Presence of Nosema ceranae in honeybees (Apis mellifera) in Uruguay

Beneficial Bacteria and Plant Extracts Promote Honey Bee Health and Reduce Nosema ceranae Infection

The research aims to give new insights on the effect of administering selected bacterial strains, isolated from honey bee gut, and/or a commercial plant extract blend (HiveAlive®) on Nosema ceranae. Analyses were first performed under laboratory conditions such as different infective doses of N. ceranae, the effect of single strains and their mixture and the influence of pollen administration. Daily survival and feed consumption rate were recorded and pathogen development was analysed using qPCR and microscope counts. Biomarkers of immunity and physiological status were also evaluated for the different treatments tested using one bacterial strain, a mixture of all the bacteria and/or a plant extract blend as treatments. The results showed an increase of abaecin transcript levels in the midgut of the honey bees treated with the bacterial mixture and an increased expression of the protein vitellogenin in the haemolymph of honey bees treated with two separate bacterial strains (Bifidobacterium coryneforme and Apilactobacillus kunkeei). A significant effectiveness in reducing N. ceranae was shown by the bacterial mixture and the plant extract blend regardless of the composition of the diet. This bioactivity was seasonally linked. Quantitative PCR and microscope counts showed the reduction of N. ceranae under different experimental conditions. The antiparasitic efficacy of the treatments at field conditions was studied using a semi-field approach which was adapted from research on insecticides for the first time, to analyse antiparasitic activity against N. ceranae. The approach proved to be reliable and effective in validating data obtained in the laboratory. Both the mixture of beneficial bacteria and its association with Hive Alive® are effective in controlling the natural infection of N. ceranae in honey bee colonies.

A tale of two parasites: Responses of honey bees infected with Nosema ceranae and Lotmaria passim

Nosema ceranae and Lotmaria passim are two commonly encountered digestive tract parasites of the honey bee that have been associated with colony losses in Canada, the United States, and Europe. Though honey bees can be co-infected with these parasites, we still lack basic information regarding how they impact bee health at the individual and colony level. Using locally-isolated parasite strains, we investigated the effect of single and co-infections of these parasites on individual honey bee survival, and their responsiveness to sucrose. Results showed that a single N. ceranae infection is more virulent than both single L. passim infections and co-infections. Honey bees singly infected with N. ceranae reached < 50% survival eight days earlier than those inoculated with L. passim alone, and four days earlier than those inoculated with both parasites. Honey bees infected with either one, or both, parasites had increased responsiveness to sucrose compared to uninfected bees, which could correspond to higher levels of hunger and increased energetic stress. Together, these findings suggest that N. ceranae and L. passim pose threats to bee health, and that the beekeeping industry should monitor for both parasites in an effort correlate pathogen status with changes in colony-level productivity and survival.

Significant, but not biologically relevant: Nosema ceranae infections and winter losses of honey bee colonies

The Western honey bee Apis mellifera, which provides about 90% of commercial pollination, is under threat from diverse abiotic and biotic factors. The ectoparasitic mite Varroa destructor vectoring deformed wing virus (DWV) has been identified as the main biotic contributor to honey bee colony losses worldwide, while the role of the microsporidium Nosema ceranae is still controversially discussed. In an attempt to solve this controversy, we statistically analyzed a unique data set on honey bee colony health collected from a cohort of honey bee colonies over 15 years and comprising more than 3000 data sets on mite infestation levels, Nosema spp. infections, and winter losses. Multivariate statistical analysis confirms that V. destructor is the major cause of colony winter losses. Although N. ceranae infections are also statistically significantly correlated with colony losses, determination of the effect size reveals that N. ceranae infections are of no or low biological relevance.

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

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

Vairimorpha ceranae was the only detected microsporidian species from Iranian honey bee colonies: a molecular and phylogenetic study

Nosemosis caused by Vairimorpha ceranae is one of the most important threats to honeybee colonies worldwide. This study aimed to determine the prevalence and intensity of Vairimorpha infection in different types of colonies and locations in Iran. In October 2017 and May 2018, 376 colonies from 97 apiaries were selected for each month according to a randomly clustered design. By considering 3-5 colonies for each apiary, 20 adult bees as pooled samples were collected from each colony. In microscopic analysis, 46.52% and 46.1% of samples in May and October showed Vairimorpha spores, respectively. The infection intensities in May and October were 5.94 ± 0.19 (× 10⁶) and 5.86 ± 0.23 (× 10⁶) spores/bee in a pooled sample, respectively. The mean infection intensity ranged from 1.8 to 12.5 (× 10⁶) spores/bee. Statistically, there were no significant differences in the prevalence and intensity of V. ceranae infection between May and October samples. No significant differences were found among the prevalence rates of infection in the types of colonies; however, the intensity was significantly higher in migratory and mountainous colonies in May and only in migratory colonies in October. There was a significant correlation between the prevalence and intensity of V. ceranae infection (r² = 0.695). PCR analysis showed that the samples were only infected with V. ceranae. No intraspecific variation to V. ceranae was found by direct sequencing of the amplified fragment of 16S rRNA. The obtained sequence was mainly 100% similar to those of V. ceranae isolates from European countries.

Honey bees with a drinking problem: potential routes of Nosema ceranae spore transmission

Nosema apis and N. ceranae are the two causative agents of Nosema disease in adult honey bees (Apis mellifera L.). Nosema apis has been a recognized parasite for over a century and its epizootiology is well known. In contrast, N. ceranae is an emerging parasite of honey bees, which is now globally prevalent and the dominant Nosema spp. in many parts of the world. Despite this, many gaps in our knowledge exist regarding this species. For example, we do not fully understand all of the routes of transmission of N. ceranae among bees, or how long this parasite is capable of surviving in honey bee colonies. Here we investigated the viability and infectivity of N. ceranae spores in water and 2 M sucrose over time after storage at 33, 20, −12 and −20°C. Spores in both 2 M sucrose and water maintained high viability, except in water at −20°C over the course of the 6-week experiment. Infectivity was variable for spores after storage at all four temperatures, but all were infective at the last time point. The results provide evidence for cold tolerance and suggest that both water and 2 M sucrose (fall bee feed) could act as routes of transmission for N. ceranae. This work also contains information that may help influence management recommendations for the parasite.

Factors Associated with Honey Bee Colony Losses: A Mini-Review

The Western honey bee (Apis mellifera L., Hymenoptera: Apidae) is a species of crucial economic, agricultural and environmental importance. In the last ten years, some regions of the world have suffered from a significant reduction of honey bee colonies. In fact, honey bee losses are not an unusual phenomenon, but in many countries worldwide there has been a notable decrease in honey bee colonies. The cases in the USA, in many European countries, and in the Middle East have received considerable attention, mostly due to the absence of an easily identifiable cause. It has been difficult to determine the main factors leading to colony losses because of honey bees’ diverse social behavior. Moreover, in their daily routine, they make contact with many agents of the environment and are exposed to a plethora of human activities and their consequences. Nevertheless, various factors have been considered to be contributing to honey bee losses, and recent investigations have established some of the most important ones, in particular, pests and diseases, bee management, including bee keeping practices and breeding, the change in climatic conditions, agricultural practices, and the use of pesticides. The global picture highlights the ectoparasitic mite Varroa destructor as a major factor in colony loss. Last but not least, microsporidian parasites, mainly Nosema ceranae, also contribute to the problem. Thus, it is obvious that there are many factors affecting honey bee colony losses globally. Increased monitoring and scientific research should throw new light on the factors involved in recent honey bee colony losses. The present review focuses on the main factors which have been found to have an impact on the increase in honey bee colony losses.

Nosema ceranae (Microspora: Nosematidae): A Sweet Surprise? Investigating the Viability and Infectivity of N. ceranae Spores Maintained in Honey and on Beeswax

Nosema disease is a prominent malady among adult honey bees [Apis mellifera L. (Hymenoptera: Apidae)], caused by the microsporidian parasites, Nosema apis Zander (Microspora: Nosematidae) and N. ceranae Fries et al. 1996. The biology of N. apis is well understood, as this parasite was first described over a century ago. As N. ceranae is an emerging parasite of the honey bee, we do not yet understand how long spores of this parasite survive in honey bee colonies, or all the potential modes of transmission among bees. We investigated the viability and infectivity of N. ceranae spores in honey and on beeswax over time after exposure to 33, 20, -12, and -20°C. Spores in honey maintained viability at freezing temperatures for up to 1 yr and remained viable considerably longer than those on beeswax. Based on this evidence, honey may act as an important reservoir for infective spores to initiate or perpetuate N. ceranae infections in honey bee colonies. This work provides information that may help enhance current management recommendations for apiculturalists.

A combined LC-MS and NMR approach to reveal metabolic changes in the hemolymph of honeybees infected by the gut parasite Nosema ceranae

Nosema ceranae is an emerging and invasive gut pathogen in Apis mellifera and is considered as a factor contributing to the decline of honeybee populations. Here, we used a combined LC-MS and NMR approach to reveal the metabolomics changes in the hemolymph of honeybees infected by this obligate intracellular parasite. For metabolic profiling, hemolymph samples were collected from both uninfected and N. ceranae-infected bees at two time points, 2 days and 10 days after the experimental infection of emergent bees. Hemolymph samples were individually analyzed by LC-MS, whereas each NMR spectrum was obtained from a pool of three hemolymphs. Multivariate statistical PLS-DA models clearly showed that the age of bees was the parameter with the strongest effect on the metabolite profiles. Interestingly, a total of 15 biomarkers were accurately identified and were assigned as candidate biomarkers representative of infection alone or combined effect of age and infection. These biomarkers included carbohydrates (α/β glucose, α/β fructose and hexosamine), amino acids (histidine and proline), dipeptides (Glu-Thr, Cys-Cys and γ-Glu-Leu/Ile), metabolites involved in lipid metabolism (choline, glycerophosphocholine and O-phosphorylethanolamine) and a polyamine compound (spermidine). Our study demonstrated that this untargeted metabolomics-based approach may be useful for a better understanding of pathophysiological mechanisms of the honeybee infection by N. ceranae.

Seasonality of Nosema ceranae Infections and Their Relationship with Honey Bee Populations, Food Stores, and Survivorship in a North American Region

Nosema ceranae is an emerging pathogen of the western honey bee (Apis mellifera L.), and thus its seasonality and impact on bee colonies is not sufficiently documented for North America. This study was conducted to determine the infection intensity, prevalence, and viability of N. ceranae in >200 honey bee colonies during spring, summer, and fall, in a North American region. We also determined the relationship of N. ceranae infections with colony populations, food stores, bee survivorship, and overwinter colony mortality. The highest rates of N. ceranae infection, prevalence, and spore viability were found in the spring and summer, while the lowest were recorded in the fall. N. ceranae spore viability was significantly correlated with its prevalence and infection intensity in bees. Threshold to high levels of N. ceranae infections (>1,000,000 spores/bee) were significantly associated with reduced bee populations and food stores in colonies. Furthermore, worker bee survivorship was significantly reduced by N. ceranae infections, although no association between N. ceranae and winter colony mortality was found. It is concluded that N. ceranae infections are highest in spring and summer and may be detrimental to honey bee populations and colony productivity. Our results support the notion that treatment is justified when infections of N. ceranae exceed 1,000,000 spores/bee.

Effect of Feeding Honey Bee (Apis mellifera Hymenoptera: Apidae) Colonies With Honey, Sugar Solution, Inverted Sugar, and Wheat Starch Syrup on Nosematosis Prevalence and Intensity

Here, we present the results of a 2-year field trial aimed at testing the effect of overwintering on different feeds on the course of Nosema ceranae infection. In August 2015, four experimental bee colony groups were established. After the last honey harvest, each colony was provided with 20 kg of feed, either honey, sugar (3:2 solution in tap water), inverted syrup made of sucrose, or wheat starch syrup. Samples of live bees were collected from each beehive in August (before feeding), November, and May. The following year, feeding and sampling were performed in the same way. Bees were examined microscopically to estimate the percentage of Nosema-infected individuals in the sample and the spore number per bee. Fitness parameters were also measured in all colonies. In all hives, presence of N. ceranae was confirmed through polymerase chain reaction. Nosema apis was not detected in the apiary. Significant differences in nosematosis prevalence and/or intensity were observed between the experimental groups. For most parameters, best results were recorded in the group fed with honey. Worst fitness and highest nosematosis prevalence and intensity were found in colonies fed with wheat starch syrup.

Consequences of a short time exposure to a sublethal dose of Flupyradifurone (Sivanto) pesticide early in life on survival and immunity in the honeybee (Apis mellifera)

Dramatic losses of pollinating insects have become of global concern, as they threaten not only key ecosystem services but also human food production. Recent research provided evidence that interactions between ecological stressors are drivers of declining pollinator health and responsible for observed population collapses. We used the honeybee Apis mellifera and conducted a series of experiments to test for long-term effects of a single short exposure to the agricultural pesticide flupyradifurone to a second environmental stressor later in life. To do this, we exposed individuals during their larval development or early adulthood to sublethal dosages of flupyradifurone (0.025 μg for larvae and 0.645 μg for imagos), either pure or as part of an agricultural formulation (Sivanto). We afterwards exposed bees to a second ecological stressor infecting individuals with 10,000 spores of the fungal gut parasite Nosema ceranae. We found that pesticide exposures significantly reduced survival of bees and altered the expression of several immune and detoxification genes. The ability of bees to respond to these latter effects differed significantly between colonies, offering opportunities to breed bees with elevated levels of pesticide tolerance in the future. We conclude that short episodes of sublethal pesticide exposures during development are sufficient to trigger effects later in life and could therefore contribute to the widespread declines in bee health.

The levels of natural Nosema spp. infection in Apis mellifera iberiensis brood stages

Nosema ceranae is the most prevalent endoparasite of Apis mellifera iberiensis and it is a major health problem for bees worldwide. The infective capacity of N. ceranae has been demonstrated experimentally in honey bee brood, however no data are available about its prevalence in brood under natural conditions. Thus, brood combs from 10 different hives were analyzed over two consecutive years, taking samples before and after winter. A total of 1433 larvae/pupae were analyzed individually and N. ceranae (3.53%) was the microsporidian most frequently detected, as opposed to Nosema apis (0.42%) which was more frequently detected in conjunction with N. ceranae (0.71%). The active multiplication of both microsporidians was confirmed by the expression (real-time-PCR) of the N. ceranae polar tube protein 3 gene and/or the N. apis RNA polymerase II gene in 24% of the brood samples positive for Nosema spp. Both genes are related to microsporidian multiplication. As such, N. ceranae multiplication was confirmed in 1.06% of the samples, while N. apis multiplication was only observed in co-infections with N. ceranae (0.07%). Brood cells were analyzed for the presence of Nosema spp., as those are the immediate environment where the brood stages develop. The brood samples infected by Nosema spp. were in brood cells in which that microsporidians were not detected, while brood cells positive for N. ceranae hosted brood stages that were not apparently infected, indicating that this is unlikely to be the main pathway of infection. Finally, the colonies with brood infected by N. ceranae showed higher levels (numbers) of infected adult bees, although the differences were not significant before (P = 0.260), during (P = 0.055) or after (P = 0.056) brood sampling. These results show that N. ceranae is a bee parasite ubiquitous to all members of the colony, irrespective of the age of the bee. It is also of veterinary interest and should be considered when studying the epidemiology of the disease.

Detection of two Microsporidia pathogens of the European honey bee Apis Mellifera (Insecta: Apidae) in Western Siberia

Two species of microsporidia, Nosema apis and Nosema ceranae, occur regularly and cause significant losses in apiculture throughout the world. N. ceranae is thought to be an emerging pathogen of the European honey bee which is replacing N. apis. Microscopic analysis of honey bees collected in Tyumen region, South-Western Siberia, suggested presence of two microsporidial pathogens slightly differing in spore size and shape. PCR detection using species-specific primer sets 312APIS and 218MITOC followed by PCR product sequencing confirmed the diagnosis of N. apis and N. ceranae, respectively. Microsporidia were present in private apiaries through 2008-2010, and among 21 colonies from 7 localities, two colonies were infected with both pathogens, while infections with N. apis only were detected in 8, and with N. ceranae only in 13 colonies. These data suggest that N. ceranae is widely spread in South-Western Siberia alongside with N. apis and is able to persist in the regions with average January temperatures below -18°C.

Nosema ceranae infection in honeybee samples from Tuscanian Archipelago (Central Italy) investigated by two qPCR methods

Nosema apis and Nosema ceranae are microsporidian parasite worldwide spread causing an emerging infectious disease of European honeybee Apis mellifera. The Nosema presence was deeply investigated in several countries but low information are presents about islands. In this investigation was evaluated the presence N. ceranae and N. apis in apiaries located in Tuscanian Archipelago islands (Central Italy). For N. ceranae detection, two different Real-Time PCR (qPCR) methods, the 16S rRNA and Hsp70 gene amplification qPCR, were performed on honey bee samples; while, for N. apis only the 16S rRNA qPCR amplification was performed. On all islands, only N. ceranae was present, while N. apis was not found in the samples. The two qPCR showed significant difference (p < 0.040) in N. ceranae spores quantification. The single-copy Hsp70 gene method qPCR assay systematically detected a lower amount of N. ceranae copies compared to the multi-copy 16S rRNA gene method.

Distribution of Nosema Spp. in climatic regions of Iran

‎Nosemosis is one of the most prevalent bee diseases in the world causing significant ‎economic losses in the global bee-keeping industry. This cross-sectional study was conducted during April-September, 2016 to investigate the prevalence of nosemosis in different climatic regions of Iran. A total of 183 ‎apiaries were selected based on cluster sampling and the climate of apiaries under study was classified using Domarten method. In each apiary, five percent of the colonies were ‎ randomly sampled. A total of 183 adult bee samples were taken and examined by microscopic and polymerase chain reaction (PCR) methods for the presence of Nosema infections. According to the results, infection caused by Nosema ceranae was observed in all regions under study. The prevalence of N.ceranae was 46.40% (42.70–50.10). However, infection with Nosema apis was not observed in the samples in either pure form or as ‎associated infection. Based on the results of PCR, the prevalence of N. ceranae was ‎53.80% (46.60– 61.00) ‎ in ‎humid, ‎71.00% (53.70–77.50) ‎ in semi-humid‎, ‎68.10% (61.40–74.80) ‎ in very humid, ‎29.40% (22.70–36.10) in arid, ‎34.30% (27.40–41.20) in semi-‎arid and ‎24.00% (17.90–30.00)‎ in Mediterranean climates. The prevalence of ‎infection in different climatic zones of the country was found to have significant ‎differences (p < 0.001). ‎ According to the findings, N. ceranae ‎ was the only Nosema species in honeybees with a broad geographical dispersion in Iran. It seems that climate can influence the prevalence of mentioned parasite. ‎

Nosemosis control in European honey bees, Apis mellifera, by silencing the gene encoding Nosema ceranae polar tube protein 3

RNA interference (RNAi) is a post-transcriptional gene silencing mechanism triggered by double-stranded RNA (dsRNA) that is homologous in sequence to the silenced gene and is conserved in a wide range of eukaryotic organisms. The RNAi mechanism has provided unique opportunities for combating honey bee diseases caused by various parasites and pathogens. Nosema ceranae is a microsporidian parasite of European honey bees, Apis mellifera, and has been associated with honey bee colony losses in some regions of the world. Here we explored the possibility of silencing the expression of a N. ceranae putative virulence factor encoding polar tube protein 3 (ptp3) which is involved in host cell invasion as a therapeutic strategy for controlling Nosema parasites in honey bees. Our studies showed that the oral ingestion of a dsRNA corresponding to the sequences of N. ceranae ptp3 could effectively suppress the expression of the ptp3 gene in N. ceranae-infected bees and reduce Nosema load. In addition to the knockdown of ptp3 gene expression, ingestion of ptp3-dsRNA also led to improved innate immunity in bees infected with N. ceranae along with an improvement in physiological performance and lifespan compared with untreated control bees. These results strongly suggest that RNAi-based therapeutics hold real promise for the effective treatment of honey bee diseases in the future, and warrant further investigation.

Chronic Nosema ceranae infection inflicts comprehensive and persistent immunosuppression and accelerated lipid loss in host Apis mellifera honey bees

Nosema ceranae is an intracellular microsporidian parasite of the Asian honey bee Apis cerana and the European honey bee Apis mellifera. Until relatively recently, A. mellifera honey bees were naïve to N. ceranae infection. Symptoms of nosemosis, or Nosema disease, in the infected hosts include immunosuppression, damage to gut epithelium, nutrient and energetic stress, precocious foraging and reduced longevity of infected bees. Links remain unclear between immunosuppression, the symptoms of nutrient and energetic stress, and precocious foraging behavior of hosts. To clarify physiological connections, we inoculated newly emerged A. mellifera adult workers with N. ceranae spores, and over 21 days post inoculation (21 days pi), gauged infection intensity and quantified expression of genes representing two innate immune pathways, Toll and Imd. Additionally, we measured each host's whole-body protein, lipids, carbohydrates and quantified respirometric and activity levels. Results show sustained suppression of genes of both humorally regulated immune response pathways after 6 days pi. At 7 days pi, elevated protein levels of infected bees may reflect synthesis of antimicrobial peptides from an initial immune response, but the lack of protein gain compared with uninfected bees at 14 days pi may represent low de novo protein synthesis. Carbohydrate data do not indicate that hosts experience severe metabolic stress related to this nutrient. At 14 days pi infected honey bees show high respirometric and activity levels, and corresponding lipid loss, suggesting lipids may be used as fuel for increased metabolic demands resulting from infection. Accelerated lipid loss during nurse honey bee behavioral development can have cascading effects on downstream physiology that may lead to precocious foraging, which is a major factor driving colony collapse.

The first report of the prevalence of Nosema ceranae in Bulgaria

Nosema apis and Nosema ceranae are the two main microsporidian parasites causing nosematosis in the honey bee Apis mellifera. The aim of the present study is to investigate the presence of Nosema apis and Nosema ceranae in the area of Bulgaria. The 16S (SSU) rDNA gene region was chosen for analysis. A duplex PCR assay was performed on 108 honey bee samples from three different parts of the country (South, North and West Bulgaria). The results showed that the samples from the northern part of the country were with the highest prevalence (77.2%) for Nosema ceranae while those from the mountainous parts (the Rodopa Mountains, South Bulgaria) were with the lowest rate (13.9%). Infection with Nosema apis alone and co-infection N. apis/N. ceranae were not detected in any samples. These findings suggest that Nosema ceranae is the dominant species in the Bulgarian honey bee. It is not known when the introduction of Nosema ceranae in Bulgaria has occurred, but as in the rest of the world, this species has become the dominant one in Bulgarian Apis mellifera. In conclusion, this is the first report for molecular detection of Nosema infection of honey bee in Bulgaria. The results showed that N. ceranae is the main Nosema species in Bulgaria.

Nosema ceranae in South American Native Stingless Bees and Social Wasp

Besides the incipient research effort, the role of parasites as drivers of the reduction affecting pollinator populations is mostly unknown. Given the worldwide extension of the beekeeping practice and the diversity of pathogens affecting Apis mellifera populations, honey bee colonies are a certain source of parasite dispersion to other species. Here, we communicate the detection of the microsporidium Nosema ceranae, a relatively new parasite of honey bees, in stingless bees (Meliponini) and the social wasp Polybia scutellaris (Vespidae) samples from Argentina and Brazil by means of duplex PCR. Beyond the geographic location of the nests, N. ceranae was detected in seven from the eight Meliponini species analyzed, while Nosema apis, another common parasite of A. mellifera, was absent in all samples tested. Further research is necessary to determine if the presence of the parasite is also associated with established infection in host tissues. The obtained information enriches the current knowledge about pathologies that can infect or, at least, be vectored by native wild pollinators from South America.

Determination of spore longevity and viability of Nosema apis and Nosema ceranae according to storage conditions

Honey bee colonies are often infected with Nosema apis and Nosema ceranae which cause adult honey bee disease called nosemosis. All honey bee colony members can be infected with these species. In addition, it is claimed to be the main cause of honey bee winter losses in many countries. Nosema spores are expected to resistant the environmental conditions and their infectivity continues for a long time because of long-term durability of fungal spores. In this study, the viability of Nosema spores were investigated in terms of storage situations under laboratory conditions. Honey bee samples that were collected from apiaries in 2011 were investigated to detect the presence of Nosema species with real-time PCR amplification studies. After determination of Nosema species, each sample was divided in two groups. One of these groups was used to find Nosema spore concentration. Nosema solutions were divided and stored at both -20°C and +4°C. The spore concentration was measured every year in the period 2011-2015. Other group of honey bee samples was also stored at -20°C and every year was used for Nosema spore counting. Furthermore, it was examined the infectivity of Nosema spores with sugar solutions which obtained each sample using cage experiment techniques. According to results, when we compare the solutions annually, there is no change at Nosema spore concentration of the solution in -20°C and honeybee samples in -20°C. But reduction was seen at Nosema spore concentration of the solution in +4°C. Nosema spore infectivity tests revealed that infectivity of Nosema spores has not changed significantly between 2011 and 2015. This is the first time mixed Nosema spores found more infective than one-type spore after prolonged exposure to different conditions.

Long-Term Temporal Trends of Nosema spp. Infection Prevalence in Northeast Germany: Continuous Spread of Nosema ceranae, an Emerging Pathogen of Honey Bees (Apis mellifera), but No General Replacement of Nosema apis

The Western honey bee (Apis mellifera) is widely used as commercial pollinator in worldwide agriculture and, therefore, plays an important role in global food security. Among the parasites and pathogens threatening health and survival of honey bees are two species of microsporidia, Nosema apis and Nosema ceranae. Nosema ceranae is considered an emerging pathogen of the Western honey bee. Reports on the spread of N. ceranae suggested that this presumably highly virulent species is replacing its more benign congener N. apis in the global A. mellifera population. We here present a 12 year longitudinal cohort study on the prevalence of N. apis and N. ceranae in Northeast Germany. Between 2005 and 2016, a cohort of about 230 honey bee colonies originating from 23 apiaries was sampled twice a year (spring and autumn) resulting in a total of 5,600 bee samples which were subjected to microscopic and molecular analysis for determining the presence of infections with N. apis or/and N. ceranae. Throughout the entire study period, both N. apis- and N. ceranae-infections could be diagnosed within the cohort. Logistic regression analysis of the prevalence data demonstrated a significant increase of N. ceranae-infections over the last 12 years, both in autumn (reflecting the development during the summer) and in spring (reflecting the development over winter) samples. Cell culture experiments confirmed that N. ceranae has a higher proliferative potential than N. apis at 27° and 33°C potentially explaining the increase in N. ceranae prevalence during summer. In autumn, characterized by generally low infection prevalence, this increase was accompanied by a significant decrease in N. apis-infection prevalence. In contrast, in spring, the season with a higher prevalence of infection, no significant decrease of N. apis infections despite a significant increase in N. ceranae infections could be observed. Therefore, our data do not support a general advantage of N. ceranae over N. apis and an overall replacement of N. apis by N. ceranae in the studied honey bee population.

Characterization of Nosema ceranae Genetic Variants from Different Geographic Origins

In recent years, large-scale colony losses of honey bees (Apis mellifera) have been reported and the infection with the microsporidia Nosema ceranae has been involved. However, the effect of N. ceranae at the colony level and its role in colony losses vary in different geographic areas. This difference may be related to the presence of multiple N. ceranae genetic variants resulting in different biological consequences. In this study, we analyzed the genetic diversity of 75 N. ceranae samples obtained from 13 countries and Hawaii through inter-sequence single repetition (ISSR) and evaluated if two of these genetic variants triggered different immune responses when infecting Apis mellifera iberiensis. The genetic diversity analysis showed that 41% of the samples had the same DNA amplification pattern, including samples from most European countries except Spain, while the remaining samples showed high variability. Infection assays were performed to analyze the infection levels and the immune response of bees infected with N. ceranae from Spain and Uruguay. The infected bees presented similar infection levels, and both isolates downregulated the expression of abaecin, confirming the ability of the microsporidia to depress the immune response. Only N. ceranae from Uruguay downregulated the expression level of imd compared to control bees. On the other hand, both genetic variants triggered different expression levels of lysozyme. As imd and lysozyme play important roles in the response to pathogens, these results could reflect differences in the biological consequences of N. ceranae variants in A. mellifera infection.

Host sharing by the honey bee parasites Lotmaria passim and Nosema ceranae

The trypanosome Lotmaria passim and the microsporidian Nosema ceranae are common parasites of the honey bee, Apis mellifera, intestine, but the nature of interactions between them is unknown. Here, we took advantage of naturally occurring infections and quantified infection loads of individual workers (N = 408) originating from three apiaries (four colonies per apiary) using PCR to test for interactions between these two parasites. For that purpose, we measured the frequency of single and double infections, estimated the parasite loads of single and double infections, and determined the type of correlation between both parasites in double infections. If interactions between both parasites are strong and antagonistic, single infections should be more frequent than double infections, double infections will have lower parasite loads than single infections, and double infections will present a negative correlation. Overall, a total of 88 workers were infected with N. ceranae, 53 with L. passim, and eight with both parasites. Although both parasites were found in all three apiaries, there were significant differences among apiaries in the proportions of infected bees. The data show no significant differences between the expected and observed frequencies of single‐ and double‐infected bees. While the infection loads of individual bees were significantly higher for L. passim compared to N. ceranae, there were no significant differences in infection loads between single‐ and double‐infected hosts for both parasites. These results suggest no strong interactions between the two parasites in honey bees, possibly due to spatial separation in the host. The significant positive correlation between L. passim and N. ceranae infection loads in double‐infected hosts therefore most likely results from differences among individual hosts rather than cooperation between parasites. Even if hosts are infected by multiple parasites, this does not necessarily imply that there are any significant interactions between them.

Nosema ceranae Winter Control: Study of the Effectiveness of Different Fumagillin Treatments and Consequences on the Strength of Honey Bee (Hymenoptera: Apidae) Colonies

OVERVIEW

In Uruguay, colonies of honey bees moving to Eucalyptus grandis plantation in autumn habitually become infected with the microsporidian Nosema ceranae , a parasite that attacks the digestive system of bees. Beekeepers attributed to N. ceranae depopulation of the colonies that often occurs at the end of the blooming period, and many use the antibiotic fumagillin to reduce the level of infection. The aim of this study was to compare the effectiveness of four different fumagillin treatments and determine how this antibiotic affects the strength of the colonies during the winter season. The colonies treated with fumagillin in July showed less spore load at the end of applications, being the most effective the following treatments: the four applications sprayed over bees of 30 mg of fumagillin in 100 ml of sugar syrup 1:1, and four applications of 90 mg of fumagillin in 250 ml of sugar syrup 1:1 using a feeder. However, 2 month after the treatment applications, the colonies treated with fumagillin were the same size as the untreated colonies. In September, the colonies treated and not treated with fumagillin did not differ in colony strength (adult bee population and brood area) or spores abundance. Our study demonstrates that fumagillin treatment temporarily decreased the spore load of N. ceranae , but this was not reflected in either the size of the colonies or the probability of surviving the winter regardless of the dose or the administration strategy applied. Given the results obtained, we suggest to not perform the pharmacological treatment under the conditions described in the experiment.

RESUMEN

En Uruguay las colonias de abejas melíferas que se trasladan a las forestaciones de Eucalyptus grandis en otoño indefectiblemente se infectan con el microsporido Nosema ceranae , parásito que ataca el sistema digestivo de las abejas. Los apicultores atribuyen a N. ceranae el despoblamiento de las colonias que ocurre con frecuencia al terminar el periodo de floración y muchos emplean el antibiótico fumagilina para reducir el nivel de infección. El objetivo de este estudio fue comparar la eficacia de cuatro tratamientos diferentes con fumagilina y determinar cómo incide en la fortaleza de las colonias durante la invernada. Las colonias tratadas con fumagilina en julio presentaron una menor carga de esporas al terminar las aplicaciones, siendo los tratamientos más eficaces el de 4 aplicaciones mediante asperjado sobre las abejas de 30 mg de fumagilina en 100 ml de jarabe de azúcar 1:1, y el de 4 aplicaciones de 90 mg de fumagilina en 250 ml de jarabe de azúcar 1:1 utilizando un alimentador. Sin embargo, durante el período de experimentación, las colonias tratadas con antibiótico presentaron igual tamaño que las colonias no tratadas. En setiembre, las colonias tratadas y no tratadas con fumagilina no se diferenciaron en la intensidad de infección ni en su tamaño. En las condiciones en que se realizó el estudio, la aplicación de fumagilina disminuyó temporalmente la carga de esporas de N. ceranae pero esto no se reflejó en el tamaño de las colonias ni en la probabilidad de sobrevivir el invierno.

Nosema ceranae is an old resident of honey bee (Apis mellifera) colonies in Mexico, causing infection levels of one million spores per bee or higher during summer and fall

This study was conducted to identify Nosema spp. and to determine their infection levels in honey bee (Apis mellifera) samples collected in Mexico in 1995-1996. Samples of historical surveys from different countries are of particular interest to support or challenge the hypothesis that the microsporidium Nosema ceranae is a new parasite of A. mellifera that has recently dispersed across the world. We demonstrate that N. ceranae has parasitized honey bees in Mexico since at least 1995 and that the infection levels of this parasite during summer and fall, exceed the threshold at which treatment of honey bee colonies is recommended.

Silencing the Honey Bee (Apis mellifera) Naked Cuticle Gene (nkd) Improves Host Immune Function and Reduces Nosema ceranae Infections

Nosema ceranae is a new and emerging microsporidian parasite of European honey bees, Apis mellifera, that has been implicated in colony losses worldwide. RNA interference (RNAi), a posttranscriptional gene silencing mechanism, has emerged as a potent and specific strategy for controlling infections of parasites and pathogens in honey bees. While previous studies have focused on the silencing of parasite/pathogen virulence factors, we explore here the possibility of silencing a host factor as a mechanism for reducing parasite load. Specifically, we used an RNAi strategy to reduce the expression of a honey bee gene, naked cuticle (nkd), which is a negative regulator of host immune function. Our studies found that nkd mRNA levels in adult bees were upregulated by N. ceranae infection (and thus, the parasite may use this mechanism to suppress host immune function) and that ingestion of double-stranded RNA (dsRNA) specific to nkd efficiently silenced its expression. Furthermore, we found that RNAi-mediated knockdown of nkd transcripts in Nosema-infected bees resulted in upregulation of the expression of several immune genes (Abaecin, Apidaecin, Defensin-1, and PGRP-S2), reduction of Nosema spore loads, and extension of honey bee life span. The results of our studies clearly indicate that silencing the host nkd gene can activate honey bee immune responses, suppress the reproduction of N. ceranae, and improve the overall health of honey bees. This study represents a novel host-derived therapeutic for honey bee disease treatment that merits further exploration.

IMPORTANCE

Given the critical role of honey bees in the pollination of agricultural crops, it is urgent to develop strategies to prevent the colony decline induced by the infection of parasites/pathogens. Targeting parasites and pathogens directly by RNAi has been proven to be useful for controlling infections in honey bees, but little is known about the disease impacts of RNAi silencing of host factors. Here, we demonstrate that knocking down the honey bee immune repressor-encoding nkd gene can suppress the reproduction of N. ceranae and improve the overall health of honey bees, which highlights the potential role of host-derived and RNAi-based therapeutics in controlling the infections in honey bees. The information obtained from this study will have positive implications for honey bee disease management practices.

Viability and infectivity of fresh and cryopreserved Nosema ceranae spores

The microsporidium fungus Nosema ceranae is an intracellular parasite that infects the midgut of the honey bee, Apis mellifera. A major limitation of research on N. ceranae is that the fungus is non-culturable and thus studying it depends on the seasonal availability of Nosema spores. Also, spore viability and infectivity can vary considerably, and thus there is a need for reliable methods for determining those traits. This study examined different conditions for N. ceranae spore cryopreservation at -70°C, assessing spore viability and infectivity. Viability was determined by a staining procedure counting total spores numbers with bright field microscopy and un-viable spore numbers with the fluorescent dye, propidium iodide. Spore infectivity was determined with a dilution inoculation assay. Infectivity was dependent on the inoculum dose for the proportion of bees with detectable Nosema infections based on the number of spores per bee at 18days after inoculation; 4000 spores per bee or higher were needed to get approx. 100% of the inoculated bees infected. The median infective dose (ID₅₀) was 149 spores per bee, and the minimum dose capable of causing a detectable infection was 1.28 spores. The proportion of N. ceranae infected bees correlated significantly with the number of spores per bee (r=0.98, P<0.0001). N. ceranae spores cryopreserved in water or 10% glycerol did not differ in viability compared to fresh spores, but lost infectivity when inoculated into bees. This study shows that while cryopreservation of N. ceranae spores can preserve viability, the spores can have reduced infectivity.

Colony Level Prevalence and Intensity of Nosema ceranae in Honey Bees (Apis mellifera L.)

Nosema ceranae is a widely prevalent microsporidian parasite in the western honey bee. There is considerable uncertainty regarding infection dynamics of this important pathogen in honey bee colonies. Understanding the infection dynamics at the colony level may aid in development of a reliable sampling protocol for N. ceranae diagnosis, and provide insights into efficient treatment strategies. The primary objective of this study was to characterize the prevalence (proportion of the sampled bees found infected) and intensity (number of spores per bee) of N. ceranae infection in bees from various age cohorts in a colony. We examined N. ceranae infection in both overwintered colonies that were naturally infected with N. ceranae and in quadruple cohort nucleus colonies that were established and artificially inoculated with N. ceranae. We also examined and quantified effects of N. ceranae infection on hypopharyngeal gland protein content and gut pH. There was no correlation between the prevalence and intensity of N. ceranae infection in composite samples (pooled bee samples used for analysis). Our results indicated that the prevalence and intensity of N. ceranae infection is significantly influenced by honey bee age. The N. ceranae infection prevalence values from composite samples of background bees (unmarked bees collected from four different locations in a colony) were not significantly different from those pertaining to marked-bee age cohorts specific to each sampling date. The foraging-aged bees had a higher prevalence of N. ceranae infection when compared to nurse-aged bees. N. ceranae did not have a significant effect on hypopharyngeal gland protein content. Further, there was no significant difference in mean gut pH of N. ceranae infected bees and non-infected bees. This study provides comprehensive insights into N. ceranae infection dynamics at the colony level, and also demonstrates the effects of N. ceranae infection on hypopharyngeal gland protein content and midgut pH.

Approaches and Challenges to Managing Nosema (Microspora: Nosematidae) Parasites in Honey Bee (Hymenoptera: Apidae) Colonies

The microsporidia Nosema apis (Zander) and Nosema ceranae (Fries) are common intestinal parasites in honey bee (Apis mellifera L.) colonies. Though globally prevalent, there are mixed reports of Nosema infection costs, with some regions reporting high parasite virulence and colony losses, while others

REPORT

high Nosema prevalence but few costs. Basic and applied studies are urgently needed to help beekeepers effectively manage Nosema spp., ideally through an integrated pest management approach that allows beekeepers to deploy multiple strategies to control Nosema when Nosema is likely to cause damage to the colonies, rather than using prophylactic treatments. Beekeepers need practical and affordable technologies that facilitate disease diagnosis and science-backed guidelines that recommend when, if at all, to treat infections. In addition, new treatment methods are needed, as there are several problems associated with the chemical use of fumagillin (the only currently extensively studied, but not globally available treatment) to control Nosema parasites. Though selective breeding of Nosema-resistant or tolerant bees may offer a long-term, sustainable solution to Nosema management, other treatments are needed in the interim. Furthermore, the validation of alternative treatment efficacy in field settings is needed along with toxicology assays to ensure that treatments do not have unintended, adverse effects on honey bees or humans. Finally, given variation in Nosema virulence, development of regional management guidelines, rather than universal guidelines, may provide optimal and cost-effective Nosema management, though more research is needed before regional plans can be developed.

Do managed bees drive parasite spread and emergence in wild bees?

Bees have been managed and utilised for honey production for centuries and, more recently, pollination services. Since the mid 20th Century, the use and production of managed bees has intensified with hundreds of thousands of hives being moved across countries and around the globe on an annual basis. However, the introduction of unnaturally high densities of bees to areas could have adverse effects. Importation and deployment of managed honey bee and bumblebees may be responsible for parasite introductions or a change in the dynamics of native parasites that ultimately increases disease prevalence in wild bees. Here we review the domestication and deployment of managed bees and explain the evidence for the role of managed bees in causing adverse effects on the health of wild bees. Correlations with the use of managed bees and decreases in wild bee health from territories across the globe are discussed along with suggestions to mitigate further health reductions in wild bees.

Seasonal Variation of Honeybee Pathogens and its Association with Pollen Diversity in Uruguay

Honeybees are susceptible to a wide range of pathogens, which have been related to the occurrence of colony loss episodes reported mainly in north hemisphere countries. Their ability to resist those infections is compromised if they are malnourished or exposed to pesticides. The aim of the present study was to carry out an epidemiological study in Uruguay, South America, in order to evaluate the dynamics and interaction of honeybee pathogens and evaluate their association with the presence of external stress factors such as restricted pollen diversity and presence of agrochemicals. We monitored 40 colonies in two apiaries over 24 months, regularly quantifying colony strength, parasite and pathogen status, and pollen diversity. Chlorinated pesticides, phosphorus, pyrethroid, fipronil, or sulfas were not found in stored pollen in any colony or season. Varroa destructor was widespread in March (end of summer-beginning of autumn), decreasing after acaricide treatments. Viruses ABPV, DWV, and SBV presented a similar trend, while IAPV and KBV were not detected. Nosema ceranae was detected along the year while Nosema apis was detected only in one sample. Fifteen percent of the colonies died, being associated to high V. destructor mite load in March and high N. ceranae spore loads in September. Although similar results have been reported in north hemisphere countries, this is the first study of these characteristics in Uruguay, highlighting the regional importance. On the other side, colonies with pollen of diverse botanical origins showed reduced viral infection levels, suggesting that an adequate nutrition is important for the development of healthy colonies.

Effects, but no interactions, of ubiquitous pesticide and parasite stressors on honey bee (Apis mellifera) lifespan and behaviour in a colony environment

Interactions between pesticides and parasites are believed to be responsible for increased mortality of honey bee (Apis mellifera) colonies in the northern hemisphere. Previous efforts have employed experimental approaches using small groups under laboratory conditions to investigate influence of these stressors on honey bee physiology and behaviour, although both the colony level and field conditions play a key role for eusocial honey bees. Here, we challenged honey bee workers under in vivo colony conditions with sublethal doses of the neonicotinoid thiacloprid, the miticide tau-fluvalinate and the endoparasite Nosema ceranae, to investigate potential effects on longevity and behaviour using observation hives. In contrast to previous laboratory studies, our results do not suggest interactions among stressors, but rather lone effects of pesticides and the parasite on mortality and behaviour, respectively. These effects appear to be weak due to different outcomes at the two study sites, thereby suggesting that the role of thiacloprid, tau-fluvalinate and N. ceranae and interactions among them may have been overemphasized. In the future, investigations into the effects of honey bee stressors should prioritize the use of colonies maintained under a variety of environmental conditions in order to obtain more biologically relevant data.

Recent worldwide expansion of Nosema ceranae (Microsporidia) in Apis mellifera populations inferred from multilocus patterns of genetic variation

Nosema ceranae has been found infecting Apismellifera colonies with increasing frequency and it now represents a major threat to the health and long-term survival of these honeybees worldwide. However, so far little is known about the population genetics of this parasite. Here, we describe the patterns of genetic variation at three genomic loci in a collection of isolates from all over the world. Our main findings are: (i) the levels of genetic polymorphism (πS≈1%) do not vary significantly across its distribution range, (ii) there is substantial evidence for recombination among haplotypes, (iii) the best part of the observed genetic variance corresponds to differences within bee colonies (up to 88% of the total variance), (iv) parasites collected from Asian honeybees (Apis cerana and Apis florea) display significant differentiation from those obtained from Apismellifera (8-16% of the total variance, p<0.01) and (v) there is a significant excess of low frequency variants over neutral expectations among samples obtained from A. mellifera, but not from Asian honeybees. Overall these results are consistent with a recent colonization and rapid expansion of N. ceranae throughout A. mellifera colonies.

Infra-population and -community dynamics of the parasites Nosema apis and Nosema ceranae, and consequences for honey bee (Apis mellifera) hosts

Nosema spp. fungal gut parasites are among myriad possible explanations for contemporary increased mortality of western honey bees (Apis mellifera, hereafter honey bee) in many regions of the world. Invasive Nosema ceranae is particularly worrisome because some evidence suggests it has greater virulence than its congener N. apis. N. ceranae appears to have recently switched hosts from Asian honey bees (Apis cerana) and now has a nearly global distribution in honey bees, apparently displacing N. apis. We examined parasite reproduction and effects of N. apis, N. ceranae, and mixed Nosema infections on honey bee hosts in laboratory experiments. Both infection intensity and honey bee mortality were significantly greater for N. ceranae than for N. apis or mixed infections; mixed infection resulted in mortality similar to N. apis parasitism and reduced spore intensity, possibly due to inter-specific competition. This is the first long-term laboratory study to demonstrate lethal consequences of N. apis and N. ceranae and mixed Nosema parasitism in honey bees, and suggests that differences in reproduction and intra-host competition may explain apparent heterogeneous exclusion of the historic parasite by the invasive species.

Comprehensive bee pathogen screening in Belgium reveals Crithidia mellificae as a new contributory factor to winter mortality

Since the last decade, unusually high honey bee colony losses have been reported mainly in North-America and Europe. Here, we report on a comprehensive bee pathogen screening in Belgium covering 363 bee colonies that were screened for 18 known disease-causing pathogens and correlate their incidence in summer with subsequent winter mortality. Our analyses demonstrate that, in addition to Varroa destructor, the presence of the trypanosomatid parasite Crithidia mellificae and the microsporidian parasite Nosema ceranae in summer are also predictive markers of winter mortality, with a negative synergy being observed between the two in terms of their effects on colony mortality. Furthermore, we document the first occurrence of a parasitizing phorid fly in Europe, identify a new fourth strain of Lake Sinai Virus (LSV), and confirm the presence of other little reported pathogens such as Apicystis bombi, Aphid Lethal Paralysis Virus (ALPV), Spiroplasma apis, Spiroplasma melliferum and Varroa destructor Macula-like Virus (VdMLV). Finally, we provide evidence that ALPV and VdMLV replicate in honey bees and show that viruses of the LSV complex and Black Queen Cell Virus tend to non-randomly co-occur together. We also noticed a significant correlation between the number of pathogen species and colony losses. Overall, our results contribute significantly to our understanding of honey bee diseases and the likely causes of their current decline in Europe.

Do the honeybee pathogens Nosema ceranae and deformed wing virus act synergistically?

The honeybee pathogens Nosema ceranae and deformed wing virus (DWV) cause the collapse of honeybee colonies. Therefore, it is plausible that these two pathogens act synergistically to increase colony losses, since N.ceranae causes damage to the mid-gut epithelial ventricular cells and actively suppresses the honeybees' immune response, either of which could increase the virulence of viral pathogens within the bee. To test this hypothesis we exploited 322 Hawaiian honeybee colonies for which DWV prevalence and load is known. We determined via PCR that N.ceranae was present in 89-95% of these colonies, with no Nosema apis being detected. We found no significant difference in spore counts in colonies infected with DWV and those in which DWV was not detected, either on any of the four islands or across the entire honeybee population. Furthermore, no significant correlation between DWV loads (ΔCT levels) and N.ceranae spore counts was found, so these two pathogens are not acting synergistically. Although the Hawaiian honeybees have the highest known prevalence of N.ceranae in the world, with average number of spores been 2.7 million per bee, no acute Nosema related problems i.e. large-scale colony deaths, have been reported by Hawaiian beekeepers.

New insights on the genetic diversity of the honeybee parasiteNosema ceranaebased onmultilocussequence analysis

The microsporidian parasiteNosema ceranaeis a common pathogen of the Western honeybee (Apis mellifera) whose variable virulence could be related to its genetic polymorphism and/or its polyphenism responding to environmental cues. Since the genotyping ofN. ceranaebased on unique marker sequences had been unsuccessful, we tested whether amultilocusapproach, assessing the diversity of ten genetic markers – encoding nine proteins and the small ribosomal RNA subunit – allowed the discrimination betweenN. ceranaevariants isolated from singleA. melliferaindividuals in four distant locations. High nucleotide diversity and allele content were observed for all genes. Most importantly, the diversity was mainly present within parasite populations isolated from single honeybee individuals. In contrast the absence of isolate differentiation precluded anytaxadiscrimination, even through amultilocusapproach, but suggested that similar populations of parasites seem to infect honeybees in distant locations. As statistical evolutionary analyses showed that the allele frequency is under selective pressure, we discuss the origin and consequences ofN. ceranaeheterozygosity in a single host and lack of population divergence in the context of the parasite natural and evolutionary history.

Comparative susceptibility of three Western honeybee taxa to the microsporidian parasite Nosema ceranae

Genetic diversity of a host species is a key factor to counter infection by parasites. Since two separation events and the beginning of beekeeping, the Western honeybee, Apis mellifera, has diverged in many phylogenetically-related taxa that share common traits but also show specific physiological, behavioural and morphological traits. In this study, we tested the hypothesis that A. mellifera taxa living in a same habitat should respond differently to parasites like Nosema ceranae, a microsporidia living in host's midgut. We used the Poulin and Combes' concept of virulence to compare the susceptibility of three A. mellifera taxa to N. ceranae infection. Three criteria were measured 10 days post-infection (dpi): the host mortality, the host sugar consumption and the development success of the parasite (i.e. number of spores produced). Interestingly, we showed that the observed variation in susceptibility to infection by N. ceranae is not linked to honeybee taxa but results from the variability between colonies, and that those differences are probably linked to genetic variations. The use of these three criteria allows us to conclude that the differences in susceptibility are mediated by a genetic variability in honeybee workers from resistance to tolerance. Finally, we discuss the consequences of our findings for beekeeping management.

Temporal study of Nosema spp. in a cold climate

In a nationwide Swedish survey, 967 honey bee colonies from 521 beekeepers were sampled in the spring of 2007 and the samples assayed for Nosema spp. infections. Of the 319 positive samples, only 32 samples contained a proportion of N. ceranae DNA in mixed infections with both Nosema spp. above the cut-off point chosen for comparisons of 1%. Only one pure N. ceranae infection was found, with the rest 284 infected samples assayed being pure N. apis infections. In 2009 and 2011, beekeepers or bee inspectors providing N. ceranae mixed positive bee samples in 2007 were again asked to submit samples (2009, n = 96; 2011, n = 83). No trend of an increased proportion of N. ceranae-infected samples could be found. The proportion of N. ceranae DNA in samples with mixed infection did not increase between 2007 and 2011. It is concluded that N. apis is still the dominating Microsporidia infection in honey bees in Sweden and that there is no tendency for one species replacing the other.

Molecular differentiation of Nosema apis and Nosema ceranae based on species-specific sequence differences in a protein coding gene

Nosema apis and Nosema ceranae are two microsporidian pathogens of the European honey bee, Apis mellifera. There is evidence that N. ceranae is more virulent than N. apis subject to environmental factors like climate. This makes N. ceranae one of the suspects in the increasing colony losses recently observed in many regions of the world. Correct differentiation between N. apis and N. ceranae is important and best accomplished by molecular methods. So far only protocols based on species-specific sequence differences in the 16S rRNA gene are available. However, recent studies indicated that these methods may lead to confusing results due to polymorphisms in and recombination between the multi-copy 16S rRNA genes. To solve this problem and to provide a reliable molecular tool for the differentiation between the two bee pathogenic microsporidia we here present and evaluate a duplex-PCR protocol based on species-specific sequence differences in the highly conserved gene coding for the DNA-dependent RNA polymerase II largest subunit. A total of 102 honey bee samples were analyzed by the novel PCR protocol and the results were compared with the results of the originally published PCR-RFLP analysis and two recently published differentiation protocols, based on 16S rRNA sequence differences. Although the novel PCR protocol proved to be as reliable as the 16S rRNA gene based PCR-RFLP it was superior to simple 16S rRNA based PCR protocols which tended to overestimate the rate of N. ceranae infections. Therefore, we propose that species-specific sequence differences of highly conserved protein coding genes should become the preferred molecular tool for differentiation of Nosema spp.