Influence of pollen nutrition on honey bee health: do pollen quality and diversity matter?

Floral resources shape parasite and pathogen dynamics in bees facing urbanization

Urbanization is associated with increases in impervious land cover, which alters the distribution of resources available to wildlife and concentrates activity in un-built spaces such as parks and gardens. How resource shifts alter the dynamics of parasite and pathogen transmission has not been addressed for many important species in urban systems. We focus on urban gardens, resource-rich "islands" within the urban matrix, to examine how the availability of floral resources at local and landscape scales influences the prevalence of 6 RNA viruses and 3 parasites in honey bees and bumble bees. Because parasites and pathogens are transmitted at flowers between visitors, we expected that floral abundance would concentrate bees within gardens, amplifying infection rates in pollinators, unless increases in floral resources would enhance bee diversity enough to dilute transmission. We found that garden size and flowering perennial plant abundance had a positive, direct effect on parasite and pathogen richness in bumble bees, suggesting that resource provisioning amplifies transmission. We also found that parasitism rates in honey bees were positively associated with parasites and pathogens in bumble bees, suggesting spillover between species. Encouragingly, we found evidence that management may mitigate parasitism through indirect effects: garden size had a positive impact on bee diversity, which in-turn was negatively associated with parasite and pathogen richness in bumble bees. Unexpectedly, we observed that that parasite and pathogen richness in honey bees had no significant predictors, highlighting the complexity of comparing transmission dynamics between species. Although floral resources provide bees with food, we suggest more research on the tradeoffs between resource provisioning and disease transmission to implement conservation plantings in changing landscapes.

Sunflower pollen induces rapid excretion in bumble bees: Implications for host-pathogen interactions

Host diet can have a profound effect on host-pathogen interactions, including indirect effects on pathogens mediated through host physiology. In bumble bees (Bombus impatiens), the consumption of sunflower (Helianthus annuus) pollen dramatically reduces infection by the gut protozoan pathogen Crithidia bombi. One hypothesis for the medicinal effect of sunflower pollen is that consumption changes host gut physiological function, causing rapid excretion that flushes C. bombi from the system. We tested the effect of pollen diet and C. bombi infection on gut transit properties using a 2x2 factorial experiment in which bees were infected with C. bombi or not and fed sunflower or wildflower pollen diet. We measured several non-mutually exclusive physiological processes that underlie the insect excretory system, including gut transit time, bi-hourly excretion rate, the total number of excretion events and the total volume of excrement. Sunflower pollen significantly reduced gut transit time in uninfected bees, and increased the total number of excretion events and volume of excrement by 66 % and 68 %, respectively, in both infected and uninfected bees. Here we show that a sunflower pollen diet can affect host physiology gut function, causing more rapid and greater excretion. These results provide important insight into a mechanism that could underlie the medicinal effect of sunflower pollen for bumble bees.

High nutritional status promotes vitality of honey bees and mitigates negative effects of pesticides

Honey bee health is affected by multiple stressors, such as the exposure to plant protection products (PPPs), dietary limitation, monofloral diets and pressure of diseases and pathogens and their interactions. Here, we analysed the interacting effects of plant protection products and low nutritional pollen source on honey bee health under semi-field conditions. We established a healthy honey bee colony in each of 24 tents, planted either with monofloral maize, maize with a diverse flower strip or with monofloral Phacelia tanacetifolia. To evaluate the interaction between exposure to PPPs and nutritional status, a mixture of the insecticide thiacloprid and the fungicide prochloraz was applied. For each colony, we investigated brood capping rate as well as adult longevity, body and head weight, and enzyme activity of acetylcholinesterase and P450 reductase of newly hatched worker bees. We found a significant reduced capping rate in treated maize compared to flowering strips and Phacelia, but no interaction effect between pesticide treatment and nutritional status on capping rate. The response to treatment on the longevity of adults differed significantly between maize and Phacelia, with flower strips being intermediate, indicating interaction effects of PPP treatment and low pollen quality in maize compared to Phacelia and flowering strip treatments. Head weight of newly hatched worker bees showed significant interaction of nutritional status and treatment of PPPs. PPPs slightly increased body weight in all nutritional statuses, except for Phacelia. Enzyme activity of acetylcholinesterase and P450 reductase showed significant different responses between maize and Phacelia to PPP exposure, but not between maize and flowering strip. Our results support the hypothesis that higher pollen quality promotes development of larvae and pupae, longevity of adults and detoxification of PPPs.

Age and Season Effect the Timing of Adult Worker Honeybee Infection by Nosema ceranae

The microsporidia Nosema ceranae is an intracellular parasite of honeybees’ midgut, highly prevalent in Apis mellifera colonies for which important epidemiological information is still unknown. Our research aimed at understanding how age and season influence the onset of infection in honeybees and its development in the colony environment. Adult worker honeybees of less than 24h were marked and introduced into 6 different colonies in assays carried out in spring and autumn. Bees of known age were individually analyzed by PCR for Nosema spp. infection and those resulting positive were studied to determine the load by Real Time-qPCR. The age of onset and development of infection in each season was studied on a total of 2401 bees and the probability and the load of infection for both periods was established with two statistical models. First N. ceranae infected honeybees were detected at day 5 post emergence (p.e.; spring) and at day 4 p.e. (autumn) and in-hive prevalence increased from that point onwards, reaching the highest mean infection on day 18 p.e. (spring). The probability of infection increased significantly with age in both periods although the age variable better correlated in spring. The N. ceranae load tended to increase with age in both periods, although the age-load relationship was clearer in spring than in autumn. Therefore, age and season play an important role on the probability and the development of N. ceranae infection in honeybees, bringing important information to understand how it spreads within a colony.

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

Background

Honey bee colonies managed for agricultural pollination are highly dependent on human inputs, especially for disease control and supplemental nutrition. Hives are routinely fed artificial “pollen substitute” diets to compensate for insufficient nutritional forage in the environment. The aim of this study was to investigate the effects of different artificial diets in a northern California, US commercial beekeeping operation from August through February. This time period represents an extended forage dearth when supplemental nutrition is used to stimulate late winter colony growth prior to almond pollination in the early spring. A total of 144 honey bee colonies were divided into 8 feeding groups that were replicated at three apiary sites. Feeding groups received commercial diets (Global, Ultra Bee, Bulk Soft, MegaBee, AP23, Healthy Bees), a beekeeper-formulated diet (Homebrew), or a sugar negative control. Diets were analyzed for macronutrient and amino acid content then evaluated with respect to honey bee colony population size, average bee weight, nutrition-related gene expression, gut microbiota abundance, and pathogen levels.

Results

Replicated at three apiary sites, two pollen-containing diets (Global and Homebrew) produced the largest colonies and the heaviest bees per colony. Two diets (Bulk Soft and AP23) that did not contain pollen led to significantly larger colonies than a sugar negative control diet. Diet macronutrient content was not correlated with colony size or health biomarkers. The sum of dietary essential amino acid deficiencies relative to leucine content were correlated with average bee weight in November and colony size used for almond pollination in February. Nutrition-related gene expression, gut microbiota, and pathogen levels were influenced by apiary site, which overrode some diet effects. Regarding microbiota, diet had a significant impact on the abundance of Bifidobacterium and Gilliamella and trended towards effects on other prominent bee gut taxa.

Conclusions

Multiple colony and individual bee measures are necessary to test diet efficacy since honey bee nutritional responses are complex to evaluate. Balancing essential amino acid content relative to leucine instead of tryptophan may improve diet protein efficiency ratios. Optimization of bee diets could improve feed sustainability and agricultural pollination efficiency by supporting larger, healthier honey bee colonies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-022-03151-5.

First report of fatty acids in Mimosadiplotricha bee pollen with in vitro lipase inhibitory activity

Bee pollen (BP) is full of nutrients and phytochemicals, and so it is widely used as a health food and alternative medicine. Its composition and bioactivity mainly depend on the floral pollens. In this work, BP collected by Apis mellifera with different monoculture flowering crops (BP1-6) were used. The types of floral pollen in each BP were initially identified by morphology, and subsequently confirmed using molecular phylogenetic analysis. Data from both approaches were consistent and revealed each BP to be monofloral and derived from the flowers of Camellia sinensis L., Helianthus annuus L., Mimosa diplotricha, Nelumbo nucifera, Xyris complanata, and Ageratum conyzoides for BP1 to BP6, respectively. The crude extracts of all six BPs were prepared by sequential partition with methanol, dichloromethane (DCM), and hexane. The crude extracts were then tested for the in vitro (i) α-amylase inhibitory, (ii) acetylcholinesterase inhibitory (AChEI), and (iii) porcine pancreatic lipase inhibitory (PPLI) activities in terms of the percentage enzyme inhibition and half maximum inhibitory concentration (IC₅₀). The DCM partitioned extract of X. complanata BP (DCMXBP) had the highest active α-amylase inhibitory activity with an IC₅₀ value of 1,792.48 ± 50.56 µg/mL. The DCM partitioned extracts of C. sinensis L. BP (DCMCBP) and M. diplotricha BP (DCMMBP) had the highest PPLI activities with an IC₅₀ value of 458.5 ± 13.4 and 500.8 ± 24.8 µg/mL, respectively), while no crude extract showed any marked AChEI activity. Here, the in vitro PPLI activity was focused on. Unlike C. sinensis L. BP, there has been no previous report of M. diplotricha BP having PPLI activity. Hence, DCMMBP was further fractionated by silica gel 60 column chromatography, pooling fractions with the same thin layer chromatography profile. The pooled fraction of DCMMBP2-1 was found to be the most active (IC₅₀ of 52.6 ± 3.5 µg/mL), while nuclear magnetic resonance analysis revealed the presence of unsaturated free fatty acids. Gas chromatography with flame-ionization detection analysis revealed the major fatty acids included one saturated acid (palmitic acid) and two polyunsaturated acids (linoleic and linolenic acids). In contrast, the pooled fraction of DCMMBP2-2 was inactive but pure, and was identified as naringenin, which has previously been reported to be present in M. pigra L. Thus, it can be concluded that naringenin was compound marker for Mimosa BP. The fatty acids in BP are nutritional and pose potent PPLI activity.

Development of colonies of uruçu stingless bees fed a vitamin-amino acid supplement

ABSTRACT This study proposes to investigate the influence of a vitamin-amino acid supplement on the weight of colonies of uruçu stingless bees (Melipona scutellaris). The experiment was carried out with 24 colonies and three treatments, which consisted of a solution of different proportions of supplement (0, 3, and 5 mL) diluted in syrup (water and sugar). Although this supplement is effective and indicated for other species of domestic animals, analysis of variance with repeated measures over time did not reveal a significant effect (P > 0.05) of its dose on the weight of the hives, showing that the supply of the vitamin-amino acid supplement does not meet the nutritional requirements of the colony. The use of this product did not have a positive effect on the development of the uruçu bee colonies, so it should not be employed as a major source of amino acids and vitamins in the diet of bees. Beekeepers are suggested to provide uruçu bees with an abundant diversity of plants so that they have access to different types of pollen as a source of nutrients.

Critical links between biodiversity and health in wild bee conservation

Wild bee populations are declining due to human activities, such as land use change, which strongly affect the composition and diversity of available plants and food sources. The chemical composition of food (i.e., nutrition) in turn determines the health, resilience, and fitness of bees. For pollinators, however, the term 'health' is recent and is subject to debate, as is the interaction between nutrition and wild bee health. We define bee health as a multidimensional concept in a novel integrative framework linking bee biological traits (physiology, stoichiometry, and disease) and environmental factors (floral diversity and nutritional landscapes). Linking information on tolerated nutritional niches and health in different bee species will allow us to better predict their distribution and responses to environmental change, and thus support wild pollinator conservation.

In Vitro Rearing Changes Social Task Performance and Physiology in Honeybees

Simple Summary

The rearing of honeybee larvae in the laboratory is an important tool for studying the effects of plant protection products or pathogens on developing and adult bees, yet how rearing under artificial conditions affects the later social behavior and physiology of the honeybees is mostly unknown. We, here, show that honeybees reared in the laboratory generally had a lower probability for performing nursing or foraging tasks compared to bees reared under natural conditions in bee colonies. Nursing behavior itself appeared normal in in vitro honeybees. In contrast, bees reared in the laboratory foraged for a shorter period in life and performed fewer trips compared to bees reared in colonies. In addition, in vitro honeybees did not display the typical increase in juvenile hormone titer, which goes hand-in-hand with the initiation of foraging in colony-reared bees.

Abstract

In vitro rearing of honeybee larvae is an established method that enables exact control and monitoring of developmental factors and allows controlled application of pesticides or pathogens. However, only a few studies have investigated how the rearing method itself affects the behavior of the resulting adult honeybees. We raised honeybees in vitro according to a standardized protocol: marking the emerging honeybees individually and inserting them into established colonies. Subsequently, we investigated the behavioral performance of nurse bees and foragers and quantified the physiological factors underlying the social organization. Adult honeybees raised in vitro differed from naturally reared honeybees in their probability of performing social tasks. Further, in vitro-reared bees foraged for a shorter duration in their life and performed fewer foraging trips. Nursing behavior appeared to be unaffected by rearing condition. Weight was also unaffected by rearing condition. Interestingly, juvenile hormone titers, which normally increase strongly around the time when a honeybee becomes a forager, were significantly lower in three- and four-week-old in vitro bees. The effects of the rearing environment on individual sucrose responsiveness and lipid levels were rather minor. These data suggest that larval rearing conditions can affect the task performance and physiology of adult bees despite equal weight, pointing to an important role of the colony environment for these factors. Our observations of behavior and metabolic pathways offer important novel insight into how the rearing environment affects adult honeybees.

Nano-La2O3 Induces Honeybee (Apis mellifera) Death and Enriches for Pathogens in Honeybee Gut Bacterial Communities

Honeybees (Apis mellifera) can be exposed via numerous potential pathways to ambient nanoparticles (NPs), including rare earth oxide (REO) NPs that are increasingly used and released into the environment. Gut microorganisms are pivotal in mediating honeybee health, but how REO NPs may affect honeybee health and gut microbiota remains poorly understood. To address this knowledge gap, honeybees were fed pollen and sucrose syrup containing 0, 1, 10, 100, and 1000mgkg-1 of nano-La2O3 for 12days. Nano-La2O3 exerted detrimental effects on honeybee physiology, as reflected by dose-dependent adverse effects of nano-La2O3 on survival, pollen consumption, and body weight (p<0.05). Nano-La2O3 caused the dysbiosis of honeybee gut bacterial communities, as evidenced by the change of gut bacterial community composition, the enrichment of pathogenic Serratia and Frischella, and the alteration of digestion-related taxa Bombella (p<0.05). There were significant correlations between honeybee physiological parameters and the relative abundances of pathogenic Serratia and Frischella (p<0.05), underscoring linkages between honeybee health and gut bacterial communities. Taken together, this study demonstrates that nano-La2O3 can cause detrimental effects on honeybee health, potentially by disordering gut bacterial communities. This study thus reveals a previously overlooked effect of nano-La2O3 on the ecologically and economically important honeybee species Apis mellifera.

Pollen Source Richness May Be a Poor Predictor of Bumblebee (Bombus terrestris) Colony Growth

Agricultural intensification has drastically altered foraging landscapes for bees, with large-scale crop monocultures associated with floral diversity loss. Research on bumblebees and honeybees has shown individuals feeding on pollen from a low richness of floral sources can experience negative impacts on health and longevity relative to higher pollen source richness of similar protein concentrations. Florally rich landscapes are thus generally assumed to better support social bees. Yet, little is known about whether the effects of reduced pollen source richness can be mitigated by feeding on pollen with higher crude protein concentration, and importantly how variation in diet affects whole colony growth, rearing decisions and sexual production. Studying queen-right bumblebee (Bombus terrestris) colonies, we monitored colony development under a polyfloral pollen diet or a monofloral pollen diet with 1.5-1.8 times higher crude protein concentration. Over 6 weeks, we found monofloral colonies performed better for all measures, with no apparent long-term effects on colony mass or worker production, and a higher number of pupae in monofloral colonies at the end of the experiment. Unexpectedly, polyfloral colonies showed higher mortality, and little evidence of any strategy to counteract the effects of reduced protein; with fewer and lower mass workers being reared, and males showing a similar trend. Our findings (i) provide well-needed daily growth dynamics of queenright colonies under varied diets, and (ii) support the view that pollen protein content in the foraging landscape rather than floral species richness per se is likely a key driver of colony health and success.

Chemical Stimulants and Stressors Impact the Outcome of Virus Infection and Immune Gene Expression in Honey Bees (Apis mellifera)

Western honey bees (Apis mellifera) are ecologically, agriculturally, and economically important plant pollinators. High average annual losses of honey bee colonies in the US have been partially attributed to agrochemical exposure and virus infections. To examine the potential negative synergistic impacts of agrochemical exposure and virus infection, as well as the potential promise of phytochemicals to ameliorate the impact of pathogenic infections on honey bees, we infected bees with a panel of viruses (i.e., Flock House virus, deformed wing virus, or Sindbis virus) and exposed to one of three chemical compounds. Specifically, honey bees were fed sucrose syrup containing: (1) thyme oil, a phytochemical and putative immune stimulant, (2) fumagillin, a beekeeper applied fungicide, or (3) clothianidin, a grower-applied insecticide. We determined that virus abundance was lower in honey bees fed 0.16 ppb thyme oil augmented sucrose syrup, compared to bees fed sucrose syrup alone. Parallel analysis of honey bee gene expression revealed that honey bees fed thyme oil augmented sucrose syrup had higher expression of key RNAi genes (argonaute-2 and dicer-like), antimicrobial peptide expressing genes (abaecin and hymenoptaecin), and vitellogenin, a putative honey bee health and age indicator, compared to bees fed only sucrose syrup. Virus abundance was higher in bees fed fumagillin (25 ppm or 75 ppm) or 1 ppb clothianidin containing sucrose syrup relative to levels in bees fed only sucrose syrup. Whereas, honey bees fed 10 ppb clothianidin had lower virus levels, likely because consuming a near lethal dose of insecticide made them poor hosts for virus infection. The negative impact of fumagillin and clothianidin on honey bee health was indicated by the lower expression of argonaute-2, dicer-like, abaecin, and hymenoptaecin, and vitellogenin. Together, these results indicate that chemical stimulants and stressors impact the outcome of virus infection and immune gene expression in honey bees.

Virulence variations between clonal complexes of Melisococcus plutonius and the possible causes

Melissococcus plutonius is a pathogenic bacterium that affects honeybee brood triggering colony collapse in severe cases. The bacterium causes a European foulbrood (EFB) disease in the honeybee populations, impacting beekeeping and agricultural industries. The pathogenesis, epidemiology, and variants of M. plutonius have been studied, but the virulence factors involved in larval infection are still unknown. Recently, an in-silico study suggested putative genes that might play a role in the pathogenesis of EFB. However, studies are required to determine their function as virulence factors. In addition, the few studies of clonal complexes (CCs), virulence factors, and variation in the honeybee larvae mortality have interfered with the development of more efficient control methods. The research, development, and differences in virulence between genetic variants (CCs) of M. plutonius and potential virulence factors implicated in honeybee larval mortality are discussed in this review.

Reviewing the Efficacy of Pollen Substitutes as a Management Tool for Improving the Health and Productivity of Western Honey Bee (Apis mellifera) Colonies

Western honey bees (Apis mellifera L.) collect pollen from flowers as their source of protein, fat, vitamins, and minerals. Beekeepers feed pollen substitutes to their honey bee colonies to mitigate a lack of natural pollen resources in the environment. Despite their widespread use, it is unclear if pollen substitutes are beneficial to colony health and productivity. Herein, we review the literature regarding pollen substitute efficacy in four major categories: (1) consumption/palatability of pollen substitutes, (2) colony productivity, (3) pest and disease response, and (4) physiological response. Collectively, the literature shows a mix of positive, neutral, and negative impacts of pollen substitutes on honey bee colony health. Additionally, we recommend areas for improvement in pollen substitute research. We hope this review will lead to more research on pollen substitutes given nutrition is a key factor impacting the health of managed honey bees globally.

Preservation methods of honey bee-collected pollen are not a source of bias in ITS2 metabarcoding

Pollen metabarcoding is emerging as a powerful tool for ecological research and offers unprecedented scale in citizen science projects for environmental monitoring via honey bees. Biases in metabarcoding can be introduced at any stage of sample processing and preservation is at the forefront of the pipeline. While in metabarcoding studies pollen has been preserved at - 20 °C (FRZ), this is not the best method for citizen scientists. Herein, we compared this method with ethanol (EtOH), silica gel (SG) and room temperature (RT) for preservation of pollen collected from hives in Austria and Denmark. After ~ 4 months of storage, DNAs were extracted with a food kit, and their quality and concentration measured. Most DNA extracts exhibited 260/280 absorbance ratios close to the optimal 1.8, with RT samples from Austria performing slightly worse than FRZ and SG samples (P < 0.027). Statistical differences were also detected for DNA concentration, with EtOH samples producing lower yields than RT and FRZ samples in both countries and SG in Austria (P < 0.042). Yet, qualitative and quantitative assessments of floral composition obtained using high-throughput sequencing with the ITS2 barcode gave non-significant effects of preservation methods on richness, relative abundance and Shannon diversity, in both countries. While freezing and ethanol are commonly employed for archiving tissue for molecular applications, desiccation is cheaper and easier to use regarding both storage and transportation. Since SG is less dependent on ambient humidity and less prone to contamination than RT, we recommend SG for preserving pollen for metabarcoding. SG is straightforward for laymen to use and hence robust for widespread application in citizen science studies.

CSI Pollen: Diversity of Honey Bee Collected Pollen Studied by Citizen Scientists

A diverse supply of pollen is an important factor for honey bee health, but information about the pollen diversity available to colonies at the landscape scale is largely missing. In this COLOSS study, beekeeper citizen scientists sampled and analyzed the diversity of pollen collected by honey bee colonies. As a simple measure of diversity, beekeepers determined the number of colors found in pollen samples that were collected in a coordinated and standardized way. Altogether, 750 beekeepers from 28 different regions from 24 countries participated in the two-year study and collected and analyzed almost 18,000 pollen samples. Pollen samples contained approximately six different colors in total throughout the sampling period, of which four colors were abundant. We ran generalized linear mixed models to test for possible effects of diverse factors such as collection, i.e., whether a minimum amount of pollen was collected or not, and habitat type on the number of colors found in pollen samples. To identify habitat effects on pollen diversity, beekeepers' descriptions of the surrounding landscape and CORINE land cover classes were investigated in two different models, which both showed that both the total number and the rare number of colors in pollen samples were positively affected by 'urban' habitats or 'artificial surfaces', respectively. This citizen science study underlines the importance of the habitat for pollen diversity for bees and suggests higher diversity in urban areas.

Effect of yeast and essential oil-enriched diets on critical determinants of health and immune function in Africanized Apis mellifera

Nutrition is vital for health and immune function in honey bees (Apis mellifera). The effect of diets enriched with bee-associated yeasts and essential oils of Mexican oregano (Lippia graveolens) was tested on survival, food intake, accumulated fat body tissue, and gene expression of vitellogenin (Vg), prophenoloxidase (proPO) and glucose oxidase (GOx) in newly emerged worker bees. The enriched diets were provided to bees under the premise that supplementation with yeasts or essential oils can enhance health variables and the expression of genes related to immune function in worker bees. Based on a standard pollen substitute, used as a control diet, enriched diets were formulated, five with added bee-associated yeasts (Starmerella bombicola, Starmerella etchellsii, Starmerella bombicola 2, Zygosaccharomyces mellis, and the brewers’ yeast Saccharomyces cerevisiae) and three with added essential oils from L. graveolens (carvacrol, thymol, and sesquiterpenes). Groups of bees were fed one of the diets for 9 or 12 days. Survival probability was similar in the yeast and essential oils treatments in relation to the control, but median survival was lower in the carvacrol and sesquiterpenes treatments. Food intake was higher in all the yeast treatments than in the control. Fat body percentage in individual bees was slightly lower in all treatments than in the control, with significant decreases in the thymol and carvacrol treatments. Expression of the genes Vg, proPO, and GOx was minimally affected by the yeast treatments but was adversely affected by the carvacrol and thymol treatments.

Honey Bee Nutrition

Optimal nutrition is crucial for honey bee colony growth and robust immune systems. Honey bee nutrition is complex and depends on the floral composition of the landscape. Foraging behavior of honey bees depends on both colony environment and external environment. There are significant gaps in knowledge regarding honey bee nutrition, and hence no optimal diet is available for honey bees, as there is for other livestock. In this review, we discuss (1) foraging behavior of honey bees, (2) nutritional needs, (3) nutritional supplements used by beekeepers, (4) probiotics, and (5) supplemental forage and efforts integrating floral diversity into cropping systems.

Mass-flowering monoculture attracts bees, amplifying parasite prevalence

As the global agricultural footprint expands, it is increasingly important to address the link between the resource pulses characteristic of monoculture farming and wildlife epidemiology. To understand how mass-flowering crops impact host communities and subsequently amplify or dilute parasitism, we surveyed wild and managed bees in a monoculture landscape with varying degrees of floral diversification. We screened 1509 bees from 16 genera in sunflower fields and in non-crop flowering habitat across 200 km² of the California Central Valley. We found that mass-flowering crops increase bee abundance. Wild bee abundance was subsequently associated with higher parasite presence, but only in sites with a low abundance of non-crop flowers. Bee traits related to higher dispersal ability (body size) and diet breadth (pollen lecty) were also positively related to parasite presence. Our results highlight the importance of non-crop flowering habitat for supporting bee communities. We suggest monoculture alone cannot support healthy bees.

Comparative assessment of various supplementary diets on commercial honey bee (Apis mellifera) health and colony performance

A healthy honey bee stock is critical to the beekeeping industry and the sustainability of the ecosystem. The quality of the supplemental diet influences the development and strength of the colony, especially during the pollen dearth period in the surrounding environment. However, the extent to which pollen substitute protein feeding affects honey bee colony parameters is not fully known. We conducted this study to test the influence of various supplemental diets on foraging effort, pollen load, capped brood area, population density, and honey yield. The treatment groups were supplied with patties of pollen substitute diets, whereas sugar syrup was given to the control group. Our results indicated that honey bees consumed a significantly higher amount of Diet 1 (45 g soybean flour + 15 g Brewer’s yeast + 75 g powdered sugar + 7.5 g skimmed milk + 7.5 g date palm pollen + 200 mL sugar syrup supplement with Vitamin C) followed by others supplemented diets. Further, pollen load, worker-sealed brood area, population strength, and honey yield differed significantly when Diet 1 was consumed instead of other supplemental diets. The proportion of biological parameters was less in the control group as compared to other treatments. This study highlights the potential of supplemental diets to improve the bee’s health and colony development when the pollens availability and diversity are insufficient.

Nutritive Value of 11 Bee Pollen Samples from Major Floral Sources in Taiwan

Bee pollen is a nutrient-rich food that meets the nutritional requirements of honey bees and supports human health. This study aimed to provide nutritive composition data for 11 popular bee pollen samples (Brassica napus (Bn), Bidens pilosa var. radiata (Bp), Camellia sinensis (Cs), Fraxinus griffithii (Fg), Prunus mume (Pm), Rhus chinensis var. roxburghii (Rc), Bombax ceiba (Bc), Hylocereus costaricensis (Hc), Liquidambar formosana (Lf), Nelumbo nucifera (Nn), and Zea mays (Zm)) in Taiwan for the global bee pollen database. Macronutrients, such as carbohydrates, proteins, and lipids, were analyzed, which revealed that Bp had the highest carbohydrate content of 78.8 g/100 g dry mass, Bc had the highest protein content of 32.2 g/100 g dry mass, and Hc had the highest lipid content of 8.8 g/100 g dry mass. Only the bee pollen Hc completely met the minimum requirements of essential amino acids for bees and humans, and the other bee pollen samples contained at least 1-3 different limiting essential amino acids, i.e., methionine, tryptophan, histidine, valine, and isoleucine. Regarding the fatty acid profile of bee pollen samples, palmitic acid (C_16:0), stearic acid (C_18:0), oleic acid (C_18:1), linoleic acid (C_18:2), and linolenic acid (C_18:3) were predominant fatty acids that accounted for 66.0-97.4% of total fatty acids. These data serve as an indicator of the nutritional quality and value of the 11 bee pollen samples.

A potential probiotic Leuconostoc mesenteroides TBE-8 for honey bee

An isolated bacterium TBE-8, was identified as Leuconostoc mesenteroides according to the sequences of 16S rDNA and the 16S-23S rDNA intergenic spacer region. The probiotic properties of the L. mesenteroides TBE-8 strain were characterized and revealed that TBE-8 could utilize various carbohydrates, exhibited high tolerance to sucrose's osmotic pressure and acidic conditions, and could mitigate the impact of the bee pathogen Paenibacillus larvae. In addition, we found that the TBE-8 broth increased the expression of the nutrition-related genes major royal jelly protein 1 and vitellogenin in bees by approximately 1400- and 20-fold, respectively. The expression of genes encoding two antibacterial peptides, hymenoptaecin and apidaecin, in the bee abdomen was significantly increased by 17- and 7-fold in bees fed with the TBE-8 fermented broth. Furthermore, we fed four-frame bee colonies with 50% sucrose syrup containing TBE-8 and can detect the presence of approximately 2 × 106 16S rDNA copies of TBE-8 in the guts of all bees in 24 h, and the retention of TBE-8 in the bee gut for at least 5 days. These findings indicate that the L. mesenteroides TBE-8 has high potential as a bee probiotic and could enhance the health of bee colonies.

Physiological and Immunological Status of Adult Honeybees (Apis mellifera) Fed Sugar Syrup Supplemented with Pentadecapeptide BPC 157

Various factors contribute to a decline in diversity and number of bees. Here, an integrated approach in experimental BPC 157 therapy was implemented, combining laboratory-controlled and field study results. The aim of a study was to assess the effects of BPC 157 additional feeding of newly emerged worker honeybees on few biochemical and immunological parameters in hemolymph (glucose, trehalose, lipids, proteins, vitellogenin, glucose-oxidase (GOX)), and hypopharyngeal gland (HPG), in laboratory-controlled conditions. Additionally, to examine the physiological status of protein digestion, the enzymatic activity of leucine aminopeptidase (LAP) in the mid-guts of worker honeybees was analyzed. It was found that individual honeybees, in hoarding cages, following BPC 157 administration through carbohydrate food, showed positive physiological changes when compared to the control groups. Those results were complemented by strong and visible LAP activity, particularly noticeable in the apical parts of the epithelial cells in the mid-guts of young worker honeybees originated from treated hives, suggesting a link between alternative oral therapy with BPC 157 and honeybees' immunity.

Specialized Metabolites in Floral Resources: Effects and Detection in Buff-Tailed Bumblebees

The selection of appropriate food resources by bees is a critical aspect for the maintenance of their populations, especially in the current context of global change and pollinator decline. Wild bees have a sophisticated ability to forage selectively on specific resources, and can assess the quality of pollen using contact chemosensory perception (taste). While numerous studies have investigated the detection of pollen macronutrients in bees and their impact on bee health and reproductive success, only a few studies have described the gustatory responses of bees toward specialized metabolites. In addition, these studies mostly focused on the response to nectar and neglected pollen, which is the main food resource for both bee imagines and larvae. Whether bees have the ability to detect specialized toxic metabolites in pollen and then rapidly adapt their foraging behavior to avoid them is very little studied. In this study, we tested whether pollen specialized metabolites affect bumblebees at both the micro-colony and individual levels (i.e., bioassays using supplemented pollen), and whether foragers detect these specialized metabolites and potentially display an avoidance behavior (i.e., preference tests using supplemented syrup). Bumblebees were fed with either amygdalin-, scopolamine- or sinigrin-supplemented pollen diets in ratios that mimic 50%, 100%, and 200% of naturally occurring concentrations. We found no effect of these specialized metabolites on resource collection, reproductive success and stress response at the micro-colony level. At the individual level, bumblebees fed on 50%-amygdalin or 50%-scopolamine diets displayed the highest scores for damage to their digestive systems. Interestingly, during the preference tests, the solution with 50%-scopolamine displayed a phagostimulatory activity, whereas solution with 50%-amygdalin had a deterrent effect and could trigger an active avoidance behavior in bumblebees, with a faster proboscis retraction. Our results suggest that regulation of toxin intake is not as well-established and effective as the regulation of nutrient intake in bees. Bees are therefore not equally adapted to all specialized pollen metabolites that they can come into contact with.

Pollen Diet-Properties and Impact on a Bee Colony

Simple Summary

In order to study the effects of malnutrition in bees, attention should be drawn to the dietary composition. A pollen diet plays an important role in the life of bees. A well-balanced diet influences the development of the larvae as well as the physiology, biochemistry, immunity and histology of the workers.

Abstract

Diet is an important factor in the proper development of the individual and the entire colony. A pollen diet affects honey bees in a number of ways. It can stimulate the number and type of hemocytes, the total number of proteins, carbohydrates and lipids, affect the histology of the middle intestine, and ensure the correct ontogenesis of the larvae. Moreover, selected single-flower diets can stimulate the development of the pharyngeal glands that produce royal jelly, thus conditioning the development of secretory immunity. Selected single-species pollen may also increase the phenol oxidase concentration, which contributes to the humoral response. A honey bee diet based on multi-flower pollen is more desirable than a mono-flower diet, but must be properly balanced.

Pollen nutrition fosters honeybee tolerance to pesticides

A reduction in floral resource abundance and diversity is generally observed in agro-ecosystems, along with widespread exposure to pesticides. Therefore, a better understanding on how the availability and quality of pollen diets can modulate honeybee sensitivity to pesticides is required. For that purpose, we evaluated the toxicity of acute exposure and chronic exposures to field realistic and higher concentrations of azoxystrobin (fungicide) and sulfoxaflor (insecticide) in honeybees provided with pollen diets of differing qualities (named S and BQ pollens). We found that pollen intake reduced the toxicity of the acute doses of pesticides. Contrary to azoxystrobin, chronic exposures to sulfoxaflor increased by 1.5- to 12-fold bee mortality, which was reduced by pollen intake. Most importantly, the risk of death upon exposure to a high concentration of sulfoxaflor was significantly lower for the S pollen diet when compared with the BQ pollen diet. This reduced pesticide toxicity was associated with a higher gene expression of vitellogenin, a glycoprotein that promotes bee longevity, a faster sulfoxaflor metabolization and a lower concentration of the phytochemical p-coumaric acid, known to upregulate detoxification enzymes. Thus, our study revealed that pollen quality can influence the ability of bees to metabolize pesticides and withstand their detrimental effects, providing another strong argument for the restoration of suitable foraging habitat.

Combined Effects of Pesticides and Electromagnetic-Fields on Honeybees: Multi-Stress Exposure

Honeybee and general pollinator decline is extensively reported in many countries, adding new concern to the general biodiversity loss. Many studies were addressed to assess the causes of pollinator decline, concluding that in most cases multi-stress effects were the most probable ones. In this research, the combined effects of two possible stress sources for bees, pesticides and electromagnetic fields (multi-stress conditions), were analyzed in the field. Three experimental sites were chosen: a control one far from direct anthropogenic stress sources, a pesticide-stress site and multi-stress one, adding to the same exposure to pesticides the presence of an electromagnetic field, coming from a high-voltage electric line. Experimental apiaries were monitored weekly for one year (from April 2017 to April 2018) by means of colony survival, queen activity, storage and brood amount, parasites and pathogens, and several biomarkers in young workers and pupae. Both exposure and effect biomarkers were analysed: among the first, acetylcholinesterase (AChE), catalase (CAT), glutathione S-transferase (GST) and alkaline phosphatase (ALP) and Reactive Oxygen Species (ROS); and among the last, DNA fragmentation (DNAFRAGM) and lipid peroxidation (LPO). Results showed that bee health conditions were the worst in the multi-stress site with only one colony alive out of the four ones present at the beginning. In this site, a complex picture of adverse effects was observed, such as disease appearance (American foulbrood), higher mortality in the underbaskets (common to pesticide-stress site), behavioral alterations (queen changes, excess of honey storage) and biochemical anomalies (higher ALP activity at the end of the season). The overall results clearly indicate that the multi-stress conditions were able to induce biochemical, physiological and behavioral alterations which severely threatened bee colony survival.

A Regional, Honey Bee-Centered Approach Is Needed to Incentivize Grower Adoption of Bee-Friendly Practices in the Almond Industry

Managed and wild bee populations contribute over $15 billion in pollination services to US agriculture, yet both are declining or becoming increasingly vulnerable to parasites and disease. The loss of healthy and diverse forage is a key driver in bee declines, so incentivizing land managers to adopt diversified bee-friendly management practices such as forage plantings and reduced pesticide use can directly increase food security, pollinator health, and farmer adaptive capacity. To better understand what might incentivize growers to adopt bee-friendly practices, we conducted a survey of California almond growers, whose orchards are entirely dependent on bee pollination and draw nearly 88% of US bee colonies each February to pollinate almond bloom. We asked 329 respondents across all major almond growing regions of CA about their adoption rate and incentives for planting cover crops, pollinator habitat, and practicing the recommended and legally required bee-friendly best management practices, as well as their interest in bee-friendly certification programs. Using a model selection framework, we evaluated which geographic, social, operational, and pollination-service related factors were predictive of bee-friendly practice adoption. We found that no single factor was a statistically significant predictor of adoption across all models, suggesting there is no silver bullet determining bee-friendly practice adoption. However, we discovered that region and concerns about future pollination services consistently emerged as important factors related to all the practices we investigated, except the adoption of legally required BMPs. These findings suggest that a regionally flexible pollinator conservation strategy focused on supporting honey bee colonies might have the highest likelihood of grower participation and adoption.

Tracing the Fate of Pollen Substitute Patties in Western Honey Bee (Hymenoptera: Apidae) Colonies

Commercial beekeepers need healthy, productive honey bee (Apis mellifera L.) colonies, even when the landscape lacks adequate pollen forage to sustain the colonies. As a result, many commercial beekeepers spend significant money and labor on the use of pollen substitutes in their colonies. However, there is little consensus in the literature about the benefits and drawbacks of pollen substitute use on honey bee colony health. In order to understand this critically, it is important to know first how honey bees distribute pollen substitute patties throughout their colonies. We traced the fate of three commercially available pollen substitute patties (MegaBee, UltraBee, AP23) dyed with a nontoxic food coloring (Brilliant Blue FCF) and undyed as negative controls, a dyed positive control (fondant), and a dyed consumption control (Crayola Model Magic Clay) in 44 honey bee colonies. Using spectrophotometry and visual inspection, we analyzed adult bee guts, larval guts, bee bread stores and colony debris underneath the hive for presence of the dye. Our data suggest that (1) a proportion of adult bees ingest the patty, (2) adult bees likely do not feed patty directly to larvae, (3) adult bees do not store patty like bee bread, and (4) only a very small proportion of patty is lost as debris. Collectively our data suggest that honey bee colonies use pollen substitute patties. However, patties likely do not replace the function of natural pollen entirely in terms of larval provisioning and long-term storage as bee bread.

A Case Report of Chronic Stress in Honey Bee Colonies Induced by Pathogens and Acaricide Residues

In this case report, we analyze the possible causes of the poor health status of a professional Apis mellifera iberiensis apiary located in Gajanejos (Guadalajara, Spain). Several factors that potentially favor colony collapse were identified, including Nosema ceranae infection, alone or in combination with other factors (e.g., BQCV and DWV infection), and the accumulation of acaricides commonly used to control Varroa destructor in the beebread (coumaphos and tau-fluvalinate). Based on the levels of residues, the average toxic unit estimated for the apiary suggests a possible increase in vulnerability to infection by N. ceranae due to the presence of high levels of acaricides and the unusual climatic conditions of the year of the collapse event. These data highlight the importance of evaluating these factors in future monitoring programs, as well as the need to adopt adequate preventive measures as part of national and international welfare programs aimed at guaranteeing the health and fitness of bees.

Odour Learning Bees Have Longer Foraging Careers Than Non-learners in a Natural Environment

Individual animals allowed the opportunity to learn generally outperform those prevented from learning, yet, within a species the capacity for learning varies markedly. The evolutionary processes that maintain this variation in learning ability are not yet well understood. Several studies demonstrate links between fitness traits and visual learning, but the selection pressures operating on cognitive traits are likely influenced by multiple sensory modalities. In addition to vision, most animals will use a combination of hearing, olfaction (smell), gustation (taste), and touch to gain information about their environment. Some animals demonstrate individual preference for, or enhanced learning performance using certain senses in relation to particular aspects of their behaviour (e.g., foraging), whereas conspecific individuals may show different preferences. By assessing fitness traits in relation to different sensory modalities we will strengthen our understanding of factors driving observed variation in learning ability. We assessed the relationship between the olfactory learning ability of bumble bees (Bombus terrestris) and their foraging performance in their natural environment. We found that bees which failed to learn this odour-reward association had shorter foraging careers; foraging for fewer days and thus provisioning their colonies with fewer resources. This was not due to a reduced propensity to forage, but may have been due to a reduced ability to return to their colony. When comparing among only individuals that did learn, we found that the rate at which floral resources were collected was similar, regardless of how they performed in the olfactory learning task. Our results demonstrate that an ability to learn olfactory cues can have a positive impact of the foraging performance of B. terrestris in a natural environment, but echo findings of earlier studies on visual learning, which suggest that enhanced learning is not necessarily beneficial for bee foragers provisioning their colony.

Effect of Honey and Syrup Diets Enriched with 1,3-1,6 β-Glucans on Honeybee Survival Rate and Phenoloxidase Activity (Apis mellifera L. 1758)

β-glucans can activate the animal innate immune system by acting as immune-modulators and inducing various stimulatory effects. The aim of this study was to investigate the effect of 1,3-1,6 β-glucans administered orally for 96 h on Apis mellifera workers (newly emerged and nurse bees). β-glucans were included in honey and syrup. Survival rate and phenoloxidase activity were measured. In both newly emerged and nurse bees, β-glucans supplementation did not affect survival rate (p > 0.05). Conversely, phenoloxidase activity was higher in both newly emerged bees (p = 0.048) and nurse bees (p = 0.014) fed with a honey diet enriched with β-glucans compared to those fed with only honey. In both the newly emerged and nurse bees, no statistical differences in phenoloxidase activity were recorded between the group fed with a syrup-based diet enriched with β-glucans and the control group (p > 0.05). The absence of significant variation in survival suggests that the potential negative effect of β-glucans in healthy bees could be mitigated by their metabolism. Conversely, the inclusion of β-glucans in a honey-based diet determined an increase of phenoloxidase activity, suggesting that the effect of β-glucan inclusion in the diet of healthy bees on phenoloxidase activity could be linked to the type of base-diet. Further investigations on β-glucans metabolism in bees, on molecular mechanism of phenoloxidase activation by 1,3-1,6 β-glucans, and relative thresholds are desirable. Moreover, investigation on the combined action of honey and β-glucans on phenoloxidase activity are needed.

Developmental environment shapes honeybee worker response to virus infection

The consequences of early-life experiences are far reaching. In particular, the social and nutritional environments that developing animals experience can shape their adult phenotypes. In honeybees, larval nutrition determines the eventual social roles of adults as reproductive queens or sterile workers. However, little is known about the effects of developmental nutrition on important adult worker phenotypes such as disease resilience. In this study, we manipulated worker developmental nutrition in two distinct ways under semi-natural field conditions. In the first experiment, we restricted access to nutrition via social isolation by temporarily preventing alloparental care. In the second experiment, we altered the diet quality experienced by the entire colony, leading to adult bees that had developed entirely in a nutritionally restricted environment. When bees from these two experiments reached the adult stage, we challenged them with a common bee virus, Israeli acute paralysis virus (IAPV) and compared mortality, body condition, and the expression of immune genes across diet and viral inoculation treatments. Our findings show that both forms of early life nutritional stress, whether induced by lack of alloparental care or diet quality restriction, significantly reduced bees' resilience to virus infection and affected the expression of several key genes related to immune function. These results extend our understanding of how early life nutritional environment can affect phenotypes relevant to health and highlight the importance of considering how nutritional stress can be profound even when filtered through a social group. These results also provide important insights into how nutritional stress can affect honeybee health on a longer time scale and its potential to interact with other forms of stress (i.e. disease).

Pollen DNA metabarcoding identifies regional provenance and high plant diversity in Australian honey

Accurate identification of the botanical components of honey can be used to establish its geographical provenance, while also providing insights into honeybee (Apis mellifera L.) diet and foraging preferences. DNA metabarcoding has been demonstrated as a robust method to identify plant species from pollen and pollen-based products, including honey. We investigated the use of pollen metabarcoding to identify the floral sources and local foraging preferences of honeybees using 15 honey samples from six bioregions from eastern and western Australia. We used two plant metabarcoding markers, ITS2 and the trnL P6 loop. Both markers combined identified a total of 55 plant families, 67 genera, and 43 species. The trnL P6 loop marker provided significantly higher detection of taxa, detecting an average of 15.6 taxa per sample, compared to 4.6 with ITS2. Most honeys were dominated by Eucalyptus and other Myrtaceae species, with a few honeys dominated by Macadamia (Proteaceae) and Fabaceae. Metabarcoding detected the nominal primary source provided by beekeepers among the top five most abundant taxa for 85% of samples. We found that eastern and western honeys could be clearly differentiated by their floral composition, and clustered into bioregions with the trnL marker. Comparison with previous results obtained from melissopalynology shows that metabarcoding can detect similar numbers of plant families and genera, but provides significantly higher resolution at species level. Our results show that pollen DNA metabarcoding is a powerful and robust method for detecting honey provenance and examining the diet of honeybees. This is particularly relevant for hives foraging on the unique and diverse flora of the Australian continent, with the potential to be used as a novel monitoring tool for honeybee floral resources.

Context-Dependent Effect of Dietary Phytochemicals on Honey Bees Exposed to a Pesticide, Thiamethoxam

Honey bees continue to face challenges relating to the degradation of natural flowering habitats that limit their access to diverse floral resources. While it is known that nectar and pollen provide macronutrients, flowers also contain secondary metabolites (phytochemicals) that impart benefits including increased longevity, improved gut microbiome abundance, and pathogen tolerance. Our study aims to understand the role of phytochemicals in pesticide tolerance when worker bees were fed with sublethal doses (1 ppb and 10 ppb) of thiamethoxam (TMX), a neonicotinoid, in 20% (w/v) sugar solution supplemented with 25 ppm of phytochemicals-caffeine, kaempferol, gallic acid, or p-coumaric acid, previously shown to have beneficial impacts on bee health. The effect of phytochemical supplementation during pesticide exposure was context-dependent. With 1 ppb TMX, phytochemical supplementation increased longevity but at 10 ppb TMX, longevity was reduced suggesting a negative synergistic effect. Phytochemicals mixed with 1 ppb TMX increased mortality in bees of the forager-age group but with 10 ppb TMX, mortality of the inhive-age group increased, implying the possibility of accumulation effect in lower sublethal doses. Given that the phytochemical composition of pollen and nectar varies between plant species, we suggest that the negative impacts of agrochemicals on honey bees could vary based on the phytochemicals in pollen and nectar of that crop, and hence the effects may vary across crops. Analyzing the phytochemical composition for individual crops may be a necessary first step prior to determining the appropriate dosage of agrochemicals so that harm to bees Apis mellifera L. is minimized while crop pests are effectively controlled.

A Potential Fungal Probiotic Aureobasidium melanogenum CK-CsC for the Western Honey Bee, Apis mellifera

Aureobasidium melanogenum has been used as an animal feed additive for improving thehealth of pets, however, it has not yet been applied in honey bees. Here, a fungal strain CK-CsC isolated from bee bread pollen, was identified as A. melanogenum. Following characterizing CK-CsC fermentation broth, the 4-days fermentation broth (SYM medium or bee pollen) of the CK-CsC was used to feed newly emerged adult honey bees in cages under laboratory-controlled conditions for analysis of survival, gene expression of nutrient and antibacterial peptide, and gut microbiota of honey bees. It was found that the CK-CsC fermentation broth (SYM medium or bee pollen) is nontoxic to honey bees, and can regularly increase nutrient gene expression of honey bees. However, significant mortality of bees was observed after bees were fed on the supernatant liquid of the fermentation broth. Notably, this mortality can be lowered by the simultaneous consumption of bee pollen. The honey bees that were fed bee pollen exhibited more γ-Proteobacteria, Bacteriodetes, and Actinobacteria in their gut flora than did the honey bees fed only crude supernatant liquid extract. These findings indicate that A. melanogenum CK-CsC has high potential as a bee probiotic when it was fermented with bee pollen.

Polyphenols as Food Supplement Improved Food Consumption and Longevity of Honey Bees (Apis mellifera) Intoxicated by Pesticide Thiacloprid

Simple Summary

Worldwide, mass losses of honey bee colonies are being observed more frequently. Poor nutrition may cause honey bees to be more susceptible to pesticides and more vulnerable to diseases, and as a direct result of this, honey bee colonies can collapse. Another cause of mass bee colony collapse that is no less important is the use of pesticides. The level of toxicity of most pesticides is greatly affected by nutrient uptake. In addition, the honey bee genome is known to be specific for a significantly lower number of genes associated with detoxification compared with other insect species. Intake of phenolic and flavonoid substances in food can lead to increased expression of genes encoding detoxification enzymes in bees. Therefore, in this study, we evaluated in vitro the effect of phenolic and flavonoid substances on bee mortality and food consumption in the case of intoxication by pesticide thiacloprid. The results of this study showed a significant positive effect on honey bee survival rate as well as increased food intake. In addition, the expression level of genes encoding detoxification enzymes was determined.

Abstract

Malnutrition is one of the main problems related to the global mass collapse of honey bee colonies, because in honey bees, malnutrition is associated with deterioration of the immune system and increased pesticide susceptibility. Another important cause of mass bee colonies losses is the use of pesticides. Therefore, the goal of this study was to verify the influence of polyphenols on longevity, food consumption, and cytochrome P450 gene expression in worker bees intoxicated by thiacloprid. The tests were carried out in vitro under artificial conditions (caged bees). A conclusively lower mortality rate and, in parallel, a higher average food intake, were observed in intoxicated bees treated using a mixture of phenolic acids and flavonoids compared to untreated intoxicated bees. This was probably caused by increased detoxification capacity caused by increased expression level of genes encoding the cytochrome P450 enzyme in the bees. Therefore, the addition of polyphenols into bee nutrition is probably able to positively affect the detoxification capacity of bees, which is often reduced by the impact of malnutrition resulting from degradation of the environment and common beekeeping management.

Natural contaminants in bee pollen: DNA metabarcoding as a tool to identify floral sources of pyrrolizidine alkaloids and fungal diversity

The use of bee pollen as a food supplement has increased in recent years as it contains several nutrients and phytochemicals. However, depending on floral composition, bee pollen can be contaminated by pyrrolizidine alkaloids (PAs), PA N-oxides (PANOs) and toxigenic fungi found in plants, which may pose a potential health risk for consumers. Thus, a DNA metabarcoding approach based on internal transcribed spacer 2 (ITS2) region was used to identify the plant sources of 17 PAs/PANOs detected by a validated method in liquid chromatography coupled to mass spectrometry (LC-MS/MS), as well as floral and fungal diversity in 61 bee pollen samples. According to LC-MS/MS analysis, 67% of the samples contained PAs/PANOs with mean concentration of 339 µg/kg. The contamination pattern was characterised by lycopsamine- and senecionine-type PAs/PANOs. PA/PANO-producing plants were identified in 54% of the PA/PANO-contaminated samples analysed by DNA metabarcoding, which also allowed identifying the overall floral and fungal composition of 56 samples. To evaluate the performance of the molecular approach, a subset of 25 samples was analysed by classical palynology. Palynological analysis partially confirmed the results of DNA metabarcoding, which had a better performance in distinguishing pollens of different genera from Asteraceae (76%) and Brassicaceae (88%). However, the molecular analysis did not identify pollens from Castanea, Eucalyptus, Hedera and Salix, which were abundant in 11 samples according to palynology. On the other hand, the molecular analysis allowed identifying several fungal genera in 33 samples, including the toxigenic fungi Alternaria and Aspergillus, which were positively correlated to the plant genus Hypericum. Despite limitations in identifying some pollen types, these preliminary results suggest that the DNA metabarcoding could be applied in a multidisciplinary approach to give a picture of floral and fungal diversity, which can be sources of natural contaminants in bee pollen and would help to control its safety.

Seed Meals from Brassica nigra and Eruca sativa Control Artificial Nosema ceranae Infections in Apis mellifera

Nosema ceranae is a widespread parasite responsible for nosemosis Type C in Apis mellifera honey bees, reducing colony survival. The antibiotic fumagillin is the only commercial treatment available, but concerns are emerging about its persistence, safety, and pathogen resistance. The use of natural substances from Brassicaceae defatted seed meals (DSMs) with known antimicrobial and antioxidant properties was explored. Artificially infected bees were fed for 8 days with candies enriched with two concentrations, 2% and 4%, of two DSMs from Brassica nigra and Eruca sativa, containing a known amount of different glucosinolates (GSLs). The food palatability, GSL intake, bee survival, and treatment effects on N. ceranae spore counts were evaluated. Food consumption was higher for the two 2% DSM patties, for both B. nigra and E. sativa, but the GSL intake did not increase by increasing DSM to 4%, due to the resulting lower palatability. The 2% B. nigra patty decreased the bee mortality, while the higher concentration had a toxic effect. The N. ceranae control was significant for all formulates with respect to the untreated control (312,192.6 +/- 14,443.4 s.e.), and was higher for 4% B. nigra (120,366.3 +/- 13,307.1 s.e.). GSL hydrolysis products, the isothiocyanates, were detected and quantified in bee gut tissues. Brassicaceae DSMs showed promising results for their nutraceutical and protective effects on bees artificially infected with N. ceranae spores at the laboratory level. Trials in the field should confirm these results.

Landscape structure affects the sunflower visiting frequency of insect pollinators

Mass-flowering crop monocultures, like sunflower, cannot harbour a permanent pollinator community. Their pollination is best secured if both managed honey bees and wild pollinators are present in the agricultural landscape. Semi-natural habitats are known to be the main foraging and nesting areas of wild pollinators, thus benefiting their populations, whereas crops flowering simultaneously may competitively dilute pollinator densities. In our study we asked how landscape structure affects major pollinator groups’ visiting frequency on 36 focal sunflower fields, hypothesising that herbaceous semi-natural (hSNH) and sunflower patches in the landscape neighbourhood will have a scale-dependent effect. We found that an increasing area and/or dispersion of hSNH areas enhanced the visitation of all pollinator groups. These positive effects were scale-dependent and corresponded well with the foraging ranges of the observed bee pollinators. In contrast, an increasing edge density of neighbouring sunflower fields resulted in considerably lower visiting frequencies of wild bees. Our results clearly indicate that the pollination of sunflower is dependent on the composition and configuration of the agricultural landscape. We conclude that an optimization of the pollination can be achieved if sufficient amount of hSNH areas with good dispersion are provided and mass flowering crops do not over-dominate the agricultural landscape.

Testing the multiple stressor hypothesis: chlorothalonil exposure alters transmission potential of a bumblebee pathogen but not individual host health

Numerous threats are putting pollinator health and essential ecosystem pollination services in jeopardy. Although individual threats are widely studied, their co-occurrence may exacerbate negative effects, as posited by the multiple stressor hypothesis. A prominent branch of this hypothesis concerns pesticide-pathogen co-exposure. A landscape analysis demonstrated a positive association between local chlorothalonil fungicide use and microsporidian pathogen (Nosema bombi) prevalence in declining bumblebee species (Bombus spp.), suggesting an interaction deserving further investigation. We tested the multiple stressor hypothesis with field-realistic chlorothalonil and N. bombi exposures in worker-produced B. impatiens microcolonies. Chlorothalonil was not avoided in preference assays, setting the stage for pesticide-pathogen co-exposure. However, contrary to the multiple stressor hypothesis, co-exposure did not affect survival. Bees showed surprising tolerance to Nosema infection, which was also unaffected by chlorothalonil exposure. However, previously fungicide-exposed infected bees carried more transmission-ready spores. Our use of a non-declining bumblebee and potential higher chlorothalonil exposures under some scenarios could mean stronger individual or interactive effects in certain field settings. Yet, our results alone suggest consequences of pesticide co-exposure for pathogen dynamics in host communities. This underlies the importance of considering both within- and between-host processes when addressing the multiple stressor hypothesis in relation to pathogens.

Pollen protein and lipid content influence resilience to insecticides in honey bees (Apis mellifera)

In honey bees (Apis mellifera), there is growing evidence that the impacts of multiple stressors can be mitigated by quality nutrition. Pollen, which is the primary source of protein and lipids in bees diets, is particularly critical for generating more resilient phenotypes. Here, we evaluate the relationship between pollen protein-to-lipid ratios (P:Ls) and honey bee insecticide resilience. We hypothesized that pollen diets richer in lipids would lead to increased survival in bees exposed to insecticides, as pollen-derived lipids have previously been shown to improve bee resilience to pathogens and parasites. Furthermore, lipid metabolic processes are altered in bees exposed to insecticides.We fed age-matched bees pollen diets of different P:Ls by altering a base pollen by either adding protein (casein powder) or lipids (canola oil) and simulating chronic insecticide exposure by feeding bees an organophosphate (Chlorpyrifos). We also tested pollen diets of naturally different P:Ls to determine if results are consistent. Linear regression analysis revealed that mean survival time for altered diets was best explained by protein concentration (p =0.04 , adjusted R2 =0.92), and that mean survival time for natural diets was best explained by P:L ratio (p =0.008 , adjusted R2 =0.93). Our results indicate that higher ratios of dietary protein to lipid has a negative effect on bee physiology when combined with insecticide exposure, while lower ratios have a positive effect. These results suggest that protein and lipid intake differentially influence insecticide response in bees, laying the groundwork for future studies of metabolic processes and development of improved diets.

The Importance of Time and Place: Nutrient Composition and Utilization of Seasonal Pollens by European Honey Bees (Apis mellifera L.)

Simple Summary

Honey bees rely on pollen and nectar to provide nutrients to support their yearly colony cycle. Specifics of the cycle differ among geographic regions as do the species of flowering plants and the nutrients they provide. We examined responses of honey bees from two different queen lines fed pollens from locations that differed in floral species composition and yearly colony cycles. We detected differences between the queen lines in the amount of pollen they consumed and the size of their hypopharyngeal glands (HPG). There were also seasonal differences between the nutrient composition of pollens. Spring pollens collected from colonies in both locations had higher amino and fatty acid concentrations than fall pollens. There also were seasonal differences in responses to the pollens consumed by bees from both queen lines. Bees consumed more spring than fall pollen, but digested less of it so that bees consumed more protein from fall pollens. Though protein consumption was higher with fall pollen, HPG were larger in spring bees.

Abstract

Honey bee colonies have a yearly cycle that is supported nutritionally by the seasonal progression of flowering plants. In the spring, colonies grow by rearing brood, but in the fall, brood rearing declines in preparation for overwintering. Depending on where colonies are located, the yearly cycle can differ especially in overwintering activities. In temperate climates of Europe and North America, colonies reduce or end brood rearing in the fall while in warmer climates bees can rear brood and forage throughout the year. To test the hypothesis that nutrients available in seasonal pollens and honey bee responses to them can differ we analyzed pollen in the spring and fall collected by colonies in environments where brood rearing either stops in the fall (Iowa) or continues through the winter (Arizona). We fed both types of pollen to worker offspring of queens that emerged and open mated in each type of environment. We measured physiological responses to test if they differed depending on the location and season when the pollen was collected and the queen line of the workers that consumed it. Specifically, we measured pollen and protein consumption, gene expression levels (hex 70, hex 110, and vg) and hypopharyngeal gland (HPG) development. We found differences in macronutrient content and amino and fatty acids between spring and fall pollens from the same location and differences in nutrient content between locations during the same season. We also detected queen type and seasonal effects in HPG size and differences in gene expression between bees consuming spring vs. fall pollen with larger HPG and higher gene expression levels in those consuming spring pollen. The effects might have emerged from the seasonal differences in nutritional content of the pollens and genetic factors associated with the queen lines we used.

Plant-based supplement containing B-complex vitamins can improve bee health and increase colony performance

It is common knowledge that nutritive stress resulting from decreased diversity and quality of food, pollution of food sources and beekeeping errors may lead to increased susceptibility of bees to pathogens and pesticides. The dearth of adequate food is frequently compensated with supplements. Thus, this research was aimed to study the effects of the plant-based supplement B + on colony strength (assessed according to open and sealed brood area, honey and pollen/bee bread reserves, and the number of adult bees). In addition, Nosema ceranae spores and viruses were quantified and the level of infestation with Varroa destructor assessed. The experiment was conducted in late summer and early spring. In colonies which were given B + in feed a significant increase (p < 0.05) in the parameters of colony strength were noticed in comparison to the control (colonies fed on sugar syrup). Moreover, it was proven that the bees from these colonies had significantly lower (p < 0.05) N. ceranae spore counts, and acute bee paralysis, deformed wing and sacbrood virus loads. Our results suggest that the addition of B + supplement to the colonies provide them with nutrients, contribute to their strengthening, might prevent nutritive stress and increase the success of bees in combating pathogens.