Scientific Advances in Controlling Nosema ceranae (Microsporidia) Infections in Honey Bees (Apis mellifera)

Non-coding RNAs and regulatory networks involved in the Ameson portunus (Microsporidia)-Portunus trituberculatus interaction

Ameson portunus, the causative agent of "toothpaste disease" in Portunus trituberculatus and "slurry-like syndrome" in Scylla paramamosain, has resulted in considerable economic losses in the marine crab aquaculture industry in China. Practical control strategies are yet unavailable. Non-coding RNAs (ncRNAs) are crucial components of gene regulation of intracellular parasites, however, their roles in regulating the microsporidia-host interaction remain limited. Here we conducted a whole-transcriptome RNA-seq analysis to identify ncRNAs and to establish the interaction regulatory networks to get further insights into the A. portunus-P. trituberculatus interaction. Totally, 2805 mRNAs, 484 lncRNAs, 5 circRNAs, and 496 miRNAs were identified from A. portunus. These ncRNAs are possibly important regulators for its own energy and substrate metabolism, thereby supporting the intracellular survival and proliferation of A. portunus. DNA replication-associated mRNAs were significantly up-regulated after P. trituberculatus infection with A. portunus. It can be hypothesized that up-regulated lncRNAs may be responsible for the up-regulation of these DNA replication-related genes by miRNAs in P. trituberculatus. The downregulation of metabolic pathways is one of possible strategies of P. trituberculatus to respond the infection of A. portunus. Cross-species miRNAs were suggested to play important roles in the cross-talk of P. trituberculatus-A. portunus, e.g. the disruption of the cytoskeletal organization and normal cell function of host by this microsporidian. The results enrich the knowledge of ncRNAs in microsporidia and offer new insights into microsporidia-host interactions.

NcSWP8, a New Spore Wall Protein, Interacts with Polar Tube Proteins in the Parasitic Microsporidia Vairimorpha (Nosema) ceranae

Vairimorpha (Nosema) ceranae is a pathogen that affects Apis mellifera and Apis ceranae Fabricius, capable of spreading within and between honeybee colonies. The spore wall of microsporidia is the initial structure to contact the host cell directly, which may play a crucial role in the infection process. Currently, several spore wall proteins have been identified in microsporidia, but only two spore wall proteins from V. ceranae have been characterized. Here, we report the expression and identification of a novel spore wall protein, NcSWP8, with a molecular mass of 21.37 kDa in V. ceranae. Subcellular localization analysis revealed that NcSWP8 was localized on the spore wall of V. ceranae. Co-immunoprecipitation and Far-Western blotting experiments demonstrated that NcSWP8 could stably interact with polar tube proteins, NcPTP2 and NcPTP3. The antibody blocking assay significantly decreased their infection rate, indicating that NcSWP8 played a significant role in the process of V. ceranae infection. These results together suggested that NcSWP8 was a new spore wall protein localized to the spore wall and interacted with the polar tube proteins, playing a crucial role in supporting the formation of the spore wall and potentially affecting the process of infection of V. ceranae.

Liposome-based RNAi delivery in honeybee for inhibiting parasite Nosema ceranae

Nosema ceranae, a parasite that parasitizes and reproduces in the gut of honeybees, has become a serious threat to the global apiculture industry. RNA interference (RNAi) technology can be used to inhibit N. ceranae growth by targeting silencing the thioredoxin reductase (TrxR) in N. ceranae. However, suitable carriers are one of the reasons limiting the application of RNAi due to the easy degradation of dsRNA in honeybees. As a vesicle composed of a lipid bilayer, liposomes are a good carrier for nucleic acid delivery, but studies in honeybees are lacking. In this study, liposomes were used for double-stranded RNA (dsRNA) dsTrxR delivery triggering RNAi to inhibit the N. ceranae growth in honeybees. Compared to naked dsTrxR, liposome-dsTrxR reduced N. ceranae numbers in the midgut and partially restored midgut morphology without affecting bee survival and gut microbial composition. The results of this study confirmed that liposomes could effectively protect dsRNA from entering the honeybee gut and provide a reference for using RNAi technology to suppress honeybee pests and diseases.

Biological control of nosemosis in Apis mellifera L. with Acacia nilotica extract

Nosemosis is one of the most devastating diseases of Apis mellifera (Honey bees) caused by the single-celled spore-forming fungi Nosema apis, N. ceranae and N. neumanii, causing a severe loss on the colony vitality and productivity. Fumagillin, a MetAP2 inhibitor, was a certified treatment for controlling nosemosis, nevertheless, due to its deleterious effects on honey bees and humans, it is prohibited. So, searching for novel biological agents with affordable selectivity to target Nosema species infecting Apis mellifera, with nil toxicity to bees and humans is the main objective of this study. Nosema species were isolated from naturally infected honey bees. The methanolic extracts of Acacia nilotica, Elaeis guineensis, and Catharanthus roseus were tested to selectively control the growth of Nosema spp of honeybees. The spores of Nosema species were molecularly and morphologically identified. Among the tested plant extracts, the methanolic extracts (0.1%) of A. nilotica had the most activity towards Nosema spp causing about 37.8 and 32.5% reduction in the spores' load at 5- and 9-days post-infection, respectively, compared to the untreated control. At 0.1%, the A. nilotica methanolic extract exhibited the highest inhibitory effect for Nosema spores, without any obvious bee mortality. Catharanthus roseus displayed a reduction of spores by 27.02%, with bee mortality rate of 27.02%. At 1% for 5 dpi, the A. nilotica extracts led to 18.18% bee mortality, while the C. roseus extracts resulted in 100% mortality, as revealed from the toxicity and quantification bioassays. So, the extracts of A. nilotica and C. roseus had a significant effect in controlling the N. apis and N. ceranae titer compared to the infected untreated control at both time points. The titer of N. apis and N. ceranae was noticeably decreased by more than 80% and 90%, in response to A. nilotica, compared to the control. From the metabolic profiling by GC-MS analysis, the most frequent active compounds of A. nilotica were 2,4,6-trihy-droxybenzoic acid, 1,2-dihydroxybenzene, myristic acid, and linoleic acid. These compounds were analyzed in silico to assess their binding affinity to the ATP binding protein, methionine aminopeptidase and polar tube protein of Nosema species as target enzymes. The compound 2,4,6-trihydroxybenzoic acid had the lowest energy to bind with ATP binding protein, methionine aminopeptidase and polar tube protein of Nosema, followed by 1,2-dihydroxybenzene and myristic acid, compared to fumagilin. So, from the experimental and molecular docking analysis, the extracts of A. nilotica had the highest activity to attack the cellular growth machinery of Nosema species without an obvious effect to the honeybees, ensuring their prospective promising application.

Microsporidia secretory effectors and their roles in pathogenesis

Microsporidia, a group of unicellular eukaryotic parasites, rely intensely on secretory effectors for successful invasion and proliferation within host cells. This review focuses on the identification, characterization, and functional roles of effectors, including secretory proteins and microRNAs. The adhesion proteins like the Ricin-B-lectin facilitate initial invasion, which binds to the host cell surface. Once inside, microsporidia deploy a range of effectors to modulate host immune responses, such as serpin proteins, and redirect host cell metabolism to meet the parasite's nutritional needs through hexokinase. Some effectors such as microRNAs, alter the host gene expression to create a more favorable intracellular parasitic environment. In conclusion, the secretory effectors of microsporidia play a pivotal role spanning from host cell invasion to intracellular establishment. In the future, more effectors secreted by microsporidia will be studied, which will not only help to elucidate the molecular mechanism of pathogenic manipulation of the host but also help to provide the potential targets for anti-parasitic treatments.

Pathogen- and host-directed pharmacologic strategies for control of Vairimorpha (Nosema) spp. infection in honey bees

Microsporidia are obligate intracellular parasites of the Fungal Kingdom that cause widespread infections in nature, with important effects on invertebrates involved in food production systems. The two microsporidian species Vairimorpha (Nosema) ceranae (and the less common Vairimorpha (Nosema) apis) can cause individual disease in honey bees and contribute to colony collapse. The efficacy, safety, and availability of fumagillin, the only drug currently approved to treat microsporidia infection in bees, is uncertain. In this review, we will discuss some of the most promising alternative strategies for the mitigation of Vairimorpha spp. with an emphasis on infection by V. ceranae, now the dominant species infecting bees. We will focus on pharmacologic interventions where the mechanism of action is known and examine both pathogen-directed and host-directed approaches. As limiting toxicity to host cells has been especially emphasized in treating bees that are already facing numerous stressors, strategies that disrupt pathogen-specific targets may be especially advantageous. Therefore, efforts to increase the knowledge and tools for facilitating the discovery of such targets and pharmacologic agents directed against them should be prioritized.

Dimethyl sulfoxide, an alternative for control of Nosema ceranae infection in honey bees (Apis mellifera)

Nosema ceranae is a microsporidian parasite that threatens current apiculture. N. ceranae-infected honey bees (Apis mellifera) exhibit morbid physiological impairments and reduced honey production, malnutrition, shorter life span, and higher mortality than healthy honey bees. In this study, we found that dimethyl sulfoxide (DMSO) could enhance the survival rate of N. ceranae-infected honey bees. Therefore, we investigated the effect of DMSO on N. ceranae-infected honey bees using comparative RNA sequencing analysis. Our results revealed that DMSO was able to affect several biochemical pathways, especially the metabolic-related pathways in N. ceranae-infected honey bees. Based on these findings, we conclude that DMSO may be a useful alternative for treating N. ceranae infection in apiculture.

Action of dithiocarbimates salts on the honey bee and its pathogen Nosema ceranae

Apis mellifera, crucial pollinators for both native and cultivated plants, also yield various products such as honey, wax, royal jelly, and propolis, extensively utilized in the food, pharmaceuticals, and cosmetics industries. Nosema ceranae, a prevalent microsporidian worldwide, stands as a significant pathogen for A. mellifera, showing resistance to conventional antibiotics. Consequently, the exploration of novel compounds for N. ceranae control becomes imperative. Dithiocarbimate derivatives emerge as promising antifungal candidates under evaluation for combating various pathogens, particularly those affecting plants. This study assessed the toxicity profile of six dithiocarbimate derivatives on A. mellifera worker survival and N. ceranae pathogen. Among these, four compounds exhibited minimal bee mortality and proceeded to further evaluation against N. ceranae. In vitro assays demonstrated their inhibitory effects on spore germination. Remarkably, the most potent compound suppressed N. ceranae spores by 62% at a concentration of 20 µmol L-1in vivo. Thus, these dithiocarbimate derivatives represent promising new antifungal agents for combatting nosemosis in honey bee populations.

A Systematic Review of Fumagillin Field Trials for the Treatment of Nosema Disease in Honeybee Colonies

This article systematically reviews controlled field trials of fumagillin dicyclohexylamine in honeybee colonies to determine whether fumagillin effectively controls nosema and whether it is beneficial to colonies. Fifty publications were found that described controlled field trials of fumagillin in honeybee colonies between 1952 and 2023. Fumagillin consistently reduced the prevalence and severity of nosema infections. Doses applied in recent studies were similar to or below those recommended historically. Furthermore, our study showed no negative effects on colony health. Improvements in colony survival, size, and honey production have been demonstrated frequently, though not consistently, in both historic and recent studies. Nevertheless, some practices are not optimal. Treatment decision thresholds based on the number of spores per bee are not well supported by evidence and may be no better than calendar-based prophylactic treatments. In addition, reasonable recommendations to employ quarantine and disinfection procedures together with fumagillin treatment do not appear to have been widely adopted. When used as stand-alone treatments, both the fall- and spring-label doses provide benefits but may be too low and short-term to ensure full control of the disease.

Identification of peptides from honeybee gut symbionts as potential antimicrobial agents against Melissococcus plutonius

Eusocial pollinators are crucial elements in global agriculture. The honeybees and bumblebees are associated with a simple yet host-restricted gut community, which protect the hosts against pathogen infections. Recent genome mining has led to the discovery of biosynthesis pathways of bioactive natural products mediating microbe-microbe interactions from the gut microbiota. Here, we investigate the diversity of biosynthetic gene clusters in the bee gut microbiota by analyzing 477 genomes from cultivated bacteria and metagenome-assembled genomes. We identify 744 biosynthetic gene clusters (BGCs) covering multiple chemical classes. While gene clusters for the post-translationally modified peptides are widely distributed in the bee guts, the distribution of the BGC classes varies significantly in different bee species among geographic locations, which is attributed to the strain-level variation of bee gut members in the chemical repertoire. Interestingly, we find that Gilliamella strains possessing a thiopeptide-like BGC show potent activity against the pathogenic Melissococcus plutonius. The spectrometry-guided genome mining reveals a RiPP-encoding BGC from Gilliamella with a 10 amino acid-long core peptide exhibiting antibacterial potentials. This study illustrates the widespread small-molecule-encoding BGCs in the bee gut symbionts and provides insights into the bacteria-derived natural products as potential antimicrobial agents against pathogenic infections.

Studies on the novel effects of electron beam treated pollen on colony reproductive output in commercially-reared bumblebees (Bombus terrestris) for mass pollination applications

Commercially-reared bumblebees provide an important pollinator service that helps support food production and security. The deployment of an appropriate non-thermal disinfection technology for the bulk treatment of pollen collected from honeybees for the feeding of commercial bumblebees is important in order to mitigate against complex diseases and unwanted pathogen spillover to native bees. High level disinfection of pollen was achieved using an electron (e)-beam dose of 100 kGy that corresponded to 78 % loss of cellular viability of bee pathogens before feeding to bumblebees as measured by the novel in vitro use of flow cytometry (FCM). Novel findings showed that e-beam treated-pollen that was fed to bumblebees produced fewer females, gynes and exhibited an absence of males when compared to control bumblebee colonies that were fed untreated commercial pollen. A similar trend emerged in bumblebee colony reproductive outputs when using membrane filtered washed pollen. Proteomic analysis of bumblebees from individual colonies fed with treated-pollen revealed a differential abundance of proteins associated with stress, immunity and metabolism when compared to the untreated pollen control group. Microbiome analysis of the bumblebee gut content revealed differences in microbiota between treated and untreated pollen in bumblebee colony studies. This novel study evaluated the impact of industrial e-beam treated-pollen on complex bee disease mitigation where physically treated-pollen fed to bumblebees was shown to substantially affect colony reproductive outputs.

Engineered symbiotic bacteria interfering Nosema redox system inhibit microsporidia parasitism in honeybees

Nosema ceranae is an intracellular parasite invading the midgut of honeybees, which causes serious nosemosis implicated in honeybee colony losses worldwide. The core gut microbiota is involved in protecting against parasitism, and the genetically engineering of the native gut symbionts provides a novel and efficient way to fight pathogens. Here, using laboratory-generated bees mono-associated with gut members, we find that Snodgrassella alvi inhibit microsporidia proliferation, potentially via the stimulation of host oxidant-mediated immune response. Accordingly, N. ceranae employs the thioredoxin and glutathione systems to defend against oxidative stress and maintain a balanced redox equilibrium, which is essential for the infection process. We knock down the gene expression using nanoparticle-mediated RNA interference, which targets the γ-glutamyl-cysteine synthetase and thioredoxin reductase genes of microsporidia. It significantly reduces the spore load, confirming the importance of the antioxidant mechanism for the intracellular invasion of the N. ceranae parasite. Finally, we genetically modify the symbiotic S. alvi to deliver dsRNA corresponding to the genes involved in the redox system of the microsporidia. The engineered S. alvi induces RNA interference and represses parasite gene expression, thereby inhibits the parasitism significantly. Specifically, N. ceranae is most suppressed by the recombinant strain corresponding to the glutathione synthetase or by a mixture of bacteria expressing variable dsRNA. Our findings extend our previous understanding of the protection of gut symbionts against N. ceranae and provide a symbiont-mediated RNAi system for inhibiting microsporidia infection in honeybees.

Mixture toxic effects of thiacloprid and cyproconazole on honey bees (Apis mellifera L.)

Pesticide exposure remains one of the main factors in the population decline of insect pollinators. It is urgently necessary to assess the effects of mixtures on pollinator risk assessments because they are often exposed to numerous agrochemicals. In the present study, we explored the mixture toxic effects of thiacloprid (THI) and cyproconazole (CYP) on honey bees (Apis mellifera L.). Our findings revealed that THI possessed higher acute toxicity to A. mellifera (96-h LC₅₀ value of 216.3 mg a.i. L^-1) than CYP (96-h LC₅₀ value of 601.4 mg a.i. L^-1). It's worth noting that the mixture of THI and CYP exerted an acute synergistic effect on honey bees. At the same time, the activities of detoxification enzyme cytochrome P450s (CYP450s) and neuro target enzyme Acetylcholinesterase (AChE), as well as the expressions of seven genes (CRBXase, CYP306A1, CYP6AS14, apidaecin, defensing-2, vtg, and gp-93) associated with detoxification metabolism, immune response, development, and endoplasmic reticulum stress, were significantly altered in the combined treatment compared with the corresponding individual exposures of THI or CYP. These data indicated that a mixture of THI and CYP could disturb the physiological homeostasis of honey bees. Our study provides a theoretical basis for in-depth studies on the impacts of pesticide mixtures on the health of honey bees. Our study also provides important guidance for the rational application of pesticide mixtures to protect pollinators in agricultural production effectively.

Natural Substances, Probiotics, and Synthetic Agents in the Treatment and Prevention of Honeybee Nosemosis

Honeybees are important pollinators, but they are continuously exposed to a variety of fungal and bacterial diseases. One of the various diseases affecting honeybees is nosemosis caused by microsporidia from the Nosema genus. Honeybees are mainly infected through consumption of infected food or faeces containing Nosema spp. spores. Nosemosis causes damage to the middle intestine epithelium, which leads to food absorption disorders and honeybee malnutrition. Fumagillin, i.e., the antibiotic used to treat nosemosis, was withdrawn in 2016 from EU countries. Therefore, researchers have been looking for compounds of both natural and synthetic origin to fight nosemosis. Such compounds should not have a negative impact on bees but is expected to inhibit the disease. Natural compounds tested against nosemosis include, e.g., essential oils (EOs), plant extracts, propolis, and bacterial metabolites, while synthetic substances tested as anti-nosemosis agents are represented by porphyrins, vitamins, antibiotics, phenolic, ascorbic acids, and others. This publication presents an 18-year overview of various studies of a number of natural and synthetic compounds used in the treatment and prevention of nosemosis cited in PubMed, GoogleScholar, and CrossRef.

High-throughput small molecule screen identifies inhibitors of microsporidia invasion and proliferation in C. elegans

Microsporidia are a diverse group of fungal-related obligate intracellular parasites that infect most animal phyla. Despite the emerging threat that microsporidia represent to humans and agricultural animals, few reliable treatment options exist. Here, we develop a high-throughput screening method for the identification of chemical inhibitors of microsporidia infection, using liquid cultures of Caenorhabditis elegans infected with the microsporidia species Nematocida parisii. We screen a collection of 2560 FDA-approved compounds and natural products, and identify 11 candidate microsporidia inhibitors. Five compounds prevent microsporidia infection by inhibiting spore firing, whereas one compound, dexrazoxane, slows infection progression. The compounds have in vitro activity against several other microsporidia species, including those known to infect humans. Together, our results highlight the effectiveness of C. elegans as a model host for drug discovery against intracellular pathogens, and provide a scalable high-throughput system for the identification and characterization of microsporidia inhibitors.

Reciprocal interactions between anthropogenic stressors and insect microbiota

Insects play many important roles in nature due to their diversity, ecological role, and impact on agriculture or human health. They are directly influenced by environmental changes and in particular anthropic activities that constitute an important driver of change in the environmental characteristics. Insects face numerous anthropogenic stressors and have evolved various detoxication mechanisms to survive and/or resist to these compounds. Recent studies highligted the pressure exerted by xenobiotics on insect life-cycle and the important role of insect-associated bacterial microbiota in the insect responses to environmental changes. Stressor exposure can have various impacts on the composition and structure of insect microbiota that in turn may influence insect biology. Moreover, bacterial communities associated with insects can be directly or indirectly involved in detoxification processes with the selection of certain microorganisms capable of degrading xenobiotics. Further studies are needed to assess the role of insect-associated microbiota as key contributor to the xenobiotic metabolism and thus as a driver for insect adaptation to polluted habitats.

Effect of amide protoporphyrin derivatives on immune response in Apis mellifera

The intracellular microsporidian parasite Nosema ceranae is known to compromise bee health by induction of energetic stress and downregulation of the immune system. Porphyrins are candidate therapeutic agents for controlling Nosema infection without adverse effects on honeybees. In the present work, the impact of two protoporphyrin IX derivatives, i.e. PP[Asp]2 and PP[Lys]2, on Apis mellifera humoral immune response has been investigated in laboratory conditions in non-infected and N. ceranae-infected honeybees. Fluorescence spectroscopy analysis of hemolymph showed for the first time that porphyrin molecules penetrate into the hemocoel of honeybees. Phenoloxidase (PO) activity and the expression of genes encoding antimicrobial peptides (AMPs: abaecin, defensin, and hymenoptaecin) were assessed. Porphyrins significantly increased the phenoloxidase activity in healthy honeybees but did not increase the expression of AMP genes. Compared with the control bees, the hemolymph of non-infected bees treated with porphyrins had an 11.3- and 6.1-fold higher level of PO activity after the 24- and 48-h porphyrin administration, respectively. Notably, there was a significant inverse correlation between the PO activity and the AMP gene expression level (r =  - 0.61696, p = 0.0143). The PO activity profile in the infected bees was completely opposite to that in the healthy bees (r =  - 0.5118, p = 0.000), which was related to the changing load of N. ceranae spores in the porphyrin treated-bees. On day 12 post-infection, the spore loads in the infected porphyrin-fed individuals significantly decreased by 74%, compared with the control bees. Our findings show involvement of the honeybee immune system in the porphyrin-based control of Nosema infection. This allows the infected bees to improve their lifespan considerably by choosing an optimal PO activity/AMP expression variant to cope with the varying level of N. ceranae infection.

Antifungal activity of "HO21-F", a formulation based on Olea europaea plant extract, in honey bees infected with Nosema ceranae

Nosema ceranae is a microsporidium parasite that silently affects honey bees, causing a disease called nosemosis. This parasite produces resistant spores and germinates in the midgut of honey bees, extrudes a polar tubule that injects an infective sporoplasm in the host cell epithelium, proliferates, and produces intestinal disorders that shorten honey bee lifespan. The rapid extension of this disease has been reported to be widespread among adult bees, and treatments are less effective and counterproductive weakening colonies. This work aimed to evaluate the antifungal activity of a prototype formulation based on a non-toxic plant extract (HO21-F) against N. ceranae. In laboratory, honey bees were infected artificially, kept in cages for 17 days and samples were taken at 7 and 14 days post infection (dpi). At the same time, in field conditions we evaluated the therapeutic effect of HO21-F for 28 days in naturally infected colonies. The effectiveness of the treatment has been demonstrated by a reduction of 83.6 % of the infection levels observed in laboratory conditions at concentrations of 0.5 and 1 g/L without affecting the survival rate. Besides, in-field conditions we reported a reduction of 88 % of the infection level at a concentration of 2.5 g/L, obtaining better antifungal effectiveness in comparison to other commercially available treatments. As a result, we observed that the use of HO21-F led to an increase in population size and honey production, both parameters associated with colony strength. The reported antifungal activity of HO21-F against N. ceranae, with a significant control of spore proliferation in worker bees, suggests the promising commercial application use of this product against nosemosis, and it will encourage new research studies to understand the mechanism of action, whether related to the spore-inhibition effect and/or a stimulating effect in natural response of colonies to counteract the disease.

Microsporidia, a Highly Adaptive Organism and Its Host Expansion to Humans

Emerging infectious disease has become the center of attention since the outbreak of COVID-19. For the coronavirus, bats are suspected to be the origin of the pandemic. Consequently, the spotlight has fallen on zoonotic diseases, and the focus now expands to organisms other than viruses. Microsporidia is a single-cell organism that can infect a wide range of hosts such as insects, mammals, and humans. Its pathogenicity differs among species, and host immunological status plays an important role in infectivity and disease severity. Disseminated disease from microsporidiosis can be fatal, especially among patients with a defective immune system. Recently, there were two Trachipleistophora hominis, a microsporidia species which can survive in insects, case reports in Thailand, one patient had disseminated microsporidiosis. This review gathered data of disseminated microsporidiosis and T. hominis infections in humans covering the biological and clinical aspects. There was a total of 22 cases of disseminated microsporidiosis reports worldwide. Ten microsporidia species were identified. Maximum likelihood tree results showed some possible correlations with zoonotic transmissions. For T. hominis, there are currently eight case reports in humans, seven of which had Human Immunodeficiency Virus (HIV) infection. It is observed that risks are higher for the immunocompromised to acquire such infections, however, future studies should look into the entire life cycle, to identify the route of transmission and establish preventive measures, especially among the high-risk groups.

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.

Bugs in Bugs: The Role of Probiotics and Prebiotics in Maintenance of Health in Mass-Reared Insects

Interactions between insects and their microbiota affect insect behaviour and evolution. When specific microorganisms are provided as a dietary supplement, insect reproduction, food conversion and growth are enhanced and health is improved in cases of nutritional deficiency or pathogen infection. The purpose of this review is to provide an overview of insect-microbiota interactions, to review the role of probiotics, their general use in insects reared for food and feed, and their interactions with the host microbiota. We review how bacterial strains have been selected for insect species reared for food and feed and discuss methods used to isolate and measure the effectiveness of a probiotic. We outline future perspectives on probiotic applications in mass-reared insects.

Frontiers in effective control of problem parasites in beekeeping

Demand for better control of certain parasites in managed western honey bees (Apis mellifera L.) remains apparent amongst beekeepers in both Europe and North America, and is of widespread public, scientific, and agricultural concern. Academically, interest from numerous fields including veterinary sciences has led to many exemplary reviews of the parasites of honey bees and the treatment options available. However, summaries of current research frontiers in treating both novel and long-known parasites of managed honey bees are lacking. This review complements the currently comprehensive body of literature summarizing the effectiveness of parasite control in managed honey bees by outlining where significant gaps in development, implementation, and uptake lie, including integration into IPM frameworks and separation of cultural, biological, and chemical controls. In particular, I distinguish where challenges in identifying appropriate controls exist in the lab compared to where we encounter hurdles in technology transfer due to regulatory, economic, or cultural contexts. I overview how exciting frontiers in honey bee parasite control research are clearly demonstrated by the abundance of recent publications on novel control approaches, but also caution that temperance must be levied on the applied end of the research engine in believing that what can be achieved in a laboratory research environment can be quickly and effectively marketed for deployment in the field.

Specific Strains of Honeybee Gut Lactobacillus Stimulate Host Immune System to Protect against Pathogenic Hafnia alvei

Honeybee gut microbiota plays an important role in host physiology and metabolism. Recent studies have shown that the influence of the resident microorganisms in the regulation of honeybee immune system is profound, which protects against the pathogen Serratia marcescens. However, only few of the core gut members in the regulation of immune functions have been studied. Here, we explored how different bee gut bacterial species aided in the clearance of the pathogenic Hafnia alvei, which causes bee septicemia with a high mortality rate. We found that both Gilliamella apicola W8136 and Lactobacillus apis W8172 protect honeybees from the opportunistic pathogen, while two other strains from Gilliamella and Lactobacillus did not affect the invasion of H. alvei. Transcriptomic analysis revealed that gut species induced different expression profiles in the gut. Specifically, two regulator genes from the Toll pathway, PGRP-S3 recognizing Gram-positive and Spätzle that bind to the Toll protein for the downstream signal transduction, were elevated by L. apis. Correspondingly, multiple genes encoding antibacterial proteins were also stimulated by L. apis. Interestingly, we found an increased expression of apidaecin, which also exhibited a high in vitro inhibitory effect on H. alvei. To elucidate the difference of strains in the host’s immune regulation, comparative genomic analyses indicate that the S-layer proteins unique to L. apis are potentially involved in honeybee Toll signaling and the activation of antibacterial protein production.

IMPORTANCE Honeybees are essential pollinators supporting global agricultural economies and food supplies. Recent honeybee decline has been linked to several factors, while pathogen infection is considered one of the most significant contributing factors. Although a limited number of bacterial pathogens have been identified, Hafnia alvei is one of the pathogens causing septicemia in adult bees. In this study, we showed that two bee gut members, Gilliamella and Lactobacillus, can clear H. alvei from invasion. Mono-colonization of specific strains can stimulate the host Toll signaling pathway and the downstream expression of AMPs. Specifically, apidaecin upregulated by the gut symbionts is more effective against the pathogen. Moreover, our genomic analysis suggests that the surface-layer proteins specific to Lactobacillus strains are an important driver of Toll signaling, highlighting the variation of bee gut strains in regulating the host immune system.

One Health, One Hive: A scoping review of honey bees, climate change, pollutants, and antimicrobial resistance

Anthropogenic climate change and increasing antimicrobial resistance (AMR) together threaten the last 50 years of public health gains. Honey bees are a model One Health organism to investigate interactions between climate change and AMR. The objective of this scoping review was to examine the range, extent, and nature of published literature on the relationship between AMR and honey bees in the context of climate change and environmental pollutants. The review followed systematic search methods and reporting guidelines. A protocol was developed a priori in consultation with a research librarian. Resulting Boolean search strings were used to search Embase® via Ovid®, MEDLINE®, Scopus®, AGRICOLA™ and Web of Science™ databases. Two independent reviewers conducted two-stage screening on retrieved articles. To be included, the article had to examine honey bees, AMR, and either climate change or environmental pollution. Data, in accordance with Joanna Briggs Institute guidelines, were extracted from relevant articles and descriptively synthesized in tables, figures, and narrative form. A total of 22 articles met the inclusion criteria, with half of all articles being published in the last five years (n = 11/22). These articles predominantly investigated hive immunocompetence and multi-drug resistance transporter downregulation (n = 11/22), susceptibility to pests (n = 16/22), especially American foulbrood (n = 9/22), and hive product augmentation (n = 3/22). This review identified key themes and gaps in the literature, including the need for future interdisciplinary research to explore the link between AMR and environmental change evidence streams in honey bees. We identified three potential linkages between pollutive and climatic factors and risk of AMR. These interconnections reaffirm the necessity of a One Health framework to tackle global threats and investigate complex issues that extend beyond honey bee research into the public health sector. It is integral that we view these "wicked" problems through an interdisciplinary lens to explore long-term strategies for change.

Glucosinolate Bioactivation by Apis mellifera Workers and Its Impact on Nosema ceranae Infection at the Colony Level

The microsporidian fungus Nosema ceranae represents one of the primary bee infection threats worldwide and the antibiotic fumagillin is the only registered product for nosemosis disease control, while few alternatives are, at present, available. Natural bioactive compounds deriving from the glucosinolate-myrosinase system (GSL-MYR) in Brassicaceae plants, mainly isothiocyanates (ITCs), are known for their antimicrobial activity against numerous pathogens and for their health-protective effects in humans. This work explored the use of Brassica nigra and Eruca sativa defatted seed meal (DSM) GSL-containing diets against natural Nosema infection in Apis mellifera colonies. DSM patties from each plant species were obtained by adding DSMs to sugar candy at the concentration of 4% (w/w). The feeding was administered in May to mildly N. ceranae-infected honey bee colonies for four weeks at the dose of 250 g/week. In the treated groups, no significant effects on colony development and bee mortality were observed compared to the negative controls. The N. ceranae abundance showed a slight but significant decrease. Furthermore, the GSL metabolism in bees was investigated, and MYR hydrolytic activity was qualitatively searched in isolated bee midgut and hindgut. Interestingly, MYR activity was detected both in the bees fed DSMs and in the control group where the bees did not receive DSMs. In parallel, ITCs were found in gut tissues from the bees treated with DSMs, corroborating the presence of a MYR-like enzyme capable of hydrolyzing ingested GSLs. On the other hand, GSLs and other GSL hydrolysis products other than ITCs, such as nitriles, were found in honey produced by the treated bees, potentially increasing the health value of the final product for human consumption. The results are indicative of a specific effect on the N. ceranae infection in managed honey bee colonies depending on the GSL activation within the target organ.

Proteasome Inhibition Is an Effective Treatment Strategy for Microsporidia Infection in Honey Bees

The microsporidia Nosema ceranae is an obligate intracellular parasite that causes honey bee mortality and contributes to colony collapse. Fumagillin is presently the only pharmacological control for N. ceranae infections in honey bees. Resistance is already emerging, and alternative controls are critically needed. Nosema spp. exhibit increased sensitivity to heat shock, a common proteotoxic stress. Thus, we hypothesized that targeting the Nosema proteasome, the major protease removing misfolded proteins, might be effective against N. ceranae infections in honey bees. Nosema genome analysis and molecular modeling revealed an unexpectedly compact proteasome apparently lacking multiple canonical subunits, but with highly conserved proteolytic active sites expected to be receptive to FDA-approved proteasome inhibitors. Indeed, N. ceranae were strikingly sensitive to pharmacological disruption of proteasome function at doses that were well tolerated by honey bees. Thus, proteasome inhibition is a novel candidate treatment strategy for microsporidia infection in honey bees.

Effects of Agaricus bisporus Mushroom Extract on Honey Bees Infected with Nosema ceranae

Simple Summary

Nosema ceranae affects honey bee (Apis mellifera L.) causing nosemosis disease that often induces serious problems in apiculture. Antibiotic fumagillin is the only licenced treatment against nosemosis, but its effectiveness is questioned and its usage associated with risk of bee mortality and appearance of residues in bee products. In search for alternative treatment for the control of nosemosis, water crude extract of Agaricus bisporus was tested on bees in laboratory (cage) experiments. Bee survival and food consumption were monitored together with Nosema infection level and expression of five genes (abaecin, hymenoptaecin, defensin, apidaecin, and vitellogenin) were evaluated in bees sampled on days 7 and 15. Apart from the gene for defensin, the expression of all tested genes was up-regulated in bees supplemented with A. bisporus extract. Both anti-Nosema and immune protective effects of A. bisporus extract were observed when supplementation started at the moment of N. ceranae infection or preventively (before or simultaneously with the Nosema infection).

Abstract

Agaricus bisporus water crude extract was tested on honey bees for the first time. The first part of the cage experiment was set for selecting one concentration of the A. bisporus extract. Concentration of 200 µg/g was further tested in the second part of the experiment where bee survival and food consumption were monitored together with Nosema infection level and expression of five genes (abaecin, hymenoptaecin, defensin, apidaecin, and vitellogenin) that were evaluated in bees sampled on days 7 and 15. Survival rate of Nosema-infected bees was significantly greater in groups fed with A. bisporus-enriched syrup compared to those fed with a pure sucrose syrup. Besides, the anti-Nosema effect of A. bisporus extract was greatest when applied from the third day which coincides with the time of infection with N. ceranae. Daily food consumption did not differ between the groups indicating good acceptability and palatability of the extract. A. bisporus extract showed a stimulative effect on four out of five monitored genes. Both anti-Nosema and nutrigenomic effects of A. bisporus extract were observed when supplementation started at the moment of N. ceranae infection or preventively (before or simultaneously with the infection).

Effect of feeding chitosan or peptidoglycan on Nosema ceranae infection and gene expression related to stress and the innate immune response of honey bees (Apis mellifera)

Nosema ceranae is a microsporidian parasite that causes nosema disease, an infection of the honey bee (Apis mellifera) midgut. Two pathogen-associated molecular patterns (PAMPs), chitosan and peptidoglycan, and N. ceranae spores were fed to worker bees in sucrose syrup and compared to non-inoculated and N. ceranae-inoculated bees without PAMPs. Both chitosan and peptidoglycan significantly increased bee survivorship and reduced spore numbers due to N. ceranae infection. To determine if these results were related to changes in health status, expression of the immune-related genes, hymenoptaecin and defensin2, and the stress tolerance-related gene, blue cheese, was compared to that of control bees. Compared to the inoculated control, bees with the dose of chitosan that significantly reduced N. ceranae spore numbers showed lower expression of hymenoptaecin and defensin2 early after infection, higher expression mid-infection of defensin2 and lower expression of all three genes late in infection. In contrast, higher expression of defensin2 early in the infection and all three genes late in the infection was observed with peptidoglycan treatment. Changes late in the parasite multiplication stage when mature spores would be released from ruptured host cells are less likely to have contributed to reduced spore production. Based on these results, it is concluded that feeding bees chitosan or peptidoglycan can reduce N. ceranae infection, which is at least partially related to altering the health of the bee by inducing immune and stress-related gene expression.

Vairimorpha (Nosema) ceranae Infection Alters Honey Bee Microbiota Composition and Sustains the Survival of Adult Honey Bees

Simple Summary

The gut microbiota, in addition to the hosts and the pathogens, has become the third factor involved in gut disease developments, including honey bees. Interestingly, various studies reported positive associations between the gut bacteria and the most commonly found microsporidian pathogen instead of negative associations. To investigate the positive associations, a prebiotic that also exists in honey was added in the trials. Bees fed the prebiotics have slightly higher pathogen counts but lower mortalities. Microbiota analyses suggested that bees with the infection have a microbiota composition similar to that of bees with a longer lifespan, and the prebiotic seemed to enhance the similarities. Since microsporidia typically cause chronic infections, the positive associations may serve to sustain the host lifespans which is the optimal outcome for the pathogen that the survived bees can withstand pathogen proliferation and transmit the pathogens. Although the mechanisms underlying the associations were not revealed, this study indicated that nosema disease management in bees through changes in microbiota may shorten the lifespans or enhance both the infection and the bee population. Such results have appeared in recent field studies. More studies will be needed for the disease management using bee gut microbiota.

Abstract

Vairimorpha (Nosema) ceranae is the most common eukaryotic gut pathogen in honey bees. Infection is typically chronic but may result in mortality. Gut microbiota is a factor that was recently noted for gut infectious disease development. Interestingly, studies identified positive, instead of negative, associations between core bacteria of honey bee microbiota and V. ceranae infection. To investigate the effects of the positive associations, we added isomaltooligosaccharide (IMO), a prebiotic sugar also found in honey, to enhance the positive associations, and we then investigated the infection and the gut microbiota alterations using qPCR and 16S rRNA gene sequencing. We found that infected bees fed IMO had significantly higher V. ceranae spore counts but lower mortalities. In microbiota comparisons, V. ceranae infections alone significantly enhanced the overall microbiota population in the honey bee hindgut and feces; all monitored core bacteria significantly increased in the quantities but not all in the population ratios. The microbiota alterations caused by the infection were enhanced with IMO, and these alterations were similar to the differences found in bees that naturally have longer lifespans. Although our results did not clarify the causations of the positive associations between the infections and microbiota, the associations seemed to sustain the host survival and benefit the pathogen. Enhancing indigenous gut microbe to control nosema disease may result in an increment of bee populations but not the control of the pathogen. This interaction between the pathogen and microbiota potentially enhances disease transmission and avoids the social immune responses that diseased bees die prematurely to curb the disease from spreading within colonies.

Transcriptome-level assessment of the impact of deformed wing virus on honey bee larvae

Deformed wing virus (DWV) prevalence is high in honey bee (Apis mellifera) populations. The virus infects honey bees through vertical and horizontal transmission, leading to behavioural changes, wing deformity, and early mortality. To better understand the impacts of viral infection in the larval stage of honey bees, artificially reared honey bee larvae were infected with DWV (1.55 × 10¹⁰ copies/per larva). No significant mortality occurred in infected honey bee larvae, while the survival rates decreased significantly at the pupal stage. Examination of DWV replication revealed that viral replication began at 2 days post inoculation (d.p.i.), increased dramatically to 4 d.p.i., and then continuously increased in the pupal stage. To better understand the impact of DWV on the larval stage, DWV-infected and control groups were subjected to transcriptomic analysis at 4 d.p.i. Two hundred fifty-five differentially expressed genes (DEGs) (fold change ≥ 2 or ≤ -2) were identified. Of these DEGs, 168 genes were downregulated, and 87 genes were upregulated. Gene Ontology (GO) analysis showed that 141 DEGs (55.3%) were categorized into molecular functions, cellular components and biological processes. One hundred eleven genes (38 upregulated and 73 downregulated) were annotated by KO (KEGG Orthology) pathway mapping and involved metabolic pathways, biosynthesis of secondary metabolites and glycine, serine and threonine metabolism pathways. Validation of DEGs was performed, and the related gene expression levels showed a similar tendency to the DEG predictions at 4 d.p.i.; cell wall integrity and stress response component 1 (wsc1), cuticular protein and myo-inositol 2-dehydrogenase (iolG) were significantly upregulated, and small conductance calcium-activated potassium channel protein (SK) was significantly downregulated at 4 d.p.i. Related gene expression levels at different d.p.i. revealed that these DEGs were significantly regulated from the larval stage to the pupal stage, indicating the potential impacts of gene expression levels from the larval to the pupal stages. Taken together, DWV infection in the honey bee larval stage potentially influences the gene expression levels from larvae to pupae and reduces the survival rate of the pupal stage. This information emphasizes the consequences of DWV prevalence in honey bee larvae for apiculture.

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

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

Current Status of Loop-Mediated Isothermal Amplification Technologies for the Detection of Honey Bee Pathogens

Approximately one-third of the typical human Western diet depends upon pollination for production, and honey bees (Apis mellifera) are the primary pollinators of numerous food crops, including fruits, nuts, vegetables, and oilseeds. Regional large scale losses of managed honey bee populations have increased significantly during the last decade. In particular, asymptomatic infection of honey bees with viruses and bacterial pathogens are quite common, and co-pathogenic interaction with other pathogens have led to more severe and frequent colony losses. Other multiple environmental stress factors, including agrochemical exposure, lack of quality forage, and reduced habitat, have all contributed to the considerable negative impact upon bee health. The ability to accurately diagnose diseases early could likely lead to better management and treatment strategies. While many molecular diagnostic tests such as real-time PCR and MALDI-TOF mass spectrometry have been developed to detect honey bee pathogens, they are not field-deployable and thus cannot support local apiary husbandry decision-making for disease control. Here we review the field-deployable technology termed loop-mediated isothermal amplification (LAMP) and its application to diagnose honey bee infections.

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

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

RNA Interference-Mediated Knockdown of Genes Encoding Spore Wall Proteins Confers Protection against Nosema ceranae Infection in the European Honey Bee, Apis mellifera

Nosema ceranae (Opisthosporidia: Microsporidia) is an emergent intracellular parasite of the European honey bee (Apis mellifera) and causes serious Nosema disease which has been associated with worldwide honey bee colony losses. The only registered treatment for Nosema disease is fumagillin-b, and this has raised concerns about resistance and off-target effects. Fumagillin-B is banned from use in honey bee colonies in many countries, particularly in Europe. As a result, there is an urgent need for new and effective therapeutic options to treat Nosema disease in honey bees. An RNA interference (RNAi)-based approach can be a potent strategy for controlling diseases in honey bees. We explored the therapeutic potential of silencing the sequences of two N. ceranae encoded spore wall protein (SWP) genes by means of the RNAi-based methodology. Our study revealed that the oral ingestion of dsRNAs corresponding to SWP8 and SWP12 used separately or in combination could lead to a significant reduction in spore load, improve immunity, and extend the lifespan of N. ceranae-infected bees. The results from the work completed here enhance our understanding of honey bee host responses to microsporidia infection and highlight that RNAi-based therapeutics are a promising treatment for honey bee diseases.

The Herbal Supplements NOZEMAT HERB® and NOZEMAT HERB PLUS®: An Alternative Therapy for N. ceranae Infection and Its Effects on Honey Bee Strength and Production Traits

Honey bees (Apis mellifera L.) are the most effective pollinators for different crops and wild flowering plants, thus maintaining numerous ecosystems in the world. However, honey bee colonies often suffer from stress or even death due to various pests and diseases. Among the latter, nosemosis is considered to be one of the most common diseases, causing serious damage to beekeeping every year. Here, we present, for the first time, the effects from the application of the herbal supplements NOZEMAT HERB^® (NH) and NOZEMAT HERB PLUS^® (NHP) for treating N. ceranae infection and positively influencing the general development of honey bee colonies. To achieve this, in autumn 2019, 45 colonies were selected based on the presence of N. ceranae infections. The treatment was carried out for 11 months (August 2019–June 2020). All colonies were sampled pre- and post-treatment for the presence of N. ceranae by means of light microscopy and PCR analysis. The honey bee colonies’ performance and health were evaluated pre- and post-treatment. The obtained results have shown that both supplements have exhibited statistically significant biological activity against N. ceranae in infected apiaries. Considerable enhancement in the strength of honey bee colonies and the amount of sealed workers was observed just one month after the application of NH and NHP. Although the mechanisms of action of NH and NHP against N. ceranae infection are yet to be completely elucidated, our results suggest a new holistic approach as an alternative therapy to control nosemosis and to improve honey bee colonies’ performance and health.

Transferrin-mediated iron sequestration suggests a novel therapeutic strategy for controlling Nosema disease in the honey bee, Apis mellifera

Nosemosis C, a Nosema disease caused by microsporidia parasite Nosema ceranae, is a significant disease burden of the European honey bee Apis mellifera which is one of the most economically important insect pollinators. Nevertheless, there is no effective treatment currently available for Nosema disease and the disease mechanisms underlying the pathological effects of N. ceranae infection in honey bees are poorly understood. Iron is an essential nutrient for growth and survival of hosts and pathogens alike. The iron tug-of-war between host and pathogen is a central battlefield at the host-pathogen interface which determines the outcome of an infection, however, has not been explored in honey bees. To fill the gap, we conducted a study to investigate the impact of N. ceranae infection on iron homeostasis in honey bees. The expression of transferrin, an iron binding and transporting protein that is one of the key players of iron homeostasis, in response to N. ceranae infection was analysed. Furthermore, the functional roles of transferrin in iron homeostasis and honey bee host immunity were characterized using an RNA interference (RNAi)-based method. The results showed that N. ceranae infection causes iron deficiency and upregulation of the A. mellifera transferrin (AmTsf) mRNA in honey bees, implying that higher expression of AmTsf allows N. ceranae to scavenge more iron from the host for its proliferation and survival. The suppressed expression levels of AmTsf via RNAi could lead to reduced N. ceranae transcription activity, alleviated iron loss, enhanced immunity, and improved survival of the infected bees. The intriguing multifunctionality of transferrin illustrated in this study is a significant contribution to the existing body of literature concerning iron homeostasis in insects. The uncovered functional role of transferrin on iron homeostasis, pathogen growth and honey bee's ability to mount immune responses may hold the key for the development of novel strategies to treat or prevent diseases in honey bees.

Know your enemy - transcriptome of myxozoan Tetracapsuloides bryosalmonae reveals potential drug targets against proliferative kidney disease in salmonids

The myxozoan Tetracapsuloides bryosalmonae is a widely spread endoparasite that causes proliferative kidney disease (PKD) in salmonid fish. We developed an in silico pipeline to separate transcripts of T. bryosalmonae from the kidney tissue of its natural vertebrate host, brown trout (Salmo trutta). After stringent filtering, we constructed a partial transcriptome assembly T. bryosalmonae, comprising 3427 transcripts. Based on homology-restricted searches of the assembled parasite transcriptome and Atlantic salmon (Salmo salar) proteome, we identified four protein targets (Endoglycoceramidase, Legumain-like protease, Carbonic anhydrase 2, Pancreatic lipase-related protein 2) for the development of anti-parasitic drugs against T. bryosalmonae. Earlier work of these proteins on parasitic protists and helminths suggests that the identified anti-parasitic drug targets represent promising chemotherapeutic candidates also against T. bryosalmonae, and strengthen the view that the known inhibitors can be effective in evolutionarily distant organisms. In addition, we identified differentially expressed T. bryosalmonae genes between moderately and severely infected fish, indicating an increased abundance of T. bryosalmonae sporogonic stages in fish with low parasite load. In conclusion, this study paves the way for future genomic research in T. bryosalmonae and represents an important step towards the development of effective drugs against PKD.

Effects of Synthetic Acaricides and Nosema ceranae (Microsporidia: Nosematidae) on Molecules Associated with Chemical Communication and Recognition in Honey Bees

Acaricides and the gut parasite Nosema ceranae are commonly present in most productive hives. Those stressors could be affecting key semiochemicals, which act as homeostasis regulators in Apis mellifera colonies, such as cuticular hydrocarbons (CHC) involved in social recognition and ethyl oleate (EO) which plays a role as primer pheromone in honey bees. Here we test the effect of amitraz, coumaphos, tau-fluvalinate and flumethrin, commonly applied to treat varroosis, on honey bee survival time, rate of food consumption, CHC profiles and EO production on N. ceranae-infected and non-infected honey bees. Different sublethal concentrations of amitraz, coumaphos, tau-fluvalinate and flumethrin were administered chronically in a syrup-based diet. After treatment, purified hole-body extracts were analyzed by gas chromatography coupled to mass spectrometry. While N. ceranae infection was also shown to decrease EO production affecting survival rates, acaricides showed no significant effect on this pheromone. As for the CHC, we found no changes in relation to the health status or consumption of acaricides. This absence of alteration in EO or CHC as response to acaricides ingestion or in combination with N. ceranae, suggests that worker honey bees exposed to those highly ubiquitous drugs are hardly differentiated by nest-mates. Having determined a synergic effect on mortality in worker bees exposed to coumaphos and Nosema infection but also, alterations in EO production as a response to N. ceranae infection it is an interesting clue to deeper understand the effects of parasite-host-pesticide interaction on colony functioning.

Extracts from Eleutherococcus senticosus (Rupr. et Maxim.) Maxim. Roots: A New Hope Against Honeybee Death Caused by Nosemosis

Pollinators, the cornerstones of our terrestrial ecosystem, have been at the very core of our anxiety. This is because we can nowadays observe a dangerous decline in the number of insects. With the numbers of pollinators dramatically declining worldwide, the scientific community has been growing more and more concerned about the future of insects as fundamental elements of most terrestrial ecosystems. Trying to address this issue, we looked for substances that might increase bee resistance. To this end, we checked the effects of plant-based adaptogens on honeybees in laboratory tests and during field studies on 30 honeybee colonies during two seasons. In this study, we have tested extracts obtained from: Eleutherococcus senticosus, Garcinia cambogia, Panax ginseng, Ginkgo biloba, Schisandra chinensis, and Camellia sinensis. The 75% ethanol E. senticosus root extract proved to be the most effective, both as a cure and in the prophylaxis of nosemosis. Therefore, Eleutherococcus senticosus, and its active compounds, eleutherosides, are considered the most powerful adaptogens, in the pool of all extracts that were selected for screening, for supporting immunity and improving resistance of honeybees. The optimum effective concentration of 0.4 mg/mL E. senticosus extract responded to c.a. 5.76, 2.56 and 0.07 µg/mL of eleutheroside B, eleutheroside E and naringenin, respectively. The effect of E. senticosus extracts on honeybees involved a similar adaptogenic response as on other animals, including humans. In this research, we show for the first time such an adaptogenic impact on invertebrates, i.e., the effect on honeybees stressed by nosemosis. We additionally hypothesised that these adaptogenic properties were connected with eleutherosides-secondary metabolites found exclusively in the Eleutherococcus genus and undetected in other studied extracts. As was indicated in this study, eleutherosides are very stable chemically and can be found in extracts in similar amounts even after two years from extraction. Considering the role bees play in nature, we may conclude that demonstrating the adaptogenic properties which plant extracts have in insects is the most significant finding resulting from this research. This knowledge might bring to fruition numerous economic and ecological benefits.

The ins and outs of host-microsporidia interactions during invasion, proliferation and exit

Microsporidia are a large group of fungal-related obligate intracellular parasites. They are responsible for infections in humans as well as in agriculturally and environmentally important animals. Although microsporidia are abundant in nature, many of the molecular mechanisms employed during infection have remained enigmatic. In this review, we highlight recent work showing how microsporidia invade, proliferate and exit from host cells. During invasion, microsporidia use spore wall and polar tube proteins to interact with host receptors and adhere to the host cell surface. In turn, the host has multiple defence mechanisms to prevent and eliminate these infections. Microsporidia encode numerous transporters and steal host nutrients to facilitate proliferation within host cells. They also encode many secreted proteins which may modulate host metabolism and inhibit host cell defence mechanisms. Spores exit the host in a non-lytic manner that is dependent on host actin and endocytic recycling proteins. Together, this work provides a fuller picture of the mechanisms that these fascinating organisms use to infect their hosts.

Impact of Protoporphyrin Lysine Derivatives on the Ability of Nosema ceranae Spores to Infect Honeybees

Simple Summary

Honeybees, which are important for the development and maintenance of natural ecosystems, are infected by microsporidia, Nosema apis and N. ceranae. These parasites induce a disease named nosemosis contributing to the impairment of digestion and nutrient absorption, ultimately leading to total colony collapse. The need for research into the control of N. ceranae has become increasingly important. Promising compounds for the treatment of nosemosis are porphyrins. In the present study, we examined the effects of three different porphyrins on the infectivity of N. ceranae microsporidia. A significantly lower level of infection was observed in the bees infected with the porphyrin-treated spores than in the control bees (infected with untreated spores). We showed that protoporphyrin lysine derivatives in particular prevented the development of Nosema spores and simultaneously extended bee life spans (up to 50%). The results also indicate that these porphyrins may contribute to the reduction in digestive nutrient absorption disorders in bees. The present findings can be used to develop a new class of drugs for combating nosemosis. These compounds may serve as preventive or disinfection agents through direct inactivation of Nosema both in the midgut and outside the host body, i.e., in the hive.

Abstract

The effect of two protoporphyrin IX derivatives conjugated with single (PP[Lys(TFA)-OH)]₂) or double (PP[Lys(TFA)-Lys(TFA)-OH]₂) lysine moieties on the infectious capacity of Nosema ceranae spores was examined, and their efficacies were compared with those of a cationic porphyrin (H₂TTMePP). Honeybees were inoculated with spores preincubated with porphyrins or with untreated spores (control). A significantly lower level of infection was observed in the bees infected with the porphyrin-treated spores than in the infected control. Porphyrins 1 and 2 reduced the infectious capability of microsporidia more efficiently than porphyrin 3, with bee mortality declining to almost 50%. Confocal analysis of the midguts of infected bees revealed distinct differences in the number of spores between the control group and the group infected with PP[Lys(TFA)-Lys(TFA)-OH]₂-treated spores. Notably, bees with a reduced level of infection consumed less sucrose syrup than the control bees, indicating a reduction in digestive disorders and an improvement in food absorption.

Bioactivity studies of porphyrinoids against microsporidia isolated from honeybees

Microsporidian infections are dangerous to honeybees due to the absence of an efficient treatment for nosemosis. In the present work, the abilities of several porphyrins to directly inactivate microsporidia derived from Nosema-infected honeybees were studied in vitro. Amide derivatives of protoporphyrin IX (PPIX) conjugated with one and two amino acid moieties were synthesized, and their activities were compared with those of two cationic porphyrins, TMePyP and TTMePP. The most active porphyrins, PP[Lys-Asp]₂, PP[Lys-TFA]₂, PP[Asp(ONa)₂]₂ and PP[Lys-Lys]₂ at concentrations as low as 10–50 µM exerted significant effects on microsporidia, reducing the number of spores by 67–80% compared to the control. Live-cell imaging of the spores treated with porphyrins showed that only 1.6% and 3.0% of spores remained alive after 24 h-incubation with 50 µM PP[Asp(ONa)₂]₂ and PP[Lys-Asp]₂, respectively. The length of the amino acid side chains and their identity in the PPIX molecules affected the bioactivity of the porphyrin. Importantly, the irradiation of the porphyrins did not enhance their potency in destroying Nosema spores. We showed that the porphyrins accumulated inside the living spores but not inside dead spores, thus the destruction of the microsporidia by non-metallated porphyrins is not dependent on photosensitization, but is associated with their active transport into the spore cell. When administered to honeybees in vivo, PPIX[Lys-TFA]₂ and PPIX[Lys-Lys]₂ reduced spore loads by 69–76% in infected individuals. They both had no toxic effect on honeybees, in contrast to zinc-coordinated porphyrin.

Propolis Consumption Reduces Nosema ceranae Infection of European Honey Bees (Apis mellifera)

Nosema ceranae is a widespread obligate intracellular parasite of the ventriculus of many species of honey bee (Apis), including the Western honey bee Apis mellifera, in which it may lead to colony death. It can be controlled in A. mellifera by feeding the antibiotic fumagillin to a colony, though this product is toxic to humans and its use has now been banned in many countries, so in beekeeping, there exists a need for alternative and safe products effective against N. ceranae. Honeybees produce propolis from resinous substances collected from plants and use it to protect their nest from parasites and pathogens; propolis is thought to decrease the microbial load of the hive. We hypothesized that propolis might also reduce N. ceranae infection of individual bees and that they might consume propolis as a form of self-medication. To test these hypotheses, we evaluated the effects of an ethanolic extract of propolis administered orally on the longevity and spore load of experimentally N. ceranae-infected worker bees and also tested whether infected bees were more attracted to, and consumed a greater proportion of, a diet containing propolis in comparison to uninfected bees. Propolis extracts and ethanol (solvent control) increased the lifespan of N. ceranae-infected bees, but only propolis extract significantly reduced spore load. Our propolis extract primarily contained derivatives of caffeic acid, ferulic acid, ellagic acid and quercetin. Choice, scan sampling and food consumption tests did not reveal any preference of N. ceranae-infected bees for commercial candy containing propolis. Our research supports the hypothesis that propolis represents an effective and safe product to control N. ceranae but worker bees seem not to use it to self-medicate when infected with this pathogen.

Natural Product Medicines for Honey Bees: Perspective and Protocols

The western honey bee remains the most important pollinator for agricultural crops. Disease and stressors threaten honey bee populations and productivity during winter- and summertime, creating costs for beekeepers and negative impacts on agriculture. To combat diseases and improve overall bee health, researchers are constantly developing honey bee medicines using the tools of microbiology, molecular biology and chemistry. Below, we present a manifesto alongside standardized protocols that outline the development and a systematic approach to test natural products as ‘bee medicines’. These will be accomplished in both artificial rearing conditions and in colonies situated in the field. Output will be scored by gene expression data of host immunity, bee survivorship, reduction in pathogen titers, and more subjective merits of the compound in question. Natural products, some of which are already encountered by bees in the form of plant resins and nectar compounds, provide promising low-cost candidates for safe prophylaxis or treatment of bee diseases.