Bacterial communities of wild bee species and the western honey bee (Apis mellifera) (Hymenoptera: Apoidea): Alpine insights

Western honey bees (Apis mellifera) are dominant crop pollinators, and access to summer forage is a critical factor influencing colony health in agricultural landscapes. In many temperate agricultural regions, honey bees forage extensively from non-native plants during the summer, but it is unclear whether the use of these species is due to honey bee preference for these plants or is a result of their relative abundance. The foraging choices made by native bees that have evolved with native plants can reveal the seasonal availability of native plant pollens, and so we quantified the pollen collected by 181 wild bee species native to Michigan. Pollen was also trapped from honey bee colonies during the summer to confirm the peak period of non-native pollen collection in this region. Across the state, the generic richness of native pollens collected by wild bees peaked in May before linearly declining into September. Wild social and solitary bees collected a similar proportion of their pollen from non-native plants from April to July, but during August and September social bees collected a significantly greater proportion from non-natives. At a local scale, honey bees collected the majority of their pollen from non-native plants between 4 July and 21 August, with the same trend seen in both social and solitary bees. Across the region, a significantly greater proportion of the solitary bee species that peak during this time are specialists, most of which collect from native plant species that are little utilised by social bees for pollen, such as Dasiphora, Helianthus, Physalis and Vernonia. Our results suggest that Michigan has relatively few native flowering resources during the height of the summer, and that many of those which flower during this time are used primarily by specialised solitary bee species rather than the social bee community, including honey bees. As a result, non-native plant species with a late summer flowering phenology fill a forage gap and thus can contribute to the diet of both honey bees and generalist wild bees during this time, despite the well-documented negative impacts of these species on native plant communities.

Maine is the largest producer of wild blueberry (Vaccinium angustifolium Aiton) in the United States. Pollination comes from combinations of honey bees (Apis mellifera (L.)), commercial bumble bees (Bombus impatiens Cresson), and wild bees. This study addresses (1) previous research addressing wild-blueberry pollination, (2) effects of wild-bee and honey-bee activity densities on fruit set, yield, and crop value, (3) the economic value of wild-bee communities, and (4) economic consequences of pollinator loss. Bee communities were sampled in 40 fields over three years (2010–2012) and bee activity densities were estimated for bumble bees, honey bees, and other wild bees. These data were applied to an economic model to estimate the value of bee taxa. Bumble bees and honey bees predicted fruit set and reduced its spatial heterogeneity. Other wild bees were not significant predictors of fruit set. Yield was predicted by fruit set and field size, but not pest management tactics. Our analysis showed that disruption in supply of honey bees would result in nearly a 30% decrease in crop yield, buffered in part by wild bees that provide “background” levels of pollination. Honey-bee stocking density and, thus, the activity density of honey bees was greater in larger fields, but not for wild bees. Therefore, a decrease in crop yield would be greater than 30% for large fields due to the proportionally greater investment in honey bees in large fields and a relatively lower contribution by wild bees.

1. A diverse array of wild bee species may provide more effective pollination than the widely employed European honey bee (Apis mellifera L.). High species richness within crop pollinator assemblages has been linked to enhanced fruit and seed yields, but species richness is often confounded with abundance in studies of pollinator communities. 2. We investigated the effects of bee diversity and species identity on pollen deposition and crop yield in the strawberry (Fragaria x ananassa) variety Jewel through a field experiment that independently manipulated the species richness and abundance of flower visitors. We used a new pollen deposition measurement technique to determine the pollen contribution of individual bees in an assemblage of flower visits. We compared the performance of wild bee species and managed honey bees, as pollinators of strawberry. We also calculated the influence of species richness, visit frequency, and visitor identity on fruit mass, using the fruit that developed from each sampled flower. 3. Species richness of flower visitors did not influence floral pollen loads or strawberry mass. Honey bees and wild bees deposited the same amount of pollen per visited flower. However, strawberries that developed from flowers visited by wild bees were heavier than flowers visited by honey bees. In addition, flowers visited by a combination of wild and honey bees produced strawberries that weighed less than flowers receiving purely wild bee visits. 4. Synthesis and applications: Our findings show that honey bee pollination results in lower yields than wild bee pollination in a strawberry crop. Consequently, if managed honey bees in strawberry fields displace wild pollinators, growers may obtain suboptimal yields. Management efforts aimed at the maintenance or enhancement of wild pollinator populations may therefore be a cost-effective way to increase both crop yield and biodiversity on strawberry farms.

The Western honey bee (Apis mellifera L.) has been managed by humans for centuries for honey, wax, and most recently, crop pollination. The deep history of human association with this species has enabled agricultural practices that reduce biodiversity of pollinating wild bees, largely through habitat modification. However, there is also interest in determining if A. mellifera presence itself contributes significantly to wild bee population declines. Here, we review the evidence of A. mellifera effects on wild bees, with a particular emphasis on critically evaluating the evidence for detrimental impacts associated with resource competition. Despite accelerated research in this area, only ∼13% of resource competition studies evaluated fitness effects of A. mellifera on wild bees, a research gap that has persisted for over 20 years. About three times as many studies have evaluated effects of A. mellifera on wild bee community parameters, including wild bee abundance, which provides a measure of a landscape's "bee carrying capacity." Just over 20% of these studies show a negative correlation with A. mellifera abundance. In a novel analysis of 68 additional studies measuring bee communities for a variety of other reasons, we found negative correlations between A. mellifera abundance and any measure of the wild bee community (richness, abundance, etc.) for nine, and the measures showing A. mellifera impacts were varied. For example, only two of these studies showed negative correlations between A. mellifera and wild bee abundances. In contrast, we also found similar numbers of positive relationships between A. mellifera and various wild bee community parameters, including ten studies that showed positive relationships between A. mellifera and wild bee abundances. Most studies (64%) showed no relationship with any factor. We found no clear pattern to explain which habitat types are more vulnerable to A. mellifera competition, nor is the literature clear on impactful densities of managed hives in particular environment types. We discuss suggestions for future research, as well as ways the research community could clarify its conservation priorities with respect to resource competition. Resource competition between A. mellifera and wild bees is clearly a concern in some cases. However, more work is needed to identify and predict where A. mellifera poses a significant threat to wild bee populations. Overall, the data do not support a generalized and widespread negative relationship between A. mellifera abundance and wild bee community health. Rather, conservation measures that reliably improve wild bee health (habitat preservation and restoration) will likely have positive effects on A. mellifera, and vice versa.

A diverse array of wild bee species may provide more effective pollination than the widely employed European honey bee (Apis mellifera L.). High species richness within crop pollinator assemblages has been linked to enhanced fruit and seed yields, but species richness is often confounded with abundance in studies of pollinator communities. We investigated the effects of bee diversity and species identity on pollen deposition and crop yield in the strawberry (Fragaria × ananassa) variety Jewel through a field experiment that independently manipulated the species richness and abundance of flower visitors. We used a new pollen deposition measurement technique to determine the pollen contribution of individual bees in an assemblage of flower visits. We compared the performance of wild bee species and managed honey bees, as pollinators of strawberry. We also calculated the influence of species richness, visit frequency and visitor identity on fruit mass, using the fruit that developed from each sampled flower. Species richness of flower visitors did not influence floral pollen loads or strawberry mass. Honey bees and wild bees deposited the same amount of pollen per visited flower. However, strawberries that developed from flowers visited by wild bees were heavier than flowers visited by honey bees. In addition, flowers visited by a combination of wild and honey bees produced strawberries that weighed less than flowers receiving purely WB visits. Synthesis and applications. Our findings show that honey bee pollination results in lower yields than wild bee pollination in a strawberry crop. Consequently, if managed honey bees in strawberry fields displace wild pollinators, growers may obtain suboptimal yields. Management efforts aimed at the maintenance or enhancement of wild pollinator populations may therefore be a cost‐effective way to increase both crop yield and biodiversity on strawberry farms.

Addition of floral resources to agricultural field margins has been shown to increase abundance of beneficial insects in crop fields, but most plants recommended for this use are non-native annuals. Native perennial plants with different bloom periods can provide floral resources for bees throughout the growing season for use in pollinator conservation projects. To identify the most suitable plants for this use, we examined the relative attractiveness to wild and managed bees of 43 eastern U.S. native perennial plants, grown in a common garden setting. Floral characteristics were evaluated for their ability to predict bee abundance and taxa richness. Of the wild bees collected, the most common species (62%) was Bombus impatiens Cresson. Five other wild bee species were present between 3 and 6% of the total: Lasioglossum admirandum (Sandhouse), Hylaeus affinis (Smith), Agapostemon virescens (F.), Halictus ligatus Say, and Ceratina calcarata/dupla Robertson/Say. The remaining wild bee species were present at <2% of the total. Abundance of honey bees (Apis mellifera L.) was nearly identical to that of B. impatiens. All plant species were visited at least once by wild bees; 9 were highly attractive, and 20 were moderately attractive. Honey bees visited 24 of the 43 plant species at least once. Floral area was the only measured factor accounting for variation in abundance and richness of wild bees but did not explain variation in honey bee abundance. Results of this study can be used to guide selection of flowering plants to provide season-long forage for conservation of wild bees.

Simple SummaryFloral resource availability is one of the keys to preserving the health of bee communities. However, flowers also present a risk of pathogen transmission, as infected pollinators could deposit pathogens while foraging, exposing other pollinators to infection via the consumption of contaminated nectar or pollen. Here, we studied, over time, the prevalence of seven viruses in bee communities that share the same small surface of floral resource in order to assess the risk of virus spillover. In total, 2057 bee specimens from 30 species were caught, identified and checked for the presence of viruses. Specimens from the Halictidae family were the dominant wild bees. The prevalence of viruses was quite high: at least one virus was detected in 78% of the samples, and co-infections were frequent. The genetic diversity of the viruses was also investigated to look for the possible association of geographic origin or host with shared ancestry.Viruses are known to contribute to bee population decline. Possible spillover is suspected from the co-occurrence of viruses in wild bees and honey bees. In order to study the risk of virus transmission between wild and managed bee species sharing the same floral resource, we tried to maximize the possible cross-infections using Phacelia tanacetifolia, which is highly attractive to honey bees and a broad range of wild bee species. Virus prevalence was compared over two years in Southern France. A total of 1137 wild bees from 29 wild bee species (based on COI barcoding) and 920 honey bees (Apis mellifera) were checked for the seven most common honey bee RNA viruses. Halictid bees were the most abundant. Co-infections were frequent, and Sacbrood virus (SBV), Black queen cell virus (BQCV), Acute bee paralysis virus (ABPV) and Israeli acute paralysis virus (IAPV) were widespread in the hymenopteran pollinator community. Conversely, Deformed wing virus (DWV) was detected at low levels in wild bees, whereas it was highly prevalent in honey bees (78.3% of the samples). Both wild bee and honey bee virus isolates were sequenced to look for possible host-specificity or geographical structuring. ABPV phylogeny suggested a specific cluster for Eucera bees, while isolates of DWV from bumble bees (Bombus spp.) clustered together with honey bee isolates, suggesting a possible spillover.

Worker honeybees (Apis mellifera) usually only lay eggs when their colony is queenless. However, an extremely rare 'anarchistic' phenotype occurs, in which workers develop functional ovaries and lay large numbers of haploid eggs which develop into adult drones despite the presence of the queen. Studies of such colonies can give important insights into the mechanisms by which worker sterility is maintained in normal colonies. Here we report on the results of a breeding programme which enhanced the frequency of the anarchistic phenotype. Colonies derived from queens inseminated only by worker-laid males showed up to 9% of workers with highly developed ovaries. In these colonies a large proportion of males arose from worker-laid eggs. Colonies headed by queens inseminated with 50% worker-laid drones and 50% queen-laid drones showed variable phenotypes. In most such colonies there was no worker reproduction. In some, many workers had highly developed ovaries, but no worker-laid eggs were reared. In one colony, many worker-laid eggs were reared to maturity. The results suggest that the anarchy phenotype results from a complex interaction of queen genotype, the worker genotype of subfamilies that successfully reproduce and of those that do not, and the external environment.

The decline of wild bee populations in North America is worrisome. Honey bee (Apis mellifera) pathogens have been mentioned as one factor that may be implicated in these declines. This review analyses evidence of pathogen spillover from Apis mellifera to wild bee species, the mechanisms involved, the role of migratory beekeeping, the different pathogens associated with spillover cases, the impact of pathogens on wild bees, and a few strategies to mitigate the issue. Honey bee pathogens have been detected in more than 50 species within five families of bees in North American countries. Data on pathogen prevalence and phylogeny strongly indicate spillover from honey bees to wild bees, as well as spillback events. Most pathogens studied are viruses, but bacteria, fungi, and protozoa causing diseases in honey bees have been also found to replicate in wild bees and, in some cases, cause damage and shorten the lifespan of the insects. Regulated movement of hives and effective control of honey bee diseases could reduce the frequency of pathogen spillover to wild bee communities because these measures would decrease the risk of transmission. Additionally, the increased use of native bees and habitat restoration could reduce the risk of pathogen spillover from honey bees to wild bees. Studies focussing on the epidemiology and effects of pathogens on wild bee species are urgently needed to develop strategies for the optimal management of honey bees and wild bee species, to protect biodiversity and ecosystems, and to ensure adequate pollination services in North America.

Evidence of inter-species pathogen transmission from managed to wild bees has sparked concern that emerging diseases could be causing or exacerbating wild bee declines. While some pathogens, like RNA viruses, have been found in pollen and wild bees, the threat these viruses pose to wild bees is largely unknown. Here, we tested 169 bees, representing 4 families and 8 genera, for five common honey bee (Apis mellifera) viruses, finding that more than 80% of wild bees harbored at least one virus. We also quantified virus titers in these bees, providing, for the first time, an assessment of viral load in a broad spectrum of wild bees. Although virus detection was very common, virus levels in the wild bees were minimal—similar to or lower than foraging honey bees and substantially lower than honey bees collected from hives. Furthermore, when we experimentally inoculated adults of two different bee species (Megachile rotundata and Colletes inaequalis) with a mixture of common viruses that is lethal to honey bees, we saw no effect on short term survival. Overall, we found that honey bee RNA viruses can be commonly detected at low levels in many wild bee species, but we found no evidence that these pathogens cause elevated short-term mortality effects. However, more work on these viruses is greatly needed to assess effects on additional bee species and life stages.

Wild bees provide pollination services and are currently declining at the global scale. A potential cause for this decline is competitive interactions with domestic honey bees. Urban beekeeping, a fairly new activity, is rapidly gaining popularity. In contrast with agricultural and natural areas, the extent of competition between honey bees and wild bees in urban areas is unclear. The objectives of this study were to quantify the impact of honey bees, urbanization, and the availability of floral resources on wild bee communities. We hypothesized that honey bees exert negative impacts on wild bees, that floral resources favor wild bee communities and mitigate the negative impacts of competition with honey bees, and that the influence of heat islands, used as a proxy for urbanization, varies between wild bees with their functional traits (nesting behavior). We tested these hypotheses with a data set of 19,077 wild bee specimens collected using colored pan-traps at 25 urban sites in 2012 and 2013. We investigated community and population patterns after accounting for imperfect detection probability. We found no evidence of competition between wild and domesticated bees. Our analyses indicate mixed effects of urban heat islands across species and positive effects of floral resources. We conclude that cities can allow the coexistence of urban beekeeping and wild bees under moderate hive densities. However, it will remain crucial to further investigate the competitive interactions between wild and honey bees to determine the threshold of hive densities beyond which competition could occur.

The spatial heterogeneity of urban landscapes, relatively low agrochemical use, and species-rich floral communities often support a surprising diversity of wild pollinators in cities. However, the management of Western honey bees (Apis mellifera L.) in urban areas may represent a new threat to wild bee communities. Urban beekeeping is commonly perceived as an environmentally friendly practice or a way to combat pollinator declines, when high-density beekeeping operations may actually have a negative influence on native and wild bee populations through floral resource competition and pathogen transmission. On the Island of Montréal, Canada there has been a particularly large increase in beekeeping across the city. Over the years following a large bee diversity survey ending in 2013, there was an influx of almost three thousand honey bee colonies to the city. In this study, we examined the wild bee communities and floral resources across a gradient of honey bee abundances in urban greenspaces in 2020, and compared the bee communities at the same sites before and after the large influx of honey bees. Overall, we found a negative relationship between urban beekeeping, pollen availability, and wild bee species richness. We also found that honey bee abundance had the strongest negative effect on small (inter-tegular span <2.25 mm) wild bee species richness. Small bee species may be at higher risk in areas with abundant honey bee populations as their limited foraging range may reduce their access to floral resources in times of increased competition. Further research on the influence of urban beekeeping on native and wild pollinators, coupled with evidence-based beekeeping regulations, is essential to ensure cities contain sufficient resources to support wild bee diversity alongside managed honey bees.

Honey bees gather pollen from flowering plants, using it as a vital protein source and, in turn, acquire pollen-associated microbes that interact with their existing gut microbiota. Despite their ecological importance, limited information exists regarding the gut microbiota of African savannah honey bees (Apis mellifera scutellata Lepeletier) and how diet and its associated microbial community influence this crucial internal ecosystem. This study aimed to investigate the differences in gut microbiota between wild honey bees collected during the flowering season and microbially depleted honey bees reared under semi-sterile conditions and fed various protein diets. To achieve this, freshly hatched worker bees were maintained in hoarding cages and assigned one of four protein diets: fresh sunflower pollen, casein, sterilised casein, or sterilised pollen. High-throughput DNA metabarcoding was then employed to compare the microbial composition of the honey bee gut across these groups. Our findings revealed that the gut of microbially depleted honey bees exhibited higher species diversity and richness. Conversely, the non-core gut microbial community predominated in wild bees and those fed the different protein diets. Specifically, Commensalibacter, Bartonella, and Bifidobacterium were the most dominant bacterial genera across all treatments. Interestingly, Gilliamella, a common core gut bacterium, was undetected, while Apibacter was exclusively found in wild honey bees. Furthermore, pollen-associated microbes such as Devosia and Pedobacter were identified solely in the gut of honey bees fed a pollen diet. Functional predictions of the gut microbial community also indicated the presence of key enzymes such as β-glucosidase, β-galactosidase, pyruvate dehydrogenase and phosphoglycerate mutase, which are crucial for enhancing nutrient absorption, digestion, and carbohydrate metabolism. These results underscore the intricate relationship between honey bees, microbes, and plants, offering valuable insights into how diet and its associated microbial communities could shape the gut microbiota of African honey bees. KEY POINTS: • The non-core gut microbiota dominates the African savannah honey bee •The type of diet influenced the microbial diversity and community abundance in the honey bee gut •Key enzymes involved in digestion, nutrition absorption, and carbohydrate metabolism were enhanced in the gut •Pollen-associated microbes found in the diet present potential avenues for probiotic development to improve honey bee health.

Honeybees (Apis mellifera) are increasingly used in commercial crop production, while wild bees are also important pollinators. Few studies have investigated the relative importance of honeybees and wild bees for apple pollination and whether the contribution of wild bees is affected by increasing numbers of honeybees. Here, we conducted experiments in 52 commercially important Fuji apple orchards across three apple production areas in China, to investigate how wild bees, honeybees and their interaction influences apple quantity (fruit set, weight) and quality (seed number). Both honeybees and wild bees contributed to apples production, resulting in an overall 996%, 26% and 64% increase of apple fruit set, fruit weight and seed number, respectively. We found a hump‐shaped relationship between bee density and fruit set and fruit weight with the maximum fruit set at intermediate bee density, but honeybees reached the maximum only with one and a half times higher numbers than wild bees. Furthermore, when honeybee activity density was low, an increase in wild bee activity density and species richness led to enhanced pollination contribution. Conversely, when honeybee activity density was high, increased wild bee activity density and species richness were associated with reduced pollination contribution. Additionally, the highest fruit set was observed at high densities of wild bees and intermediate densities of honeybees. These results indicate that high honeybee activity density may interfere with the pollination services provided by wild bees in apple orchards. Synthesis and applications. Both honeybees and wild bees contribute to apple pollination and production, but wild bees evidenced much higher pollination efficiency than honeybees. Importantly, introducing high density of honeybee colonies appeared to enhance competition with wild bees, decreasing their contribution to pollination. As highest fruit set was found with high wild bee densities, but only intermediate levels of honeybee densities, it is important to carefully assess the number of honeybee colonies before possible introduction of hives for apple production, in particular when wild bee diversity and density are high. Conserving wild bee diversity is of priority to harness pollination services in apple production, given their high diversity and pollination efficiency.

Foraging of honey bees in agricultural landscapes with changing patterns of flower resources