Bumblebee Species Research Articles

Interspecific Host Variation and Biotic Interactions Drive Pathogen Community Assembly in Chinese Bumblebees.

Bumblebees have been considered one of the most important pollinators on the planet. However, recent reports of bumblebee decline have raised concern about a significant threat to ecosystem stability. Infectious diseases caused by multiple pathogen infections have been increasingly recognized as an important mechanism behind this decline worldwide. Understanding the determining factors that influence the assembly and composition of pathogen communities among bumblebees can provide important implications for predicting infectious disease dynamics and making effective conservation policies. Here, we study the relative importance of biotic interactions versus interspecific host resistance in shaping the pathogen community composition of bumblebees in China. We first conducted a comprehensive survey of 13 pathogens from 22 bumblebee species across China. We then applied joint species distribution modeling to assess the determinants of pathogen community composition and examine the presence and strength of pathogen-pathogen associations. We found that host species explained most of the variations in pathogen occurrences and composition, suggesting that host specificity was the most important variable in predicting pathogen occurrences and community composition in bumblebees. Moreover, we detected both positive and negative associations among pathogens, indicating the role of competition and facilitation among pathogens in determining pathogen community assembly. Our research demonstrates the power of a pluralistic framework integrating field survey of bumblebee pathogens with community ecology frameworks to understand the underlying mechanisms of pathogen community assembly.

Wetland cover in agricultural landscapes is positively associated with bumblebee abundance

Abstract Conversion of land for agricultural use is a leading driver of global biodiversity loss. Natural and semi‐natural lands within agricultural landscapes are targeted for protection because they provide habitat for many organisms. Pothole (or kettle) wetlands occur across the Northern Hemisphere and are a focus for conservation both because of their location within agriculturally intensive landscapes and their importance to vertebrates, especially migratory birds. Recent evidence suggests that wetlands may also be an important habitat for arthropods, including insects that provide ecosystem services. To understand how insects associate with wetlands and landscape features, we examine the relationship between bumblebees (Bombus), and wetland area, cropland area and wetland perimeter‐area ratio. We found that wetland area is significantly positively associated with the occurrence and abundance of the species studied. We also found that the relationship between bumblebees and wetland perimeter‐area ratio varied across the growing season. This suggests that the importance of wetland edge as a foraging habitat varies across the season. These results show the utility of wetlands to bees, though their resources are likely not being used uniformly by all bumblebee species or across the entire growing season. Our results also suggest that pothole wetlands in agricultural landscapes are likely to support biodiversity, and their conservation contributes to overall ecosystem health and function.

Variance in heat tolerance in bumble bees correlates with species geographic range and is associated with several environmental and biological factors.

Globally, insects have been impacted by climate change, with bumble bees in particular showing range shifts and declining species diversity with global warming. This suggests heat tolerance is a likely factor limiting the distribution and success of these bees. Studies have shown high intraspecific variance in bumble bee thermal tolerance, suggesting biological and environmental factors may be impacting heat resilience. Understanding these factors is important for assessing vulnerability and finding environmental solutions to mitigate effects of climate change. In this study, we assess whether geographic range variation in bumble bees in the eastern United States is associated with heat tolerance and further dissect which other biological and environmental factors explain variation in heat sensitivity in these bees. We examine heat tolerance by caste, sex, and rearing condition (wild/lab) across six eastern US bumble bee species, and assess the role of age, reproductive status, body size, and interactive effects of humidity and temperature on thermal tolerance in Bombus impatiens. We found marked differences in heat tolerance by species that correlate with each species' latitudinal range, habitat, and climatic niche, and we found significant variation in thermal sensitivity by caste and sex. Queens had considerably lower heat tolerance than workers and males, with greater tolerance when queens would first be leaving their natal nest, and lower tolerance after ovary activation. Wild bees tended to have higher heat tolerance than lab reared bees, and body size was associated with heat tolerance only in wild-caught foragers. Humidity showed a strong interaction with heat effects, pointing to the need to regulate relative humidity in thermal assays and consider its role in nature. Altogether, we found most tested biological conditions impact thermal tolerance and highlight the stages of these bees that will be most sensitive to future climate change.

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.

Effects of a field-sprayed antibiotic on bee foraging behavior and pollination in pear orchards

Broadcast spraying of antibiotics in crops is widely used for controlling bacterial plant pathogens. The effects of antibiotics on non-target (and especially beneficial) organisms in cropping systems, however, are not well studied. Pollinators are of particular concern because in pear and apple crops, antibiotics for controlling fire blight (Erwinia amylovora) are sprayed during bloom, likely exposing pollinators. This is especially relevant as laboratory evidence suggests that antibiotics could have sublethal effects on bee foraging behavior and colony health. But to our knowledge these potential impacts have not been studied in field settings. Here, we compared the effects of two fire blight control methods, a single spray of an antibiotic (oxytetracycline) and a biological antagonist (Aureobasidium pullulans), on honey bee (Apis mellifera) foraging, pollination, and fruit set in pear orchards. Complementing these field assessments, we conducted laboratory experiments to examine the effects of these treatments on locomotion and foraging behavior of a bumble bee species, Bombus vosnesenskii. We found that honey bees visited fewer flowers and foraged longer on each flower in orchards sprayed with antibiotics than with a biological product, but there were no differences in crop pollination and seed set. The pear cultivars we worked in, however, can self-pollinate. In the lab, we found that feeding on high doses of either the antibiotic or the biological antagonist reduced bumble bee foraging relative to controls. The limited impact of antibiotics on pear pollination observed in this study suggest that antibiotics pose a low economic risk to pear growers, especially for self-compatible cultivars. Still, crops with higher pollinator dependence may be affected by reductions in bee visitation. Future studies should examine the impacts of multiple antibiotic sprays within a season, which are common during warm springs, and their long-term health impacts on both individual bees and colonies.

The absence of bumblebees on an oceanic island blurs the species boundary of two closely related orchids.

Oceanic islands offer valuable natural laboratories for studying evolution. The Izu Islands, with their recent geological origin, provide an exceptional opportunity to explore the initial evolution on oceanic islands. Another noteworthy aspect is the absence of bumblebee species on most Izu Islands. We used ecological, morphological, and molecular data to investigate the impact of bumblebee absence on the evolution of two closely related orchid species, Goodyera henryi and Goodyera similis, focusing on Kozu Island, the Izu Islands. Our investigation revealed that while G. henryi exclusively relies on a bumblebee species for pollination on the mainland, G. similis is pollinated by scoliid wasps on both the mainland and the island. Intriguingly, all specimens initially categorized as G. henryi on Kozu Island are hybrids of G. henryi and G. similis, leading to the absence of pure G. henryi distribution on the island. These hybrids are pollinated by the scoliid wasp species that also pollinates G. similis on the island. The absence of bumblebees might result in sporadic and inefficient pollination of G. henryi by scoliid wasps, consequently promoting hybrid proliferation on the island. Our findings suggest that the absence of bumblebees can blur plant species boundaries.

Limited introgression from non-native commercial strains and signatures of adaptation in the key pollinator Bombus terrestris.

Insect pollination is fundamental for natural ecosystems and agricultural crops. The bumblebee species Bombus terrestris has become a popular choice for commercial crop pollination worldwide due to its effectiveness and ease of mass rearing. Bumblebee colonies are mass produced for the pollination of more than 20 crops and imported into over 50 countries including countries outside their native ranges, and the risk of invasion by commercial non-native bumblebees is considered an emerging issue for global conservation and biological diversity. Here, we use genome-wide data from seven wild populations close to and far from farms using commercial colonies, as well as commercial populations, to investigate the implications of utilizing commercial bumblebee subspecies in the UK. We find evidence for generally low levels of introgression between commercial and wild bees, with higher admixture proportions in the bees occurring close to farms. We identify genomic regions putatively involved in local and global adaptation, and genes in locally adaptive regions were found to be enriched for functions related to taste receptor activity, oxidoreductase activity, fatty acid and lipid biosynthetic processes. Despite more than 30 years of bumblebee colony importation into the UK, we observe low impact on the genetic integrity of local B. terrestris populations, but we highlight that even limited introgression might negatively affect locally adapted populations.

Projected decline in European bumblebee populations in the twenty-first century.

Habitat degradation and climate change are globally acting as pivotal drivers of wildlife collapse, with mounting evidence that this erosion of biodiversity will accelerate in the following decades1-3. Here, we quantify the past, present and future ecological suitability of Europe for bumblebees, a threatened group of pollinators ranked among the highest contributors to crop production value in the northern hemisphere4-8. We demonstrate coherent declines of bumblebee populations since 1900 over most of Europe and identify future large-scale range contractions and species extirpations under all future climate and landuse changescenarios. Around 38-76% of studied European bumblebee species currently classified as 'Least Concern' are projected to undergo losses of at least 30% of ecologically suitable territory by 2061-2080 compared to 2000-2014. All scenarios highlight that parts of Scandinavia will become potential refugia for European bumblebees; it is howeveruncertain whether these areas will remain clear of additional anthropogenic stressors not accounted for in present models. Our results underline the critical role of globalchange mitigation policies as effective levers to protect bumblebees from manmade transformation of the biosphere.

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.

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.

Unexpected worker mating and colony-founding in a superorganism

The emergence of caste-differentiated colonies, which have been defined as ‘superorganisms’, in ants, bees, and wasps represents a major transition in evolution. Lifetime mating commitment by queens, pre-imaginal caste determination and lifetime unmatedness of workers are key features of these animal societies. Workers in superorganismal species like honey bees and many ants have consequently lost, or retain only vestigial spermathecal structures. However, bumble bee workers retain complete spermathecae despite 25-40 million years since their origin of superorganismality, which remains an evolutionary mystery. Here, we show (i) that bumble bee workers retain queen-like reproductive traits, being able to mate and produce colonies, underlain by queen-like gene expression, (ii) the social conditions required for worker mating, and (iii) that these abilities may be selected for by early queen-loss in these annual species. These results challenge the idea of lifetime worker unmatedness in superorganisms, and provide an exciting new tool for the conservation of endangered bumble bee species.

Landscape-scale floral resource discontinuity decreases bumble bee occurrence and alters community composition.

Agricultural practices and intensification during the past two centuries have dramatically altered the abundance and temporal continuity of floral resources that support pollinating insects such as bumble bees. Long-term trends among bumble bees within agricultural regions suggest that intensive agricultural conditions have created inhospitable conditions for some species, while other species have maintained their relative abundances despite landscape-level changes in flower availability. Bumble bee responses to spatiotemporal resource heterogeneity have been explored at the colony and behavioral level, but we have yet to understand whether these conditions drive community structure and ultimately explain the diverging patterns in long-term species trends. To explore the relationship between landscape-level floral resource continuity and the likelihood of bumble bee occurrence, we mapped the relative spatial and temporal availability of floral resources within an intensive agricultural region in the US Upper Midwest and related this resource availability with bumble bee species relative abundance. Across the bee community, we found that relative bumble bee occurrence increases in landscapes containing more abundant and more temporally continuous floral resources. Declining species, such as Bombus terricola, exhibited the strongest, positive responses to resource abundance and continuity whereas common, stable species, such as Bombus impatiens, showed no statistical relationship to either. Together with existing experimental evidence, this work suggests that efforts to increase spatiotemporal flower availability, along with overall flower abundance at landscape scales may have positive effects on bumble bee communities in the US Upper Midwest.

It is buzziness time: rearing, mating, and overwintering Bombus vosnesenskii (Hymenoptera: Apidae).

Bombus vosnesenskii Radowszkowski, 1862 is one of three bumble bee species commercially available for pollination services in North America; however, little is documented about B. vosnesenskii colony life cycle or the establishment of ex situ rearing, mating, and overwintering practices. In this study, we documented nest success, colony size, and gyne production; recorded the duration of mating events; assessed overwintering survival of mated gynes; and evaluated second-generation nest success for colonies established from low- and high-elevation wild-caught B. vosnesenskii gynes. Of the 125 gynes installed, 62.4% produced brood cells (nest initiation) and 43.2% had at least 1 worker eclose (nest establishment). High-elevation B. vosnesenskii gynes had significantly higher nest initiation and establishment success than low-elevation gynes. However, low-elevation colonies were significantly larger with queens producing more gynes on average. Mating was recorded for 200 low-elevation and 37 high-elevation gynes, resulting in a mean duration of 62 and 51 min, respectively. Mated gynes were then placed into cold storage for 54 days to simulate overwintering, which resulted in 59.1% of low-elevation gynes surviving and 91.9% of high-elevation gynes surviving. For second-generation low-elevation gynes, 26.4% initiated nesting and 14.3% established nesting. Second-generation high-elevation gynes did not initiate nesting despite CO2 narcosis treatments. Overall, these results increase our understanding of B. vosnesenskii nesting, mating, and overwintering biology from 2 elevations. Furthermore, this study provides information on successful husbandry practices that can be used by researchers and conservationists to address knowledge gaps and enhance the captive rearing of bumble bees.

Uncovering the role of juvenile hormone in ovary development and egg laying in bumble bees

Juvenile hormone (JH) regulates developmental and physiological processes in insects. In bumble bees, the hormone acts as a gonadotropin that mediates ovary development, but the exact physiological pathways involved in ovary activation and subsequent egg laying are poorly understood. In this study, we examine how queen hibernation state, caste, and species impact the gonadotropic effect of JH in bumble bee queens through methoprene (JH analogue) application. We extend previous research by assessing queen egg laying and colony initiation, alongside ovary development. Furthermore, we compared sensitivity of workers of both species to the juvenile hormone's gonadotropic effect. In both bumble bee species, the ovaries of hibernated queens were developed five to six days after breaking diapause, regardless of methoprene treatment. By contrast, methoprene did have a stimulatory effect on ovary development in non-hibernated queens. The dose needed to obtain this effect was higher in B. impatiens. Methoprene did not have gonadotropic effects in callow workers of both species. These results indicate that the physiological effect of exogenous methoprene application varies according to species, caste and hibernation status. Interestingly, despite gonadotropic effects in non-hibernated queens, oviposition was not accelerated by JH. This suggests that JH alone is insufficient to induce egg laying and that an additional stimulus, which is naturally present in hibernated queens, is required. Consequently, our findings indicate that other physiological processes, beyond a rise in JH alone, are required for oviposition and colony initiation.

Cross-mating between the alien bumblebee Bombus terrestris and two native Japanese bumblebees, B. hypocrita sapporensis and B. cryptarum florilegus, in the Nemuro Peninsula, Japan

The rapid naturalization of Bombus terrestris across the Nemuro Peninsula has led to a decline in two closely related native Japanese species, namely Bombus hypocrita sapporensis and Bombus cryptarum florilegus, both belonging to the common subgenus Bombus. Although it is widely believed that cross-mating of native and non-native species is influenced by the common male sex pheromone in this region, no study has been conducted to substantiate this claim. Thus, we investigated the cross-activities of male sex pheromones between native and non-native bumblebees, as well as the frequencies of cross-mating, using chemical and DNA assays. Our gas chromatography–electroantennographic detector analyses and behavioral tests revealed the presence of sex pheromonal cross-activities between B. terrestris and the two Japanese bumblebees species. Furthermore, DNA analyses revealed the occurrence of cross-mating between native and non-native species in the Nemuro Peninsula. Overall, these results indicate the immediate need for conservation measures to safeguard Japanese bumblebee populations in the Nemuro Peninsula.

Bumblebees and butterflies in green structure elements in Malmö, Sweden

Within the BiodiverCity project in Malmö (Sweden), green structure elements were implemented aiming to support biodiversity and enhancing amenity in denser parts of the city. In this study, bumblebee and butterfly abundances and species richness were studied in 20 green structure elements in three areas in Malmö. The investigated green structure elements consisted of objects established within the BiodiverCity project and other green structure elements in their surroundings (e.g. road verges, lawns and flowerbeds). Observed bumblebee and butterfly abundances and species richness was generally low. In total, 528 bumblebees of eight species were recorded, with 97% of all bumblebees belonging to two species, Bombus lapidarius and B. terrestris/lucorum. A total of 154 butterflies from 10 species were detected, most commonly Pieris species. There were no significant differences in mean individual or species numbers (bumblebees and butterflies) between green structure elements designed to support biodiversity and conventional ones. Bumblebee species richness and abundance were positively correlated with mean cover of flowering vegetation and mean number of flowering plant species. Butterfly species richness and abundance were positively correlated with mean number of flowering plant species and size of the green structure. Observations of flower visits showed that the two groups of insects had different preferences. The results of this study show that enhancing bumblebee and butterfly diversity and abundances in densely built city areas can be challenging. To support bumblebees and butterflies more successfully, the habitat requirements of these insect groups need to be better considered from the beginning in the design of green structure elements.

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.

Identifying conservation priority areas forNorth Americanbumble bee species inCanadaunder current and future climate scenarios

AbstractMany bumble bee species are declining globally from multiple threats including climate change. Identifying conservation priority areas with a changing climate will be important for conserving bumble bee species. Using systematic conservation planning, we identified priority areas for 44 bumble bee species in Canada under current and projected climates (year 2050). Conservation priority areas were identified as those that contained targeted amounts of each species predicted occurrence through climate envelope models, while minimizing the area cost of conserving the identified conservation priority areas. Conservation priority areas in the two periods were compared to established protected areas and land cover types to determine the area of current and future priority sites that are protected and the types of landscapes within priority areas. Notably, conservation priority areas were rarely within established protected areas. Priority areas were most often in croplands and grasslands, mainly within the mountain west, central and Southern Ontario, Northern Quebec, and Atlantic Canada under all climate scenarios. Conservation priority areas are predicted to increase in elevation and latitude with climate change. Our findings identify the most important regions in Canada for conserving bumble bee species under current and future climates including consistently selected future sites.

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.

Urban habitat fragmentation and floral resources shape the occurrence of gut parasites in two bumblebee species.

Urbanization and the expansion of human activities foster radical ecosystem changes with cascading effects also involving host-pathogen interactions. Urban pollinator insects face several stressors related to landscape and local scale features such as green habitat loss, fragmentation and availability reduction of floral resources with unpredictable effects on parasite transmission. Furthermore, beekeeping may contribute to the spread of parasites to wild pollinators by increasing the number of parasite hosts. Here we used DNA-based diagnostics tools to evaluate how the occurrence of parasites, namely microsporidians (Nosema spp.), trypanosomatids (Crithidia spp.) and neogregarines (Apicystis bombi), is shaped by the above-mentioned stressors in two bumblebee species (i.e. Bombus terrestris and Bombus pascuorum). Infection rates of the two species were different and generally higher in B. terrestris. Moreover, they showed different responses towards the same ecological variables, possibly due to differences in body size and foraging habits supposed to affect their susceptibility to parasite infection. The probability of infection was found to be reduced in B. pascuorum by green habitat fragmentation, while increased along with floral resource availability. Unexpectedly, B. terrestris had a lower parasite richness nearby apiaries maybe due to the fact that parasites are prone to be transmitted among the most abundant species. Our finding supports the need to design proper conservation measures based on species-specific knowledge, as suggested by the variation in the parasite occurrence of the two species. Moreover, conservation policies aiming at safeguarding pollinators through flower planting should consider the indirect effects of these measures for parasite transmission together with pollinator biodiversity issues.