Influence of Gelatin and Propolis Extract on Honey Gummy Jelly Properties: Optimization Using D-Optimal Mixture Design

Gelatin is commonly used as a gelling agent in gummy candy. Honey and bee products are valuable and rich sources of biologically active substances. In this study, the influence of gelatin and propolis extract on honey gummy jelly (HGJ) properties was investigated. Honey (28-32%), xylitol (13-17%), and gelatin (6-10%) were utilized to develop HGJ products by mixture design methodology. Subsequently, the optimized formulation of HGJ was fortified with 1% and 2% propolis extract to enhance its phytochemicals and antimicrobial activities. The variation in the ingredients significantly affected the physicochemical, textural, and sensory properties of the HGJ. The optimized HGJ formulation consisted of honey (32%), xylitol (14%), and gelatin (7%) and exhibited 13.35 × 103 g.force of hardness, -0.56 × 103 g.sec of adhesiveness, 11.96 × 103 N.mm of gumminess, 0.58 of resilience, and a moderate acceptance score (6.7-7.5). The fortification of HGJ with propolis extract significantly increased its phytochemical properties. Furthermore, the incorporation of propolis extract (2%) into the HGJ was able to significantly inhibit the growth of Gram-positive (Streptococcus mutans and Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria. The mixture of gelatin, xylitol, honey, and propolis extract can be utilized to develop a healthy gummy product with acceptable physicochemical, textural, and sensory qualities.

Comprehensive analysis of the microbiome in Apis cerana honey highlights honey as a potential source for the isolation of beneficial bacterial strains

Background

Honey is a nutritious food made by bees from nectar and sweet deposits of flowering plants and has been used for centuries as a natural remedy for wound healing and other bacterial infections due to its antibacterial properties. Honey contains a diverse community of bacteria, especially probiotic bacteria, that greatly affect the health of bees and their consumers. Therefore, understanding the microorganisms in honey can help to ensure the quality of honey and lead to the identification of potential probiotic bacteria.

Methods

Herein, the bacteria community in honey produced by Apis cerana was investigated by applying the next-generation sequencing (NGS) method for the V3-V4 hypervariable regions of the bacterial 16S rRNA gene. In addition, lactic acid bacteria (LAB) in the honey sample were also isolated and screened for in vitro antimicrobial activity.

Results

The results showed that the microbiota of A. cerana honey consisted of two major bacterial phyla, Firmicutes (50%; Clostridia, 48.2%) and Proteobacteria (49%; Gammaproteobacteria, 47.7%). Among the 67 identified bacterial genera, the three most predominant genera were beneficial obligate anaerobic bacteria, Lachnospiraceae (48.14%), followed by Gilliamella (26.80%), and Enterobacter (10.16%). Remarkably, among the identified LAB, Lactobacillus kunkeei was found to be the most abundant species. Interestingly, the isolated L. kunkeei strains exhibited antimicrobial activity against some pathogenic bacteria in honeybees, including Klebsiella spp., Escherichia coli, Enterococcus faecalis, Pseudomonas aeruginosa and Staphylococcus aureus. This underscores the potential candidacy of L. kunkeei for developing probiotics for medical use. Taken together, our results provided new insights into the microbiota community in the A. cerana honey in Hanoi, Vietnam, highlighting evidence that honey can be an unexplored source for isolating bacterial strains with potential probiotic applications in honeybees and humans.

1 H-NMR revealed pyruvate as a differentially abundant metabolite in the venom glands of Apis cerana and Apis mellifera

As a common defense mechanism in Hymenoptera, bee venom has complex components. Systematic and comprehensive analysis of bee venom components can aid in early evaluation, accurate diagnosis, and protection of organ function in humans in cases of bee stings. To determine the differences in bee venom composition and metabolic pathways between Apis cerana and Apis mellifera, proton nuclear magnetic resonance (1 H-NMR) technology was used to detect the metabolites in venom samples. A total of 74 metabolites were identified and structurally analyzed in the venom of A. cerana and A. mellifera. Differences in the composition and abundance of major components of bee venom from A. cerana and A. mellifera were mapped to four main metabolic pathways: valine, leucine and isoleucine biosynthesis; glycine, serine and threonine metabolism; alanine, aspartate and glutamate metabolism; and the tricarboxylic acid cycle. These findings indicated that the synthesis and metabolic activities of proteins or polypeptides in bee venom glands were different between A. cerana and A. mellifera. Pyruvate was highly activated in 3 selected metabolic pathways in A. mellifera, being much more dominant in A. mellifera venom than in A. cerana venom. These findings indicated that pyruvate in bee venom glands is involved in various life activities, such as biosynthesis and energy metabolism, by acting as a precursor substance or intermediate product.

Glyphosate exposure affected longevity-related pathways and reduced survival in asian honey bees (Apis cerana)

Glyphosate (N-(phosphonomethyl)glycine, GLY) ranks among the most extensively used and effective herbicides globally. However, excessive GLY utilization poses a substantial threat to the survival of honey bees (Apis cerana). Here we monitored the survival status of A. cerana treated with GLY, and conducted transcriptome sequencing of the bee gut and head to further explore potential GLY influences at the molecular level. We observed that the mortality rate of bees increased as GLY concentration escalated. Pivotal pathways emerged in response to the GLY treatment, with a substantial number of differentially expressed genes enriched in the longevity regulating pathway - multiple species. This strongly suggested that GLY may influence the physiological behavior of bees by impacting this particular pathway. Moreover, our analysis revealed a notable reduction in the enzymatic activities of CYP450 and AChE in both the bee head and intestines of when exposed to GLY. Conversely, the enzymatic activity of superoxide dismutase (SOD) in the head remained unaffected, whereas in the intestines, it exhibited a significant increase. Additionally, prophenol oxidase (PPO) and glutathione-S-transferases (GSTs) displayed contrasting trends in enzymatic activity in both organs. This study offers valuable insights into how GLY impacted the survival of A. cerana.

Acute and chronic effects of sublethal neonicotinoid thiacloprid to Asian honey bee (Apis cerana cerana)

Pesticide pollution is one of the most important factors for global bee declines. Despite many studies have revealed that the most important Chinese indigenous species，Apis cerana, is presenting a high risk on exposure to neonicotinoids, the toxicology information on Apis cerana remain limited. This study was aimed to determine the acute and chronic toxic effects of thiacloprid (IUPAC name: {(2Z)-3-[(6-Chloro-3-pyridinyl)methyl]-1,3-thiazolidin-2-ylidene}cyanamide) on behavioral and physiological performance as well as genome-wide transcriptome in A. cerana. We found the 1/5 LC50 of thiacloprid significantly impaired learning and memory abilities after both acute and chronic exposure, nevertheless, has no effects on the sucrose responsiveness and phototaxis climbing ability of A. cerana. Moreover, activities of detoxification enzyme P450 monooxygenases and CarE were increased by short-term exposure to thiacloprid, while prolonged exposure caused suppression of CarE activity. Neither acute nor chronic exposure to thiacloprid altered honey bee AChE activities. To further study the potential defense molecular mechanisms in Asian honey bee under pesticide stress, we analyzed the transcriptomes of honeybees in response to thiacloprid stress. The transcriptomic profiles revealed consistent upregulation of immune- and stress-related genes by both acute or chronic treatments. Our results suggest that the chronic exposure to thiacloprid produced greater toxic effects than a single administration to A. cerana. Altogether, our study deepens the understanding of the toxicological characteristic of A. cerana against thiacloprid, and could be used to further investigate the complex molecular mechanisms in Asian honey bee under pesticide stress.

Survey Results of Honey Bee Colony Losses in Winter in China (2009-2021)

There is growing concern that massive loss of honey bees can cause serious negative effects on biodiversity and ecosystems. Surveys of colony losses have been performed worldwide to monitor the dynamic changes and health status of honey bee colonies. Here, we present the results of surveys regarding winter colony losses from 21 provinces in China from 2009 to 2021, with a total of 1,744,324 colonies managed by 13,704 beekeepers. The total colony losses were low (9.84%; 95% Confidence Interval (CI): 9.60-10.08%) but varied among years, provinces, and scales of apiaries. As little is known about the overwintering mortality of Apis cerana, in this study, we surveyed and compared the loss rates between Apis mellifera and A. cerana in China. We found colonies of A. mellifera suffered significantly lower losses than A. cerana in China. Larger apiaries resulted in higher losses in A. mellifera, whereas the opposite was observed in A. cerana. Furthermore, we used generalized linear mixed-effects models (GLMMs) to evaluate the effects of potential risk factors on winter colony losses and found that the operation size, species, migration, migration×species interaction, and queen problems were significantly related to the loss rates. New queens can increase their colony overwintering survival. Migratory beekeepers and large operations reported lower loss rates.

Viral Co-Infections and Antiviral Immunity in Honey Bees

Over the past few decades, honey bees have been facing an increasing number of stressors. Beyond individual stress factors, the synergies between them have been identified as a key factor in the observed increase in colony mortality. However, these interactions are numerous and complex and call for further research. Here, in line with our need for a systemic understanding of the threats that they pose to bee health, we review the interactions between honey bee viruses. As viruses are obligate parasites, the interactions between them not only depend on the viruses themselves but also on the immune responses of honey bees. Thus, we first summarise our current knowledge of the antiviral immunity of honey bees. We then review the interactions between specific pathogenic viruses and their interactions with their host. Finally, we draw hypotheses from the current literature and suggest directions for future research.

Gut microbiota composition and gene expression changes induced in the Apis cerana exposed to acetamiprid and difenoconazole at environmentally realistic concentrations alone or combined

Apis cerana is an important pollinator of agricultural crops in China. In the agricultural environment, A. cerana may be exposed to acetamiprid (neonicotinoid insecticide) and difenoconazole (triazole fungicide), alone or in combination because they are commonly applied to various crops. At present, our understanding of the toxicological effects of acetamiprid and difenoconazole on honey bee gut microbiomes is limited. The primary objective of this study was to explore whether these two pesticides affect honey bees' gut microbiota and to analyze the transcriptional effects of these two pesticides on honey bees' head and gut. In this study, adults of A. cerana were exposed to acetamiprid and/or difenoconazole by contaminated syrup at field-realistic concentrations for 10 days. Results indicated that acetamiprid and/or difenoconazole chronic exposure did not affect honey bees' survival and food consumption, whereas difenoconazole decreased the weight of honey bees. 16S rRNA sequencing suggested that difenoconazole and the mixture of difenoconazole and acetamiprid decreased the diversity index and shaped the composition of gut bacteria microbiota, whereas acetamiprid did not impact the gut bacterial community. The ITS sequence data showed that neither of the two pesticides affected the fungal community structure. Meanwhile, we also observed that acetamiprid or difenoconazole significantly altered the expression of genes related to detoxification and immunity in honey bees' tissues. Furthermore, we observed that the adverse effect of the acetamiprid and difenoconazole mixture on honey bees' health was greater than that of a single mixture. Taken together, our study demonstrates that acetamiprid and/or difenoconazole exposure at field-realistic concentrations induced changes to the honey bee gut microbiome and gene expression.

A sublethal dose of neonicotinoid imidacloprid precisely sensed and detoxified by a C-minus odorant-binding protein 17 highly expressed in the legs of Apis cerana

As a native honeybee species in East Asia, Apis cerana is essential for the stability of local agricultural and plant ecosystems by its' olfactory system for searching nectar and pollen sources. Odorant-binding proteins (OBPs) existing in the insect's olfactory system can recognize environmental semiochemicals. It was known that sublethal doses of neonicotinoid insecticides could still cause a variety of physiological and behavioral abnormalities in bees. However, the molecular mechanism of A. cerana sensing and response for insecticide has not been further investigated. In this study, we found an A. cerana OBP17 gene significantly up-regulated expressed after exposure to sublethal doses of imidacloprid based on the transcriptomics results. The spatiotemporal expression profiles showed that OBP17 was highly expressed in the legs. Competitive fluorescence binding assays showed that OBP17 had the special and high binding affinity to imidacloprid among the 24 candidate semiochemicals, and the K_A value of OBP17 binding with imidacloprid reached the maximum (6.94 × 10⁴ L/mol) at low-temperature. Thermodynamic analysis showed that the quenching mechanism changed from dynamic to static binding interaction with the increasing temperature. Meanwhile, the force changed from hydrogen bond and van der Waals force to hydrophobic interaction and electrostatic force, indicating the interaction exhibits variability and flexibility. Molecular docking showed that Phe107 contributed the most energy. RNA interference (RNAi) results showed that OBP17 knockdown significantly enhanced the electrophysiological response of the bees' forelegs to imidacloprid. Our study indicated that OBP17 could precisely touch and sense sublethal doses of neonicotinoid imidacloprid in the natural environment through its high expression in legs, and the upregulation expression of OBP17 exposure to imidacloprid probably implied that it participate in the detoxification processes of A. cerana. Also, our research enriches the theoretical knowledge of the sensing and detoxifying activities of non-target insects' olfactory sensory system to environmental sublethal doses of systemic insecticides.

Can egg yolk antibodies terminate the CSBV infection in apiculture?

Chinese sacbrood virus (CSBV) is the most severe pathogen of Apis cerana, which leads to serious fatal diseases in bee colonies and eventual catastrophe for the Chinese beekeeping industry. Additionally, CSBV can potentially infect Apis mellifera by bridging the species barrier and significantly affect the productivity of the honey industry. Although several approaches, such as feeding royal jelly, traditional Chinese medicine, and double-stranded RNA treatments, have been employed to suppress CSBV infection, their practical applicabilities are constrained due to their poor effectiveness. In recent years, specific egg yolk antibodies (EYA) have been increasingly utilized in passive immunotherapy for infectious diseases without any side effects. According to both laboratory research and practical use, EYA have demonstrated superior protection for bees against CSBV infection. This review provided an in-depth analysis of the issues and drawbacks in this field in addition to provide a thorough summary of current advancements in CSBV studies. Some promising strategies for the synergistic study of EYA against CSBV, including the exploitation of novel antibody drugs, novel TCM monomer/formula determination, and development of nucleotide drugs, are also proposed in this review. Furthermore, the prospects for the future perspectives of EYA research and applications are presented. Collectively, EYA would terminate CSBV infection soon, as well as will provide scientific guidance and references to control and manage other viral infections in apiculture.

Ecotoxicological effects of common fungicides on the eastern honeybee Apis cerana cerana (Hymenoptera)

The widespread use of fungicides for plant protection has increased the potential for pollinator exposure. This study therefore aimed at assessing the acute and chronic effects of fungicides on pollinators. For this purpose, the acute oral toxicity of the common fungicides azoxystrobin, pyraclostrobin, and boscalid to Eastern honeybee Apis cerana cerena was first evaluated, and the chronic effects on multiple aspects were investigated after exposure to a one-tenth medium lethal dose (LD₅₀) for 10 days. This study revealed that the LD₅₀ values of azoxystrobin, pyraclostrobin and boscalid for adult Eastern honeybees were 12.7 μg/bee, 36.6 μg/bee, and >119 μg/bee, respectively. Midgut epithelial cells revealed that fungicide exposure caused increased intercellular spaces and varying degrees of vacuolization. Exposure to these three fungicides and their binary mixtures significantly affected glycerophospholipid, alanine, aspartate, and glutamate metabolism in Eastern honeybee midguts. Additionally, the relative composition of Lactobacillus, the dominant functional genus in Eastern honeybee guts decreased and microbial balance was disrupted. All fungicides and their mixtures induced strong transcriptional upregulation of genes associated with the immune response and encoding enzymes related to oxidative phosphorylation and metabolism, including abaecin, apidaecin, hymenotaecin, cyp4c3, cyp6a2 and hbg3. Our study provides important insight for understanding the effects of commonly used fungicides on nontarget pollinator and contributes to a more comprehensive assessment of fungicide effects on ecological and environmental safety.

Eastern honeybee Apis cerana sense cold flowering plants by increasing the static binding affinity of odorant-binding protein to cold floral volatiles from loquats

Eastern honeybee Apis cerana has important ecological value for the cold flowering loquat flower pollination in early winter in East Asia. However, the low-temperature adaptive pollination mechanism has not yet been revealed. One odorant-binding protein, OBP2, had been found that could bind to some plant volatiles with strong affinity before. In this study, by using competitive fluorescence binding assay, we first measured the ligand-binding profiles of recombinant OBP2 protein with nine representative aroma chemical substances from loquat flowers. Thermodynamic results showed that three loquat volatiles, 4-Methoxybenzaldehyde, (E)-Ethyl cinnamate, and Methyl cinnamate, have the strongest binding affinity with OBP2 with the static process. And interestingly their binding affinity significantly increased at low temperature (285 K/12 °C) compared to high temperature (298 K/25 °C). In addition, site-directed mutagenesis results showed that Met55 and Lys51 may be the key amino acid sites in the electrostatic and hydrophobic interactions of OBP2 interacting with Methyl cinnamate, respectively. This study suggests that OBP2 is functionally similar and universal in binding to different flower volatiles at low temperatures. Our studies interpreted a novel olfactory mechanism of A. cerana sensing loquat floral volatiles in cold early winter, and enrich a theoretical molecular basis for the temperature-adaptive ecological mechanism of insects' pollination.

A key gene for the climatic adaptation of Apis cerana populations in China according to selective sweep analysis

BACKGROUND

Apis cerana is widely distributed in China and, prior to the introduction of western honeybees, was the only bee species kept in China. During the long-term natural evolutionary process, many unique phenotypic variations have occurred among A. cerana populations in different geographical regions under varied climates. Understanding the molecular genetic basis and the effects of climate change on the adaptive evolution of A. cerana can promote A. cerana conservation in face of climate change and allow for the effective utilization of its genetic resources.

RESULT

To investigate the genetic basis of phenotypic variations and the impact of climate change on adaptive evolution, A. cerana workers from 100 colonies located at similar geographical latitudes or longitudes were analyzed. Our results revealed an important relationship between climate types and the genetic variation of A. cerana in China, and a greater influence of latitude compared with longitude was observed. Upon selection and morphometry analyses combination for populations under different climate types, we identified a key gene RAPTOR, which was deeply involved in developmental processes and influenced the body size.

CONCLUSION

The selection of RAPTOR at the genomic level during adaptive evolution could allow A. cerana to actively regulate its metabolism, thereby fine-tuning body sizes in response to harsh conditions caused by climate change, such as food shortages and extreme temperatures, which may partially elucidate the size differences of A. cerana populations. This study provides crucial support for the molecular genetic basis of the expansion and evolution of naturally distributed honeybee populations.

Prevalence of honey bee pathogens and parasites in South Korea: A five-year surveillance study from 2017 to 2021

Honey bees play an important role in the pollination of crops and wild plants and provide important products to humans. Pathogens and parasites are the main factors that threaten beekeeping in South Korea. Therefore, a nationwide detection of 14 honey bee pathogens, including parasites (phorid flies, Nosema ceranae, and Acarapis woodi mites), viruses, bacteria, and fungal pathogens, was conducted from 2017 to 2021 in the country. The infection rate and the trend of detection of each pathogenic agent were determined. A total of 830 honey bee samples from Apis cerana (n = 357) and A. mellifera (n = 473) were examined. N. ceranae (35.53%), deformed wing virus (52.63%), sacbrood virus (SBV) (52.63%), and black queen cell virus (55.26%) were the most prevalent honey bee pathogens, and their prevalence rapidly increased from 2017 to 2021. The prevalence of Paenibacillus larvae, Israeli acute paralysis virus, Ascosphaera apis, A. woodi, Melissococcus plutonius, and chronic bee paralysis virus remained stable during the surveillance period, with infection rates ranging from 5.26% to 16.45% in 2021. Other pathogens, including acute bee paralysis virus, phorid flies, Kashmir bee virus, and Aspergillus flavus, had low infection rates that gradually declined during the detection period. The occurrence of honeybee pathogens peaked in July. SBV was the most common pathogen in A. cerana, whereas N. ceranae was predominant in A. mellifera. This study provides information regarding the current status of honey bee pathogens and presents the trend of the occurrence of each pathogen in South Korea. These data are important for predicting outbreaks of honey bee diseases in the country.

Preliminary Survey of Pathogens in the Asian Honey Bee (Apis cerana) in Thailand

Widespread parasites, along with emerging threats, globalization, and climate change, have greatly affected honey bees' health, leading to colony losses worldwide. In this study, we investigated the detection of biotic stressors (i.e., viruses, microsporidian, bacteria, and fungi) in Apis cerana by surveying the colonies across different regions of Thailand (Chiang Mai in the north, Nong Khai and Khon Kaen in the northeast, and Chumphon and Surat Thani in the south, in addition to the Samui and Pha-ngan islands). In this study, we detected ABPV, BQCV, LSV, and Nosema ceranae in A. cerana samples through RT-PCR. ABPV was only detected from the samples of Chiang Mai, whereas we found BQCV only in those from Chumphon. LSV was detected only in the samples from the Samui and Pha-ngan islands, where historically no managed bees are known. Nosema ceranae was found in all of the regions except for Nong Khai and Khon Kaen in northeastern Thailand. Paenibacillus larvae and Ascosphaera apis were not detected in any of the A. cerana samples in this survey. The phylogenetic tree analysis of the pathogens provided insights into the pathogens' movements and their distribution ranges across different landscapes, indicating the flow of pathogens among the honey bees. Here, we describe the presence of emerging pathogens in the Asian honey bee as a valuable step in our understanding of these pathogens in terms of the decline in eastern honey bee populations.

A matter of the beehive sound: Can honey bees alert the pollution out of their hives?

Honey bees (Apis spp.) are often used as biological indicators of environmental changes. Recently, bees have been explored to monitor air contaminants by listening to the beehive sound. The beehive sound is believed to encode information on bee responses to chemicals outside their hives. Here we conducted an experiment to address this. First, we randomly fed colonies with pure syrup (PS), acetone-laced syrup (AS), or ethyl acetate-laced syrup (ES) in front of the beehives and collect the beehive sound. Based on the audio data, we build machine learning (ML) models to identify the types of syrup. The result shows that ML models achieved over 90% accuracy for identifying syrup types, indicating that the bees inside their hives emitted the sound associated with the chemicals outside their hives. Then, we sequentially fed the colonies in the order of PS, ES, and AS (the first session) and again in the reverse order (the second session), but did not remove the accumulated ES or AS in the alternative feeding experiment. Based on the audio data, the identification accuracy of both ES and AS by the ML model built on the randomly feeding experiment was different, indicating that the accumulated chemical residuals could confuse the ML models. Therefore, the beehive sound-based environmental monitoring should simultaneously consider the responses of bees to the chemicals outside their hives and their responses to those accumulated inside their hives, which may act simultaneously.

Effect of Ascosphaera apis Infestation on the Activities of Four Antioxidant Enzymes in Asian Honey Bee Larval Guts

Ascosphaera apis infects exclusively bee larvae and causes chalkbrood, a lethal fungal disease that results in a sharp reduction in adult bees and colony productivity. However, little is known about the effect of A. apis infestation on the activities of antioxidant enzymes in bee larvae. Here, A. apis spores were purified and used to inoculate Asian honey bee (Apis cerana) larvae, followed by the detection of the host survival rate and an evaluation of the activities of four major antioxidant enzymes. At 6 days after inoculation (dpi) with A. apis spores, obvious symptoms of chalkbrood disease similar to what occurs in Apis mellifera larvae were observed. PCR identification verified the A. apis infection of A. cerana larvae. Additionally, the survival rate of larvae inoculated with A. apis was high at 1−2 dpi, which sharply decreased to 4.16% at 4 dpi and which reached 0% at 5 dpi, whereas that of uninoculated larvae was always high at 1~8 dpi, with an average survival rate of 95.37%, indicating the negative impact of A. apis infection on larval survival. As compared with those in the corresponding uninoculated groups, the superoxide dismutase (SOD) and catalase (CAT) activities in the 5- and 6-day-old larval guts in the A. apis−inoculated groups were significantly decreased (p < 0.05) and the glutathione S-transferase (GST) activity in the 4- and 5-day-old larval guts was significantly increased (p < 0.05), which suggests that the inhibition of SOD and CAT activities and the activation of GST activity in the larval guts was caused by A. apis infestation. In comparison with that in the corresponding uninoculated groups, the polyphenol oxidase (PPO) activity was significantly increased (p < 0.05) in the 5-day-old larval gut but significantly reduced (p < 0.01) in the 6-day-old larval gut, indicating that the PPO activity in the larval guts was first enhanced and then suppressed. Our findings not only unravel the response of A. cerana larvae to A. apis infestation from a biochemical perspective but also offer a valuable insight into the interaction between Asian honey bee larvae and A. apis.

Spermatophore development in drones indicates the metabolite support for sperm storage in honey bees (Apis cerana)

Developing effective long-term sperm storage strategies to maintain activity requires an understanding of the underlying spermatophore developmental phase in drones. Here we compared the developmental processes and metabolites about seminal vesicles of drones from different parentages (0-24 d)in honeybee colonies, including mated queens, virgin queens, and worker bees. The results showed a similar developmental trend of seminal vesicles in thethree groups of drones on the whole, although there were significant differences in developmental levels, as well as in other indicators. Correlation analysis showed significant positive correlations between seminal vesicle width and sperm viability. The metabolomics of the seminal vesicles in drones from mated queens showed differences of the metabolites in each stage. Particularly, squalene identified among them was validated a protective effect on sperm vitality in vitro experiments. Together the results of these assays support that there were significant differences in the developmental levels of seminal vesicles among the three groups of drones in honeybees, wherein a significant correlation between sperm viability and the developmental levels of seminal vesicles were dissected. The metabolomics analysis and semen storage experiments in vitro display signatures of squalene that may act as an effective protective agent in maintaining sperm viability. Collectively, our findings indicate that spermatophore development in drones provides metabolite support, which contributes to research on the differences of sperm viability among drones in the future.

First Identification and Investigation of piRNAs in the Larval Gut of the Asian Honeybee, Apis cerana

Piwi-interacting RNAs (piRNAs), a class of small non-coding RNAs (ncRNAs), play pivotal roles in maintaining the genomic stability and modulating biological processes such as growth and development via the regulation of gene expression. However, the piRNAs in the Asian honeybee (Apis cerana) are still largely unknown at present. In this current work, on the basis of previously gained high-quality small RNA-seq datasets, piRNAs in the larval gut of Apis cerana cerana, the nominated species of A. cerana, were identified for the first time, followed by an in-depth investigation of the regulatory roles of differentially expressed piRNAs (DEpiRNAs) in the developmental process of the A. c. cerana. Here, a total of 621 piRNAs were identified in A. c. cerana larval guts, among which 499 piRNAs were shared by 4-(Ac4 group), 5-(Ac5 group), and 6-day-old (Ac6 group) larval guts, while the numbers of unique ones equaled 79, 37, and 11, respectively. The piRNAs in each group ranged from 24 nucleotides (nt) to 33 nt in length, and the first base of the piRNAs had a cytosine (C) bias. Additionally, five up-regulated and five down-regulated piRNAs were identified in the Ac4 vs. Ac5 comparison group, nine of which could target 9011 mRNAs; these targets were involved in 41 GO terms and 137 pathways. Comparatively, 22 up-regulated piRNAs were detected in the Ac5 vs. Ac6 comparison group, 21 of which could target 28,969 mRNAs; these targets were engaged in 46 functional terms and 164 pathways. The results suggested an overall alteration of the expression pattern of piRNAs during the developmental process of A. c. cerana larvae. The regulatory network analysis showed that piR-ace-748815 and piR-ace-512574 in the Ac4 vs. Ac5 comparison group as well as piR-ace-716466 and piR-ace-828146 in the Ac5 vs. Ac6 comparison group were linked to the highest number of targets. Further investigation indicated that targets of DEpiRNAs in the abovementioned two comparison groups could be annotated to several growth and development-associated pathways, such as the Jak/STAT, TGF-β, and Wnt signaling pathways, indicating the involvement of DEpiRNAs in modulating larval gut development via these crucial pathways. Moreover, the expression trends of six randomly selected DEpiRNAs were verified using a combination of stem-loop RT-PCR and RT-qPCR. These results not only provide a novel insight into the development of the A. c. cerana larval gut, but also lay a foundation for uncovering the epigenetic mechanism underlying larval gut development.

Genetic Structure of Apis cerana Populations from South Korea, Vietnam and the Russian Far East Based on Microsatellite and Mitochondrial DNA Polymorphism

In this article, we present the results of the genetic analysis of Apis cerana samples from the Russian Far East, South Korea and Vietnam. An analysis of the polymorphism of seven microsatellite loci and an assessment of the haplotype diversity of the mtDNA tRNAleu-COII locus were performed. A fragment of about 431 bp in tRNAleu-COII was sequenced. The analysis showed the presence of 14 haplotypes, while the predominant haplotype was Japan1. Microsatellite data revealed two differentiated clusters. The first cluster contained tropical climate A. cerana samples from Vietnam, and the second cluster combined temperate climate A. cerana samples from the Russian Far East and South Korea.

Genetic Relationships and Signatures of Adaptation to the Climatic Conditions in Populations of Apis cerana Based on the Polymorphism of the Gene Vitellogenin

Apis cerana and Apis mellifera are important honey bee species in Asia. A. cerana populations are distributed from a cold, sharply continental climate in the north to a hot, subtropical climate in the south. Due to the Sacbrood virus, almost all A. cerana populations in Asia have declined significantly in recent decades and have recovered over the past five years. This could lead to a shift in the gene pool of local A. cerana populations that could affect their sustainability and adaptation. It was assumed that adaptation of honey bees could be observed by comparative analysis of the sequences of genes involved in development, labor division, and caste differentiation, such as the gene Vitellogenin VG. The VG gene nucleotide sequences were used to assess the genetic structure and signatures of adaptation of local populations of A. cerana from Korea, Russia, Japan, Nepal, and China. A. mellifera samples from India and Poland were used as the outgroup. The signatures of adaptive selection were found in the local population of A. cerana using VG gene sequence analysis based on Jukes−Cantor genetic distances, cluster analysis, dN/dS ratio evaluation, and Tajima’s D neutrality test. Based on analysis of the VG gene sequences, Apis cerana koreana subspecies in the Korean Peninsula were subdivided into three groups in accordance with their geographic localization from north to south. The VG gene sequences are acceptable tools to study the sustainability and adaptation of A. cerana populations.

Conservation Genomic Analysis of the Asian Honeybee in China Reveals Climate Factors Underlying Its Population Decline

The Asian honeybee, Apis cerana, is one of the most important native pollinators in Asia. Asian honeybees were believed to be under significant decline in China based on a report in 2005. On the contrary, a recent survey revealed that Asian honeybee populations in China are stable and even slightly increased in some regions. Therefore, the declining status of A. cerana populations in China is still unclear. Taking advantage of the abundant, publicly available genomic data for Asian honeybees in China, we employed conservation genomics methods to understand if Asian honeybee populations in China are declining and what the underlying climate factors are. We reconstructed the changes of effective population size (Ne) within the recent past for 6 population groups of Asian honeybees and found out that only one of them (population in Bomi, Tibet) showed a consistently declining Ne from the last 100 generations to 25 generations. Selective sweep analysis suggests that genes related to the tolerance of low temperatures and strong ultraviolet radiation are under selection in the declining population, indicating that these two climate factors most likely underlie the decline of BM populations during the recent past. Our study provides insights into the dynamic changes of Asian honeybee populations in China and identifies climate factors that underlie its population decline, which is valuable for the conservation of this important pollinator.

Sex-Biased Expression of Olfaction-Related Genes in the Antennae of Apis cerana (Hymenoptera: Apidae)

The olfactory system is essential for honeybees to adapt to complex and ever-changing environments and maintain cohesiveness. The Eastern honeybee Apis cerana is native to Asia and has a long history of managed beekeeping in China. In this study, we analysed the antennal transcriptomes of A. cerana workers and drones using Illumina sequencing. A total of 5262 differentially expressed genes (DEGs) (fold change > 2) were identified between these two castes, with 2359 upregulated and 2903 downregulated in drones compared with workers. We identified 242 candidate olfaction-related genes, including 15 odourant-binding proteins (OBPs), 5 chemosensory proteins (CSPs), 110 odourant receptors (ORs), 9 gustatory receptors (GRs), 8 ionotropic receptors (IRs), 2 sensory neuron membrane proteins (SNMPs) and 93 putative odourant-degrading enzymes (ODEs). More olfaction-related genes have worker-biased expression than drone-biased expression, with 26 genes being highly expressed in workers’ antennae and only 8 genes being highly expressed in drones’ antennae (FPKM > 30). Using real-time quantitative PCR (RT-qPCR), we verified the reliability of differential genes inferred by transcriptomics and compared the expression profiles of 6 ORs (AcOR10, AcOR11, AcOR13, AcOR18, AcOR79 and AcOR170) between workers and drones. These ORs were expressed at significantly higher levels in the antennae than in other tissues (p < 0.01). There were clear variations in the expression levels of all 6 ORs between differently aged workers and drones. The relative expression levels of AcOR10, AcOR11, AcOR13, AcOR18 and AcOR79 reached a high peak in 15-day-old drones. These results will contribute to future research on the olfaction mechanism of A. cerana and will help to better reveal the odourant reception variations between different biological castes of honeybees.

The Gut Microbiota at Different Developmental Stages of Apis cerana Reveals Potential Probiotic Bacteria for Improving Honeybee Health

Honeybees play a vital role in the ecological environment and agricultural economy. Increasing evidence shows that the gut microbiome greatly influences the host's health. Therefore, a thorough understanding of gut bacteria composition can lead to the development of probiotics specific for each development stage of honeybees. In this study, the gut microbiota at different developmental stages (larvae, pupae, and adults) of the honeybees Apis cerana in Hanoi, Vietnam, was assessed by sequencing the V3-V4 region in the 16S rRNA gene using the Illumina Miseq platform. The results indicated that the richness and diversity of the gut microbiota varied over the investigated stages of A. cenara. All three bee groups showed relative abundance at both phylum and family levels. In larvae, Firmicutes were the most predominant (81.55%); however, they decreased significantly along with the bee development (33.7% in pupae and 10.3% in adults) in favor of Proteobacteria. In the gut of adult bees, four of five core bacteria were found, including Gilliamella apicola group (34.01%) Bifidobacterium asteroides group (10.3%), Lactobacillus Firm-4 (2%), and Lactobacillus Firm-5 (1%). In contrast, pupae and larvae lacked almost all core bacteria except G. apicola (4.13%) in pupae and Lactobacillus Firm-5 (4.04%) in larvae. This is the first report on the gut microbiota community at different developmental stages of A. cerana in Vietnam and provides potential probiotic species for beekeeping.

Strain-level profiling with picodroplet microfluidic cultivation reveals host-specific adaption of honeybee gut symbionts

BACKGROUND

Symbiotic gut microbes have a rich genomic and metabolic pool and are closely related to hosts' health. Traditional sequencing profiling masks the genomic and phenotypic diversity among strains from the same species. Innovative droplet-based microfluidic cultivation may help to elucidate the inter-strain interactions. A limited number of bacterial phylotypes colonize the honeybee gut, while individual strains possess unique genomic potential and critical capabilities, which provides a particularly good model for strain-level analyses.

RESULTS

Here, we construct a droplet-based microfluidic platform and generated ~ 6 × 10⁸ droplets encapsulated with individual bacterial cells from the honeybee gut and cultivate in different media. Shotgun metagenomic analysis reveals significant changes in community structure after droplet-based cultivation, with certain species showing higher strain-level diversity than in gut samples. We obtain metagenome-assembled genomes, and comparative analysis reveal a potential novel cluster from Bifidobacterium in the honeybee. Interestingly, Lactobacillus panisapium strains obtained via droplet cultivation from Apis mellifera contain a unique set of genes encoding L-arabinofuranosidase, which is likely important for the survival of bacteria in competitive environments.

CONCLUSIONS

By encapsulating single bacteria cells inside microfluidic droplets, we exclude potential interspecific competition for the enrichment of rare strains by shotgun sequencing at high resolution. The comparative genomic analysis reveals underlying mechanisms for host-specific adaptations, providing intriguing insights into microbe-microbe interactions. The current approach may facilitate the hunting for elusive bacteria and paves the way for large-scale studies of more complex animal microbial communities. Video Abstract.

Adenosine and L-proline can possibly hinder Chinese Sacbrood virus infection in honey bees via immune modulation

Sacbrood virus (SBV) infects larvae of honey bees, resulting in infected larvae becoming fluid-filled sacs. Our previous studies showed that the extract of herbal medicine, Radix Isatidis, could inhibit Chinese SBV (CSBV) infection in Asian honey bees (Apis cerana). Here, two compounds, adenosine and L-proline, which were previously reported to be associated with immune modulation, were identified in R. Isatidis extract and then selected for an evaluation of their antiviral effect on CSBV infection in A. cerana. Our results revealed that both adenosine and L-proline could significantly mitigate the impact of CSBV on the growth and development of infected larvae and modulate hosts' immune responses by downregulating the expression of immune genes in infected larvae. The results gained from this study suggest that adenosine and L-proline could possibly interfere CSBV infection via immune modulation to avoid exacerbations and nonspecific damage to infected larvae's own tissues.

Effects of honeybee (Apis cerana) visiting behaviour on toxic plant (Tripterygium hypoglaucum) reproduction

Honeybees play a significant role in the plant-pollinator interactions of many flowering plants. The ecological and evolutionary consequences of plant-pollinator interactions vary by geographic region, and the effects of honeybees on the reproduction of toxic plants have not been well studied. We measured the florescence of toxic plants, the flower-visiting behaviour of honeybees and the effects of pollination on the fertility, weight and moisture content of seeds. The effects of climatic factors on the number of flowers, and the spatial and temporal variation in pollinator visits were evaluated, and the effects of pollinator visits on seed quality were evaluated. Flower visitors were diverse, climatic factors had a great impact on spatio-temporal flowering variation and the number of bee visits was strongly correlated with the spatio-temporal variation in the number of flowers. Honeybees strongly increase the fullness and weight of seeds. Our study demonstrated a good ecological fit between the spatio-temporal variation in the flowering of toxic plants and the general validity of honeybee pollination syndrome in the south of Hengduan Mountains in East Asia. A linear relationship between honeybee visitation and plant reproduction can benefit the stabilization of plant reproduction.

Geographical resistome profiling in the honeybee microbiome reveals resistance gene transfer conferred by mobilizable plasmids

BACKGROUND

The spread of antibiotic resistance genes (ARGs) has been of global concern as one of the greatest environmental threats. The gut microbiome of animals has been found to be a large reservoir of ARGs, which is also an indicator of the environmental antibiotic spectrum. The conserved microbiota makes the honeybee a tractable and confined ecosystem for studying the maintenance and transfer of ARGs across gut bacteria. Although it has been found that honeybee gut bacteria harbor diverse sets of ARGs, the influences of environmental variables and the mechanism driving their distribution remain unclear.

RESULTS

We characterized the gut resistome of two closely related honeybee species, Apis cerana and Apis mellifera, domesticated in 14 geographic locations across China. The composition of the ARGs was more associated with host species rather than with geographical distribution, and A. mellifera had a higher content of ARGs in the gut. There was a moderate geographic pattern of resistome distribution, and several core ARG groups were found to be prevalent among A. cerana samples. These shared genes were mainly carried by the honeybee-specific gut members Gilliamella and Snodgrassella. Transferrable ARGs were frequently detected in honeybee guts, and the load was much higher in A. mellifera samples. Genomic loci of the bee gut symbionts containing a streptomycin resistance gene cluster were nearly identical to those of the broad-host-range IncQ plasmid, a proficient DNA delivery system in the environment. By in vitro conjugation experiments, we confirmed that the mobilizable plasmids could be transferred between honeybee gut symbionts by conjugation. Moreover, "satellite plasmids" with fragmented genes were identified in the integrated regions of different symbionts from multiple areas.

CONCLUSIONS

Our study illustrates that the gut microbiota of different honeybee hosts varied in their antibiotic resistance structure, highlighting the role of the bee microbiome as a potential bioindicator and disseminator of antibiotic resistance. The difference in domestication history is highly influential in the structuring of the bee gut resistome. Notably, the evolution of plasmid-mediated antibiotic resistance is likely to promote the probability of its persistence and dissemination. Video Abstract.

Probiotic Potential and Effects on Gut Microbiota Composition and Immunity of Indigenous Gut Lactobacilli in Apis cerana

This study aimed to investigate the probiotic potential of gut indigenous lactic acid bacteria (LAB) originated from Apis cerana. Six Limosilactobacillus reuteri and one Lactobacillus helveticus were isolated from gut samples of A. cerana adult worker bee. All isolates antagonized the growth of pathogens including Salmonella typhimurium, Escherichia coli, Shigella flexneri, and Flavobacterium frigidimaris, and L. helveticus KM7 showed the greatest antimicrobial activity among them. All strains were sensitive to cefotaxime, amoxicillin, cephalothin, penicillin G, kanamycin, and vancomycin, moderately sensitive to novobiocin and resistant to gentamicin. Six out of seven strains were sensitive to ampicillin. L. helveticus KM7 was chosen to evaluate in vivo probiotic effect of adult worker bees of A. cerana through fed sucrose syrup supplemented with KM7. Administration of KM7 increased survival rate and gut LAB but decreased gut fungi and Enterococcus in honeybees. Expressions of genes related to antimicrobial peptides (AMPs) including Abaecin and Defensin were also induced in the gut of honeybees. The results suggested that L. helveticus KM7 with greater probiotic properties could improve the survival rate of adult worker honeybees of A. cerana through regulating gut microbiota and AMPs genes expression.

Distinct gut microbiota profiles of Asian honey bee (Apis cerana) foragers

Bee gut microbial communities have been studied extensively and linked to honey bee biology in terms of stages of bee development and behavior. Associations of bee gut microbiota in health and disease have also been explored. A large number of studies have centered on the gut microbiome of Apis mellifera, with similar investigations lagging far behind in Asian honey bee foragers. In this study, we characterized and compared the gut bacterial profiles of foragers and nurse bees of A. cerana and A. mellifera. Analysis of 16S rRNA partial gene sequences revealed significant differences in gut bacterial communities between the two honey bee species. Despite sharing dominant taxa, Bacteroides was more abundant in A. cerana, while Proteobacteria was higher in A. mellifera. Specific gut members are distinctly associated with hosts performing different tasks (i.e. nurse bees versus foragers). An exclusive abundance of Apibacter detected in Asian honey bee seemed to be a microbial signature of A. cerana foragers. Overall, our study highlights that variations in gut microbiota could be linked to task-specific (nurse bees and foragers) bacterial species associated with honey bees. Future investigations on the symbiotic relationship between host and the resident microbiota would be beneficial for improving honey bee health.

Toxicological Effect and Molecular Mechanism of the Chiral Neonicotinoid Dinotefuran in Honeybees

With the increasing demand for pollinating services, the wellness of honeybees has received widespread attention. Recent evidence indicated honeybee health might be posed a potential threat by widely used neonicotinoids worldwide. However, little is known about the molecular mechanism of these insecticides in honeybees especially at an enantiomeric level. In this study, we selected two species of bees, Apis mellifera (A. mellifera) and Apis cerana (A. cerana), to assess the toxicity and molecular mechanism of neonicotinoid dinotefuran and its enantiomers. The results showed that S-dinotefuran was more toxic than rac-dinotefuran and R-dinotefuran to honeybees by oral and contact exposures as much as 114 times. A. cerana was more susceptible to highly toxic enantiomer S-dinotefuran. S-dinotefuran induced the immune system response in A. cerana after 48 h exposure and significant changes were observed in the neuronal signaling of A. mellifera under three forms of dinotefuran exposure. Moreover, molecular docking also revealed that S-dinotefuran formed more hydrogen bonds than R-dinotefuran with nicotinic acetylcholine receptor, indicating the higher toxicity of S-dinotefuran. Data provided here show that R-dinotefuran may be a safer alternative to control pests and protect pollinators than rac-dinotefuran.

In vitro Effects of Prebiotics and Synbiotics on Apis cerana Gut Microbiota

This study aimed to investigate in vitro effects of the selected prebiotics alone, and in combination with two potential probiotic Lactobacillus strains on the microbial composition of Apis cerana gut microbiota and acid production. Four prebiotics, inulin, fructo-oligosaccharides, xylo-oligosaccharides, and isomalto-oligosaccharides were chosen, and glucose served as the carbon source. Supplementation of this four prebiotics increased numbers of Bifidobacterium and lactic acid bacteria while decreasing the pH value of in vitro fermentation broth inoculated with A. cerana gut microbiota compared to glucose. Then, two potential probiotics derived from A. cerana gut at different dosages, Lactobacillus helveticus KM7 and Limosilactobacillus reuteri LP4 were added with isomalto-oligosaccharides in fermentation broth inoculated with A. cerana gut microbiota, respectively. The most pronounced impact was observed with isomalto-oligosaccharides. Compared to isomalto-oligosaccharides alone, the combination of isomalto-oligosaccharides with both lactobacilli strains induced the growth of Bifidobacterium, LAB, and total bacteria and reduced the proliferation of Enterococcus and fungi. Consistent with these results, the altered metabolic activity was observed as lowered pH in in vitro culture of gut microbiota supplemented with isomalto-oligosaccharides and lactobacilli strains. The symbiotic impact varied with the types and concentration of Lactobacillus strains and fermentation time. The more effective ability was observed with IMO combined with L. helveticus KM7. These results suggested that isomalto-oligosaccharides could be a potential prebiotic and symbiotic with certain lactobacilli strains on A. cerana gut microbiota.

Genetic diversity and phylogenetic relationship among the western and the Asian honey bees based on two mitochondrial gene segments (COI and ND5)

The Asian honey bee species i.e., Apis cerana (the eastern honey bee), A. dorsata (the giant honey bee), and the western or European honey bee (A. mellifera) collected from Pakistan were studied using partial sequences from two mitochondrial genes (i) the Cytochrome c oxidase I (COI) and (ii) the mitochondrially encoded NADH dehydrogenase 5 (ND5) and then compared with other honey bees sequences (already submitted from different countries around the globe) obtained after the national center for biotechnology information (NCBI). DNA sequences were analyzed employing molecular evolutionary genetics analysis and Kimura 2-parameter model, neighbor-joining method was applied to investigate phylogenetic relationships, and DNA sequence polymorphism was applied to measure the genetic diversity within the genus Apis. The phylogenetic analyses yielded consistent results. Based on COI gene fragment in two Asian and European honey bee species from Pakistan and from other countries showed considerable genetic diversity levels and deviation among the species. While in contrast the phylogenetic analyses based on ND5 gene fragment in Asian and European honey bee species from Pakistan and other countries showed comparatively higher genetic diversity indices and variations than the COI gene. So, in the genus Apis, the mitochondrial ND5 region has shown the possibility to answer the interactions among species. A further detailed work (by linking the analysis of other genomic and mitochondrial genes) is required for good quality solution to establish the concise genetic diversity and interaction among the Apis species. The objective of this study was to explore the extent of genetic differences and phylogenetic links among the three kinds of honey bee species from Pakistan and comparing them with other bee species around the globe.

Anti-Breast Cancer Activity on MCF-7 Cells of Melittin from Indonesia's Apis cerana: An In Vitro Study

Objective:

Breast cancer is the most common case of cancers. Apitheraphy has been traditionally used for abundance diseases. This study aims to evaluate and compare the anti-breast cancer activity of melittin from Indonesia’s Apic cerana as a potential drug for treating breast cancer.

Methods:

Apis cerana bee venom (BV) was collected from a bee farm in Cikurutung, Bandung using an electrical venom device. The BV was then purified using the ÄKTA Start system and HiTrap™ SP HP cation exchange chromatography column. Sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE) was used to identify melittin based on its molecular mass and lowry’s protein assay to measure melittin concentration. Melittin cytotoxicity was measured with brine shrimp lethality test (BSLT), while MCF-7 breast cancer cells MTT assay was used to measure its anti-breast cancer activity, based on inhinition rate.

Results:

95.432 μg/mL melittin is purified from 62.8 mg/L BV, using cation exchange chromatography. Melittin in vitro analysis with MCF-7 MTT assay is used to determine anti-breast cancer activity in dose dependent manner. Furthermore, melttin BSLT result showed a LC₅₀ 16.67675 μg/mL. Therefore, the MTT assay was conducted in 5, 10 and 15 μg/mL with MCF-7 inhibition values of 0.768 ± 0.014, 3.303 ± 0.011, and 35.714 ± 0.009 %, respectively.

Conclusion:

Indonesia’s Apis cerana has the potential to be used as a therapeutic peptide for breast cancer treatment.

Sacbrood viruses cross-infection between Apis cerana and Apis mellifera: Rapid detection, viral dynamics, evolution and spillover risk assessment

Recent outbreaks of sacbrood virus (SBV) have caused serious epizootic disease in Apis cerana populations across Asia including Taiwan. Earlier phylogenetic analyses showed that cross-infection of AcSBV and AmSBV in both A. cerana and A. mellifera seems common, raising a concern of cross-infection intensifying the risk of disease resurgence in A. cerana. In this study, we analyzed the dynamics of cross-infection in three different types of apiaries (A. mellifera-only, A. cerana-only and two species co-cultured apiaries) over one year in Taiwan. Using novel, genotype-specific primer sets, we showed that SBV infection status varies across apiaries: AmSBV-AM and AcSBV-AC were the major genotype in the A. mellifera-only and the A. cerana-only apiaries, respectively, while AmSBV-AC and AcSBV-AC were the dominant genotypes in the co-cultured apiaries. Interestingly, co-cultured apiaries were among the only apiary type that harbored all variants and dual infections (i.e., AC and AM genotype co-infection in a single sample), indicating the interactions between hosts may form a conduit for cross-infection. The cross-infection between the two honey bee species appears to occur in a regular cycle with temporal fluctuation of AmSBV-AC and AcSBV-AC prevalence synchronized to each other in the co-cultured apiaries. Artificial infection of AcSBV in A. mellifera workers showed the suppression of viral replication, suggesting the potential of A. mellifera serving as a AcSBV reservoir that may contribute to virus spillover. Furthermore, the survival rate of A. cerana larvae was significantly reduced after artificial infections of both SBVs, indicating fitness costs of cross-infection on A. cerana and thus a high risk of disease resurgence in co-cultured apiaries. Our field and laboratory data provide baseline information that facilitates understanding of the risk of SBV cross-infection, and highlights the urgent need of SBV monitoring in co-cultured apiaries.

Strain-level analysis reveals the vertical microbial transmission during the life cycle of bumblebee

BACKGROUND

Microbial acquisition and development of the gut microbiota impact the establishment of a healthy host-microbes symbiosis. Compared with other animals, the eusocial bumblebees and honeybees possess a simple, recurring, and similar set of gut microbiota. However, all bee gut phylotypes have high strain-level diversity. Gut communities of different bee species are composed of host-specific groups of strains. The variable genomic regions among strains of the same species often confer critical functional differences, such as carbon source utilization, essential for the natural selection of specific strains. The annual bumblebee colony founded by solitary queens enables tracking the transmission routes of gut bacteria during development stages.

RESULTS

Here, we first showed the changes in the microbiome of individual bumblebees across their holometabolous life cycle. Some core gut bacteria persist throughout different stages of development. Gut microbiota of newly emerged workers always resembles those of their queens, suggesting a vertical transmission of strains from queens to the newborn workers. We then follow the dynamic changes in the gut community by comparing strain-level metagenomic profiles of queen-worker pairs longitudinally collected across different stages of the nest development. Species composition of both queen and worker shifts with the colony's growth, and the queen-to-worker vertical inheritance of specific strains was identified. Finally, comparative metagenome analysis showed clear host-specificity for microbes across different bee hosts. Species from honeybees often possess a higher level of strain variation, and they also exhibited more complex gene repertoires linked to polysaccharide digestion. Our results demonstrate bacterial transmission events in bumblebee, highlighting the role of social interactions in driving the microbiota composition.

CONCLUSIONS

By the community-wide metagenomic analysis based on the custom genomic database of bee gut bacteria, we reveal strain transmission events at high resolution and the dynamic changes in community structure along with the colony development. The social annual life cycle of bumblebees is key for the acquisition and development of the gut microbiota. Further studies using the bumblebee model will advance our understanding of the microbiome transmission and the underlying mechanisms, such as strain competition and niche selection. Video Abstract.

De Novo Genome Assembly of Chinese Plateau Honeybee Unravels Intraspecies Genetic Diversity in the Eastern Honeybee, Apis cerana

Simple Summary

In this study, we obtained a chromosome-scale assembly genome of Apis cerana abansis, which lives in the southeastern margin of the Titan Plateau, by using PacBio, Illumina and high-throughput chromatin conformation capture (Hi-C) sequencing technologies. With a more comprehensive annotation pipeline, we obtained an ampler and more accurate Apis cerana genome than previous studies. Comparative genomic analysis was performed to identify the divergence among different A. cerana genomes by studying two aspects: the differential content of repeat content and the gene loss/gain events occurred in chemosensory receptors and immune-related proteins. Our results show that the content of repetitive sequences differ in types and quantity among four A. cerana strains; the gene loss/gain events in chemoreceptor- and immune-related proteins occur in different A. cerana strains, especially in A. cerana abansis (Aba strain). Specifically, while compared with the other three published genomes, the Aba strain contains the largest number of repeat contents and loses the largest number of both chemosensory-receptor- and immune-related proteins, as well as subfamilies, whereas the Baisha strain contains the largest number of chemoreceptor- and immune-related proteins. We hypothesized that gene loss/gain may be evolutionary strategies used by the different A. cerana strains to adapt to their respective environments.

Abstract

Apis cerana abansis, widely distributed in the southeastern margin of the Qinghai-Tibet Plateau, is considered an excellent model to study the phenotype and genetic variation for highland adaptation of Asian honeybee. Herein, we assembled and annotated the chromosome-scale assembly genome of A. cerana abansis with the help of PacBio, Illumina and Hi-C sequencing technologies in order to identify the genome differences between the A. cerana abansis and the published genomes of different A. cerana strains. The sequencing methods, assembly and annotation strategies of A. cerana abansis were more comprehensive than previously published A. cerana genomes. Then, the intraspecific genetic diversity of A. cerana was revealed at the genomic level. We re-identified the repeat content in the genome of A. cerana abansis, as well as the other three A. cerana strains. The chemosensory and immune-related proteins in different A. cerana strains were carefully re-identified, so that 132 odorant receptor subfamilies, 12 gustatory receptor subfamilies and 22 immune-related pathways were found. We also discovered that, compared with other published genomes, the A. ceranaabansis lost the largest number of chemoreceptors compared to other strains, and hypothesized that gene loss/gain might help different A. cerana strains to adapt to their respective environments. Our work contains more complete and precise assembly and annotation results for the A. cerana genome, thus providing a resource for subsequent in-depth related studies.

The cell invasion preference of Varroa destructor between the original and new honey bee hosts

Honey bees (Apis) are important pollinators for food crops and wild plants, but are facing great threats from pathogens and parasites, especially an obligate ectoparasitic mite, Varroa destructor. Cell invasion is a key step for V. destructor to reproduce, and the parasite displays remarkable host preference in this process. Varroa destructor made its host-shift from its original host, the Asian honey bee Apis cerana, to the new host, the European honey bee Apis mellifera several decades ago. However, it remains largely unstudied whether V. destructor shows a cell invasion preference between the two host species. Using cell invasion bioassays on a modified four-well arena, we showed that V. destructor significantly preferred to invade the worker and drone larvae of A. mellifera rather than A. cerana, suggesting that the new host is much more attractive to the parasite than the original one. Using gas chromatography-mass spectrometry (GC-MS), we revealed significant differences between the cuticular hydrocarbon (CHC) profiles of worker and drone larvae of the two bee hosts. The amounts of methyl-branched alkanes and alkenes (unsaturated CHCs), but not n-alkanes, were significantly different, and A. mellifera worker and drone larvae were found to express significantly higher amounts of methyl-alkanes, while A. cerana larvae produced higher amounts of alkenes. Cell invasion bioassays with glass dummies showed that the mites preferred the glass dummies coated with the CHCs of A. mellifera worker or drone larvae, which indicates a role of larval CHCs in mediating the preferential cell invasion of Varroa. The findings from this study extend our understanding of the host preference of V. destructor, and can potentially contribute to the development of effective strategies for mite control.

Identification of an Apis cerana zinc finger protein 41 gene and its involvement in the oxidative stress response

Zinc finger proteins (ZFPs) are a class of transcription factors that contain zinc finger domains and play important roles in growth, aging, and responses to abiotic and biotic stresses. These proteins activate or inhibit gene transcription by binding to single-stranded DNA or RNA and through RNA/DNA bidirectional binding and protein-protein interactions. However, few studies have focused on the oxidation resistance functions of ZFPs in insects, particularly Apis cerana. In the current study, we identified a ZFP41 gene from A. cerana, AcZFP41, and verified its function in oxidative stress responses. Real-time quantitative polymerase chain reaction showed that the transcription level of AcZFP41 was upregulated to different degrees during exposure to oxidative stress, including that induced by extreme temperature, UV radiation, or pesticides. In addition, the silencing of AcZFP41 led to changes in the expression patterns of some known antioxidant genes. Moreover, the activities of the antioxidant enzymes catalase (CAT), superoxide dismutase (SOD), peroxidase (POD), and glutathione S-transferase (GST) in AcZFP41-silenced honeybees were higher than those in a control group. In summary, the data indicate that AcZFP41 is involved in the oxidative stress response. The results provide a theoretical basis for further studies of zinc finger proteins and improve our understanding of the antioxidant mechanisms of honeybees.

Immune Response of Eastern Honeybee Worker to Nosema ceranae Infection Revealed by Transcriptomic Investigation

Simple Summary

Currently, knowledge regarding Apis cerana–Nosema ceranae interaction is very limited, though A. cerana is the original host of N. ceranae. Apis cerana cerana is a subspecies of A. cerana and a major bee species used in the beekeeping industry in China and other countries. Here, the effective infection of A. c. cerana workers by N. ceranae was verified, followed by transcriptomic investigation of host responses. Furthermore, immune responses between A. c. cerana and Apis mellifera ligustica were deeply compared and discussed. In total, 1127 and 957 N. ceranae-responsive genes were identified in the infected midguts at 7 d post-inoculation (dpi) and 10 dpi, respectively. Additionally, DEGs in workers’ midguts at both 7 dpi and 10 dpi were associated with six cellular immune pathways and three humoral immune pathways. Noticeably, one up-regulated gene was enriched in the NF-κB signaling pathway in the midgut at 10 dpi. Further analysis indicated that different cellular and humoral immune responses were employed by A. c. cerana and A. m. ligustica workers to combat N. ceranae. Our findings provide a foundation for clarifying the mechanisms regulating the immune response of A. c. cerana workers to N. ceranae invasion and developing new approaches to control bee microsporidiosis.

Abstract

Here, a comparative transcriptome investigation was conducted based on high-quality deep sequencing data from the midguts of Apis cerana cerana workers at 7 d post-inoculation (dpi) and 10 dpi with Nosema ceranae and corresponding un-inoculated midguts. PCR identification and microscopic observation of paraffin sections confirmed the effective infection of A. c. cerana worker by N. ceranae. In total, 1127 and 957 N. ceranae-responsive genes were identified in the infected midguts at 7 dpi and 10 dpi, respectively. RT-qPCR results validated the reliability of our transcriptome data. GO categorization indicated the differentially expressed genes (DEGs) were respectively engaged in 34 and 33 functional terms associated with biological processes, cellular components, and molecular functions. Additionally, KEGG pathway enrichment analysis showed that DEGs at 7 dpi and 10 dpi could be enriched in 231 and 226 pathways, respectively. Moreover, DEGs in workers’ midguts at both 7 dpi and 10 dpi were involved in six cellular immune pathways such as autophagy and phagosome and three humoral immune pathways such as the Toll/Imd signaling pathway and Jak-STAT signaling pathway. In addition, one up-regulated gene (XM_017055397.1) was enriched in the NF-κB signaling pathway in the workers’ midgut at 10 dpi. Further investigation suggested the majority of these DEGs were engaged in only one immune pathway, while a small number of DEGs were simultaneously involved in two immune pathways. These results together demonstrated that the overall gene expression profile in host midgut was altered by N. ceranae infection and some of the host immune pathways were induced to activation during fungal infection, whereas some others were suppressed via host–pathogen interaction. Our findings offer a basis for clarification of the mechanism underlying the immune response of A. c. cerana workers to N. ceranae infection, but also provide novel insights into eastern honeybee-microsporodian interaction.

Antibacterial potential of hive bees honey from Himachal Pradesh, India

This paper presents a pioneer study on the microbial diversity and antibacterial potential of hive bees (Apis cerana and A. mellifera) honey collected from Himachal Pradesh. In total, 26 bacteria (14 from A. cerana and 12 from A. mellifera) but no fungal isolate were recovered. Bee species and locations comparison in terms of bacterial load (log CFU/g) revealed maximum loads of 3.74 and 3.99 in the honey from A. cerana and Mandi location, respectively. The most prevalent strains (HC3, HC5, HC6, HC8 and HM2) were identified (16S rRNA ribotyping) as Staphylococcus haemolyticus (MT742636), "Bacillus subtilis subsp. stecoris" (MT742637), Bacillus safensis subsp. safensis (MT742638), "Bacillus zanthoxyli" (MT742639) and Bacillus safensis subsp. safensis (MT938911). The apiary honey displayed good to excellent inhibitory activity against Escherichia coli ATCC1041 whereas, fair to good against Bacillus subtilis ATCC6633, Pseudomonas aeruginosa ATCC10662, Salmonella typhi NCTC786 and Klebsiella pneumoniae ATCC13883, highlighting its use as a therapeutic agent. Furthermore, it can be effective in minimizing numerous side effects associated with the consumption of synthetic drugs for treating bacterial infections thereby signifying the role of honey as a healthier substitute for synthetic drugs.

Genome Sequence of the Asian Honeybee in Pakistan Sheds Light on Its Phylogenetic Relationship with Other Honeybees

Simple Summary

The Asian honeybee, Apis cerana, is used for honey production and pollination services in Pakistan. However, its genome sequence is still unknown. We collected A. cerana samples from its main rearing region in Pakistan and performed whole genome sequencing. We obtained a remarkably complete genome sequence for A. cerana in Pakistan, from which we identified a total of 11,864 protein-coding genes. Phylogeny analysis indicated an unexpectedly close relationship between A. cerana in Pakistan and those in China, suggesting a potential human introduction of the species between the two countries. Our results will facilitate the genetic improvement and conservation of A. cerana in Pakistan.

Abstract

In Pakistan, Apis cerana, the Asian honeybee, has been used for honey production and pollination services. However, its genomic makeup and phylogenetic relationship with those in other countries are still unknown. We collected A. cerana samples from the main cerana-keeping region in Pakistan and performed whole genome sequencing. A total of 28 Gb of Illumina shotgun reads were generated, which were used to assemble the genome. The obtained genome assembly had a total length of 214 Mb, with a GC content of 32.77%. The assembly had a scaffold N50 of 2.85 Mb and a BUSCO completeness score of 99%, suggesting a remarkably complete genome sequence for A. cerana in Pakistan. A MAKER pipeline was employed to annotate the genome sequence, and a total of 11,864 protein-coding genes were identified. Of them, 6750 genes were assigned at least one GO term, and 8813 genes were annotated with at least one protein domain. Genome-scale phylogeny analysis indicated an unexpectedly close relationship between A. cerana in Pakistan and those in China, suggesting a potential human introduction of the species between the two countries. Our results will facilitate the genetic improvement and conservation of A. cerana in Pakistan.

Visual detection thresholds in the Asian honeybee, Apis cerana

To understand how insect pollinators find flowers against complex backgrounds in diverse natural habitats, it is required to accurately estimate the thresholds for target detection. Detection thresholds for single targets vary between bee species and have been estimated in the Western honeybee, a species of bumblebee and in a stingless bee species. We estimated the angular range of detection for coloured targets in the Asian honeybee Apis cerana. Using a Y-maze experimental set up, we show that targets that provided both chromatic and green receptor contrast were detected at a minimum visual angle of 7.7°, while targets with only chromatic contrast were detected at a minimum angle of 13.2°. Our results thus provide a robust foundation for future studies on the visual ecology of bees in a comparative interspecific framework.

Proboscis behavioral response of four honey bee Apis species towards different concentrations of sucrose, glucose, and fructose

Honey bees forage for pollen and nectar. Sugar is an important stimulus for foraging and a major source of energy for honey bees. Any differential response of bees to different concentrations of sugary nectar can affect their foraging. The sugar responsiveness of Apis species (Apis dorsata, Apis florea, and Apis cerana) was determined in comparison to that of Apis mellifera by evaluating the proboscis extension response (PER) with eight serial concentrations (0.00001, 0.0001, 0.001, 0.01, 0.1, 0.5, 1.0, and 1.5 M) of sucrose, glucose and fructose. Nectar foragers of bee species (A. dorsata, A. florea, A. cerana, and A. mellifera) exhibited an equal response for sucrose, glucose, and fructose, with no significant differences in their PER at all tested concentrations of these sugars within the same species. The inter-species comparison between Apis species revealed the differential responsiveness to the different concentrations of sugars, and the lowest concentration at which a response occurs was considered as the response threshold of these bee species for sugar solutions. A. mellifera presented significantly higher responsiveness than A. dorsata to low concentrations (0.00001, 0.0001, 0.001, 0.01, and 0.1 M) of sucrose, glucose and fructose. A. mellifera displayed a significantly higher response to water than A. dorsata. A. florea and A. mellifera presented no significant difference in their responsiveness to sucrose, glucose, and fructose at all tested concentrations, and their water responsiveness was also significantly at par but relatively higher in A. mellifera than in A. florea. Likewise, the responsiveness of A. cerana and A. mellifera to different concentrations of sucrose, glucose and fructose was significantly at par with no difference in their water responsiveness. This study represents preliminary research comparing the response of different honey bee species to three sugar types at different concentrations. The results imply that the native species are all better adapted than A. mellifera under local climate conditions.

Transcriptome Profiling Reveals a Novel Mechanism of Antiviral Immunity Upon Sacbrood Virus Infection in Honey Bee Larvae (Apis cerana)

The honey bee is one of the most important pollinators in the agricultural system and is responsible for pollinating a third of all food we eat. Sacbrood virus (SBV) is a member of the virus family Iflaviridae and affects honey bee larvae and causes particularly devastating disease in the Asian honey bees, Apis cerana. Chinese Sacbrood virus (CSBV) is a geographic strain of SBV identified in China and has resulted in mass death of honey bees in China in recent years. However, the molecular mechanism underlying SBV infection in the Asian honey bee has remained unelucidated. In this present study, we employed high throughput next-generation sequencing technology to study the host transcriptional responses to CSBV infection in A. cerana larvae, and were able to identify genome-wide differentially expressed genes associated with the viral infection. Our study identified 2,534 differentially expressed genes (DEGs) involved in host innate immunity including Toll and immune deficiency (IMD) pathways, RNA interference (RNAi) pathway, endocytosis, etc. Notably, the expression of genes encoding antimicrobial peptides (abaecin, apidaecin, hymenoptaecin, and defensin) and core components of RNAi such as Dicer-like and Ago2 were found to be significantly upregulated in CSBV infected larvae. Most importantly, the expression of Sirtuin target genes, a family of signaling proteins involved in metabolic regulation, apoptosis, and intracellular signaling was found to be changed, providing the first evidence of the involvement of Sirtuin signaling pathway in insects’ immune response to a virus infection. The results obtained from this study provide novel insights into the molecular mechanism and immune responses involved in CSBV infection, which in turn will contribute to the development of diagnostics and treatment for the diseases in honey bees.

The Nasonov gland pheromone as a potential source of death cue in Apis cerana

The ability to detect and remove dead adult bees is an essential part of honeybee colony fitness that prevents the spread of pathogens. Fatty acid olfactory cues stimulate undertaking behavior among different social species within Hymenoptera, but the chemicals responsible for the death cue in Apis cerana have not yet been identified. We explored the Nasonov gland as a potential source of these chemicals in A. cerana. Gas chromatography indicated that unlike A. mellifera, the A. cerana Nasonov gland does not contain any volatile terpenes, only fatty acids. As a bioassay, dead honeybees were rinsed free of their individual cuticular hydrocarbons via dichloromethane and two concentrations of oleic acid and a synthetic blend of the Nasonov pheromone in A. cerana were applied to the dummies. Results showed that oleic acid did not stimulate corpse removal in A. cerana. However, the synthetic pheromone blend of A. cerana Nasonov did stimulate removal.

Antiviral Activities of a Medicinal Plant Extract Against Sacbrood Virus in Honeybees

Background

Sacbrood is an infectious disease of the honey bee caused by Scbrood virus (SBV) which belongs to the family Iflaviridae and is especially lethal for Asian honeybee Apis cerana. Chinese Sacbrood virus (CSBV) is a geographic strain of SBV. Currently, there is a lack of an effective antiviral agent for controlling CSBV infection in honey bees.

Methods

Here, we explored the antiviral effect of a Chinese medicinal herb Radix isatidis on CSBV infection in A. cerana by inoculating the 3rd instar larvae with purified CSBV and treating the infected bee larvae with R. isatidis extract at the same time. The growth, development, and survival of larvae between the control and treatment groups were compared. The CSBV copy number at the 4th instar, 5th instar, and 6th instar larvae was measured by the absolute quantification PCR method.

Results

Bioassays revealed that R. isatidis extract significantly inhibited the replication of CSBV, mitigated the impacts of CSBV on larval growth and development, reduced the mortality of CSBV-infected A. cerana larvae, and modulated the expression of immune transcripts in infected bees.

Conclusion

Although the mechanism underlying the inhibition of CSBV replication by the medicine plant will require further investigation, this study demonstrated the antiviral activity of R. isatidis extract and provides a potential strategy for controlling SBV infection in honey bees.

The Succession of the Gut Microbiota in Insects: A Dynamic Alteration of the Gut Microbiota During the Whole Life Cycle of Honey Bees (Apis cerana)

The Asian honey bee Apis cerana is a valuable biological resource insect that plays an important role in the ecological environment and agricultural economy. The composition of the gut microbiota has a great influence on the health and development of the host. However, studies on the insect gut microbiota are rarely reported, especially studies on the dynamic succession of the insect gut microbiota. Therefore, this study used high-throughput sequencing technology to sequence the gut microbiota of A. cerana at different developmental stages (0 days post emergence (0 dpe), 1 dpe, 3 dpe, 7 dpe, 12 dpe, 19 dpe, 25 dpe, 30 dpe, and 35 dpe). The results of this study indicated that the diversity of the gut microbiota varied significantly at different developmental stages (ACE, P = 0.045; Chao1, P = 0.031; Shannon, P = 0.0019; Simpson, P = 0.041). In addition, at the phylum and genus taxonomic levels, the dominant constituents in the gut microbiota changed significantly at different developmental stages. Our results also suggest that environmental exposure in the early stages of development has the greatest impact on the gut microbiota. The results of this study reveal the general rule of gut microbiota succession in the A. cerana life cycle. This study not only deepens our understanding of the colonization pattern of the gut microbiota in workers but also provides more comprehensive information for exploring the colonization of the gut microbiota in insects and other animals.

Distance estimation by Asian honey bees in two visually different landscapes

Honey bees estimate distances to food sources using image motion experienced on the flight path and they use this measure to tune the waggle phase duration in their dance communication. Most studies on the dance-related odometer are based on experiments with Apis mellifera foragers trained into small tunnels with black and white patterns which allowed quantifiable changes in the optic flow. In this study, we determined the calibration curves of two Asian honey bee species, A. florea and A. cerana, in two different natural environments with clear differences in the vegetation conditions and hence visual contrast. We found that the dense vegetation condition (with higher contrast) elicited a more rapid increase in the waggle phase duration with distance than the sparse vegetation in A. florea but not in A. cerana Our findings suggest that contrast sensitivity of the waggle dance odometer might vary among honey bee species.

nov., isolated from the gut of honeybee (Apis cerana)

A novel Gram-reaction positive-, catalase and oxidase negative-, rod-shaped, facultatively anaerobic bacterial strain, DCY120^T_, was isolated from the gut of honeybee (Apis cerana) in Gyeonggi-do, South Korea. Strain DCY120^T belongs to the genus Bombilactobacillus and is moderately related to Bombilactobacillus mellis Hon2^T (94.1% similarity), Bombilactobacillus bombi BTLCH M1/2^T (93.8%), and Bombilactobacillus mellifer Bin4N^T (93.5%) based on 16S rRNA gene sequence analysis. The genome of strain DCY120^T was sequenced and the average nucleotide identity (ANI) between strain DCY120^T and the related Bombilactobacillus type strains were below the threshold value (95-96%) for species delineation. The major fatty acids were C_16:0, C_18:1 ω9c, Summed C_19:1 ω6c/C_19:0 cyclo ω10c/C_19:0 ω6 and Summed C_18:1 ω7c/C_18:1 ω6c. The major polar lipids were diphosphatidylglycerol (DPG), phosphatidylglycerol (PG), one glycolipid (GL), and one unidentified aminophospholipid (APL). The amino acids in peptidoglycan of strain DCY120^T were lysine, alanine, glutamic acid, and aspartic acid. In conclusion, the description of phenotypic and genotypic properties support strain DCY120^T as a novel species within the genus Bombilactobacillus, for which the name Bombilactobacillus apium sp. nov. is proposed. The type strain is DCY120^T (= KCTC 43194^T = JCM 34006^T).