Infected Honey Bees Research Articles

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

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.

Virion Structure of Israeli Acute Bee Paralysis Virus.

ABSTRACTThe pollination services provided by the western honeybee (Apis mellifera) are critical for agricultural production and the diversity of wild flowering plants. However, honeybees suffer from environmental pollution, habitat loss, and pathogens, including viruses that can cause fatal diseases. Israeli acute bee paralysis virus (IAPV), from the family Dicistroviridae, has been shown to cause colony collapse disorder in the United States. Here, we present the IAPV virion structure determined to a resolution of 4.0 Å and the structure of a pentamer of capsid protein protomers at a resolution of 2.7 Å. IAPV has major capsid proteins VP1 and VP3 with noncanonical jellyroll β-barrel folds composed of only seven instead of eight β-strands, as is the rule for proteins of other viruses with the same fold. The maturation of dicistroviruses is connected to the cleavage of precursor capsid protein VP0 into subunits VP3 and VP4. We show that a putative catalytic site formed by the residues Asp-Asp-Phe of VP1 is optimally positioned to perform the cleavage. Furthermore, unlike many picornaviruses, IAPV does not contain a hydrophobic pocket in capsid protein VP1 that could be targeted by capsid-binding antiviral compounds.IMPORTANCE Honeybee pollination is required for agricultural production and to sustain the biodiversity of wild flora. However, honeybee populations in Europe and North America are under pressure from pathogens, including viruses that cause colony losses. Viruses from the family Dicistroviridae can cause honeybee infections that are lethal, not only to individual honeybees, but to whole colonies. Here, we present the virion structure of an Aparavirus, Israeli acute bee paralysis virus (IAPV), a member of a complex of closely related viruses that are distributed worldwide. IAPV exhibits unique structural features not observed in other picorna-like viruses. Capsid protein VP1 of IAPV does not contain a hydrophobic pocket, implying that capsid-binding antiviral compounds that can prevent the replication of vertebrate picornaviruses may be ineffective against honeybee virus infections.

Analysis of the complete genome sequence of black queen cell virus JL1 from infected honeybees in China.

There are six strains of the complete genomic sequences of black queen cell virus (BQCV) published in the GenBank, including South Africa (AF183905), South Korea (JX149531), Hungary 10 (EF517515), Poland 4 (EF517519), Poland 5 (EF517520) and Poland 6 (EF517521). Based on the six BQCV strains published in the GenBank, ten pairs of primers were designed in the present study using reverse transcription polymerase chain reaction to obtain the first complete genome sequence of a BQCV strain in China, called the BQCV China-JL1 strain (KP119603). A phylogenetic tree was then built to analyse their genetic relationships. The BQCV China-JL1 strain showed 86-93% similarity with the six strains published in the GenBank. The BQCV China-JL1 strain consisted of 8358 nucleotides (nt). The 5'-proximal open reading frame (ORF1) initiated at nt position 546 and terminated at nt position 4676, ORF3 initiated at nt position 4891 and terminated at nt position 5433, and the 3'-proximal ORF (ORF2) was located between nt positions 5750 and 8203.

Bay laurel (Laurus nobilis) as potential antiviral treatment in naturally BQCV infected honeybees

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.

Nosema spp. infections cause no energetic stress in tolerant honeybees.

Host-pathogen coevolution leads to reciprocal adaptations, allowing pathogens to increase host exploitation or hosts to minimise costs of infection. As pathogen resistance is often associated with considerable costs, tolerance may be an evolutionary alternative. Here, we examined the effect of two closely related and highly host dependent intracellular gut pathogens, Nosema apis and Nosema ceranae, on the energetic state in Nosema tolerant and sensitive honeybees facing the infection. We quantified the three major haemolymph carbohydrates fructose, glucose, and trehalose using high-performance liquid chromatography (HPLC) as a measure for host energetic state. Trehalose levels in the haemolymph were negatively associated with N. apis infection intensity and with N. ceranae infection regardless of the infection intensity in sensitive honeybees. Nevertheless, there was no such association in Nosema spp. infected tolerant honeybees. These findings suggest that energy availability in tolerant honeybees was not compromised by the infection. This result obtained at the individual level may also have implications at the colony level where workers in spite of a Nosema infection can still perform as well as healthy bees, maintaining colony efficiency and productivity.

Effects of Nosema apis, N. ceranae, and coinfections on honey bee (Apis mellifera) learning and memory.

Western honey bees (Apis mellifera) face an increasing number of challenges that in recent years have led to significant economic effects on apiculture, with attendant consequences for agriculture. Nosemosis is a fungal infection of honey bees caused by either Nosema apis or N. ceranae. The putative greater virulence of N. ceranae has spurred interest in understanding how it differs from N. apis. Little is known of effects of N. apis or N. ceranae on honey bee learning and memory. Following a Pavlovian model that relies on the proboscis extension reflex, we compared acquisition learning and long-term memory recall of uninfected (control) honey bees versus those inoculated with N. apis, N. ceranae, or both. We also tested whether spore intensity was associated with variation in learning and memory. Neither learning nor memory differed among treatments. There was no evidence of a relationship between spore intensity and learning, and only limited evidence of a negative effect on memory; this occurred only in the co-inoculation treatment. Our results suggest that if Nosema spp. are contributing to unusually high colony losses in recent years, the mechanism by which they may affect honey bees is probably not related to effects on learning or memory, at least as assessed by the proboscis extension reflex.

Experimental bacteriophage treatment of honeybees (Apis mellifera) infected with Paenibacillus larvae, the causative agent of American Foulbrood Disease.

ABSTRACTAmerican Foulbrood Disease (AFB) is an infection of honeybees caused by the bacterium Paenibacillus larvae. One potential remedy involves using biocontrol, such as bacteriophages (phages) to lyse P. larvae. Therefore, bacteriophages specific for P. larvae were isolated to determine their efficacy in lysing P. larvae cells. Samples from soil, beehive materials, cosmetics, and lysogenized P. larvae strains were screened; of 157 total samples, 28 were positive for at least one P. larvae bacteriophage, with a total of 30. Newly isolated bacteriophages were tested for the ability to lyse each of 11 P. larvae strains. Electron microscopy demonstrated that the phage isolates were from the family Siphoviridae. Seven phages with the broadest host ranges were combined into a cocktail for use in experimental treatments of infected bee larvae; both prophylactic and post-infection treatments were conducted. Results indicated that although both pre- and post-treatments were effective, prophylactic administration of the phages increased the survival of larvae more than post-treatment experiments. These preliminary experiments demonstrate the likelihood that phage therapy could be an effective method to control AFB.

Impact of vertebrate probiotics on honeybee yeast microbiota and on the course of nosemosis

The natural intestine microbiota of honeybees is dominated by Gram-negative bacteria from such families as: Enterobacteriaceae, Alcaligenaceae and Pseudomonadaceae, less numerous are Gram-positive bacteria, yeasts and other fungi. Our research was focused on the impact of commercial vertebrae probiotics, on honeybees’ intestine yeast number, hemolymph lysozyme activity and nosemosis development. The diet of honeybees was supplemented with two vertebrate probiotics recommended in beekeeping management. The former consisted of Lactobacillus casei, L. plantarum, Saccharomyces cerevisiae, and Rhodopseudomonas palustris. The latter consisted of L. acidophilus, L. delbrueckii, and Bifidobacterium bifidum. Yeasts isolated from honeybees’ intestine and detected in our research belonged to two genera: Candida and Saccharomyces. The average number of yeast Colony Forming Units (CFUs) in uninfected honeybees fed only sugar syrup was 3850 (±400.33) and after Nosema spp. infection the number rose to 19500 (±1644.40) per one honeybee. The addition of a probiotic decreased the number of detected yeast CFUs in both groups of infected and uninfected honeybees. Nosema infection did not affect lysozyme activity; therefore it was the administration of probiotics that had the main impact on the rise of lysozyme level. Most likely very vivid probiotic bacteria were treated as invaders by honeybees’ immune defense, which resulted in almost 40% rise observed in lysozyme activity. Furthermore, probiotic supplementation accelerated the nosemosis development even twofold. Probably, increased acidity of the honeybees’ intestine, which is a consequence of the uncontrolled growth of lactic acid bacteria, created conditions favorable to faster nosemosis development. Therefore, every administration of diet supplements with live microorganisms whose impact on honeybees biology and physiology is not well studied should be carried out with the greatest caution.

Comparison of genomic rnA sequences of different isolates of thai Sac Brood Virus attacking Indian honeybee,Apis cerana indicaFab. in tamil nadu by reverse transcriptase-polymerase chain reaction method

A variant of SBV known as thai Sac Brood Virus (tSBV) infects larvae of the Indian honeybee (Apis cerana indica F.), resulting in failure to pupate and death. rt-Pcr method was used to detect the tSBV infection in honeybee larvae originating from geographically distinct regions. Presence of TSBV was confirmed with two sets of forward and reverse primers of SBV. The RT-PCR assay proved to be a rapid, specific, and sensitive diagnostic tool for the direct detection of tSBV nucleic acid in samples of infected honeybees and brood regardless of geographic origin. Sequencing of amplification products and phylogenetic analysis suggested that the tSBV infecting A. cerana indica collected from two locations in tamil nadu even though distinct from one another belonged to the same cluster and had maximum similarity with one another and a Bangalore strain. However the present samples showed lesser relationship with uK and Japan strains.

Population Genetics of Nosema apis and Nosema ceranae: One Host (Apis mellifera) and Two Different Histories.

Two microsporidians are known to infect honey bees: Nosema apis and Nosema ceranae. Whereas population genetics data for the latter have been released in the last few years, such information is still missing for N. apis. Here we analyze the patterns of nucleotide polymorphism at three single-copy loci (PTP2, PTP3 and RPB1) in a collection of Apis mellifera isolates from all over the world, naturally infected either with N. apis (N = 22) or N. ceranae (N = 23), to provide new insights into the genetic diversity, demography and evolution of N. apis, as well as to compare them with evidence from N. ceranae. Neutral variation in N. apis and N. ceranae is of the order of 1%. This amount of diversity suggests that there is no substantial differentiation between the genetic content of the two nuclei present in these parasites, and evidence for genetic recombination provides a putative mechanism for the flow of genetic information between chromosomes. The analysis of the frequency spectrum of neutral variants reveals a significant surplus of low frequency variants, particularly in N. ceranae, and suggests that the populations of the two pathogens are not in mutation-drift equilibrium and that they have experienced a population expansion. Most of the variation in both species occurs within honey bee colonies (between 62%-90% of the total genetic variance), although in N. apis there is evidence for differentiation between parasites isolated from distinct A. mellifera lineages (20%-34% of the total variance), specifically between those collected from lineages A and C (or M). This scenario is consistent with a long-term host-parasite relationship and contrasts with the lack of differentiation observed among host-lineages in N. ceranae (< 4% of the variance), which suggests that the spread of this emergent pathogen throughout the A. mellifera worldwide population is a recent event.

English

Pathogen infection of honeybees can lead to economic losses in apiculture. The earlier the pathogen contamination can be found the better it will likely be for the treatment of the infected colony and prevention of the spread of the pathogen within and between colonies. A total of 50 colonies of Apis cerana were sampled in Samut-Songkhram (five colonies) and Chumphon (45 colonies) provinces in the central and the south of Thailand, respectively. Diagnostic multiplex polymerase chain reaction (PCR) revealed that 20, 6, 4, 20 and 0% of the samples were infected by Paenibacillus larvae, Nosema ceranae, Nosema apis, Ascosphaera apis and Sacbrood virus (Morator aetatulus), respectively. Positive amplified PCR products of target genes were sequenced. A phylogenetic tree was constructed by the neighbor-joining (NJ) distance based, using the Phylogenetic Analysis Using Parsimony (PAUP 4.0b10) program. The phylogenetic relationship of each pathogen, based on the partial sequence of the 16S rRNA of P. larvae, N. ceranae and N. apis, and of the 5.8S rRNA of A. apis, revealed a significant difference from the non-Thai isolates of these pathogens, but no significant geographical isolation between the different Thai apiaries, although it separated some into closely related clusters. In order to reduce the use of antibiotics in an apiary, bacteria in the gut of healthy bees were focused. Interestingly, Bifidobacterium species, Lactobacillus species, Bacillus species, Lactobacillus spp. and other lactic acid bacteria, were isolated from larvae and adult workers, but gave conflicting preliminary identities based on their biochemistry-morphology versus sequence analysis of a partial fragment (1.4 kb) of their 16S rRNA. Key words: Apis cerana indica, bee pathogens, gut bacteria, multiplex polymerase chain reaction (PCR), 16S rRNA.

Identification of microRNA-like small RNAs from fungal parasite Nosema ceranae

We previously found transcripts encoding Dicer and Argonaute which are involved in the production of microRNAs, in the honey bee parasite Nosema ceranae. In order to identify microRNAs in N. ceranae, we sequenced small RNAs from midgut tissues of infected honey bees at 24h intervals for 6days post infection, covering the complete reproduction cycle for this intracellular parasite. We predicted six microRNA-like small RNAs, all of which were confirmed via RT-qPCR assays. This is the first evidence for microRNA-like small RNAs generated by a microsporidian species, providing new insights into host–parasite interactions involving this widespread taxonomic group.

First molecular detection of chronic bee paralysis virus (CBPV) in Iran.

Among the viruses infecting honey bees, chronic bee paralysis virus (CBPV) is known to induce significant losses in honey bee colonies. CBPV is an unclassified polymorphic single stranded RNA virus. Using RT-PCR, the virus infections in honey bees can be detected in a rapid and accurate manner. Bee samples were collected from 23 provinces of Iran, between July-September 2011 and 2012. A total of 160 apiaries were sampled and submitted for virus screening. RNA extraction and RT-PCR were performed with QIAGEN kits. The primers lead to a fragment of 315 bp. The PCR products were electrophoresed in a 1.2 % agarose gel. Following the RT-PCR reaction with the specific primers, out of the 160 apiaries examined, 12 (7.5 %) were infected with CBPV. This is the first study of CBPV detection in Iranian apiaries. We identified CBPV in the collected samples from different geographic regions of Iran.

Effects of stingless bee propolis on Nosema ceranae infected Asian honey bees, Apis cerana

Since Nosema ceranae causes mortality in honey bee populations in both managed apiaries and in the wild, many chemical compounds have been screened and tested for their abilities to suppress populations of N. ceranae. However, the use of synthetic substances has resulted in residues in colonies and honey bee products. The development of new methods for the control of nosema disease is therefore much needed by beekeepers and bee scientists. We evaluated the effects of propolis from the stingless bee Trigona apicalis on N. ceranae-infected Asian honey bees, Apis cerana. One-day-old N. ceranae free worker bees were individually inoculated with 2 μl of 50% sucrose solution containing 80,000 N. ceranae spores per bee and then fed with 50 and 70% (v/v) propolis extract in water. All propolis-treated bees had significantly higher survival rates than untreated bees (F5 = 92.6, p < 0.0001). Bees treated with the highest propolis concentration (70%) had the lowest infection ratio of cells, while the significantly highest spore count in a single bee was found in control bees (F5 = 390.3, p < 0001, F5 = 309.0, p < 0.001). These results suggest that the propolis may have toxic effects on N. ceranae spores, and could have potential use in disease management.

Are commercial probiotics and prebiotics effective in the treatment and prevention of honeybee nosemosis C?

The study was conducted to investigate the effect of Lactobacillus rhamnosus (a commercial probiotic) and inulin (a prebiotic) on the survival rates of honeybees infected and uninfected with Nosema ceranae, the level of phenoloxidase (PO) activity, the course of nosemosis, and the effect on the prevention of nosemosis development in bees. The cells of L. rhamnosus exhibited a high rate of survival in 56.56 % sugar syrup, which was used to feed the honeybees. Surprisingly, honeybees fed with sugar syrup supplemented with a commercial probiotic and a probiotic + prebiotic were more susceptible to N. ceranae infection, and their lifespan was much shorter. The number of microsporidian spores in the honeybees fed for 9 days prior to N. ceranae infection with a sugar syrup supplemented with a commercial probiotic was 25 times higher (970 million spores per one honeybee) than in a control group fed with pure sucrose syrup (38 million spores per one honeybee). PO activity reached its highest level in the hemolymph of this honeybee control group uninfected with N. ceranae. The addition of probiotics or both probiotics and prebiotics to the food of uninfected bees led to the ~2-fold decrease in the PO activity. The infection of honeybees with N. ceranae accompanied an almost 20-fold decrease in the PO level. The inulin supplemented solely at a concentration of 2 μg/mL was the only administrated factor which did not significantly affect honeybees’ survival, the PO activity, or the nosemosis infection level. In conclusion, the supplementation of honeybees’ diet with improperly selected probiotics or both probiotics and prebiotics does not prevent nosemosis development, can de-regulate insect immune systems, and may significantly increase bee mortality.

Genome-wide characterization of long intergenic non-coding RNAs (lincRNAs) provides new insight into viral diseases in honey bees Apis cerana and Apis mellifera.

BackgroundLong non-coding RNAs (lncRNAs) are a class of RNAs that do not encode proteins. Recently, lncRNAs have gained special attention for their roles in various biological process and diseases.ResultsIn an attempt to identify long intergenic non-coding RNAs (lincRNAs) and their possible involvement in honey bee development and diseases, we analyzed RNA-seq datasets generated from Asian honey bee (Apis cerana) and western honey bee (Apis mellifera). We identified 2470 lincRNAs with an average length of 1011 bp from A. cerana and 1514 lincRNAs with an average length of 790 bp in A. mellifera. Comparative analysis revealed that 5 % of the total lincRNAs derived from both species are unique in each species. Our comparative digital gene expression analysis revealed a high degree of tissue-specific expression among the seven major tissues of honey bee, different from mRNA expression patterns. A total of 863 (57 %) and 464 (18 %) lincRNAs showed tissue-dependent expression in A. mellifera and A. cerana, respectively, most preferentially in ovary and fat body tissues. Importantly, we identified 11 lincRNAs that are specifically regulated upon viral infection in honey bees, and 10 of them appear to play roles during infection with various viruses.ConclusionsThis study provides the first comprehensive set of lincRNAs for honey bees and opens the door to discover lincRNAs associated with biological and hormone signaling pathways as well as various diseases of honey bee.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1868-7) contains supplementary material, which is available to authorized users.

First Insights into the Genome of Fructobacillus sp. EFB-N1, Isolated from Honey Bee Larva Infected with European Foulbrood.

European foulbrood is a worldwide disease affecting the honey bee brood. Here, we report the draft genome sequence of Fructobacillus sp. EFB-N1, which was isolated from an infected honey bee larva derived from a Swiss European foulbrood outbreak. The genome consists of 68 contigs and harbors 1,629 predicted protein-encoding genes.

Differential diagnosis of the honey bee trypanosomatids Crithidia mellificae and Lotmaria passim

Trypanosomatids infecting honey bees have been poorly studied with molecular methods until recently. After the description of Crithidia mellificae (Langridge and McGhee, 1967) it took about forty years until molecular data for honey bee trypanosomatids became available and were used to identify and describe a new trypanosomatid species from honey bees, Lotmaria passim (Evans and Schwarz, 2014). However, an easy method to distinguish them without sequencing is not yet available. Research on the related bumble bee parasites Crithidia bombi and Crithidia expoeki revealed a fragment length polymorphism in the internal transcribed spacer 1 (ITS1), which enabled species discrimination. In search of fragment length polymorphisms for differential diagnostics in honey bee trypanosomatids, we studied honey bee trypanosomatid cell cultures of C. mellificae and L. passim. This research resulted in the identification of fragment length polymorphisms in ITS1 and ITS1-2 markers, which enabled us to develop a diagnostic method to differentiate both honey bee trypanosomatid species without the need for sequencing. However, the amplification success of the ITS1 marker depends probably on the trypanosomatid infection level. Further investigation confirmed that L. passim is the dominant species in Belgium, Japan and Switzerland. We found C. mellificae only rarely in Belgian honey bee samples, but not in honey bee samples from other countries. C. mellificae was also detected in mason bees (Osmia bicornis and Osmia cornuta) besides in honey bees. Further, the characterization and comparison of additional markers from L. passim strain SF (published as C. mellificae strain SF) and a Belgian honey bee sample revealed very low divergence in the 18S rRNA, ITS1-2, 28S rRNA and cytochrome b sequences. Nevertheless, a variable stretch was observed in the gp63 virulence factor.

Overwintering Is Associated with Reduced Expression of Immune Genes and Higher Susceptibility to Virus Infection in Honey Bees.

The eusocial honey bee, Apis mellifera, has evolved remarkable abilities to survive extreme seasonal differences in temperature and availability of resources by dividing the worker caste into two groups that differ in physiology and lifespan: summer and winter bees. Most of the recent major losses of managed honey bee colonies occur during the winter, suggesting that winter bees may have compromised immune function and higher susceptibility to diseases. We tested this hypothesis by comparing the expression of eight immune genes and naturally occurring infection levels of deformed wing virus (DWV), one of the most widespread viruses in A. mellifera populations, between summer and winter bees. Possible interactions between immune response and physiological activity were tested by measuring the expression of vitellogenin and methyl farnesoate epoxidase, a gene coding for the last enzyme involved in juvenile hormone biosynthesis. Our data show that high DWV loads in winter bees correlate with reduced expression of genes involved in the cellular immune response and physiological activity and high expression of humoral immune genes involved in antibacterial defense compared with summer bees. This expression pattern could reflect evolutionary adaptations to resist bacterial pathogens and economize energy during the winter under a pathogen landscape with reduced risk of pathogenic viral infections. The outbreak of Varroa destructor infestation could have overcome these adaptations by promoting the transmission of viruses. Our results suggest that reduced cellular immune function during the winter may have increased honey bee’s susceptibility to DWV. These results contribute to our understanding of honey bee colony losses in temperate regions.

The Effect of Oral Administration of dsRNA on Viral Replication and Mortality in Bombus terrestris.

Israeli acute paralysis virus (IAPV), a single-stranded RNA virus, has a worldwide distribution and affects honeybees as well as other important pollinators. IAPV infection in honeybees has been successfully repressed by exploiting the RNA interference (RNAi) pathway of the insect’s innate immune response with virus-specific double stranded RNA (dsRNA). Here we investigated the effect of IAPV infection in the bumblebee Bombus terrestris and its tissue tropism. B. terrestris is a common pollinator of wild flowers in Europe and is used for biological pollination in agriculture. Infection experiments demonstrated a similar pathology and tissue tropism in bumblebees as reported for honeybees. The effect of oral administration of virus-specific dsRNA was examined and resulted in an effective silencing of the virus, irrespective of the length. Interestingly, we observed that non-specific dsRNA was also efficient against IAPV. However further study is needed to clarify the precise mechanism behind this effect. Finally we believe that our data are indicative of the possibility to use dsRNA for a broad range viral protection in bumblebees.