Bombus Species Research Articles

Thermodynamics, thermal performance and climate change: temperature regimes for bumblebee (Bombus spp.) colonies as examples of superorganisms

Evidence is widespread that many species of Bombus are in population and biogeographical decline in response to adverse effects of global climate warming. The complex interactions of the mechanisms at the root of the declines are poorly understood. Among the numerous factors, we posit that heat stress in the nests could play a key role in the decline of bumblebee species. The similarity of the optimum temperature range in incubating nests is remarkable, about 28–32 °C regardless of species from the cold High Arctic to tropical environments indicates that the optimal temperature for rearing of brood in Bombus spp. is a characteristic common to bumblebees (perhaps a synapomorphy) and with limited evolutionary plasticity. We do note that higher brood rearing temperature for the boreal and Arctic species that have been tested is stressfully high when compared with that for B. terrestris. The Thermal Neutral Zone (TNZ), temperatures over which metabolic expenditure is minimal to maintain uniform nest temperatures, has not been studied in Bombus and may differ between species and biogeographic conditions. That heat stress is more serious than chilling is illustrated by the Thermal Performance Curve Relationship (TPC) (also sometimes considered as a Thermal Tolerance Relationship). The TPC indicates that development and activity increase more slowly as conditions become warmer until reaching a plateau of the range of temperatures over which rates of activity do not change markedly. After that, activity rates decline rapidly, and death ensues. The TPC has not been studied in eusocial bees except Apis dorsata but may differ between species and biogeographic conditions. The importance of the TPC and the TNZ indicates that environmental temperatures in and around bumblebee nests (which have been rarely studied especially in the contexts of nest architecture and substrate thermal characteristics) are factors central to understanding the adverse effects of heat stress and climatic warming on bumblebee populations, health, and biogeographical decline.

Assessing the effects of cold storage regimes of North American Bombus Gynes

AbstractBumble bees are the primary commercial pollinators for greenhouse‐grown crops and managing them requires insight into the Bombus life cycle. However, some aspects of the life cycle are not fully understood. Once mated, adult Bombus gynes can be stored for a short term at a constant low temperature (CLT). However, survival rates for some species are low during CLT, particularly when storage periods exceed a month. To address this, we tested the hypothesis that Bombus gynes stored in a fluctuating thermal regime (FTR) have increased survival compared to gynes stored in CLT. Specifically, the FTR had a baseline temperature of 2°C, with a daily fluctuation to 20°C relative to the CLT of 2°C with no warming pulse. We tested the effects of FTR on gyne survival and post‐cold storage lipid content in three species used for commercial pollination in North America: B. vosnesenskii, B. huntii and B. impatiens. We further assessed how additional factors influence cold storage survival, including gyne body weight, body size and colony age. Survival responses varied among species. Bombus vosnesenskii and B. huntii had a lower survival rate in FTR compared to CLT, but B. impatiens gynes had a significantly higher survival rate in FTR. We did not observe significant effects of FTR on lipid stores for any species, but survival increased with an increasing initial weight prior to cold storage. Moreover, gynes produced later in the colony life cycle had lower body weight and decreased survival compared to early emerging gynes. Our study provides insight into how cold storage conditions interact with colony and gyne characteristics to influence captive overwintering survival. Our findings have economic applications for improving commercial rearing and efforts for conservation rearing of at‐risk Bombus species.

Structure of a metacommunity of urban bees: Species diversity and spatio-temporal modularity

As the globe gets more urbanised, the question about how natural biodiversity is structured in cities becomes increasingly pertinent. To contribute to an answer, we studied species richness and spatio-temporal structure of bees in a North European metropolitan area. A gradient of 13 sites in the city of Aarhus, Denmark, was censused from April to September 2016. Forty species, i.e. 29 solitary species (40 % of all individuals), ten Bombus species (28 %), and Apis mellifera (32 %), were sampled monthly in pan traps. (i) Information about species traits was extracted from the literature, and trait values were correlated and used to characterize the fauna. Most were soil-nesters, pollen generalists, and common. (ii) Habitat diversity within five concentric circles with trap at the centre and radii from 50 m to 1000 m was related to bee α diversity. The relationship was significant only within 1,000 m for all bees and for bumblebees. Solitary bee diversity was uncorrelated with habitat diversity at all spatial levels. (iii) Spatio-temporal structure was analysed as two networks, one for bees linked to sites, and one for bees linked to months. Link patterns were analysed for levels of nestedness, modularity, and spatio-temporal β diversity. The two networks were weakly and non-significantly nested, but strongly modular, being composed of five and four modules of co-occurring bees, respectively. (iv) Finally, we studied total β diversity, βTOTAL, being the sum of species turnover, βTURN, and species loss/gain or nestedness, βNEST. For both site and season, βTURN was higher than βNEST, and site βTOTAL was higher than season βTOTAL. One reason for this metacommunity structure may be a high spatio-temporal habitat patchiness, sustaining a rich biodiversity. Thus, a few large areas may not compensate for the loss of several small patches. Consequently, establishment of many green, even small habitats is recommended.

Niche analyses and the potential distribution of four invasive bumblebees worldwide.

The introduction of bees for agricultural production in distinct parts of the world and poor management have led to invasion processes that affect biodiversity, significantly impacting native species. Different Bombus species with invasive potential have been recorded spreading in different regions worldwide, generating ecological and economic losses. We applied environmental niche and potential distribution analyses to four species of the genus Bombus to evaluate the similarities and differences between their native and invaded ranges. We found that B. impatiens has an extended environmental niche, going from dry environmental conditions in the native range to warmer and wetter conditions in the invaded range. Bombus ruderatus also exhibited an extended environmental niche with drier and warmer conditions in the invaded range than in its native range. Bombus subterraneus expanded its environmental niche from cooler and wetter conditions in the native range to drier and warmer conditions in the invaded range. Finally, B. terrestris showed the most significant variation in the environmental niche, extending to areas with similar and different environmental conditions from its native range. The distribution models agreed with the known distributions for the four Bombus species, presenting geographic areas known to be occupied by each species in different regions worldwide. The niche analysis indicate shifts in the niches from the native to the invaded distribution area of the bee species. Still, niche similarities were observed in the areas of greatest suitability in the potential distribution for B. ruderatus, B. subterraneus, and B. terrestris, and to a lesser degree in the same areas with B. impatiens. These species require similar environmental conditions as in their native ranges to be established in their introduced ranges. Still, they can adapt to changes in temperature and humidity, allowing them to expand their ranges into new climatic conditions.

Colony performance of threenative bumblebee species from South China and association with their gut microbiome.

Bumblebees play an important ecological economic role as pollinators in nature and agriculture. For reasons of biosecurity, many countries promote the cultivation of native bumblebee species for crop pollination instead of importing "alien" species. In South China, a few bumblebee species are considered useful in this way, particularly, Bombus atripes, Bombus bicoloratus and Bombus breviceps. However, whether they are suitable for artificial rearing and forming healthy colonies for pollination, remains unknown. In this project, queens from the 3 native species of Guizhou Province were collected and colonies were started under standardized conditions. The colonies were scored based on 19 parameters, including the stage of colony development, number and weight of offspring, and diet consumed. The data revealed that B.breviceps had the best performance, produced more workers and consumed the smallest diet. Next, we performed 16S rDNA sequencing of the bacterial communities found in the guts of offspring workers, and then a correlation analysis between colony performance and gut bacteria was conducted. Here, B.breviceps showed the highest diversity in gut bacterial composition, dominated by the bacteria Gilliamella, Snodgrassella, Enterobacter, and Lactobacillus Firm5. The higher the abundance of Snodgrassella, the better the performance of the colony in the foundation stage, and later Lactobacillus Firm5, Apibacter and Bifidobacterium were beneficial during the stages of rapid growth and colony decline. Although we do not understand all of the interactions yet, these correlations explain why B.breviceps demonstrated better colony performance. Our data provide valuable information for breeding local Bombus species and will contribute to developing strong colonies for crop pollination.

Foraging preferences of bumble bee castes are weakly related to plant species cover on two arable agri-environment habitat types

Arable field margins provide important floral resources for insect foragers. This study assessed the significance of cultivated margins and floristically enhanced margins, both English agri-environment scheme (AES) options, to foraging bumble bees (Bombus species). We examined plant foraging preferences in each habitat according to species and caste. Additionally, detailed botanical surveys were carried out to determine vascular plant densities on the study margins. Overall, our results emphasised the importance of spontaneous (Asteraceae) species emerging from the seed bank in the provision of forage across Bombus species and castes, and highlighted that Bombus foraging preferences appeared to be only weakly related to floral species densities. Although found only occasionally in high densities, the popularity of these dicots was likely due to high nectar sugar mass. Bombus queens were recorded relatively infrequently, implying that these habitats are failing to provide the preferred floral resources of all Bombus spp. queens. Queens that were observed were found to favour earlier-flowering species (e.g. Anchusa arvensis) and species with longer corollas (e.g. Vicia sativa). Worker bees across Bombus spp. showed high overlap in plant preferences (e.g. Cirsium arvense, Ononis spinosa). However, some variability in preferences between castes within a species were noted, for example, only B. terrestris/lucorum drones were found to forage on Crepis vesicaria in cultivated margins. Additionally, bumble bee abundance was only found to increase as dicot cover increased. Overall, our findings highlight the importance of continuing to utilise multiple AES types in order to fully support Bombus and other pollinating insect populations on farmland.

Conserved, yet disruption-prone, gut microbiomes in neotropical bumblebees.

Social bees are an important model for the ecology and evolution of gut microbiomes. These bees harbor ancient, specific, and beneficial gut microbiomes and are crucial pollinators. However, most of the research has concentrated on managed honeybees and bumblebees in the temperate zone. Here we used 16S rRNA gene sequencing to characterize gut microbiomes in wild neotropical bumblebee communities from Colombia. We also analyzed drivers of microbiome structure across our data and previously published data from temperate bumblebees. Our results show that lineages of neotropical bumblebees not only retained their ancient gut bacterial symbionts during dispersal from North America but also are prone to major disruption, a shift that is strongly associated with parasite infection. Finally, we also found that microbiomes are much more strongly structured by host phylogeny than by geography, despite the very different environmental conditions and plant communities in the two regions.

Occupancy of Bombus affinis (Hymenoptera: Apidae) in Minnesota is highest in developed areas when standardized surveys are employed.

Mounting evidence of bumble bee declines and the listing of the rusty patched bumble bee (Bombus affinis Cresson) as federally endangered in the United States in 2017 and Canada in 2012 has stimulated an interest in monitoring and conservation. Understanding the influence of land use on occupancy patterns of imperiled species is crucial to successful recovery planning. Using detection data from community surveys, we assessed land use associations for 7 bumble bee species in Minnesota, USA, including B. affinis. We used multispecies occupancy models to assess the effect of 3 major land use types (developed, agricultural, and natural) within 0.5 and 1.5 km on occupancy of 7 Bombus (Hymenoptera: Apidae) species, while accounting for detection uncertainty. We found that B. affinis occupancy and detection were highest in developed landscapes and lowest in agricultural landscapes, representing an inverse relationship with the relative landcover ratios of these landscapes in Minnesota. Occupancy of 2 bumble bee species had strong positive associations with natural landscapes within 1.5 km and 2 species had strong negative associations with agricultural landscapes within 1.5 km. Our results suggest that best practices for imperiled Bombus monitoring and recovery planning depends upon the surrounding major land use patterns. We provide recommendations for urban planning to support B. affinis based on conservation success in the metropolitan areas of Minneapolis-St. Paul. We also encourage substantial survey effort be employed in agricultural and natural regions of the state historically occupied by B. affinis to determine the current occupancy state.

Community dynamics of bumblebee across elevation gradients and habitat mosaics in Chitwan Annapurna Landscape, Nepal

The species composition of bumblebees (Bombus species) across the elevation gradients in Chitwan-Annapurna Landscape (CHAL) was studied from April to November 2019. We performed opportunistic surveys to collect the bumblebee specimens. The walking transects were followed in the accessible places along the Kaligandaki, Marshyandi, and Budhigandaki river basins in different habitats (e.g., agricultural, forest, grassland and home garden). We identified 16 Bombus species from the sampling areas. The highest relative abundance was of B. haemorrhoidalis (20%), followed by B. festivus (20%) and B. eximius (19%). The least abundant species were B. branickii, B. miniatus, B. novus, and B. pressus with 1% relative abundance of each. We examined the effects of elevation on bumblebee richness and found a significant relationship. The Highest species richness was detected in the mid-elevation. Likewise, the highest species richness and diversity were found in the forest habitat in Gorkha site (n = 12, Shannon index H’ = 2.18) followed by the grassland habitat of the Mustang site (n = 11, Shannon index H’ = 2.10). Whereas, comparatively, species diversity was higher in habitats of the Gorkha site comparing Manang and Mustang. The elevation gradients create immense variations in microclimatic conditions and vegetation dynamics, which influence bumblebee abundance, species richness and diversities in different habitats in the study area. The mid-elevation range (2000–3000 m asl) of CHAL exhibited the highest species richness probably due to the higher availability of pollinator-dependent flowering plants in this range. The landcover composition and anthropogenic activities along the elevation gradient is the governing factor for the species composition, distribution and diversity of bumblebees in CHAL. We recommend to decision-makers for formulating their conservation strategies under a socio-ecological framework.

Long-term changes in the composition and distribution of the Hungarian bumble bee fauna (Hymenoptera, Apidae, Bombus)

One of the most important pollinator taxa is Bombus (Hymenoptera, Apidae), the genus of bumble bees, since they are important, often specialized, pollinators of many plants. As a result of climate change, warming winters and changes in landscape structure, the distribution and frequency of Bombus species is constantly changing. To develop appropriate protection strategies, it is essential to monitor them and update the occurrence and threat status of the species. The last review of the distribution of Bombus species in Hungary was completed 20 years ago. Here we present updated distribution maps based on published data from the last 20 years together with unpublished data collected in 2018–2021. Based on the new data, we examine changes in the last two decades. In the case of 9 species further studies should be carried out to confirm the presence of stable populations, while 3 species are recommended for protection by law in Hungary. Seven species showed increasing frequency, B. argillaceus and B. haematurus.

Increasing sampling efficiency of Bombus communities with rare and endangered species by optimizing detection probabilities: A multi-species occupancy modelling approach using roadsides as a case study

Nearly one-quarter of bumble bee species assessed by the International Union for the Conservation of Nature are considered to be in decline, necessitating monitoring to support recovery planning. A key element of robust wildlife monitoring is accounting for imperfect detection in the observation process and efforts to understand sources of detection uncertainty in bumble bee surveys began recently in response to the listing of the rusty patched bumble bee, Bombus affinis, as federally endangered in the U.S. and Canada. We investigated within-community variation in detection probabilities among eight species that vary in occupancy, including B. affinis. We sampled bumble bees along roadsides in the greater metropolitan area of Minneapolis-St. Paul, Minnesota in the United States in 2018. We generated estimates of occupancy, detection probability, and cumulative detection probability from a multispecies occupancy model using a Bayesian framework that included covariates on occupancy and detection. Covariates selected a priori included floral cover and impervious surface effects on occupancy, and date, time of day, and observer effects on detection. We found that Bombus species with low occurrence are not necessarily less detectable than common species with higher occurrence, and that species reach their peak detection probability at different dates. Detection was higher in the afternoon and varied among observers. Well-designed Bombus monitoring programs can reduce sampling effort and optimize detection by sampling on dates near species detection peaks, sampling in the afternoon, and using cumulative detection probabilities to determine optimum sampling effort.

In Which Way Do the Flower Properties of the Specialist Orchid Goodyera repens Meet the Requirements of Its Generalist Pollinators?

This article is the next part of a series of studies documenting the influence of flower traits on the reproductive success (RS) of orchids. Knowledge of factors influencing RS helps to understand the mechanisms and processes crucial for shaping plant-pollinator interactions. The aim of the present study was to determine the role of flower structure and nectar composition in shaping the RS of the specialist orchid Goodyea repens, which is pollinated by generalist bumblebees. We found a high level of pollinaria removal (PR) and female reproductive success (fruiting, FRS) as well as a high level of variation between populations, although in certain populations pollination efficiency was low. Floral display traits, mainly inflorescence length, influenced FRS in certain populations. Among the flower traits, only the height of flowers was correlated with FRS in one population, suggesting that the flower structure of this orchid is well adapted to pollination by bumblebees. The nectar of G. repens is diluted and dominated by hexoses. Sugars were less important in shaping RS than amino acids. At the species level, twenty proteogenic and six non-proteogenic AAs were noted, along with their differentiated amounts and participation in particular populations. We found that distinct AAs or their groups mainly shaped PR, especially when correlations were considered at the species level. Our results suggest that both the individual nectar components and the ratios between them have an impact on G. repens RS. Because different nectar components influence the RS parameters in different ways (i.e., negatively or positively), we suggest that different Bombus species play the role of main pollinators in distinct populations.

Variation in North American bumble bee nest success and colony sizes under captive rearing conditions.

Of the 265 known bumble bee (Bombus) species, knowledge of colony lifecycle is derived from relatively few species. As interest in Bombus commercialization and conservation grows, it is becoming increasingly important to understand colony growth dynamics across a variety of species since variation exists in nest success, colony growth, and reproductive output. In this study, we reported successful nest initiation and establishment rates of colonies and generated a timeline of colony development for 15 western North American Bombus species, which were captively reared from wild-caught gynes from 2009 to 2019. Additionally, we assessed variation in colony size among 5 western North American Bombus species from 2015 to 2018. Nest initiation and establishment rates varied greatly among species, ranging from 5-76.1% and 0-54.6%, respectively. Bombus griseocollis had the highest rates of nest success across the 11-yr period, followed by B. occidentalis, B. vosnesenskii, and B. huntii. Furthermore, days to nest initiation and days to nest establishment varied among species, ranging from 8.4 to 27.7 days and 32.7 to 47 days. Colony size also differed significantly among species with B. huntii and B. vosnesenskii producing more worker/drone cells than B. griseocollis, B. occidentalis, and B. vancouverensis. Additionally, gyne production differed significantly among species with B. huntii colonies producing more gynes than B. vosnesenskii. Results from this study increase knowledge of systematic nesting biology for numerous western North American Bombus species under captive rearing conditions, which can further improve rearing techniques available to conservationists and researchers.

Tailoring your bee sampling protocol: Comparing three methods reveals the best approaches to capturing bees

Abstract Bees are prolific, vital pollinators in agricultural and natural settings, but some taxa are declining. Surveying bees is crucial to understand the needs of these taxa; however, we lack a fine‐grained understanding of assemblages associated with different sampling methods that would enable us to analyse data range‐wide. Here we examine the difference in abundance and richness of bees (bee bowls and vane traps only) and bumble bees (genus Bombus; bee bowls, blue vane traps and target netting) sampled with these methods from mixed‐grass prairie to alpine habitats in Wyoming, USA. We collected four times more bees and twice as many genera of bees in vane traps than bee bowls. Vane traps captured more individuals of abundant genera than bee bowls. Bombus species abundance did not vary between vane traps and target netting; however, richness was higher in vane traps. Bee bowls captured few Bombus species. Overall, we recommend using vane traps to sample most bees, and a combination of vane traps and target netting to collect bumble bees. We evaluated how three sampling techniques perform when surveying for wild bees, which will aid in identifying declining species as well as monitoring species of conservation concern.

Pollinators Diversity and Bumblebee Abundance in Rawalpindi/Islamabad and Naran Kaghan Valley, Pakistan

Indigenous bumblebee Bombus haemorrhoidalis, the only Bombus of Lower Northern Pakistan plays a significant role in wild floral pollination. Present study compared the relative abundance and diversity of B. haemorrhoidalis with other insect pollinators. Monthly population level field surveys were conducted from Rawalpindi/Islamabad and Naran Kaghan Valley during 2012 and 2013. Hymenopteran insect pollinators were the most abundant taxa with six species followed by Lepidoptera with five. Syrphus species (Dipteran) were recorded with maximum abundance after B. haemorrhoidalis from all study locations. Pollinator diversity indices were at their highest in Naran and F9 Park (Islamabad) areas. Such ecological information are important for possible utilization in further biological experimentations, commercial pollination services and environmental conservation. This study also focuses the importance to conserve the only Bombus species in these areas.

Niche modeling of bumble bee species (Hymenoptera, Apidae, Bombus) in Colombia reveals highly fragmented potential distribution for some species

Insect population decline has been reported worldwide, including those of pollinators important for ecosystem services. Therefore, conservation actions which rely on available rigorous species distribution data are necessary to protect biodiversity. Niche modeling is an appropriate approach to distribution maps, but when it comes to bumble bees, few studies have been performed in South America. We modeled ecological niches of nine Colombian Bombus species with MAXENT 3.4 software using bioclimatic variables available from WorldClim. This resulted in maps for each species that show the potential distribution area at the present time. Modeled species maps accurately represent potential niches according to the description of bioclimatic conditions in the species’ habitat. We grouped the species into three clusters based on our results, as well as on distributional information from literature on the topic: High Mountain, Mid- Mountain and inter-Andean, and the Amazon and Eastern Plains Basin. Niche modeling depicted bumble bee species’ distribution in Colombia, the results of which can serve as a useful tool for conservation policies in the country.

Bee diversity on urban rooftop food gardens

Green infrastructure on rooftops in urban areas can enhance important ecosystem services. In addition to mitigating water runoff and regulating building temperatures, green roofs can provide food and nesting resources for wildlife. Rooftop gardens can also be utilized to cultivate food crops, giving them the potential to attenuate instances of food insecurity which are commonplace in many urban areas. Given that many crops depend on bee pollination, it is imperative to characterize the rooftop bee community. Therefore, we sampled three urban food roofs near downtown St. Louis, MO during the 2017 and 2018 growing seasons. We found 38 bee species utilizing the rooftop farms. We then compared the rooftop bee communities to those of two nearby ground-level community gardens. The roofs had lower abundances of Bombus species than the ground-level sites while non-native cavity nesters in the genus Megachile were overrepresented. These results indicate that the rooftop bee communities represent a nested subset of the species found at ground level. This has important implications for the management of green roofs for growing crops, as this shift in bee community structure may play a role in determining which crops can be adequately supported with pollination services.

Diversity of Bumblebees (Bombini, Apidae: Hymenoptera) in Chitwan Annapurna Landscape (CHAL) of Central Himalaya, Nepal

Bumblebees (Hymenoptera: Apidae: genus Bombus Latreille, 1802) are the effective group of pollinators for various crops and wild plants in the north high-hills of Nepal. Over the past few decades, it has been expected that the population of these insects has declined since there are still unexplored areas and rich floral and faunal diversity. However, there are very few scientific publications as well as little researches have been carried out focusing on bumble bees in high-hills of Nepal. Therefore, this research was focused to explore the bumblebees in Chitwan Annapurna Landscape (CHAL) in Manang, Mustang and Gorkha districts with altitudinal gradients from 500 -2700 m asl from June to September 2019. The data were collected following accessible walking trails by opportunistic survey method and specimens were captured using sweeping net. Total 7 subgenera with 8 species of genus Bombus were identified. Bombus festivus (subgenus: Festivobombus) was the most dominant species. The diversity of bumblebee species was more in Gorkha site compared to the Manang and Mustang sites. Bombus haemorrhoidalis, B. eximus, and B. rotundiceps were the dominant species in Gorkha site, whereas B. festivus, B. lepidus, and B. tunicatus were dominant in Manang districts. Bombus festivus, B. tunicatus, and B. turneri were the most encountered species in Mustang. This study indicates that each district has the unique diversity of bumblebees particularly a site-specific variation of the Bombus species, which are likely to the variations in floral resources, microclimate and habitat types.

A checklist of South Dakota bumble bees (Hymenoptera, Apidae)

Several bumble bee species (Bombus Latreille) are declining and efforts to conserve populations will be strengthened by an improved knowledge of their geographic distribution. Knowledge gaps exist, however, especially in central portions of North America. Here we report 29 species of bumble bees from South Dakota in the north-central USA, based on 130 years of records from 1891 to 2021. Specimens or observations were available for >90% of the 66 counties, though they were not distributed evenly as most records came from Pennington, Lawrence, Custer, Brookings, and Day Counties. The five most commonly collected or reported bumble bee species were B. griseocollis (54 counties), B. pensylvanicus (41 counties), B. fervidus (39 counties), B. huntii (27 counties), and B. bimaculatus (25 counties). Twenty species were recorded from 10 or fewer counties. Despite differences in occurrence, 66% of the Bombus species in South Dakota were collected or observed since 2020, including six of the nine species of conservation concern (B. fraternus, B. pensylvanicus, B. fervidus, B. occidentalis, B. terricola, and B. morrisoni). However, the critically endangered B. affinis, B. variabilis, and B. suckleyi have not been collected or observed for over 50 years. While this checklist is the first for South Dakota bumble bees in nearly 100 years, data are still lacking as ~55% of counties had fewer than five species reported. We suggest future efforts should focus on these under-sampled areas to fill in baseline knowledge of the wild bee fauna towards completing a more holistic view of bumble bee distributions across the Great Plains.

Do exotic plants and flower colour facilitate bumblebee invasion? Insights from citizen science data

Invasive species are one of the most important drivers of biodiversity loss worldwide. As exotic species invade new ecosystems, they establish ecological interactions with the existing species, which may facilitate their spread. Flower colour is an important trait that influences pollination and pollinator preferences. To determine the role of these variables on the bumblebee preferences, we compared the floral associations of two exotic bumblebee species: Bombus terrestris and B. ruderatus (introduced two decades ago for crop pollination) and the native B. dahlbomii with native and exotic plants in Chile. We analysed 3,019 citizen science records in order to understand bumblebee associations with native and exotic plant species regarding flower colour. We found that the exotic bumblebees were mainly recorded visiting flowers of exotic plants (86% for B. terrestris and 93% for B. ruderatus), while the native B. dahlbomii visited exotic and native plant species in a similar proportion. Also, the exotic bumblebees visited purple and pink flowers more often, while the native bumblebee species frequently visited white, pink, and purple flowers. Although the three species share trichromatic vision, they seem to have different flower colour preferences. The association of B. terrestris and B. ruderatus with exotic non-crop species (i.e., exotic ornamental plants) may be acting as steppingstones from croplands to other habitats, facilitating the bee invasion process. Despite its inherent limitations, citizen science data provide large amounts of valuable information that is difficult to be obtained otherwise, which can be used to improve our understanding of invasion processes, as is the case of exotic Bombus species in southern South America.