specimen records housed in natural history collections. To improve upon these maps, and help inform conservation decisions, this research aimed to (1) update existing Texas bumble bee presence databases to include recent (2007–2016) data from citizen science repositories and targeted field studies, (2) model statewide species distributions of the most common bumble bee species in Texas using MaxEnt, and (3) identify conservation target areas for the state that are most likely to contain habitat suitable for multiple declining species. The resulting Texas bumble bee database is comprised of 3,580 records, to include previously compiled museum records dating from 1897, recent field survey data, and vetted records from citizen science repositories. These data yielded an updated state species list that includes 11 species, as well as species distribution models (SDMs) for the most common Texas bumble bee species, including two that have shown evidence of range-wide declines: B. fraternus (Smith, 1854) and B. pensylvanicus (DeGeer, 1773). Based on analyses of these models, we have identified conservation priority areas within the Texas Cross Timbers, Texas Blackland Prairies, and East Central Texas Plains ecoregions where suitable habitat for both B. fraternus and B. pensylvanicus are highly likely to co-occur.

Different but the same: bumblebee species collect pollen of different plant sources but similar amino acid profiles

Access to abundant and diverse floral plant sources is essential for generalist bees as they obtain all energy and nutrients required from pollen and nectar. Despite their importance, we still know little about the precise nutritional requirements of most bee species. Here, we investigated differences in floral and amino acid profiles of pollen collected by five bumblebee species in southern Germany, which had access to the same spectrum of plant species and thus sources of nutrition. We found that different bumblebee species visited different floral spectra for pollen collection but nevertheless had highly similar pollen amino acid profiles. This finding suggests that common bumblebee species only slightly differ in their nutritional target for amino acids in pollen. In fact, floral and chemical composition of pollen loads appear to be largely determined by the plant community present at a site as bumblebees attempt to maximize site-specific nutrient collection efficiency.

Addressing bumblebee faunistic and ecology using Citizen Science – reviewing a two years’ experience

Addressing bumblebee faunistic and ecology using Citizen Science – reviewing a two years’ experience

Variable effects of nicotine, anabasine, and their interactions on parasitized bumble bees.

Secondary metabolites in floral nectar have been shown to reduce parasite load in two common bumble bee species. Previous studies on the effects of nectar secondary metabolites on parasitized bees have focused on single compounds in isolation; however, in nature, bees are simultaneously exposed to multiple compounds. We tested for interactions between the effects of two alkaloids found in the nectar of Nicotiana spp. plants, nicotine and anabasine, on parasite load and mortality in bumble bees ( Bombus impatiens) infected with the intestinal parasite Crithidia bombi. Adult worker bees inoculated with C. bombi were fed nicotine and anabasine diet treatments in a factorial design, resulting in four nectar treatment combinations: 2 ppm nicotine, 5 ppm anabasine, 2ppm nicotine and 5 ppm anabasine together, or a control alkaloid-free solution. We conducted the experiment twice: first, with bees incubated under variable environmental conditions ('Variable'; temperatures varied from 10-35°C with ambient lighting); and second, under carefully controlled environmental conditions ('Stable'; 27°C incubator, constant darkness). In 'Variable', each alkaloid alone significantly decreased parasite loads, but this effect was not realized with the alkaloids in combination, suggesting an antagonistic interaction. Nicotine but not anabasine significantly increased mortality, and the two compounds had no interactive effects on mortality. In 'Stable', nicotine significantly increased parasite loads, the opposite of its effect in 'Variable'. While not significant, the relationship between anabasine and parasite loads was also positive. Interactive effects between the two alkaloids on parasite load were non-significant, but the pattern of antagonistic interaction was similar to that in the variable experiment. Neither alkaloid, nor their interaction, significantly affected mortality under controlled conditions. Our results do not indicate synergy between Nicotiana nectar alkaloids; however, they do suggest a complex interaction between secondary metabolites, parasites, and environmental variables, in which secondary metabolites can be either toxic or medicinal depending on context.

Variable effects of nicotine, anabasine, and their interactions on parasitized bumble bees

Secondary metabolites in floral nectar have been shown to reduce parasite load in two common bumble bee species. Previous studies on the effects of nectar secondary metabolites on parasitized bees have focused on single compounds in isolation; however, in nature, bees are simultaneously exposed to multiple compounds. We tested for interactions between the effects of two alkaloids found in the nectar of Nicotiana spp. plants, nicotine and anabasine, on parasite load and mortality in bumble bees ( Bombus impatiens) infected with the intestinal parasite Crithidia bombi. Adult worker bees inoculated with C. bombi were fed nicotine and anabasine diet treatments in a factorial design, resulting in four nectar treatment combinations: 2 ppm nicotine, 5 ppm anabasine, 2ppm nicotine and 5 ppm anabasine together, or a control alkaloid-free solution. We conducted the experiment twice: first, with bees incubated under variable environmental conditions (‘Variable’; temperatures varied from 10-35°C with ambient lighting); and second, under carefully controlled environmental conditions (‘Stable’; 27°C incubator, constant darkness). In ‘Variable’, each alkaloid alone significantly decreased parasite loads, but this effect was not realized with the alkaloids in combination, suggesting an antagonistic interaction. Nicotine but not anabasine significantly increased mortality, and the two compounds had no interactive effects on mortality. In ‘Stable’, nicotine significantly increased parasite loads, the opposite of its effect in ‘Variable’. While not significant, the relationship between anabasine and parasite loads was also positive. Interactive effects between the two alkaloids on parasite load were non-significant, but the pattern of antagonistic interaction was similar to that in the variable experiment. Neither alkaloid, nor their interaction, significantly affected mortality under controlled conditions. Our results do not indicate synergy between Nicotiana nectar alkaloids; however, they do suggest a complex interaction between secondary metabolites, parasites, and environmental variables, in which secondary metabolites can be either toxic or medicinal depending on context.

Variable effects of nicotine and anabasine on parasitized bumble bees

Secondary metabolites in floral nectar have been shown to reduce parasite load in two common bumble bee species. Previous studies on the effects of nectar secondary metabolites on parasitized bees have focused on single compounds in isolation; however, in nature, bees are simultaneously exposed to multiple compounds. We tested for synergistic effects of two alkaloids found in the nectar of Nicotiana spp. plants, nicotine and anabasine, on parasite load and mortality in bumble bees ( Bombus impatiens) infected with the intestinal parasite Crithidia bombi. Adult worker bees inoculated with C. bombi were fed nicotine and anabasine diet treatments in a factorial design, resulting in four nectar treatment combinations: 2 ppm nicotine, 5 ppm anabasine, 2ppm nicotine and 5 ppm anabasine together, or a control alkaloid-free solution. We conducted the experiment twice: first, with bees incubated under variable environmental conditions ('Variable'; temperatures varied from 10-35°C); and second, under carefully controlled environmental conditions ('Controlled'; 27°C incubator, constant darkness). In 'Variable', each alkaloid alone significantly decreased parasite loads, but this effect was not realized with the alkaloids in combination, suggesting an antagonistic interaction. Nicotine but not anabasine significantly increased mortality, and the two compounds had no interactive effects on mortality. In 'Controlled', nicotine significantly increased parasite loads, the opposite of its effect in 'Variable'. While not significant, the relationship between anabasine and parasite loads was also positive. Interactive effects between the two alkaloids on parasite load were non-significant, but the pattern of antagonistic interaction was similar to that in the variable experiment. Neither alkaloid, nor their interaction, significantly affected mortality under controlled conditions. Our results do not indicate synergy between Nicotiana nectar alkaloids; however, they do suggest a complex interaction between secondary metabolites, parasites, and environmental variables, in which secondary metabolites can be either toxic or medicinal depending on context.

Bumble Bees (Hymenoptera: Apidae) of Oklahoma: Past and Present Biodiversity

Bumble bees (Bombus Latreille) provide indispensable ecosystem services for natural and agricultural systems by increasing crop yield and quality. With documented bumble bee declines throughout the world, the need for baseline data on these important insects becomes apparent. The bumble bees of Oklahoma have previously not been surveyed, hampering assessment of temporal change. The objectives of this study were to determine the past and present bumble bee species richness of Oklahoma and indicate possible temporal trends. Records were gathered from museum and university collections, as well as from a field survey of 46 sites in 21 counties. Historical records indicated ten bumble bee species in Oklahoma, four of which had fewer than ten total records. Only five species have been recorded since 2000, four being found in the targeted survey: B. pensylvanicus (DeGeer), B. griseocollis (DeGeer), B. fraternus (Smith) and B. impatiens (Cresson). The American bumble bee (B. pensylvanicus) has been, and continues to be, the most common bumble bee species in Oklahoma, despite showing clear patterns of decline in other regions of North America. Our results parallel several recent studies that failed to locate extant populations of the variable cuckoo bee, Bombus variabilis (Cresson), supporting possible extirpation in portions of its North American range. A targeted survey for this species is warranted, as its host, B. pensylvanicus, remains common in Oklahoma.

Pollinator behaviour on a food-deceptive orchid Calypso bulbosa and coflowering species.

Food deception as a pollination strategy has inspired many studies over the last few decades. Pollinator deception has evolved in many orchids possibly to enhance outcrossing. Food-deceptive orchids usually have low pollinator visitation rates as compared to rewarding species. They may benefit in visitations from the presence (magnet-species hypothesis) or, alternatively, absence of coflowering rewarding species (competition hypothesis). We present data on pollinator visitations on a deceptive, terrestrial orchid Calypso bulbosa, a species with a single flower per plant and whose flowering period partly overlaps with rewarding, early flowering willows (Salix sp.) and later-flowering bilberry (Vaccinium myrtillus). When surveying inactive bumblebee queens on willows in cool weather, about 7% of them carried Calypso pollinia. Most common bumblebee species appeared to visit and thus pollinate Calypso. Bumblebees typically visited one to three Calypso flowers before flying away, providing some support for the outcrossing hypothesis. We conclude that, regarding the pollinations strategy, both magnet-species and competition hypotheses have a role in the pollination of Calypso, but on different spatial scales. On a large scale rewarding species are important for attracting pollinators to a given region, but on a small scale absence of competition ensures sufficient pollination rate for the deceptive orchid.