Pollen and yeast change nectar aroma and nutritional content alone and together, but honey bee foraging reflects only the avoidance of yeast

Microbiome and floral associations of a wild bee using biodiversity survey collections

The health of bees can be assessed through their microbiome, which serves as a biomarker indicating the presence of both beneficial and harmful microorganisms within a bee community. This study presents the characterisation of the bacterial, fungal, and plant composition on the cuticle of adult bicoloured sweat bees (Agapostemon virescens). These bees were collected using various methods such as pan traps, blue vane traps and sweep netting across the northern extent of their habitat range. Non-destructive methods were employed to extract DNA from the whole pinned specimens of these wild bees. Metabarcoding of the 16S rRNA, ITS and rbcL regions was then performed. The study found that the method of collection influenced the detection of certain microbial and plant taxa. Among the collection methods, sweep net samples showed the lowest fungal alpha diversity. However, minor differences in bacterial or fungal beta diversity suggest that no single method is significantly superior to others. Therefore, a combination of techniques can cater to a broader spectrum of microbial detection. The study also revealed regional variations in bacterial, fungal and plant diversity. The core microbiome of A. virescens comprises two bacteria, three fungi and a plant association, all of which are commonly detected in other wild bees. These core microbes remained consistent across different collection methods and locations. Further extensive studies of wild bee microbiomes across various species and landscapes will help uncover crucial relationships between pollinator health and their environment.

A quantitative survey of the blueberry (Vaccinium spp.) culturable nectar microbiome: variation between cultivars, locations, and farm management approaches

Microbes in floral nectar can impact both their host plants and floral visitors, yet little is known about the nectar microbiome of most pollinator-dependent crops. In this study, we examined the abundance and composition of the fungi and bacteria inhabiting Vaccinium spp. nectar, as well as nectar volume and sugar concentrations. We compared wild V. myrsinites with two field-grown V. corymbosum cultivars collected from two organic and two conventional farms. Differences in nectar traits and microbiomes were identified between V. corymbosum cultivars but not Vaccinium species. The microbiome of cultivated plants also varied greatly between farms, whereas management regime had only subtle effects, with higher fungal populations detected under organic management. Nectars were hexose-dominant, and high cell densities were correlated with reduced nectar sugar concentrations. Bacteria were more common than fungi in blueberry nectar, although both were frequently detected and co-occurred more often than would be predicted by chance. "Cosmopolitan" blueberry nectar microbes that were isolated in all plants, including Rosenbergiella sp. and Symmetrospora symmetrica, were identified. This study provides the first systematic report of the blueberry nectar microbiome, which may have important implications for pollinator and crop health.

A New Isolated Fungus and Its Pathogenicity for Apis mellifera Brood in China

In this article, we report the pathogenicity of a new strain of fungus, Rhizopus oryzae to honeybee larvae, isolated from the chalkbrood-diseased mummies of honeybee larvae and pupae collected from apiaries in China. Based on morphological observation and internal transcribed spacer (ITS) region analyses, the isolated pathogenic fungus was identified as R. oryzae. Koch's postulates were performed to determine the cause-and-effect pathogenicity of this isolate fungus. The in vitro pathogenicity of this virulent fungus in honeybees was tested by artificially inoculating worker larvae in the lab. The pathogenicity of this new fungus for honeybee larvae was both conidial-concentration and exposure-time dependent; its highly infectious and virulent effect against the larvae was observed at 1 × 105 conidia/larva in vitro after 96 h of challenge. Using probit regression analysis, the LT50 value against the larvae was 26.8 h at a conidial concentration of 1 × 105 conidia/larva, and the LC50 was 6.2 × 103 conidia/larva. These results indicate that the new isolate of R. oryzae has considerable pathogenicity in honeybee larvae. Additionally, this report suggests that pathogenic phytofungi may harm their associated pollinators. We recommend further research to quantify the levels, mechanisms, and pathways of the pathogenicity of this novel isolated pathogen for honeybee larvae at the colony level.

Chemistry, biosynthesis and biology of floral volatiles: roles in pollination and other functions

Covering: 2010 to 2023Floral volatiles are a chemically diverse group of plant metabolites that serve multiple functions. Their composition is shaped by environmental, ecological and evolutionary factors. This review will summarize recent advances in floral scent research from chemical, molecular and ecological perspectives. It will focus on the major chemical classes of floral volatiles, on notable new structures, and on recent discoveries regarding the biosynthesis and the regulation of volatile emission. Special attention will be devoted to the various functions of floral volatiles, not only as attractants for different types of pollinators, but also as defenses of flowers against enemies. We will also summarize recent findings on how floral volatiles are affected by abiotic stressors, such as increased temperatures and drought, and by other organisms, such as herbivores and flower-dwelling microbes. Finally, this review will indicate current research gaps, such as the very limited knowledge of the isomeric pattern of chiral compounds and its importance in interspecific interactions.

Blueberry floral probiotics: nectar microbes inhibit the growth of Colletotrichum pathogens

AIMS

To identify whether microorganisms isolated from blueberry flowers can inhibit the growth of Colletotrichum, an opportunistic plant pathogen that infects flowers and threatens yields, and to assess the impacts of floral microbes and Colletotrichum pathogens on artificial nectar sugars and honey bee consumption.

METHODS AND RESULTS

The growth inhibition of Colletotrichum (Colletotrichum acutatum, Colletotrichum fioriniae, and Colletotrichum gloeosporioides) was screened using both artificial nectar co-culture and dual culture plate assays. All candidate nectar microbes were screened for antagonism against a single C. acutatum isolate. Then, the top four candidate nectar microbes showing the strongest inhibition of C. acutatum (Neokomagataea thailandica, Neokomagataea tanensis, Metschnikowia rancensis, and Symmetrospora symmetrica) were evaluated for antagonism against three additional C. acutatum isolates, and single isolates of both C. fioriniae and C. gloeosporioides. In artificial nectar assays, single and three-species cultures inhibited the growth of two of four C. acutatum isolates by ca. 60%, but growth of other Colletotrichum species was not affected. In dual culture plate assays, inhibition was observed for all Colletotrichum species for at least three of four selected microbial antagonists (13%‒53%). Neither honey bee consumption of nectar nor nectar sugar concentrations were affected by any microbe or pathogen tested.

CONCLUSIONS

Selected floral microbes inhibited growth of all Colletotrichum species in vitro, although the degree of inhibition was specific to the assay and pathogen examined. In all microbial treatments, nectar sugars were preserved, and honey bee preference was not affected.

Blueberries infected with the fungal pathogen Colletotrichum fioriniae release odors that repel Drosophila suzukii

BACKGROUND

Spotted-wing drosophila, Drosophila suzukii, is a serious pest of thin-skinned fruits. Alternative methods to control this pest are needed to reduce insecticide use, including new repellents. Previous research demonstrated that D. suzukii adults use odor cues to avoid blueberries infected with the fungal pathogen Colletotrichum fioriniae, which causes the disease anthracnose. To identify novel D. suzukii repellents, we investigated the volatile emission from experimentally-infected fruit, which were inoculated with C. fioriniae isolates in the laboratory, and from field-collected fruit, which were naturally infected and harvested from a field. We then tested the pathogen-induced volatiles on D. suzukii adult behavior.

RESULTS

Volatile emission was similar between all five C. fioriniae strains, with good agreement between experimentally-infected and field-collected berries. In total, 14 volatiles were found to be more abundant in infected versus uninfected fruit headspace. In multiple-choice bioassays, nine of the 14 volatiles elicited repellency responses from adult D. suzukii. These nine volatiles were further evaluated in dual choice assays, where all nine reduced fly capture by 43-96% compared to the control. The most repellent compounds tested were the esters ethyl butanoate and ethyl (E)-but-2-enoate, which were more or equally repellent to the known D. suzukii repellents 1-octen-3-ol, geosmin, and 2-pentylfuran. Dose-response assays identified concentration-dependent effects on D. suzukii repellency and oviposition when applied individually and consistent aversion observed across doses of a 1:1 blend.

CONCLUSION

We report two repellents from C. fioriniae-infected blueberries that could be useful semiochemicals for the behavioral manipulation of D. suzukii in the field. © 2023 Society of Chemical Industry. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Solitary Bees Host More Bacteria and Fungi on Their Cuticle than Social Bees

Bees come into contact with bacteria and fungi from flowering plants during their foraging trips. The Western honeybee (Apis mellifera) shows a pronounced hygienic behavior with social interactions, while the solitary red mason bee (Osmia bicornis) lacks a social immune system. Since both visit the same floral resources, it is intriguing to speculate that the body surface of a solitary bee should harbor a more complex microbiome than that of the social honeybee. We compared the cuticular microbiomes of A. mellifera (including three European subspecies) and O. bicornis for the first time by bacterial 16S rRNA and fungal ITS gene-based high-throughput amplicon sequencing. The cuticular microbiome of the solitary O. bicornis was significantly more complex than that of the social A. mellifera. The microbiome composition of A. mellifera subspecies was very similar. However, we counted significantly different numbers of fungi and a higher diversity in the honeybee subspecies adapted to warmer climates. Our results suggest that the cuticular microbiome of bees is strongly affected by visited plants, lifestyle and adaptation to temperature, which have important implications for the maintenance of the health of bees under conditions of global change.

Bees just wanna have fungi: a review of bee associations with nonpathogenic fungi

Bee-fungus associations are common, and while most studies focus on entomopathogens, emerging evidence suggests that bees associate with a variety of symbiotic fungi that can influence bee behavior and health. Here, we review nonpathogenic fungal taxa associated with different bee species and bee-related habitats. We synthesize results of studies examining fungal effects on bee behavior, development, survival, and fitness. We find that fungal communities differ across habitats, with some groups restricted mostly to flowers (Metschnikowia), while others are present almost exclusively in stored provisions (Zygosaccharomyces). Starmerella yeasts are found in multiple habitats in association with many bee species. Bee species differ widely in the abundance and identity of fungi hosted. Functional studies suggest that yeasts affect bee foraging, development, and pathogen interactions, though few bee and fungal taxa have been examined in this context. Rarely, fungi are obligately beneficial symbionts of bees, whereas most are facultative bee associates with unknown or ecologically contextual effects. Fungicides can reduce fungal abundance and alter fungal communities associated with bees, potentially disrupting bee-fungi associations. We recommend that future study focus on fungi associated with non-honeybee species and examine multiple bee life stages to document fungal composition, abundance, and mechanistic effects on bees.

Colonization of Honey Bee Digestive Tracts by Environmental Yeast Lachancea thermotolerans Is Naturally Occurring, Temperature Dependent, and Impacts the Microbiome of Newly Emerged Bees

Honey bees are critical pollinators in both agricultural and ecological settings. Recent declines in honey bee colonies in the United States have put increased strain on agricultural pollination. Although there are many environmental stressors implicated in honey bee disease, there has been intensifying focus on the role of microbial attacks on honey bee health. Despite the long-standing appreciation for the association of fungi of various groups with honey bees and their broader environment, the effects of these interactions on honey bee health are incompletely understood. Here, we report the discovery of colonization of the honey bee digestive tract by the environmental yeast Lachancea thermotolerans. Experimental colonization of honey bee digestive tracts by L. thermotolerans revealed that this yeast species maintains high levels in the honey bee midgut only at temperatures below the typical colony temperature. In newly eclosed bees, L. thermotolerans colonization alters the microbiome, suggesting that environmental yeasts can impact its composition. Future studies should be undertaken to better understand the role of L. thermotolerans and other environmental yeasts in honey bee health. IMPORTANCE Although many fungal species are found in association with honey bees and their broader environment, the effects of these interactions on honey bee health are largely unknown. Here, we report the discovery that a yeast commonly found in the environment can be found at high levels in honey bee digestive tracts. Experimentally feeding this yeast to honey bees showed that the yeast's ability to maintain high levels in the digestive tract is influenced by temperature and can lead to alterations of the microbiome in young bees. These studies provide a foundation for future studies to better understand the role of environmental yeasts in honey bee health.

The effects of urban land use gradients on wild bee microbiomes

Bees and their microbes interact in complex networks in which bees form symbiotic relationships with their bacteria and fungi. Microbial composition and abundance affect bee health through nutrition, immunity, and fitness. In ever-expanding urban landscapes, land use development changes bee habitats and floral resource availability, thus altering the sources of microbes that wild bees need to establish their microbiome. Here, we implement metabarcoding of the bacterial 16S and fungal ITS regions to characterize the diversity and composition of the microbiome in 58 small carpenter bees, Ceratina calcarata, across urban land use gradients (study area 6,425 km2). By categorizing land use development, green space, precipitation, and temperature variables as indicators of habitat across the city, we found that land use variables can predict microbial diversity. Microbial composition was also found to vary across urban land use gradients, with certain microbes such as Acinetobacter and Apilactobacillus overrepresented in less urban locations and Penicillium more abundant in developed areas. Environmental features may also lead to differences in microbe interactions, as co-occurrences between bacteria and fungi varied across percent land use development, exemplified by the correlation between Methylobacterium and Sphingomonas being more prevalent in areas of higher urban development. Surrounding landscapes change the microbial landscape in wild bees and alter the relationships they have with their microbiome. As such, urban centres should consider the impact of growing cities on their pollinators' health and protect wild bees from the effects of anthropogenic activities.

Impact of genus (Geotrigona, Melipona, Scaptotrigona) in the targeted 1H-NMR organic profile, and authenticity test by interphase emulsion of honey processed in cerumen pots by stingless bees in Ecuador

The biodiversity of Ecuadorian stingless bees is almost 200 species. Traditional pot-honey harvest in Ecuador is mostly done from nests of the three genera selected here Geotrigona Moure, 1943, Melipona Illiger, 1806, and Scaptotrigona Moure, 1942. The 20 pot-honey samples collected from cerumen pots and three ethnic honeys "abeja de tierra", "bermejo", and "cushillomishki" were analyzed for qualitative and quantitative targeted 1H-NMR honey profiling, and for the Honey Authenticity Test by Interphase Emulsion (HATIE). Extensive data of targeted organic compounds (41 parameters) were identified, quantified, and described. The three honey types were compared by ANOVA. Amino acids, ethanol, hydroxymethylfurfural, aliphatic organic acids, sugars, and markers of botanical origin. The number of phases observed with the HATIE were one in Scaptotrigona and three in Geotrigona and Melipona honeys. Acetic acid (19.60 ± 1.45 g/kg) and lactic acid (24.30 ± 1.65 g/kg) were particularly high in Geotrigona honey (in contrast to 1.3 g/kg acetic acid and 1.6 g/kg lactic acid in Melipona and Scaptotrigona), and with the lowest fructose + glucose (18.39 ± 1.68) g/100g honey compared to Melipona (52.87 ± 1.75) and Scaptotrigona (52.17 ± 0.60). Three local honeys were tested using PCA (Principal Component Analysis), two were assigned with a correct declared bee origin, but "bermejo" was not a Melipona and grouped with the Scaptotrigona cluster. However after HCA (Hierarchical Cluster Analysis) the three honeys were positioned in the Melipona-Scaptotrigona cluster. This research supports targeted 1H-NMR-based profiling of pot-honey metabolomics approach for multi-parameter visualization of organic compounds, as well as descriptive and pertained multivariate statistics (HCA and PCA) to discriminate the stingless bee genus in a set of Geotrigona, Melipona and Scaptotrigona honey types. The NMR characterization of Ecuadorian honey produced by stingless bees emphasizes the need for regulatory norms. A final note on stingless bee markers in pot-honey metabolites which should be screened for those that may extract phylogenetic signals from nutritional traits of honey. Scaptotrigona vitorum honey revealed biosurfactant activity in the HATIE, originating a fingerprint Honey Biosurfactant Test (HBT) for the genus in this set of pot-honeys.

Potential effects of nectar microbes on pollinator health

Floral nectar is prone to colonization by nectar-adapted yeasts and bacteria via air-, rain-, and animal-mediated dispersal. Upon colonization, microbes can modify nectar chemical constituents that are plant-provisioned or impart their own through secretion of metabolic by-products or antibiotics into the nectar environment. Such modifications can have consequences for pollinator perception of nectar quality, as microbial metabolism can leave a distinct imprint on olfactory and gustatory cues that inform foraging decisions. Furthermore, direct interactions between pollinators and nectar microbes, as well as consumption of modified nectar, have the potential to affect pollinator health both positively and negatively. Here, we discuss and integrate recent findings from research on plant-microbe-pollinator interactions and their consequences for pollinator health. We then explore future avenues of research that could shed light on the myriad ways in which nectar microbes can affect pollinator health, including the taxonomic diversity of vertebrate and invertebrate pollinators that rely on this reward. This article is part of the theme issue 'Natural processes influencing pollinator health: from chemistry to landscapes'.

Do amino and fatty acid profiles of pollen provisions correlate with bacterial microbiomes in the mason bee Osmia bicornis?

Bee performance and well-being strongly depend on access to sufficient and appropriate resources, in particular pollen and nectar of flowers, which constitute the major basis of bee nutrition. Pollen-derived microbes appear to play an important but still little explored role in the plant pollen-bee interaction dynamics, e.g. through affecting quantities and ratios of important nutrients. To better understand how microbes in pollen collected by bees may affect larval health through nutrition, we investigated correlations between the floral, bacterial and nutritional composition of larval provisions and the gut bacterial communities of the solitary megachilid bee Osmia bicornis. Our study reveals correlations between the nutritional quality of pollen provisions and the complete bacterial community as well as individual members of both pollen provisions and bee guts. In particular pollen fatty acid profiles appear to interact with specific members of the pollen bacterial community, indicating that pollen-derived bacteria may play an important role in fatty acid provisioning. As increasing evidence suggests a strong effect of dietary fatty acids on bee performance, future work should address how the observed interactions between specific fatty acids and the bacterial community in larval provisions relate to health in O. bicornis. This article is part of the theme issue 'Natural processes influencing pollinator health: from chemistry to landscapes'.

Sweet solutions: nectar chemistry and quality

Nectar, the main floral reward for pollinators, varies greatly in composition and concentration. The assumption that nectar quality is equivalent to its sugar (energy) concentration is too simple. Diverse non-sugar components, especially amino acids and secondary metabolites, play various roles in nutrition and health of pollinators. Many nectar compounds have indirect effects by altering the foraging behaviour of pollinators or protecting them from disease. This review also emphasizes the water component of nectar, often ignored because of evaporative losses and difficulties in sampling small nectar volumes. Nectar properties vary with environmental factors, pollinator visits and microbial contamination. Pollination mutualisms depend on the ability of insect and vertebrate pollinators to cope with and benefit from the variation and diversity in nectar chemistry. This article is part of the theme issue 'Natural processes influencing pollinator health: from chemistry to landscapes'.

Going wild: ecology and genomics are crucial to understand yeast evolution

Improved and more accessible genome-sequencing approaches have allowed the analysis of large sets of natural yeast isolates. As a consequence, this unprecedented level of description of yeast-genome characteristics and variations in natural environments has provided crucial insights on yeast ecology and evolution. Here, we review some of the most relevant and intriguing aspects of yeast evolution pointed out, thanks to the combination of yeast ecology and genomics, and critically examine the resulting improvement of our knowledge on this field. Only integrated approaches, taking into consideration not only the characteristics of the microbe but also those of the hosting environment, will significantly move forward the exploration of yeast diversity, ecology, and evolution.

Isolation, identification, and characterization of wild budding yeasts from rose flowers in Fukuyama city, Hiroshima, Japan, and their application in bread and wine production

In this study, we isolated 741 wild budding yeast strains from the flowers of 45 rose cultivars growing in Fukuyama city, Hiroshima, Japan. Of these 741 strains, 21 were found to have high fermentation abilities in yeast extract-peptone-dextrose (YPD) medium. Four of the 21 strains were able to ferment bread dough to make bread. These yeasts were identified as Saccharomyces cerevisiae, Lachancea fermentati, Lachancea kluyveri, and a Torulaspora sp. based on DNA sequences from the 26S rDNA D1/D2 regions. The CO₂ production profiles of the bread dough generated by the rose yeasts were evaluated using a Fermograph. Saccharomyces cerevisiae FRY2915 exhibited the highest fermentation capacity. Furthermore, FRY2915 was able to ferment grape juice to produce wine, yielding an alcohol concentration of more than 12%. The four rose yeasts isolated during this study have the potential to produce various types of unique fermented foods, thus enhancing the value of the microbiota associated with rose flowers.