Distribution and variability of deformed wing virus of honeybees (Apis mellifera) in the Middle East and North Africa

Molecular investigation and infection patterns of seven viruses of honey bee (Apis mellifera L, 1758) populations from southeastern Morocco

An epidemiological survey of honey bee viruses was conducted on 87 clinically healthy beehives located in southeastern Morocco. The sampled colonies were analyzed by reverse transcriptase (RT)-PCR / Real Time RT-qPCR with the aim of detecting and / or quantifying the following viruses: acute bee paralysis virus (ABPV), chronic bee paralysis virus (CBPV), deformed wing virus (DWV), sacbrood virus (SBV), black queen cell virus (BQCV), Kashmir bee virus (KBV) and Israeli acute paralysis virus (IAPV). With the exception of the last two of these viruses, all the other five were detected with different prevalence rates. DWV showed the highest prevalence rate (89.65 %), followed by BQCV (17.24 %), ABPV (8.04 %), CBPV (4.59 %), and SBV (2.29 %). This study represents the first molecular detection of BQCV in the country. Among all investigated colonies, only eight were virus free (9.2 %). By contrast, single infection was detected in 64.37 % of colonies, 21.8 % showed mixed infection with two viruses, while 4.6 % showed three. Nucleotide sequences of a portion of the DWV polyprotein gene obtained for six honey bee samples showed the greatest nucleotide identity with sequences of DWV from Sweden and Ireland. The negative effect of migratory beekeeping as opposed to stationary beekeeping was highlighted given that stationary beehives showed infection with up to three viruses only, while migratory beehives showed up to five viruses. The results of this study are of crucial importance as they shed light on the current status of honey bee health in southeastern Morocco.

Cold case: The disappearance of Egypt bee virus, a fourth distinct master strain of deformed wing virus linked to honeybee mortality in 1970's Egypt

In 1977, a sample of diseased adult honeybees (Apis mellifera) from Egypt was found to contain large amounts of a previously unknown virus, Egypt bee virus, which was subsequently shown to be serologically related to deformed wing virus (DWV). By sequencing the original isolate, we demonstrate that Egypt bee virus is in fact a fourth unique, major variant of DWV (DWV-D): more closely related to DWV-C than to either DWV-A or DWV-B. DWV-A and DWV-B are the most common DWV variants worldwide due to their close relationship and transmission by Varroa destructor. However, we could not find any trace of DWV-D in several hundred RNA sequencing libraries from a worldwide selection of honeybee, varroa and bumblebee samples. This means that DWV-D has either become extinct, been replaced by other DWV variants better adapted to varroa-mediated transmission, or persists only in a narrow geographic or host range, isolated from common bee and beekeeping trade routes.

Genetic variability and phylogenetic analysis among strains of deformed wing virus infesting honey bees and other organisms

Various viruses can infect honey bees, but deformed wing virus (DWV) is considered the most dangerous virus to them and has role in the sudden decline of bee colonies. This virus has different strains; however, there are no available studies to compare the characteristics of these strains utilizing bioinformatics. In this study, 27 strains of deformed wing virus were analyzed based on their sequences and their genetic relationships. Also, some primers were designed and tested to identify their ability to separate DWV strains. The percentages range from 28.99% to 29.63%, 22.28% to 22.78%, 15.73% to 16.28%, and 31.71% to 32.86% for nucleotides A, G, C, and T, respectively in all strains. The numbers of polymorphic sites as well as nucleotide diversity were highly similar in all strains. Statistical analyses generally showed the absence of high variations between sequences. Also, the phylogenetic tree classified strains into three groups. The network between strains of each group was established and discussed based on their geographical locations. Two groups contained strains from USA and Europe while one group contained strains from Asia. Rapid variations and mutations in the sequences of DWV were suggested. Notably, genetic studies on DWV are lacking in some geographical regions. The variations between strains detected in honey bees and other organisms were discussed. Four primers were designed and tested beside two reference primers. One of the designed primers showed the best results in binding with all DWV strains except one.

Assessment of lethal and sublethal effects of imidacloprid, ethion, and glyphosate on aversive conditioning, motility, and lifespan in honey bees (Apis mellifera L.)

Honeybees (Apis mellifera) play an important role in agriculture worldwide. Several factors including agrochemicals can affect honey bee health including habitat fragmentation, pesticide application, and pests. The growing human population and subsequent increasing crop production have led to widespread use of agrochemicals and there is growing concern that pollinators are being negatively impacted by these pesticides. The present study compares acute exposure to imidacloprid (0.2 and 0.4 mgL-1), ethion (80 and 106.7 mgL-1) or glyphosate (0.12 and 0.24 mgL-1) on aversive learning and movement, to chronic exposure at these and higher concentrations on movement, circadian rhythms, and survival in honey bee foragers. For acute learning studies, a blue/yellow shuttle box experiment was conducted; we observed honey bee choice following aversive and neutral stimuli. In learning studies, control bees spent >50% of the time on yellow which is not consistent with previous color bias literature in the subspecies or region of the study. The learning apparatus was also used to estimate mobility effects within 20 min of exposure. Chronic exposure (up to 2 weeks) with the above metrics was recorded by an automated monitoring system. In chronic exposure experiments, RoundUp®, was also tested to compare to its active ingredient, glyphosate. We found that imidacloprid and ethion have negative impacts on aversive learning and movement following a single-dose and that chronic exposure effects were dose-dependent for these two insecticides. In contrast, glyphosate had no effect on learning and less of an effect on movement; RoundUp® showed dose-dependent results on circadian rhythmicity. Overall, the results suggest that short-term exposure to imidacloprid and ethion adversely affect honey bee foragers and chronic exposure to glyphosate may affect pollination success.

Metagenomic Approach with the NetoVIR Enrichment Protocol Reveals Virus Diversity within Ethiopian Honey Bees (Apis mellifera simensis)

Metagenomics studies have accelerated the discovery of novel or divergent viruses of the honey bee. However, most of these studies predominantly focused on RNA viruses, and many suffer from the relatively low abundance of viral nucleic acids in the samples (i.e., compared to that of the host). Here, we explored the virome of the Ethiopian honey bee, Apis mellifera simensis, using an unbiased metagenomic approach in which the next-generation sequencing step was preceded by an enrichment protocol for viral particles. Our study revealed five well-known bee viruses and 25 atypical virus species, most of which have never been found in A. mellifera before. The viruses belong to Iflaviridae, Dicistroviridae, Secoviridae, Partitiviridae, Parvoviridae, Potyviridae, and taxonomically unclassified families. Fifteen of these atypical viruses were most likely plant-specific, and the remaining ten were presumed to be insect-specific. Apis mellifera filamentous virus (AmFV) was found in one sampling site out of 10. Two samples contained high read counts of a virus similar to Diatraea saccharales densovirus (DsDNV), which is a virus that causes high mortality in the sugarcane borer. AmFV and the DsDNV-like virus were the only DNA viruses found. Three viruses that primarily infect Drosophila spp. were also discovered: La Jolla virus (LJV), Kilifi virus (KiV), and Thika virus. Our study suggests that phoretic varroa mites are involved in the transmission of LJV and KiV and that both viruses replicate in mites and adult bees. We also found an overwhelming dominance of the deformed wing virus type B variant, which fits well with the apparently harmless infestation by Varroa destructor. It was suggested that Ethiopian bees have developed tolerance against virus infections as the result of natural selection.

Diversity and Global Distribution of Viruses of the Western Honey Bee, Apis mellifera

In the past centuries, viruses have benefited from globalization to spread across the globe, infecting new host species and populations. A growing number of viruses have been documented in the western honey bee, Apis mellifera. Several of these contribute significantly to honey bee colony losses. This review synthetizes the knowledge of the diversity and distribution of honey-bee-infecting viruses, including recent data from high-throughput sequencing (HTS). After presenting the diversity of viruses and their corresponding symptoms, we surveyed the scientific literature for the prevalence of these pathogens across the globe. The geographical distribution shows that the most prevalent viruses (deformed wing virus, sacbrood virus, black queen cell virus and acute paralysis complex) are also the most widely distributed. We discuss the ecological drivers that influence the distribution of these pathogens in worldwide honey bee populations. Besides the natural transmission routes and the resulting temporal dynamics, global trade contributes to their dissemination. As recent evidence shows that these viruses are often multihost pathogens, their spread is a risk for both the beekeeping industry and the pollination services provided by managed and wild pollinators.

The honeybee (Apis mellifera) developmental state shapes the genetic composition of the deformed wing virus-A quasispecies during serial transmission

The main biological threat to the western honeybee (Apis mellifera) is the parasitic mite Varroa destructor, largely because it vectors lethal epidemics of honeybee viruses that, in the absence of this mite, are relatively innocuous. The severe pathology is a direct consequence of excessive virus titres caused by this novel transmission route. However, little is known about how the virus adapts genetically during transmission and whether this influences the pathology. Here, we show that upon injection into honeybee pupae, the deformed wing virus type-A (DWV-A) quasispecies undergoes a rapid, extensive expansion of its sequence space, followed by strong negative selection towards a uniform, common shape by the time the pupae have completed their development, with no difference between symptomatic and asymptomatic adults in either DWV titre or genetic composition. This suggests that the physiological and molecular environment during pupal development has a strong, conservative influence on shaping the DWV-A quasispecies in emerging adults. There was furthermore no evidence of any progressive adaptation of the DWV-A quasispecies to serial intra-abdominal injection, simulating mite transmission, despite the generation of ample variation immediately following each transmission, suggesting that the virus either had already adapted to transmission by injection, or was unaffected by it.

Rapid detection of deformed wing virus in honeybee using ultra-rapid qPCR and a DNA-chip

Fast and accurate detection of viral RNA pathogens is important in apiculture. A polymerase chain reaction (PCR)-based detection method has been developed, which is simple, specific, and sensitive. In this study, we rapidly (in 1 min) synthesized cDNA from the RNA of deformed wing virus (DWV)-infected bees (Apis mellifera), and then, within 10 min, amplified the target cDNA by ultra-rapid qPCR. The PCR products were hybridized to a DNA-chip for confirmation of target gene specificity. The results of this study suggest that our method might be a useful tool for detecting DWV, as well as for the diagnosis of RNA virus-mediated diseases on-site.

Genetic Diversity of Deformed Wing Virus From Apis mellifera carnica (Hymenoptera: Apidae) and Varroa Mite (Mesostigmata: Varroidae)

Deformed wing virus (DWV) is one of the most widespread viruses that infect honey bee colonies. The route of infection is directly through contaminated food, feces, and air, or indirectly through the varroa mite, which acts as a vector. Positive DWV samples were obtained from Carniolan honey bee (Apis mellifera carnica) colonies and of varroa mites from the whole territory of Slovenia during a survey between 2007 and 2014. Nucleotide sequences of 471 nucleotides for the L protein gene and 573 nucleotides for the helicase gene were compared. High genetic diversity was observed among these Slovenian Carniolan honey bee DWV field samples, as well as with almost all the strains previously found in other countries in Europe. Phylogenetic analyses in two regions of the viral genome show that several of the DWV strains obtained from honey bees and varroa are genetically very closely related, confirming the important role of varroa in the transmission of DWV. Identification of closely related sequences also confirmed that the same strains of DWV have been successfully transmitted between various honey bee colonies and apiaries. It has also been established that simultaneous infection, in one apiary, of honey bees with two or more different strains of DWV is quite frequent. This is phylogenetic study that compares honey bee and varroa DWV strains from Carniolan honeybees.

Next-generation sequence data demonstrate several pathogenic bee viruses in Middle East and African honey bee subspecies (Apis mellifera syriaca, Apis mellifera intermissa) as well as their cohabiting pathogenic mites (Varroa destructor)

RNA viruses are associated with honey bee (Apis mellifera) colony losses in many parts of the world. Their consequences may be exacerbated when the ectoparasite mite Varroa destructor is present in hives. While evidence of pathogenic, viral-induced disease is abundant in western honey bees (Apis mellifera mellifera) from many parts of the world, less information exists regarding the pathogen load of Apis mellifera syriaca and Apis mellifera intermissa, honey bees from the Middle East and North Africa (MENA) that play substantial roles in regional beekeeping. Here, we used next-generation sequencing to evaluate the viral populations of these subspecies and their associated mites. We found that both A. m. syriaca and A. m. intermissa, as well as the Varroa mites infecting their colonies, bear a suite of RNA viruses including major pathogenic viruses like Deformed wing virus, Acute bee paralysis virus, Black queen cell virus and Sacbrood virus, and less common viruses (e.g., bee Macula-like virus and Apis mellifera filamentous virus). The two native honey bee MENA subspecies have acquired different but overlapping suites of pathogens, which also differ, but overlap, with the suites detected in the mites. The presence of plant viruses suggests that they were acquired from foraging for pollen and nectar. Phylogenetic analysis of the above common pathogenic RNA viruses showed unexpected genetic relationships with other known strains, indicative of import to MENA from outside of the region. Our findings indicate that it is important to carefully consider the impact of the movement of queens and mobile colonies, and the effects such movement have, on the transmission of disease.