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Environmental monitoring involves the quantification of microscopic cells and particles such as algae, plant cells, pollen, or fungal spores. Traditional methods using conventional microscopy require expert knowledge, are time-intensive and not well-suited for automated high throughput. Multispectral imaging flow cytometry (MIFC) allows measurement of up to 5000 particles per second from a fluid suspension and can simultaneously capture up to 12 images of every single particle for brightfield and different spectral ranges, with up to 60x magnification. The high throughput of MIFC has high potential for increasing the amount and accuracy of environmental monitoring, such as for plant-pollinator interactions, fossil samples, air, water or food quality that currently rely on manual microscopic methods. Automated recognition of particles and cells is also possible, when MIFC is combined with deep-learning computational techniques. Furthermore, various fluorescence dyes can be used to stain specific parts of the cell to highlight physiological and chemical features including: vitality of pollen or algae, allergen content of individual pollen, surface chemical composition (carbohydrate coating) of cells, DNA- or enzyme-activity staining. Here, we outline the great potential for MIFC in environmental research for a variety of research fields and focal organisms. In addition, we provide best practice recommendations.

Nosema ceranae is a ubiquitous microsporidian pathogen infecting the midgut of honey bees. The infection causes bee nosemosis, a disease associated with malnutrition, dysentery, and lethargic behavior, and results in considerable economic losses in apiculture. The use of a rapid, sensitive, and inexpensive DNA-based molecular detection method assists in the surveillance and eventual control of this pathogen. To this end, a loop-mediated isothermal amplification (LAMP) assay targeting the single-copy gene encoding the polar tube protein 3 (PTP3) has been developed. Genomic DNA of N. ceranae-infected forager bees sampled from distant geographic regions could be reliably amplified using the established LAMP assay. The N. ceranae-LAMP showed higher sensitivity than a classical reference PCR (98.6 vs 95.7%), when both approaches were applied to the detection of N. ceranae. LAMP detected a ten-fold lower infection rate than the reference PCR (1 pg vs 10 pg genomic DNA, respectively). In addition, we show highly specific and sensitive detection of N. ceranae from spore preparations in a direct LAMP format. No cross-reactions with genomic DNA and/or spores from N. apis, often co-infecting A. mellifera, or from N. bombi, infecting bumble bees, were observed. This low-cost and time-saving molecular detection method can be easily applied in simple laboratory settings, facilitating a rapid detection of N. ceranae in honey bees in epidemiological studies, surveillance and control, as well as evaluation of therapeutic measures against nosemosis.

Post-surgery liver failure is a serious complication for patients after extended partial hepatectomies (ePHx). Previously, we demonstrated in the pig model that transplantation of mesenchymal stromal cells (MSC) improved circulatory maintenance and supported multi-organ functions after 70% liver resection. Mechanisms behind the beneficial MSC effects remained unknown. Here we performed 70% liver resection in pigs with and without MSC treatment, and animals were monitored for 24 h post surgery. Gene expression profiles were determined in the lung and liver. Bioinformatics analysis predicted organ-independent MSC targets, importantly a role for thrombospondin-1 linked to transforming growth factor-β (TGF-β) and downstream signaling towards providing epithelial plasticity and epithelial-mesenchymal transition (EMT). This prediction was supported histologically and mechanistically, the latter with primary hepatocyte cell cultures. MSC attenuated the surgery-induced increase of tissue damage, of thrombospondin-1 and TGF-β, as well as of epithelial plasticity in both the liver and lung. This suggests that MSC ameliorated surgery-induced hepatocellular stress and EMT, thus supporting epithelial integrity and facilitating regeneration. MSC-derived soluble factor(s) did not directly interfere with intracellular TGF-β signaling, but inhibited thrombospondin-1 secretion from thrombocytes and non-parenchymal liver cells, therewith obviously reducing the availability of active TGF-β.

Pollinating bees are stressed by highly variable environmental conditions, malnutrition, parasites and pathogens, but may also by getting in contact with microorganisms or entomopathogenic nematodes that are used to control plant pests and diseases. While foraging for water, food, or nest material social as well as solitary bees have direct contact or even consume the plant protection product with its active substance (e.g., viruses, bacteria, fungi, etc.). Here, we summarize the results of cage, microcolony, observation hive assays, semi-field and field studies using full-size queen-right colonies. By now, some species and subspecies of the Western and Eastern honey bee (Apis mellifera, A. cerana), few species of bumble bees, very few stingless bee species and only a single species of leafcutter bees have been studied as non-target host organisms. Survival and reproduction are the major criteria that have been evaluated. Especially sublethal effects on the bees' physiology, immune response and metabolisms will be targets of future investigations. By studying infectivity and pathogenic mechanisms, individual strains of the microorganism and impact on different bee species are future challenges, especially under field conditions. Overall, it became evident that honey bees, bumble bees and few stingless bee species may not be suitable surrogate species to make general conclusions for biological mechanisms of bee-microorganism interactions of other social bee species. Solitary bees have been studied on leafcutter bees (Megachile rotundata) only, which shows that this huge group of bees (∼20,000 species worldwide) is right at the beginning to get an insight into the interaction of wild pollinators and microbial plant protection organisms.

To avoid potential adverse side effects of chemical plant protection products, microbial pest control products (MPCP) are commonly applied as biological alternatives. This study aimed to evaluate the biosafety of a MPCP with the active organism Bacillus thuringiensis ssp. aizawai (strain: ABTS-1857). An in-hive feeding experiment was performed under field-realistic conditions to examine the effect of B. thuringiensis (B. t.) on brood development and the bacterial abundance of the core gut microbiome (Bifidobacterium asteroids, Gilliamella apicola, the group of Lactobacillus and Snodgrasella alvi) in Apis mellifera worker bees. We detected a higher brood termination rate and a non-successful development into worker bees of treated colonies compared to those of the controls. For the gut microbiome, all tested core members showed a significantly lower normalized abundance in bees of the treated colonies than in those of the controls; thus, a general response of the gut microbiome may be assumed. Consequently, colony exposure to B. t. strain ABTS-1857 had a negative effect on brood development under field-realistic conditions and caused dysbiosis of the gut microbiome. Further studies with B. t.–based products, after field-realistic application in bee attractive crops, are needed to evaluate the potential risk of these MPCPs on honey bees.

Honey bees (Apis mellifera) perform pollination service for many agricultural crops and contribute to the global economy in agriculture and bee products. However, honey bee health is an ongoing concern, as illustrated by persistent local population decline, caused by some severe bee diseases (e.g., nosemosis, AFB, EFB, chalkbrood). Three natural recipes are in development based on the bioactive compounds of different plants extract (Agastache foeniculum, Artemisia absinthium, Evernia prunastri, Humulus lupulus, Laurus nobilis, Origanum vulgare and Vaccinium myrtillus), characterised by HPLC-PDA. The antimicrobial activity of these recipes was tested in vitro against Paenibacillus larvae, Paenibacillus alvei, Brevibacillus laterosporus, Enterococcus faecalis, Ascosphaera apis and in vivo against Nosema ceranae. A mix of 20% blueberry, 40% absinthium, 10% oakmoss, 10% oregano, 10% Brewers Gold hops, 5% bay laurel and 5% anise hyssop extract showed the strongest antibacterial and antifungal activity. Combing several highly active plant extracts might be an alternative treatment against bee-disease-associated parasites and pathogens, in particular to replace synthetic antibiotics.

In the European honey bee (Apis mellifera), the olfactory system is essential for foraging and intraspecific communication via pheromones. Honey bees are equipped with a large repertoire of olfactory receptors belonging to the insect odorant receptor (OR) family. Previous studies have indicated that the transcription level of a few OR types including OR11, a receptor activated by the queen-released pheromone compound (2E)-9-oxodecenoic acid (9-ODA), is significantly higher in the antenna of males (drones) than in female workers. However, the number and distribution of antennal cells expressing male-biased ORs is elusive. Here, we analyzed antennal sections from bees by in situ hybridization for the expression of the male-biased receptors OR11, OR18, and OR170. Our results demonstrate that these receptors are expressed in only moderate numbers of cells in the antennae of females (workers and queens), whereas substantially higher cell numbers express these ORs in drones. Thus, the reported male-biased transcript levels are due to sex-specific differences in the number of antennal cells expressing these receptors. Detailed analyses for OR11 and OR18 in drone antennae revealed expression in two distinct subsets of olfactory sensory neurons (OSNs) that in total account for about 69% of the OR-positive cells. Such high percentages of OSNs expressing given receptors are reminiscent of male-biased ORs in moths that mediate the detection of female-released sex pheromone components. Collectively, our findings indicate remarkable similarities between male antenna of bees and moths and support the concept that male-biased ORs in bee drones serve the detection of female-emitted sex pheromones. This article is protected by copyright. All rights reserved.

European foulbrood (EFB), caused by Melissococcus plutonius, is a globally distributed bacterial brood disease affecting Apis mellifera larvae. There is some evidence, even if under debate, that spreading of the disease within the colony is prevented by worker bees performing hygienic behaviour, including detection and removal of infected larvae. Olfactory cues (brood pheromones, signature mixtures, diagnostic substances) emitted by infected individuals may play a central role for hygienic bees to initiate the disease-specific behaviour. However, the mechanisms of cue detection and brood removal, causing hygienic behaviour in EFB affected colonies, are poorly understood. Here, coupled gas chromatography-mass spectrometry (GC–MS) was used to detect disease-specific substances, changes in cuticular hydrocarbon (CHC) profiles, and brood ester pheromones (BEPs) of honey bee larvae artificially infected with M. plutonius. Although no diagnostic substances were found in significant quantities, discriminant analysis revealed specific differences in CHC and BEP profiles of infected and healthy larvae. β-Ocimene, a volatile brood pheromone related to starvation and hygienic behaviour, was present in all larvae with highest quantities in healthy young larvae; whereas oleic acid, a non-volatile necromone, was present only in old infected larvae. Furthermore, γ-octalactone (newly discovered in A. mellifera in this study) was detectable in trace amounts only in infected larvae. We propose that the deviation from the olfactory profile of healthy brood is supposed to trigger hygienic behaviour in worker bees. To confirm the relevance of change in the chemical bouquet (CHCs, BEPs, γ-octalactone, etc.), a field colony bioassay is needed, using healthy brood and hygienic bees to determine if bouquet changes elicit hygienic behaviour.

Natural honey bee products, especially propolis are well known for their biological properties. However, less well known are the impact of propolis’ single phenolic substances and variation across ...

Paenibacillus larvae is the etiological agent of American Foulbrood (AFB), a highly contagious brood disease of honey bees (Apis mellifera). AFB requires mandatory reporting to the veterinary authority in many countries and until now four genotypes, P. larvae ERIC I-IV, have been identified. We isolated a new genotype, ERIC V, from a Spanish honey sample. After a detailed phenotypic comparison with the reference strains of the ERIC I-IV genotypes, including spore morphology, non-ribosomal peptide (NRP) profiling, and in vivo infections of A. mellifera larvae, we established a genomic DNA Macrorestriction Fragment Pattern Analysis (MRFPA) scheme for future epidemiologic discrimination. Whole genome comparison of the reference strains and the new ERIC V genotype (DSM 106052) revealed that the respective virulence gene inventories of the five genotypes corresponded with the time needed to kill 100 % of the infected bee larvae (LT100) in in vivo infection assays. The rarely isolated P. larvae genotypes ERIC II I-V with a fast-killing phenotype (LT100 3 days) harbor genes with high homology to virulence factors of other insect pathogens. These virulence genes are absent in the epidemiologically prevalent genotypes ERIC I (LT100 12 days) and ERIC II (LT100 7 days), which exhibit slower killing phenotypes. Since killing-retardation is known to reduce the success of hygienic cleaning by nurse bees, the identified absence of virulence factors might explain the epidemiological prevalences of ERIC genotypes. The discovery of the P. larvae ERIC V isolate suggests that more unknown ERIC genotypes exist in bee colonies. Since inactivation or loss of a few genes can transform a fast-killing phenotype into a more dangerous slow-killing phenotype, these rarely isolated genotypes may represent a hidden reservoir for future AFB outbreaks.

Social insects are the target of numerous pathogens. This is because the high density of closely-related individuals frequently interacting with each other enhances the transmission and establishment of pathogens. This high selective pressure results in the rapid evolution of immune genes, which might be counteracted by a reduced effective population size (Ne) lowering the effectiveness of selection. We tested the effect of Ne on the evolutionary rate of an important immune gene for the antimicrobial peptide Hymenoptaecin in two common central European bumblebee species: Bombus terrestris and Bombus lapidarius. Both species are similar in their biology and are expected to be under similar selective pressures because pathogen prevalence does not differ between species. However, previous studies indicated a higher Ne in B. terrestris compared to B. lapidarius. We found high intraspecific variability in the coding sequence but low variability for silent polymorphisms in B. lapidarius. Estimates of long- and short-term Ne were three- to four-fold higher Ne in B. terrestris, although the species did not differ in census population sizes. The difference in Ne might result in less efficient selection and suboptimal adaptation of immune genes (e.g. hymenoptaecin) in B. lapidarius, and thus this species might become less resistant and more tolerant, turning into a superspreader of diseases.

Honeybee collected pollen exhibits high nutritional and pharmaceutical benefits for the human diet and medicine. Pollen’s antioxidant, anti-ageing, anti-inflammatory, anti-atherosclerosis, and cardioprotective activity, depending on the floral origin, are well known. Recent studies proposed that pollen may also be an excellent cancer-fighting candidate, as pollen harbours high amounts of phenolic substances. In our study, Filipendula ulmaria pollen (bee collected) was methanol-water extracted and used to verify its in vitro pharmacological activities on C26 mice cancer tumour cells. Three different concentrations of the extract were tested in antitumour assays. Monitoring was done after 6, 12, 24, and 48 hours. Promising results were obtained for antiproliferative and apoptotic activity of the pollen extracts, with high efficiency for the highest concentration (1 mg/mL). For both activities, time and concentration-dependent effects were observed. Pollen extracts or bee collected pollen has a high potential as an antitumour agent for use in human medicine, because they are both rich in bioactive compounds.

Recent losses of honeybee (Apis mellifera) colonies have been linked to several non-exclusive factors; such as pests, parasites, pesticides (e.g., neonicotinoids) and other toxins. Whereas these losses pose a threat to apiculture, the number of globally managed colonies appeared to be less affected because beekeepers replace lost colonies. From a socioeconomic and ecological perspective the number of managed colonies is arguably more relevant when addressing the issue of apiculture and pollination services provided by honeybees. We here use the FAO data base to dissect the interactions between the global honey market and the number of colonies. Global scale analyses do not show a general colony decline. Whereas Western Europe and the US show suffer colony declines, other regions show considerable increase. We could not find any link between the colony dynamics and the occurrence of specific pathogens or the use of pesticides. In contrast, changes in the political and socioeconomic system show strong effects on apiculture. In addition, many countries show a tight negative correlation between honey import and the number of managed colonies. For some countries, the amount of honey produced per colony is highly positively correlated with the amount of honey imports, and we cannot exclude large scale relabeling of imported to nationally produced honey. It is very clear that honey trade is a dominating factor for the number of managed colonies since countries with a strong import and export ratio are those suffering most strongly from colony declines.

Honey bees directly affect and are influenced by their local environment, in terms of food sources, pollinator densities, pathogen and toxin exposure and climate. Currently, there is a lack of studies analyzing these data with Geographic Information Systems (GIS) to investigate spatial relationships with the environment. Particularly for inter-colonial pathogen transmission, it is known that the likelihood of a healthy colony to become infested (e.g., Varroosis) or infected (e.g., American foulbrood—AFB, European foulbrood—EFB) increases with higher colony density. Whether these transmission paths can actually be asserted at apiary level is largely unknown. Here, we unraveled spatial distribution and high-resolution density of apiaries and bacterial honey bee brood diseases in Switzerland based on available GIS data. Switzerland as ‘model country’ offers the unique opportunity to get apiary data since 2010 owing to compulsory registration for every beekeeper. Further, both destructive bee brood diseases (AFB and EFB) are legally notifiable in Switzerland, and EFB has an epizootic character for the last decades. As governmental data sets have to be ameliorated, raw data from the cantonal agricultural or veterinary offices have been included. We found a mean density of 0.56 apiaries per km2, and high resolution spatial analyzes showed strong correlation between density of apiaries and human population density as well as agricultural landscape type. Concerning two bacterial bee brood diseases (AFB, EFB), no significant correlation was detectable with density of apiaries on cantonal level, though a high correlation of EFB cases and apiary density became obvious on higher resolution (district level). Hence, Swiss EFB epizootics seem to have benefited from high apiary densities, promoting the transmission of pathogens by adult bees. The GIS-based method presented here, might also be useful for other bee diseases, anthropogenic or environmental factors affecting bee colonies.

Honey bees are highly prone to infectious diseases, causing colony losses in the worst case. However, they combat diseases through a combination of their innate immune system and social defence behaviours like foraging for health-enhancing plant products (e.g. nectar, pollen and resin). Plant secondary metabolites are not only highly active against bacteria and fungi, they might even enhance selective foraging and feeding decisions in the colony. Here, we tested six major plant terpenes and their corresponding acetates, characterizing six natural Thymus vulgaris chemotypes, for their antimicrobial activity on bacteria associated with European foulbrood. Comparison of the inhibitory activity revealed the highest activity for carvacrol and thymol whereas the acetates mostly did not inhibit bacterial growth. All terpenes and acetates are present in the nectar and pollen of thyme, with pollen containing concentrations higher by several orders of magnitude. The physiological response was tested on forager and freshly emerged bees by means of antennal electroantennography. Both responded much stronger to geraniol and trans-sabinene hydrate compared to carvacrol and thymol. In conclusion, bee-forageable thyme product terpenes (mainly from pollen) yield effective antibiotic activity by reducing the growth of bee disease-associated bacteria and can be detected with different response levels by the honey bees’ antennae. This is a further step forward in understanding the complex pathogen-pollinator-plant network.

Several environmental factors (e.g. food source, pesticides, toxins, parasites and pathogens) influence development and maturation of honey bees (Apis mellifera). Therefore, controlled experimental conditions are mandatory when studying the impact of environmental factors: particularly food quality and nutrient consumption. In vitro larval rearing is a standard approach for monitoring food intake of larvae and the labelling of food is necessary to quantify intake in controlled feeding experiments. Here, we tested the suitability of two food dyes, Allura Red and Brilliant Blue, in an experimental set up using in vitro reared honey bee larvae and freshly hatched adult workers. Absorbance of both dyes was measured, in food and dye-fed larvae, to determine the optimal dye concentrations for accurate detection and quantification. By quantifying relative dye concentrations in dye mixtures, relative concentrations of mixed dyes can be estimated independent of the total food consumed by the larvae. Survival assays were conducted to test the impact of both dyes on larval and worker bee survival. Worker bees showed no increase in adult mortality, when fed with dyed honey. Larval survival was not significantly different until the late pupal stage. The physiological impact of dye feeding was tested by measuring larval immune response. No changes in innate immune gene expression were detectable for larvae fed with dyed and non-dyed food. In conclusion, we established a non-invasive food labelling protocol for food intake quantification in in vitro reared honey bee larvae, using non-toxic, inexpensive, and easy to apply food dyes.

Ongoing intensification of rice production systems in Southeast Asia is causing devastating yield losses each year due to rice hoppers. Their continuing development of immunity to resistant rice varieties and pesticide applications further complicates this problem. Hence, there is a high demand for biological control agents of rice hoppers. Egg parasitoid wasps are among the most important natural enemies of rice hoppers, such as Nilaparvata lugens and Nephotettix spp. However, our knowledge of their diversity is still very limited, due to their small size and the lack of available morphological information. Classifying these parasitoids is the first step to properly understanding their role in the rice agroecosystem. We used traditional morphological identification, as well as DNA sequencing of the 28S rRNA and the COI genes, to investigate the diversity of four important hopper egg parasitoid genera in the Philippines. Parasitoids of the genera Anagrus, Oligosita, Gonatocerus, and Paracentrobia were collected in eight study landscapes located in Luzon. Our findings illustrate that characterization of species diversity using morphological and molecular analyses were concordant only for the genus Paracentrobia. The genera Anagrus and Gonatocerus exhibited more genetic diversity than estimated with the morphological analysis, while the opposite was observed for Oligosita. This is the first study investigating the molecular diversity of rice hopper parasitoids in the Philippines. More research combining morphological, behavioral, and molecular methods, as well as the establishment of a comprehensive DNA database, are urgently needed to assess the performance and suitability of these organisms as biocontrol agents.

Social insects have evolved enormous capacities to collectively build nests and defend their colonies against both predators and pathogens. The latter is achieved by a combination of individual immune responses and sophisticated collective behavioral and organizational disease defenses, that is, social immunity. We investigated how the presence or absence of these social defense lines affects individual‐level immunity in ant queens after bacterial infection. To this end, we injected queens of the ant Linepithema humile with a mix of gram+ and gram− bacteria or a control solution, reared them either with workers or alone and analyzed their gene expression patterns at 2, 4, 8, and 12 hr post‐injection, using RNA‐seq. This allowed us to test for the effect of bacterial infection, social context, as well as the interaction between the two over the course of infection and raising of an immune response. We found that social isolation per se affected queen gene expression for metabolism genes, but not for immune genes. When infected, queens reared with and without workers up‐regulated similar numbers of innate immune genes revealing activation of Toll and Imd signaling pathways and melanization. Interestingly, however, they mostly regulated different genes along the pathways and showed a different pattern of overall gene up‐regulation or down‐regulation. Hence, we can conclude that the absence of workers does not compromise the onset of an individual immune response by the queens, but that the social environment impacts the route of the individual innate immune responses.

Honeybees are prone to parasite and pathogen infestations/infections due to their social colony life. Bacterial pathogens in particular lead to destructive infections of the brood. European foulbrood is caused by the bacterium Melissococcus plutonius in combination with several other Gram-positive bacteria (Achromobacter eurydice, Bacillus pumilus, Brevibacillus laterosporus, Enterococcus faecalis, Paenibacillus alvei, Paenibacillus dendritiformis) involved as secondary invaders following the initial infection. More than a century ago, A. eurydice was discovered to be associated with European foulbrood and morphologically and biochemically characterized. However, since the 1950s-1960s, only a few studies are known covering the biological relevance of this bacterium. Here, we review the biology, ecology, morphology, and biochemistry and discuss the still unclear systematic classification of A. eurydice.

The Brandenburg State Agency for Rural Development, Agriculture and Land Consolidation to the HOSIMET (Homogenous sperm mixing technology in Europe-wide Varroa Tolerance Breeding) breeding program (State association of Buckfast beekeepers Berlin-Brandenburg e.V.).

Honeybee colonies offer an excellent environment for microbial pathogen development. The highest virulent, colony killing, bacterial agents are Paenibacillus larvae causing American foulbrood (AFB), and European foulbrood (EFB) associated bacteria. Besides the innate immune defense, honeybees evolved behavioral defenses to combat infections. Foraging of antimicrobial plant compounds plays a key role for this “social immunity” behavior. Secondary plant metabolites in floral nectar are known for their antimicrobial effects. Yet, these compounds are highly plant specific, and the effects on bee health will depend on the floral origin of the honey produced. As worker bees not only feed themselves, but also the larvae and other colony members, honey is a prime candidate acting as self-medication agent in honeybee colonies to prevent or decrease infections. Here, we test eight AFB and EFB bacterial strains and the growth inhibitory activity of three honey types. Using a high-throughput cell growth assay, we show that all honeys have high growth inhibitory activity and the two monofloral honeys appeared to be strain specific. The specificity of the monofloral honeys and the strong antimicrobial potential of the polyfloral honey suggest that the diversity of honeys in the honey stores of a colony may be highly adaptive for its “social immunity” against the highly diverse suite of pathogens encountered in nature. This ecological diversity may therefore operate similar to the well-known effects of host genetic variance in the arms race between host and parasite.

Honeybees, Apis mellifera, have several prophylactic disease defense strategies, including the foraging of antibiotic, antifungal, and antiviral compounds of plant products. Hence, honey and pollen contain many compounds that prevent fungal and bacterial growth and inhibit viral replication. Since these compounds are also fed to the larvae by nurse bees, they play a central role for colony health inside the hive. Here, we show that honeybee nurse bees, infected with the microsporidian gut parasite Nosema ceranae, show different preferences for various types of honeys in a simultaneous choice test. Infected workers preferred honeys with a higher antibiotic activity that reduced the microsporidian infection after the consumption of the honey. Since nurse bees feed not only the larvae but also other colony members, this behavior might be a highly adaptive form of therapeutic medication at both the individual and the colony level.

In the honeybee, Apis mellifera, the queen larvae are fed with a diet exclusively composed of royal jelly (RJ), a secretion of the hypopharyngeal gland of young worker bees that nurse the brood. Up to 15% of RJ is composed of proteins, the nine most abundant of which have been termed major royal jelly proteins (MRJPs). Although it is widely accepted that RJ somehow determines the fate of a female larva and in spite of considerable research efforts, there are surprisingly few studies that address the biochemical characterisation and functions of these MRJPs. Here we review the research on MRJPs not only in honeybees but in hymenopteran insects in general and provide metadata analyses on genome organisation of mrjp genes, corroborating previous reports that MRJPs have important functions for insect development and not just a nutritional value for developing honeybee larvae.

Viral diseases are one of the multiple factors associated with honeybee colony losses. Apart from their innate immune system, including the RNAi machinery, honeybees can use secondary plant metabolites to reduce or fully cure pathogen infections. Here, we tested the antiviral potential of Laurus nobilis leaf ethanolic extracts on forager honeybees naturally infected with BQCV (Black queen cell virus). Total viral loads were reduced even at the lowest concentration tested (1mg/ml). Higher extract concentrations (≥5mg/ml) significantly reduced virus replication. Measuring vitellogenin gene expression as an indicator for transcript homeostasis revealed constant RNA levels before and after treatment, suggesting that its expression was not impacted by the L. nobilis treatment. In conclusion, plant secondary metabolites can reduce virus loads and virus replication in naturally infected honeybees.

International audience; AbstractApitherapy promises cures for diseases in human folk medicine, but the effects of honeybee produced and foraged compounds on bee health are less known. Yet, hive products should chiefly facilitate medication and sanitation of the honeybees themselves rather than other organisms. We here review the impact of both self-produced gland secretions and foraged hive products (pharmacognosy) on colony health. Although foraged plant-derived compounds vary highly in antibiotic activity depending on the floral and regional origins, secondary plant metabolites in honey, pollen and propolis are important for the antibiotic activity against pathogens and parasites. However, specific bee health-enhancing activities of bee products should clearly be distinguished from the effects of an intact nutrition ensuring the basic immune competence of bees. Further unravelling the interactions among groups of active substances or individual compounds used in concert with specific behavioural adaptations will deepen our understanding of the natural potential of honeybees to maintain colony health.

Local adaptation within host-parasite systems can evolve by several non-exclusive drivers (e.g., host species-genetic adaptation; ecological conditions-ecological adaptation, and time-temporal adaptation). Social insects, especially bumblebees, with an annual colony life history not only provide an ideal system to test parasite transmission within and between different host colonies, but also parasite adaptation to specific host species and environments. Here, we study local adaptation in a multiple-host parasite characterized by high levels of horizontal transmission. Crithidia bombi occurs as a gut parasite in several bumblebee species. Parasites were sampled from five different host species in two subsequent years. Population genetic tools were used to test for the several types of adaptation. Although we found no evidence for local adaptation of the parasite toward host species, there was a slight temporal differentiation of the parasite populations, which might have resulted from severe bottlenecks during queen hibernation. Parasite populations were in Hardy-Weinberg equilibrium and showed no signs of linkage disequilibrium suggesting that sexual reproduction is an alternative strategy in this otherwise clonal parasite. Moreover, high levels of multiple infections were found, which might facilitate sexual genetic exchange. The detection of identical clones in different host species suggested that horizontal transmission occurs between host species and underpins the lack of host-specific adaptation.

Social insects are prone to attack by parasites as they provide numerous resources of food and brood, homeostatic nest conditions and a high density of individuals, enhancing the transmission of parasites. The defence of social insects might occur at different levels, the individual and the group. Individual defence occurs in part via the innate immune system resulting in the expression of antimicrobial substances. Group level defences, summarised as ‘social immunity’, represent a suite of behavioural and organisational features. Here, all effects contributing to social immunity except for the social context were removed from bumblebee (Bombus terrestris) workers, kept either in groups or solitarily. The gene expression of six effector molecules of the immune system was monitored in both groups and in controls from the same source colonies. The social treatment has a highly significant effect on immune gene expression, with groups exhibiting higher levels of two antimicrobial peptides (AMPs) and two lysozymes. Phenoloxidase is affected at the regulatory level, with a strong upregulation of its suppressor Spn27A in groups suggesting a trade-off with antimicrobial activity. AMPs are strongly upregulated in groups, whereas lysozymes are strongly downregulated in solitary treatments suggesting another trade-off. Clearly, social immunity impacts elements of individual immunity.