Effects of different artificial diets on commercial honey bee colony performance, health biomarkers, and gut microbiota

Enhancing Honey Bee Health: Evaluating Pollen Substitute Diets in Field and Cage Experiments

Honey bees (Apis mellifera L.) play vital roles as agricultural pollinators and honey producers. However, global colony losses are increasing due to multiple stressors, including malnutrition. Our study evaluated the effects of four pollen substitute diets (Diet 1, Diet 2, Diet 3, and Control) through field and cage experiments, analyzing 11 parameters and 21 amino acids. Notably, Diet 1 demonstrated significantly superior performance in the field experiment, including the number of honey bees, brood area, consumption, preference, colony weight, and honey production. In the cage experiment, Diet 1 also showed superior performance in dried head and thorax weight and vitellogenin (vg) gene expression levels. Canonical discriminant and principle component analyses highlighted Diet 1's distinctiveness, with histidine, diet digestibility, consumption, vg gene expression levels, and isoleucine identified as key factors. Arginine showed significant correlations with a wide range of parameters, including the number of honey bees, brood area, and consumption, with Diet 1 exhibiting higher levels. Diet 1, containing apple juice, soytide, and Chlorella as additive components, outperformed the other diets, suggesting an enhanced formulation for pollen substitute diets. These findings hold promise for the development of more effective diets, potentially contributing to honey bee health.

Vairimorpha (Nosema) ceranae can promote Serratia development in honeybee gut: an underrated threat for bees?

The genus Serratia harbors opportunistic pathogenic species, among which Serratia marcescens is pathogenic for honeybees although little studied. Recently, virulent strains of S. marcescens colonizing the Varroa destructor mite's mouth were found vectored into the honeybee body, leading to septicemia and death. Serratia also occurs as an opportunistic pathogen in the honeybee's gut with a low absolute abundance. The Serratia population seems controlled by the host immune system, but its presence may represent a hidden threat, ready to arise when honeybees are weakened by biotic and abiotic stressors. To shed light on the Serratia pathogen, this research aims at studying Serratia's development dynamics in the honeybee body and its interactions with the co-occurring fungal pathogen Vairimorpha ceranae. Firstly, the degree of pathogenicity and the ability to permeate the gut epithelial barrier of three Serratia strains, isolated from honeybees and belonging to different species (S. marcescens, Serratia liquefaciens, and Serratia nematodiphila), were assessed by artificial inoculation of newborn honeybees with different Serratia doses (104, 106, and 108 cells/mL). The absolute abundance of Serratia in the gut and in the hemocoel was assessed in qPCR with primers targeting the luxS gene. Moreover, the absolute abundance of Serratia was assessed in the gut of honeybees infected with V. ceranae at different development stages and supplied with beneficial microorganisms and fumagillin. Our results showed that all tested Serratia strains could pass through the gut epithelial barrier and proliferate in the hemocoel, with S. marcescens being the most pathogenic. Moreover, under cage conditions, Serratia better proliferates when a V. ceranae infection is co-occurring, with a positive and significant correlation. Finally, fumagillin and some of the tested beneficial microorganisms could control both Serratia and Vairimorpha development. Our findings suggest a correlation between the two pathogens under laboratory conditions, a co-occurring infection that should be taken into consideration by researches when testing antimicrobial compounds active against V. ceranae, and the related honeybees survival rate. Moreover, our findings suggest a positive control of Serratia by the environmental microorganism Apilactobacillus kunkeei in a in vivo model, confirming the potential of this specie as beneficial bacteria for honeybees.

Prospects of probiotics in beekeeping: a review for sustainable approach to boost honeybee health

Honeybees are vital for global crop pollination, making indispensable contributions to agricultural productivity. However, these vital insects are currently facing escalating colony losses on a global scale, primarily attributed to parasitic and pathogenic attacks. The prevalent response to combat these infections may involve the use of antibiotics. Nevertheless, the application of antibiotics raises concerns regarding potential adverse effects such as antibiotic resistance and imbalances in the gut microbiota of bees. In response to these challenges, this study reviews the utilization of a probiotic-supplemented pollen substitute diet to promote honeybee gut health, enhance immunity, and overall well-being. We systematically explore various probiotic strains and their impacts on critical parameters, including survival rate, colony strength, honey and royal jelly production, and the immune response of bees. By doing so, we emphasize the significance of maintaining a balanced gut microbial community in honeybees. The review also scrutinizes the factors influencing the gut microbial communities of bees, elucidates the consequences of dysbiosis, and evaluates the potential of probiotics to mitigate these challenges. Additionally, it delineates different delivery mechanisms for probiotic supplementation and elucidates their positive effects on diverse health parameters of honeybees. Given the alarming decline in honeybee populations and the consequential threat to global food security, this study provides valuable insights into sustainable practices aimed at supporting honeybee populations and enhancing agricultural productivity.

Comparative Study of the Effect of Pollen Substitute Diets on Honey Bees during Early Spring

The nutritional quality of a colony significantly affects its health and strength, particularly because it is required for population growth in the early spring. We investigated the impact of various artificial pollen substitute diets on colony performance in the Republic of Korea during early spring, a critical period for colony health and growth. The colonies were provided with different diets, including the commercial product Megabee (positive control), our developed diet Test A, and four upgraded versions (Diet 1, Diet 2, Diet 3, and Diet 4) of Test A. The negative control group received no supplementary feed. Over 63 days, we observed 24 experimental colonies and assessed various parameters at the colony and individual levels. The results revealed that Diet 2 had the highest consumption and had the most positive impact on population growth, the capped brood area, colony weight, honey bees' weight, and vitellogenin levels. These findings suggested that Diet 2 is most attractive to honey bees and thus holds great promise for improving colony maintenance and development during the crucial early spring period.

Pollen Diet Diversity does not Affect Gut Bacterial Communities or Melanization in a Social and Solitary Bee Species

Pollinators face many stressors, including reduced floral diversity. A low-diversity diet can impair organisms' ability to cope with additional stressors, such as pathogens, by altering the gut microbiome and/or immune function, but these effects are understudied for most pollinators. We investigated the impact of pollen diet diversity on two ecologically and economically important generalist pollinators, the social bumble bee (Bombus impatiens) and the solitary alfalfa leafcutter bee (Megachile rotundata). We experimentally tested the effect of one-, two-, or three-species pollen diets on gut bacterial communities in both species, and the melanization immune response in B. impatiens. Pollen diets included dandelion (Taraxacum officinale), staghorn sumac (Rhus typhina), and hawthorn (Crataegus sp.) alone, each pair-wise combination, or a mix of all three species. We fed bees their diet for 7 days and then dissected out guts and sequenced 16S rRNA gene amplicons to characterize gut bacterial communities. To assess melanization in B. impatiens, we inserted microfilament implants into the bee abdomen and measured melanin deposition on the implant. We found that pollen diet did not influence gut bacterial communities in M. rotundata. In B. impatiens, pollen diet composition, but not diversity, affected gut bacterial richness in older, but not newly-emerged bees. Pollen diet did not affect the melanization response in B. impatiens. Our results suggest that even a monofloral, low-quality pollen diet such as dandelion can support diverse gut bacterial communities in captive-reared adults of these bee species. These findings shed light on the effects of reduced diet diversity on bee health.

A case study of the diet-microbiota-parasite interplay in bumble bees

AIMS

Diets and parasites influence the gut bacterial symbionts of bumble bees, but potential interactive effects remain overlooked. The main objective of this study was to assess the isolated and interactive effects of sunflower pollen, its phenolamides, and the widespread trypanosomatid Crithidia sp. on the gut bacterial symbionts of Bombus terrestris males.

METHODS AND RESULTS

Bumble bee males emerged in microcolonies fed on either (i) willow pollen (control), (ii) sunflower pollen, or (iii) willow pollen spiked with phenolamide extracts from sunflower pollen. These microcolonies were infected by Crithidia sp. or were pathogen-free. Using 16S rRNA amplicon sequencing (V3-V4 region), we observed a significant alteration of the beta diversity but not of the alpha diversity in the gut microbial communities of males fed on sunflower pollen compared to males fed on control pollen. Similarly, infection by the gut parasite Crithidia sp. altered the beta diversity but not the alpha diversity in the gut microbial communities of males, irrespective of the diet. By contrast, we did not observe any significant alteration of the beta or alpha diversity in the gut microbial communities of males fed on phenolamide-enriched pollen compared to males fed on control pollen. Changes in the beta diversity indicate significant dissimilarities of the bacterial taxa between the treatment groups, while the lack of difference in alpha diversity demonstrates no significant changes within each treatment group.

CONCLUSIONS

Bumble bees harbour consistent gut microbiota worldwide, but our results suggest that the gut bacterial communities of bumble bees are somewhat shaped by their diets and gut parasites as well as by the interaction of these two factors. This study confirms that bumble bees are suitable biological surrogates to assess the effect of diet and parasite infections on gut microbial communities.

Gut Transplants from Bees Fed an Antipathogenic Pollen Diet Do Not Confer Pathogen Resistance to Recipients

Pollinators are threatened by diverse stressors, including microbial pathogens such as Crithidia bombi. Consuming sunflower pollen dramatically reduces C. bombi infection in the bumble bee Bombus impatiens, but the mechanism behind this medicinal effect is unclear. We asked whether diet mediates resistance to C. bombi through changes in the gut microbiome. We hypothesized that sunflower pollen changes the gut microbiome, which in turn reduces Crithidia infection. To test this, we performed a gut transplant experiment. We fed donor bees either a sunflower pollen treatment or buckwheat pollen as a control treatment and then inoculated recipient bees with homogenized guts from either sunflower-fed or buckwheat-fed donor bees. All recipient bees were then fed a wildflower pollen diet. Two days after the transplant, we infected recipients with C. bombi, and 2 days later, we provided another donor gut transplant. To quantify infection, we performed both fecal screens and dissections of the recipient bees. We found no significant differences in C. bombi infection intensity or presence between bees that received sunflower-fed microbiomes versus buckwheat-fed microbiomes. This suggests that sunflower pollen's effects on pathogen resistance are not mediated by gut microbiota.

Effects of ingested essential oils and propolis extracts on honey bee (Hymenoptera: Apidae) health and gut microbiota

Managed honey bee (Hymenoptera: Apidae: Apis mellifera Linnaeus) hives require frequent human inputs to maintain colony health and productivity. A variety of plant natural products (PNPs) are delivered via feeding to control diseases and reduce the use of synthetic chemical treatments. However, despite their prevalent use in beekeeping, there is limited information regarding the impact of ingested PNPs on bee health. Here, we tested the effects of different essential oils and propolis extracts on honey bee life span, nutrient assimilation, xenobiotic detoxification, and gut microbiota abundance. Brazilian propolis extract lengthened worker life span, while the other PNPs (Louisiana propolis extract, lemongrass oil, spearmint oil, and thyme oil) exerted variable and dose-dependent effects on life span. Vitellogenin (vg) gene expression was reduced by Brazilian propolis extract at high doses. Expression of CYP6AS1, a detoxification-related gene, was reduced by low doses of thyme oil. The abundances of 8 core gut microbiota taxa were largely unaffected by host consumption of PNPs. Our results suggest that in addition to propolis's structural and immunomodulatory roles in the colony, it may also exert beneficial health effects when ingested. Thyme oil, a commonly used hive treatment, was toxic at field-realistic dosages, and its use as a feed additive should be viewed with caution until its effects on bee health are more thoroughly investigated. We conclude that the tested propolis extracts, lemongrass oil, and spearmint oil are generally safe for bee consumption, with some apparent health-promoting effects.

Hive Transplantation Has Minimal Impact on the Core Gut Microbiome of the Australian Stingless Bee, Tetragonula carbonaria

Bacteria residing in the guts of pollinating insects play a key role in nutrient acquisition, digestion, and resistance to pests and diseases. Imbalances in microbial flora in response to environmental change and stress can therefore impact insect health and resilience. This study is aimed at defining the core gut microbiome of the Australian native stingless bee, Tetragonula carbonaria, and exploring the impact of colony transplantation on gut health. The gut microbiomes of nine forager bees from natural (log) and manufactured (box) hives were examined via 16S rRNA gene amplicon sequencing. Some differences were observed at the ASV level between the microbiomes of log and box hive bees. However, a core microbiome, dominated by Lactobacillus spp., unclassified Acetobacteraceae spp., and Bombella spp., was maintained. Further, the inferred functional potential of the microbiomes was consistent across all individuals. This study highlights that although hive transplantation has an impact on the overall diversity of stingless bee gut microbiomes, it is unlikely to have a significant negative impact on the overall health and resilience of the colony.

Delivery mechanism can enhance probiotic activity against honey bee pathogens

Managed honey bee (Apis mellifera) populations play a crucial role in supporting pollination of food crops but are facing unsustainable colony losses, largely due to rampant disease spread within agricultural environments. While mounting evidence suggests that select lactobacilli strains (some being natural symbionts of honey bees) can protect against multiple infections, there has been limited validation at the field-level and few methods exist for applying viable microorganisms to the hive. Here, we compare how two different delivery systems-standard pollen patty infusion and a novel spray-based formulation-affect supplementation of a three-strain lactobacilli consortium (LX3). Hives in a pathogen-dense region of California are supplemented for 4 weeks and then monitored over a 20-week period for health outcomes. Results show both delivery methods facilitate viable uptake of LX3 in adult bees, although the strains do not colonize long-term. Despite this, LX3 treatments induce transcriptional immune responses leading to sustained decreases in many opportunistic bacterial and fungal pathogens, as well as selective enrichment of core symbionts including Bombilactobacillus, Bifidobacterium, Lactobacillus, and Bartonella spp. These changes are ultimately associated with greater brood production and colony growth relative to vehicle controls, and with no apparent trade-offs in ectoparasitic Varroa mite burdens. Furthermore, spray-LX3 exerts potent activities against Ascosphaera apis (a deadly brood pathogen) likely stemming from in-hive dispersal differences, whereas patty-LX3 promotes synergistic brood development via unique nutritional benefits. These findings provide a foundational basis for spray-based probiotic application in apiculture and collectively highlight the importance of considering delivery method in disease management strategies.

Low Levels of Hive Stress Are Associated with Decreased Honey Activity and Changes to the Gut Microbiome of Resident Honey Bees

Honey bees (Apis mellifera) face increasing threats to their health, particularly from the degradation of floral resources and chronic pesticide exposure. The properties of honey and the bee gut microbiome are known to both affect and be affected by bee health. Using samples from healthy hives and hives showing signs of stress from a single apiary with access to the same floral resources, we profiled the antimicrobial activity and chemical properties of honey and determined the bacterial and fungal microbiome of the bee gut and the hive environment. We found honey from healthy hives was significantly more active than honey from stressed hives, with increased phenolics and antioxidant content linked to higher antimicrobial activity. The bacterial microbiome was more diverse in stressed hives, suggesting they may have less capacity to exclude potential pathogens. Finally, bees from healthy and stressed hives had significant differences in core and opportunistically pathogenic taxa in gut samples. Our results emphasize the need for understanding and proactively managing bee health. IMPORTANCE Honey bees serve as pollinators for many plants and crops worldwide and produce valuable hive products such as honey and wax. Various sources of stress can disrupt honey bee colonies, affecting their health and productivity. Growing evidence suggests that honey is vitally important to hive functioning and overall health. In this study, we determined the antimicrobial activity and chemical properties of honey from healthy hives and hives showing signs of stress, finding that honey from healthy hives was significantly more antimicrobial, with increased phenolics and antioxidant content. We next profiled the bacterial and fungal microbiome of the bee gut and the hive environment, finding significant differences between healthy and stressed hives. Our results underscore the need for greater understanding in this area, as we found even apparently minor stress can have implications for overall hive fitness as well as the economic potential of hive products.

Homeostatic Regulation of the Duox-ROS Defense System: Revelations Based on the Diversity of Gut Bacteria in Silkworms (Bombyx mori)

The Duox-ROS defense system plays an important role in insect intestinal immunity. To investigate the role of intestinal microbiota in Duox-ROS regulation herein, 16S rRNA sequencing technology was utilized to compare the characteristics of bacterial populations in the midgut of silkworm after different time-periods of treatment with three feeding methods: 1-4 instars artificial diet (AD), 1-4 instars mulberry leaf (ML) and 1-3 instars artificial diet + 4 instar mulberry leaf (TM). The results revealed simple intestinal microbiota in the AD group whilst microbiota were abundant and variable in the ML and TM silkworms. By analyzing the relationship among intestinal pH, reactive oxygen species (ROS) content and microorganism composition, it was identified that an acidic intestinal environment inhibited the growth of intestinal microbiota of silkworms, observed concurrently with low ROS content and a high activity of antioxidant enzymes (SOD, TPX, CAT). Gene expression associated with the Duox-ROS defense system was detected using RT-qPCR and identified to be low in the AD group and significantly higher in the TM group of silkworms. This study provides a new reference for the future improvement of the artificial diet feeding of silkworm and a systematic indicator for the further study of the relationship between changes in the intestinal environment and intestinal microbiota balance caused by dietary alterations.

Honey Production and Climate Change: Beekeepers' Perceptions, Farm Adaptation Strategies, and Information Needs

Because climate change has severely impacted global bee populations by depleting their habitats and food sources, beekeepers must implement management practices to adapt to changing climates. However, beekeepers in El Salvador lack information about necessary climate change adaptation strategies. This study explored Salvadoran beekeepers' experiences adapting to climate change. The researchers used a phenomenological case study approach and conducted semi-structured interviews with nine Salvadoran beekeepers who were members of The Cooperative Association for Marketing, Production, Savings, and Credit of Beekeepers of Chalatenango (ACCOPIDECHA). The beekeepers perceived water and food scarcity, as well as extreme weather events (e.g., increasing temperature, rain, winds), as the leading climate change-induced challenges to their production. Such challenges have augmented their honey bees' physiological need for water, limited their movement patterns, decreased apiary safety, and increased the incidence of pests and diseases, all of which have led to honey bee mortality. The beekeepers shared adaptation strategies, including box modification, apiary relocation, and food supplementation. Although most beekeepers accessed climate change information using the internet, they struggled to understand and apply pertinent information unless they received it from trusted ACCOPIDECHA personnel. Salvadoran beekeepers require information and demonstrations to improve their climate change adaptation strategies and implement new ones to address the challenges they experience.

The microbiome and gene expression of honey bee workers are affected by a diet containing pollen substitutes

Pollen is the primary source of dietary protein for honey bees. It also includes complex polysaccharides in its outer coat, which are largely indigestible by bees but can be metabolized by bacterial species within the gut microbiota. During periods of reduced availability of floral pollen, supplemental protein sources are frequently provided to managed honey bee colonies. The crude proteins in these supplemental feeds are typically byproducts from food manufacturing processes and are rarely derived from pollen. Our experiments on the impact of different diets showed that a simplified pollen-free diet formulated to resemble the macronutrient profile of a monofloral pollen source resulted in larger microbial communities with reduced diversity, reduced evenness, and reduced levels of potentially beneficial hive-associated bacteria. Furthermore, the pollen-free diet sharply reduced the expression of genes central to honey bee development. In subsequent experiments, we showed that these shifts in gene expression may be linked to colonization by the gut microbiome. Lastly, we demonstrated that for bees inoculated with a defined gut microbiota, those raised on an artificial diet were less able to suppress infection from a bacterial pathogen than those that were fed natural pollen. Our findings demonstrate that a pollen-free diet significantly impacts the gut microbiota and gene expression of honey bees, indicating the importance of natural pollen as a primary protein source.

Honey Bees Prefer Pollen Substitutes Rich in Protein Content Located at Short Distance from the Apiary

The availability of floral resources is crucial for honey bee colonies because it allows them to obtain protein from pollen and carbohydrates from nectar; typically, they consume these nutrients in the form of bee bread, which has undergone fermentation. However, the intensification of agriculture, urbanization, changes to the topography, and harsh environmental conditions are currently impacting foraging sites due to habitat loss and scarcity of food resources. Thus, this study aimed to assess honey bee preference for various pollen substitute diet compositions. Bee colonies perform poorly because of specific environmental problems, which ultimately result in pollen scarcity. Pollen substitutes located at various distance from the bee hive were also investigated in addition to determining the preferences of honey bees for various pollen substitute diets. The local honey bee (Apis mellifera jemenitica) colonies and different diets (four main treatments, namely, chickpea flour, maize flour, sorghum flour, wheat flour; each flour was further mixed with cinnamon powder, turmeric powder, flour only, flour mixed with both cinnamon and turmeric powder) were used. Bee pollen was used as a control. The best performing pollen substitutes were further placed at 10, 25, and 50 m distances from the apiary. Maximum bee visits were observed on bee pollen (210 ± 25.96) followed by chickpea flour only (205 ± 19.32). However, there was variability in the bee visits to the different diets (F (16,34) = 17.91; p < 0.01). In addition, a significant difference in diet consumption was observed in control (576 ± 58.85 g) followed by chickpea flour only (463.33 ± 42.84 g), compared to rest of the diets (F (16,34) = 29.75; p < 0.01). Similarly, foraging efforts differed significantly (p < 0.01) at the observed time of 7-8 A.M., 11-12 A.M., and 4-5 P.M. at the distance of 10, 25, and 50 m away from the apiary. Honey bees preferred to visit the food source that was closest to the hive. This study should be very helpful for beekeepers in supplementing their bee colonies when there is a shortage or unavailability of pollens, and it is much better to keep the food source near the apiary. Future research needs to highlight the effect of these diets on bee health and colony development.

Flight performance of pollen starved honey bees and incomplete compensation through ingestion after early life pollen deprivation

We investigated the effect of adult honey bee pollen nutrition on the flight performance of honey bees. Therefore, caged bees were allowed to perform 30 min of defecation/training flights every second day before flight performance of pollen-fed bees and pollen-deprived bees older than 16 days were compared in a flight mill. We first fed 10 µL of 1 M glucose solution to bees, and after they metabolized this during flight, they were fed 10 µL of 2 M glucose solution for a second flight test. Pollen-deprived bees flew longer and further than pollen-fed bees in both flights. Pollen-fed bees flew faster in the early period at the beginning of flights, whereas pollen-deprived bees were faster in the final phases. Pollen-fed bees were able to raise their maximum flight speed in 2 M glucose solution flights, whereas pollen-constraint bees were not. The two groups did not differ in abdomen fresh weight, but the fresh weight of the head and thorax and dry weight of the head, thorax and abdomen were higher in pollen-fed bees. In a second experiment, we constrained pollen consumption of caged bees during the first 7 days and compared daily consumption of bees from day 8-16 to consumption of bees unrestricted in pollen. We found that pollen-deprived bees perceive the pollen shortage and try to compensate for their needs by consuming significantly more pollen at the later phase of their life than pollen-fed bees of the same age. Still, bees constrained from pollen in the first 7 days did only reach 51.1% of the lifetime consumption of unconstrained bees. This shows that bees can sense the need for essential nutrients from pollen, but their physiological apparatus does not allow them to fully compensate for their early life constraint. Pollen deprivation only in the first 7 days of worker life likewise significantly reduced fresh and dry weights of the body sections (head, thorax, and abdomen) and survival. This underlines the importance of protein consumption in a short critical period early in adult bees' lives for their development and their performance later in life.

Fine-scale assessment of Chlorella syrup as a nutritional supplement for honey bee colonies

Habitat loss, climate change, and global agriculture have a non-negligible effect on the reduced abundance and diversity of floral resources. Malnutrition and nutritional stress are consequences of the combination of these factors with considerable impact on honey bee health and colony losses. The solution to inadequate natural sources for beekeeping is the additional feeding of honey bee colonies with food supplements. The algae Chlorella is a natural food source, with a nutrient profile similar to natural pollen, thus it has promising application in beekeeping. We evaluated Chlorella vulgaris syrup as a dietary supplement in the view of the oxidative stress that may be caused by long term administration to the colonies. Consuming Chlorella syrup did not influence the activity of digestive enzymes of summer honey bee workers, however, lipase activity insignificantly increased. After Chlorella application to colonies, we also observed insignificantly higher gene expression of antioxidant enzymes catalase and superoxid dismutase1 in adult workers; however, in larvae the expression of those genes was not affected. Surprisingly, the gene expression did not correspond with enzyme activity in adult bee abdomens. In Chlorella fed colonies, we recorded a higher concentration of vitellogenin, which plays multiple roles in honey bee physiology, i.e., antioxidant, storage protein, or immunity-related functions. Our new findings brought evidence that Chlorella did not negatively affect the digestion or oxidative balance of honey bees, thus its application as a pollen supplement can be fully recommended for maintaining the health of honey bee colonies during periods of dearth.

Uses and benefits of algae as a nutritional supplement for honey bees

Honey bees are essential agricultural pollinators that are threatened by various interacting stressors, posing risks to beekeeping industries and human food security. Malnutrition is a major factor underlying managed bee colony losses that can be countered by feeding artificial diets, which aim to deliver essential macro- and micronutrients. Current bee nutritional supplements show room for improvement and require resources that compete with human food production. Algae and microalgae in particular have been gaining traction in the literature as alternative feed sources and nutritional supplements for livestock, including honey bees. Herein, we review the current literature and categorize the effects of algae supplementation on honey bee colony productivity as well as effects on individual bee physiology and health. In general, we conclude that algae biomass appears to be suitable for use as a bee feed additive and as a source of health-stimulating natural products. Additionally, we suggest research areas that could improve the development of sustainable algae-based nutrition supplements for honey bees.

Changes in Vitellogenin (Vg) and Stress Protein (HSP 70) in Honey Bee (Apis mellifera anatoliaca) Groups under Different Diets Linked with Physico-Chemical, Antioxidant and Fatty and Amino Acid Profiles

Honey bee colonies are often subjected to diseases, nutrition quality, temperature and other stresses depending on environmental and climatic conditions. As a result of malnutrition, the level of Vg protein decreases, leading to overwintering losses. The Vg values must be high for a successful wintering, especially before wintering. If good nutrition is not reached, the long winter period may cause an increase in colony losses. Supplementary feeding is essential for colony sustainability when floral resources are insufficient, as in recent years with the emerging climate changes. Furthermore, quality food sources or nutrients are significant for maintaining honey bee health and longevity. This study examined the changes in HSP 70 and Vg proteins in 6 groups of 48 colonies fed with five different nutrients. The fatty acids that are present in the highest amount in Cistus creticus (Pink rock-rose), Papaver somniferum (Opium poppy) and mixed pollen samples were linoleic, palmitic and cis-9-oleic acids. The highest values in proline, lysine and glutamic acid were determined in C. creticus pollen. Regarding the P. somniferum pollen, the highest values were observed in lysine, proline, glutamic and aspartic acids. The highest values in lysine, proline, leucine and aspartic acid were noticed in mixed pollen. The effect of different feeding on Vg protein in nurse and forager bee samples was higher in the mixed pollen group in the fall period. In nurse bees, the mixed pollen group was followed by Cistus creticus pollen > Papaver somniferum pollen > sugar syrup > commercial bee cake > control group, respectively (p < 0.05). In forager bees, the order was mixed pollen, P. somniferum pollen, C. creticus pollen, commercial bee cake, sugar syrup and control. In the early spring period, the Vg levels were high in the mixed pollen group in the nurse bees and the commercial bee cake group in the forager bees. In the fall period, the HSP 70 value of the forager and nurse bees was the lowest in the C. creticus group (p < 0.05). In early spring, the active period of flora, a statistical difference was found between the treatment groups.

Bumble Bee Breeding on Artificial Pollen Substitutes

Bumble bees are important pollinators for many temperate crops. Because of the growing demand for food from entomophilous crops, bumble bee colonies are commercially reared and placed in fields or greenhouses to guarantee sufficient pollination services. Besides, commercial colonies are increasingly used in laboratories for various bioassays under controlled conditions. For both usages, bumble bee colonies are commonly provided with sugar solution and honey bee-collected pollen pellets. However, the latter display several disadvantages since they may contain pollutants, pathogens, or toxic phytochemicals. Consequently, companies have developed pollen-free artificial diets to sustain colonies. Such diets are designed to boost worker health in the field, in complement of floral pollen collected by workers outside the colonies, but their suitability in 'closed' systems without access to floral pollen, such as in laboratory bioassays, is arguable. Here, we used microcolonies of the commercially important bumble bee Bombus terrestris L. (Hymenoptera: Apidae) to assess the suitability of five artificial pollen substitutes and three mixed diets. We also assessed the evaporation rate of the different diets as it could impact their suitability. At the end of the bioassays, microcolonies fed the artificial diets showed a reduced offspring development when compared to microcolonies fed natural pollen, which was partly offset by mixing these diets with natural pollen. By contrast, the artificial diets did not have deleterious effects on worker's health. We discuss the potential nutritional and physical causes of artificial diets unsuitability for offspring development and encourage further research to accordingly establish appropriate pollen-free diets for bumble bee breeding.

Metabolomics-Guided Comparison of Pollen and Microalgae-Based Artificial Diets in Honey Bees

Managed honey bee colonies used for crop pollination are fed artificial diets to offset nutritional deficiencies related to land-use intensification and climate change. In this study, we formulated novel microalgae diets using Chlorella vulgaris and Arthrospira platensis (spirulina) biomass and fed them to young adult honey bee workers. Diet-induced changes in bee metabolite profiles were studied relative to a natural pollen diet using liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS) metabolomics. Untargeted analyses of pollen- and microalgae-fed bees revealed significant overlap, with 248 shared features determined by LC-MS and 87 shared features determined by GC-MS. Further metabolomic commonalities were evident upon subtraction of unique diet features. Twenty-five identified metabolites were influenced by diet, which included complex lipids, essential fatty acids, vitamins, and phytochemicals. The metabolomics results are useful to understand mechanisms underlying favorable growth performance as well as increased antioxidant and heat shock protein gene expression in bees fed the microalgae diets. We conclude that the tested microalgae have potential as sustainable feed additives and as a source of bee health-modulating natural products. Metabolomics-guided diet development could eventually help tailor feed interventions to achieve precision nutrition in honey bees and other livestock animals.

Pollinator nutrition and its role in merging the dual objectives of pollinator health and optimal crop production

Bee and non-bee insect pollinators play an integral role in the quantity and quality of production for many food crops, yet there is growing evidence that nutritional challenges to pollinators in agricultural landscapes are an important factor in the reduction of pollinator populations worldwide. Schemes to enhance crop pollinator health have historically focused on floral resource plantings aimed at increasing pollinator abundance and diversity by providing more foraging opportunities for bees. These efforts have demonstrated that improvements in bee diversity and abundance are achievable; however, goals of increasing crop pollination outcomes via these interventions are not consistently met. To support pollinator health and crop pollination outcomes in tandem, habitat enhancements must be tailored to meet the life-history needs of specific crop pollinators, including non-bees. This will require greater understanding of the nutritional demands of these taxa together with the supply of floral and non-floral food resources and how these interact in cropping environments. Understanding the mechanisms underlying crop pollination and pollinator health in unison across a range of taxa is clearly a win–win for industry and conservation, yet achievement of these goals will require new knowledge and novel, targeted methods.

This article is part of the theme issue ‘Natural processes influencing pollinator health: from chemistry to landscapes’.

Recent Advances in the Biocontrol of Nosemosis in Honey Bees (Apis mellifera L.)

Nosemosis is a disease triggered by the single-celled spore-forming fungi Nosema apis and Nosema ceranae, which can cause extensive colony losses in honey bees (Apis mellifera L.). Fumagillin is an effective antibiotic treatment to control nosemosis, but due to its toxicity, it is currently banned in many countries. Accordingly, in the beekeeping sector, there is a strong demand for alternative ecological methods that can be used for the prevention and therapeutic control of nosemosis in honey bee colonies. Numerous studies have shown that plant extracts, RNA interference (RNAi) and beneficial microbes could provide viable non-antibiotic alternatives. In this article, recent scientific advances in the biocontrol of nosemosis are summarized.