Mellifera Populations Research Articles

Darwinian black box selection for resistance to settled invasive Varroa destructor parasites in honey bees

Established invasive species can pose a continuous threat to biodiversity and food security, thereby calling for sustainable mitigation. There is a consensus that the ubiquitous ecto-parasitic mite Varroa destructor, an invasive species from Asia, is the main biological threat to global apiculture with Apis mellifera. V. destructor has almost completely wiped out wild European honey bee (Apis mellifera) populations. The only remedy for apiculture, to date, is frequent control measures against the mite throughout the season, which prevents possible adaptations. While targeted breeding efforts have, so far, not achieved the selection of tolerant or resistant bees, natural selection approaches have succeeded at least seven times. Here, we propose to take advantage of natural selection for honey bee resistance by stopping mite treatment in managed colonies. The main principles are within population mating of the colonies’ own virgin queens and drones and selection based on survival and proliferous development of colonies. Being used for 10 years, it has shown to result in grosso modo ‘normal’ colonies with a high level of resistance to V. destructor. Here, we call for local groups of beekeepers and scientists to join a novel natural selection program that has started so far on three locations. This will eventually lead to several locally adapted V. destructor resistant honey bee populations around the world, and help global apiculture becoming more sustainable.

Occurrence of deformed wing virus variants in the stingless bee Melipona subnitida and honey bee Apis mellifera populations in Brazil.

The global spread of the parasitic Varroa mite has introduced a new bee to the bee horizontal transmission route for several RNA viruses that bypasses existing barriers in honey bees. From among these viruses, deformed wing virus (DWV) is now among the most widespread insect pathogens in the world. Brazilian stingless bees are a diverse group often managed in close proximity to honey bees. Therefore, we investigated the prevalence and load of DWV in 21 stingless bee (Melipona subnitida) and 26 honey bee (Apis mellifera) colonies from Brazil. DWV was detected in all colonies with DWV-A and DWV-C dominating in M. subnitida, while DWV-A dominated in A. mellifera. Average total viral loads per bee were 8.8E+07 and 6.3E+07 in M. subnitida and A. mellifera, respectively, which are much lower than DWV levels (>1E+10) found in honey bees in the northern hemisphere. In colonies introduced 30 years ago to the remote island of Fernando de Noronha, the DWV load was low (<1E+03) in honey bees but we detected higher loads (1.6E+08) in all M. subnitida colonies on the island. This may suggest that minimal, if any, viral transmission of DWV from stingless bees to honey bees has occurred on this island. Furthermore, the ubiquitous presence of the DWV-C variant in M. subnitida colonies, and its rarity in A. mellifera, may again suggest that limited viral exchange between these two species is occurring.

Genetic origins of honey bees (Apis mellifera) on Kangaroo Island and Norfolk Island (Australia) and the Kingdom of Tonga

We examine the origin of honey bee (Apis mellifera) populations in Kangaroo Island (Australia), Norfolk Island (Australia) and the Kingdom of Tonga using a highly polymorphic mitochondrial DNA region and a panel of 37 single nucleotide polymorphisms that assigns ancestry to three evolutionary lineages: Eastern Europe, Western Europe and Africa. We also examine inbreeding coefficients and genetic variation using microsatellites and mitochondrial sequencing. The honey bees of Kangaroo Island have a high proportion of Eastern European ancestry (90.2%), consistent with claims that they are of the subspecies A. m. ligustica. The honey bees of Norfolk Island also had a majority of ancestry from Eastern Europe (73.1%) with some contribution from Western Europe (21.2%). The honey bees of Tonga are mainly of Western European (70.3%) origin with some Eastern European ancestry (27.4%). Despite the suspected severe bottlenecks experienced by these island population, inbreeding coefficients were low.

Cell size and Varroa destructor mite infestations in susceptible and naturally-surviving honeybee (Apis mellifera) colonies

The ectoparasitic mite Varroa destructor is a key threat for European honeybee subspecies (Apis mellifera) globally. However, some A. mellifera populations are known to survive mite infestations by means of natural selection (naturally surviving), likely due to reduced mite reproductive success. The effect of small brood cell size on mite reproductive success has not been investigated in these surviving populations and we have little knowledge of its relationship with mite-surviving traits. Here we tested the impact of smaller worker brood cell size on mite reproductive success in susceptible and naturally surviving colonies in Norway. The data show that mite reproductive success was significantly reduced in smaller cells in susceptible colonies (higher rates of non-reproduction, delayed reproduction, and male absence), but not in the surviving colonies. The results support the claim that smaller cell size can have an impact on V. destructor reproductive success, but this seems not to work in tandem with mite-surviving mechanisms favored by natural selection.

Genetic and Genome Analyses Reveal Genetically Distinct Populations of the Bee Pathogen Nosema ceranae from Thailand

The recent global decline in Western honeybee (Apis mellifera) populations is of great concern for pollination and honey production worldwide. Declining honeybee populations are frequently infected by the microsporidian pathogen Nosema ceranae. This species was originally described in the Asiatic honeybee (Apis cerana), and its identification in global A. mellifera hives could result from a recent host transfer. Recent genome studies have found that global populations of this parasite are polyploid and that humans may have fueled their global expansion. To better understand N. ceranae biology, we investigated its genetic diversity within part of their native range (Thailand) and among different hosts (A. mellifera, A. cerana) using both PCR and genome-based methods. We find that Thai N. ceranae populations share many SNPs with other global populations and appear to be clonal. However, in stark contrast with previous studies, we found that these populations also carry many SNPs not found elsewhere, indicating that these populations have evolved in their current geographic location for some time. Our genome analyses also indicate the potential presence of diploidy within Thai populations of N. ceranae.

Genetic Characterisation of Honey Bees (Apis mellifera) Populations from Kurdistan Region of Iraq via ISSR Markers

Genetic Characterisation of Honey Bees (Apis mellifera) Populations from Kurdistan Region of Iraq via ISSR Markers

An update of Africanization in honey bee (Apis mellifera) populations in Buenos Aires, Argentina

European and African honey bee populations have been separated and influenced by different environments. Furthermore, Apis mellifera is the only species of honey bees that evolved in Europe, the Middle East, and Africa, where several subspecies are recognized. A. m. scutellata was introduced in Brazil in 1956, resulting in the spread of African bees throughout South and Central America. The aim of the present study was to determine the prevalence and geographical distribution of Africanized bees in Buenos Aires province (Argentina) employing a mtDNA cytochrome b polymorphism. A total of 430 colonies were sampled between 2013 and 2014; eighteen out of them (4,2%) belonged to African linage. Our results confirm that European haplotypes are the most prevalent in Buenos Aires Province, and that the process of African gene introgression remains stable since 2005.

Apis mellifera (Insecta: Hymenoptera) in the target of neonicotinoids: A one-way ticket? Bioinsecticides can be an alternative

The recent decline of Apis mellifera populations around the world has been subject of intense research due to ecological and economic damages resulting from the loss of pollination services. The intensive use of insecticides from the neonicotinoids group is among the possible causal factors of this decline, including also sub-lethal effects. However, the use of synthetic insecticides has been increased on a global scale in the recent decades. In order to evaluate an alternative to the use of neonicotinoids, this work investigated the effects of a bioinsecticide and its major compound on A. mellifera (Apidae: Hymenoptera), one of the main pollinators of crop plants. For this, bees were exposed, by contact and ingestion, to the essential oil of Cymbopogon martinii (Poaceae: Poales), to geraniol (major compound) and the insecticide imidacloprid to evaluate the toxicity and behavioral effects as well as the locomotion changes and immune responses of bees treated with these compounds. In general, toxicity was greater through ingestion and the insecticide imidacloprid was more toxic to A. mellifera compared to the essential oil and its major compound. The individual and collective behaviors (i.e. trophallaxis, grooming, avoidance) as well as the immune responses of bees were not significantly affected by bioinsecticides. However, the locomotion response and flight orientation of the bees were significantly altered by insecticide when administered by ingestion. Our results highlight the potential of C. martinii essential oil and its major compound as a possible alternative to mitigate the harmful effects of neonicotinoids on bees.

Investigating the viral ecology of global bee communities with high-throughput metagenomics

Bee viral ecology is a fascinating emerging area of research: viruses exert a range of effects on their hosts, exacerbate impacts of other environmental stressors, and, importantly, are readily shared across multiple bee species in a community. However, our understanding of bee viral communities is limited, as it is primarily derived from studies of North American and European Apis mellifera populations. Here, we examined viruses in populations of A. mellifera and 11 other bee species from 9 countries, across 4 continents and Oceania. We developed a novel pipeline to rapidly and inexpensively screen for bee viruses. This pipeline includes purification of encapsulated RNA/DNA viruses, sequence-independent amplification, high throughput sequencing, integrated assembly of contigs, and filtering to identify contigs specifically corresponding to viral sequences. We identified sequences for (+)ssRNA, (−)ssRNA, dsRNA, and ssDNA viruses. Overall, we found 127 contigs corresponding to novel viruses (i.e. previously not observed in bees), with 27 represented by >0.1% of the reads in a given sample, and 7 contained an RdRp or replicase sequence which could be used for robust phylogenetic analysis. This study provides a sequence-independent pipeline for viral metagenomics analysis, and greatly expands our understanding of the diversity of viruses found in bee communities.

Rapid parallel evolution overcomes global honey bee parasite

In eusocial insect colonies nestmates cooperate to combat parasites, a trait called social immunity. However, social immunity failed for Western honey bees (Apis mellifera) when the ectoparasitic mite Varroa destructor switched hosts from Eastern honey bees (Apis cerana). This mite has since become the most severe threat to A. mellifera world-wide. Despite this, some isolated A. mellifera populations are known to survive infestations by means of natural selection, largely by supressing mite reproduction, but the underlying mechanisms of this are poorly understood. Here, we show that a cost-effective social immunity mechanism has evolved rapidly and independently in four naturally V. destructor-surviving A. mellifera populations. Worker bees of all four ‘surviving’ populations uncapped/recapped worker brood cells more frequently and targeted mite-infested cells more effectively than workers in local susceptible colonies. Direct experiments confirmed the ability of uncapping/recapping to reduce mite reproductive success without sacrificing nestmates. Our results provide striking evidence that honey bees can overcome exotic parasites with simple qualitative and quantitative adaptive shifts in behaviour. Due to rapid, parallel evolution in four host populations this appears to be a key mechanism explaining survival of mite infested colonies.

A significant pure population of the dark European honey bee (Apis mellifera mellifera) remains in Ireland

The natural range of the dark European honey bee, Apis mellifera mellifera has been significantly reduced in recent years as a result of importation and replacement of queens with those of other Apis subspecies. Previous studies have indicated that a substantial amount of A. m. mellifera populations throughout Europe are heavily hybridized but that pockets of pure populations do still exist and need to be protected as this subspecies is a highly valuable gene pool and is of considerable conservational interest. Small numbers of Irish bees have been included in previous studies, but scientific information is limited and questions remain about the genetic diversity of bees in Ireland and the extent of introgression into apparent black bees from introduced races and hybrids. The objective of this study was to investigate the genetic composition of the A. m. mellifera population on the island of Ireland with both nuclear (microsatellites) and mitochondrial markers. Molecular data was generated from 412 bees sampled from 24 counties across the island. Mitochondrial data identified 34 different haplotypes, with 63% of bees having sequences identical to three European haplotypes but all other haplotypes being novel. Population structure analysis using microsatellite markers indicates that the Irish population is genetically diverse and that 97.8% of sampled bees were determined to be pure A. m. mellifera. Results from cluster analysis using a Bayesian model approach, and the presence of novel alleles, shows evidence of distinctiveness within the Irish population.

Gamma irradiation inactivates honey bee fungal, microsporidian, and viral pathogens and parasites.

Managed honey bee (Apis mellifera) populations are currently facing unsustainable losses due to a variety of factors. Colonies are challenged with brood pathogens, such as the fungal agent of chalkbrood disease, the microsporidian gut parasite Nosema spp., and several viruses. These pathogens may be transmitted horizontally from worker to worker, vertically from queen to egg and via vectors like the parasitic mite, Varroa destructor. Despite the fact that these pathogens are widespread and often harbored in wax comb that is reused from year to year and transferred across beekeeping operations, few, if any, universal treatments exist for their control. In order to mitigate some of these biological threats to honey bees and to allow for more sustainable reuse of equipment, investigations into techniques for the sterilization of hive equipment and comb are of particular significance. Here, we investigated the potential of gamma irradiation for inactivation of the fungal pathogen Ascosphaera apis, the microsporidian Nosema ceranae and three honey bee viruses (Deformed wing virus [DWV], Black queen cell virus [BQCV], and Chronic bee paralysis virus [CBPV]), focusing on the infectivity of these pathogens post-irradiation. Results indicate that gamma irradiation can effectively inactivate A. apis, N. ceranae, and DWV. Partial inactivation was noted for BQCV and CBPV, but this did not reduce effects on mortality at the tested, relatively high doses. These findings highlight the importance of studying infection rate and symptom development post-treatment and not simply rate or quantity detected. These findings suggest that gamma irradiation may function as a broad treatment to help mitigate colony losses and the spread of pathogens through the exchange of comb across colonies, but raises the question why some viruses appear to be unaffected. These results provide the basis for subsequent studies on benefits of irradiation of used comb for colony health and productivity.

Prevalence of honey bee (Apis mellifera) parasites across Texas

We conducted a statewide study, in June and July 2016, of feral colonies and domesticated hives to understand the current and potential impacts of invasive parasites and pests on honey bee (Apis mellifera) populations in Texas. We identify the subspecies for each colony sampled in addition to reporting the presence of parasites. The most common subspecies found were Apis mellifera scutellata, Apis mellifera carnica, and Apis mellifera ligustica. We confirmed the presence of Apis mellifera syriaca and Apis mellifera macedonica in Texas. Varroa destructor and Nosema ceranae were the most common parasites, found in eight and nine ecoregions, respectively. Aethina tumida was found in only 4 of the 10 ecoregions.

Molecular methods indicate lack of spread of Acarapis woodi introduced to honey bees in western Norway.

The tracheal mite, Acarapis woodi, may be one of many factors contributing to the decline in honey bee (Apis mellifera) populations. Databases on the widespread distribution of A. woodi exist, but the data seem patchy. Norway is not listed as being infested, although there have been at least two separate introductions of the parasite. Investigations in 2003, 2006, and 2009 using standard microscopy methods indicated persistence of A. woodi in honey bees in this region. In 2013, we conducted another survey. Samples were sent in from 335 beehives belonging to 39 apiaries, and all were asked to complete a questionnaire. Analysis for A. woodi in the submitted samples was by PCR, with sequencing of positive results. The results described in this article indicate that this parasite still persists in some apiaries in this region, but at a low, and possibly decreasing, level, with positive results obtained from just two (5.1%) of the apiaries. Of the 17 beekeepers that answered the questionnaire, none reported symptoms of infestation with A. woodi. Sequencing of PCR products indicated a difference between the two A. woodi isolates. Our results were generally encouraging regarding the apparent lack of spread of A. woodi, within the County. Furthermore, the sequencing results may indicate two separate introductions rather than spread. Nevertheless, the scarcity of data, the vulnerability of honey bee populations globally, and the potential contribution of this parasite to reduced survival, indicate that the situation should be continued to be monitored. In addition, Norwegian beekeepers should be made aware of, and follow, restrictions regarding import and transport of bees, both nationally and internationally.

Norwegian honey bees surviving Varroa destructor mite infestations by means of natural selection.

BackgroundManaged, feral and wild populations of European honey bee subspecies, Apis mellifera, are currently facing severe colony losses globally. There is consensus that the ectoparasitic mite Varroa destructor, that switched hosts from the Eastern honey bee Apis cerana to the Western honey bee A. mellifera, is a key factor driving these losses. For >20 years, breeding efforts have not produced European honey bee colonies that can survive infestations without the need for mite control. However, at least three populations of European honey bees have developed this ability by means of natural selection and have been surviving for >10 years without mite treatments. Reduced mite reproductive success has been suggested as a key factor explaining this natural survival. Here, we report a managed A. mellifera population in Norway, that has been naturally surviving consistent V. destructor infestations for >17 years.MethodsSurviving colonies and local susceptible controls were evaluated for mite infestation levels, mite reproductive success and two potential mechanisms explaining colony survival: grooming of adult worker bees and Varroa Sensitive Hygiene (VSH): adult workers specifically detecting and removing mite-infested brood.ResultsMite infestation levels were significantly lower in surviving colonies and mite reproductive success was reduced by 30% when compared to the controls. No significant differences were found between surviving and control colonies for either grooming or VSH.DiscussionOur data confirm that reduced mite reproductive success seems to be a key factor for natural survival of infested A. mellifera colonies. However, neither grooming nor VSH seem to explain colony survival. Instead, other behaviors of the adult bees seem to be sufficient to hinder mite reproductive success, because brood for this experiment was taken from susceptible donor colonies only. To mitigate the global impact of V. destructor, we suggest learning more from nature, i.e., identifying the obviously efficient mechanisms favored by natural selection.

Use of Nepeta clarkei extracts for controlling honey bee pathogenic bacteria and mosquito larvae

ABSTRACTHoneybee (Apis mellifera) population is going down across the globe due to honeybee pathogens. This greatly influences the bee-associated commercial food products production. Likewise, mosquitoes are prominent vector responsible for spreading life-threatening human diseases, including malaria and dengue. The plant-based insecticides are a better substitute to the recent control practices of honeybee pathogenic bacteria and mosquito. Here, we performed in vitro screening of Nepeta clarkei Hook. f. (Labiatae) aqueous extracts against three honey bee gut bacterial isolates including Paenibacillus larvae an infamous honeybee bacterial pathogen. The inhibitory zone was produced in the range of 6–14 mm diameters against three honey bee bacterial isolates. Likewise, fourth instars larvae of Culex (Diptera/Culicidae) were also subjected to check the possible larvicidal efficacy of N. clarkei. A normal media supplemented with N. clarkei in different concentrations (0.025% 0.05%, 0.1%, 0.15%, and 0.2%) affected the growth of larvae significantly. The lethal concentration at which 50% of larvae failed to become pupate was found to be 0.1% after 24 h of exposure. Considerable reductions in larval growth and pupal development of mosquito suggested that this plant should be utilized in mosquito control programmes.

Absence of deformed wing virus and Varroa destructor in Australia provides unique perspectives on honeybee viral landscapes and colony losses

Honeybee (Apis mellifera) health is threatened globally by the complex interaction of multiple stressors, including the parasitic mite Varroa destructor and a number of pathogenic viruses. Australia provides a unique opportunity to study this pathogenic viral landscape in the absence of V. destructor. We analysed 1,240A. mellifera colonies across Australia by reverse transcription-polymerase chain reaction (RT-PCR) and next-generation sequencing (NGS). Five viruses were prevalent: black queen cell virus (BQCV), sacbrood virus (SBV), Israeli acute paralysis virus (IAPV) and the Lake Sinai viruses (LSV1 and LSV2), of which the latter three were detected for the first time in Australia. We also showed several viruses were absent in our sampling, including deformed wing virus (DWV) and slow bee paralysis virus (SBPV). Our findings highlight that viruses can be highly prevalent in A. mellifera populations independently of V. destructor. Placing these results in an international context, our results support the hypothesis that the co-pathogenic interaction of V. destructor and DWV is a key driver of increased colony losses, but additional stressors such as pesticides, poor nutrition, etc. may enable more severe and frequent colony losses to occur.

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

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

Naturally selected honey bee (Apis mellifera) colonies resistant to Varroa destructor do not groom more intensively

The ectoparasitic mite Varroa destructor is an important cause of high colony losses of the honey bee Apis mellifera. In The Netherlands, two resistant A. mellifera populations developed naturally after ceasing varroa control. As a result, mite infestation levels of the colonies of these populations are generally between 5–10%. However, the mechanisms behind mite resistance are still unclear. Since grooming behavior is a typical resistance trait that occurs in A. mellifera, we compared grooming between colonies of these two resistant populations and control colonies that had been treated against varroa twice a year in previous years. Grooming was investigated by measuring mite fall in broodless colonies in the field and in small cages with a fixed number of mites and bees in the lab. Furthermore, grooming was investigated at the individual level by measuring the effectiveness to remove dust by individual bees from the resistant and control colonies. We found that the grooming behavior of resistant colonies was unexpectedly equally or even less effective than that of control colonies. These results were supported by the effectiveness of individual bees to remove dust. Based on our results, we discuss that the trigger for grooming behavior may be density-dependent: grooming may be only beneficial at high mite infestation levels. Other resistance mechanisms than grooming are more likely to explain the varroa resistance of our two populations.

Large-scale mitochondrial DNA analysis of native honey bee Apis mellifera populations reveals a new African subgroup private to the South West Indian Ocean islands

BackgroundThe South West Indian Ocean (SWIO) archipelagos and Madagascar constitute a hotspot of biodiversity with a high rate of endemism. In this area, the endemic subspecies A. m. unicolor has been described in Madagascar. It belongs to the African lineage, one of the four described evolutionary lineages in honey bees. Despite a long beekeeping tradition and several recorded European introductions, few studies have been carried out on the diversity and proportion of honey bee subspecies.In order to identify and define which evolutionary lineages and potential sub-lineages are present in the SWIO, the COI-COII intergenic region and the ND2 gene of the mtDNA were sequenced in honey bee colonies from three archipelagos. An extensive sampling (n = 1184 colonies) was done in the Mascarene (La Réunion, Mauritius, Rodrigues), Seychelles (Mahé, Praslin, La Digue) and Comoros (Grande Comore, Mohéli, Anjouan, Mayotte) archipelagos. Islands genetic diversity was compared to newly sampled populations from Madagascar, continental African and European populations.ResultsAfrican lineage haplotypes were found in all islands (except for Rodrigues). Madagascar, Comoros and Seychelles had 100% of A lineage, 95.5% in La Réunion and 56.1% in Mauritius. Among all African colonies detected in the SWIO, 98.1% (n = 633) of COI-COII haplotypes described the presence of the subspecies A. M. unicolor. Both genetic markers revealed i) a new private AI mitochondrial group shared by the SWIO archipelagos and Madagascar distant from continental populations; ii) the private African haplotypes for each island suggested diversity radiation in the archipelagos; iii) the detection of the Comoros archipelago as a possible contact area between insular and continental African populations.The exotic European C and M lineages were only detected in the Mascarene archipelago, but striking differences of proportion were observed among islands. Merely 4.6% of European colonies were found in La Réunion whereas Mauritius cumulated 44%. Here, among the 84 observed COI-COII haplotypes, 50 were newly described including 13 which were private to the SWIO archipelagos and Madagascar. Similarly, 24 of the 34 found ND2 haplotypes were novel which included six haplotypes particular to the SWIO populations.ConclusionA new African subgroup was described in the SWIO region with mitochondrial genetic evidence that A. m. unicolor is the indigenous subspecies of the archipelagos surrounding Madagascar.