South American native bumblebees (Hymenoptera: Apidae) infected by Nosema ceranae (Microsporidia), an emerging pathogen of honeybees (Apis mellifera)

Do managed bees drive parasite spread and emergence in wild bees?

Bees have been managed and utilised for honey production for centuries and, more recently, pollination services. Since the mid 20th Century, the use and production of managed bees has intensified with hundreds of thousands of hives being moved across countries and around the globe on an annual basis. However, the introduction of unnaturally high densities of bees to areas could have adverse effects. Importation and deployment of managed honey bee and bumblebees may be responsible for parasite introductions or a change in the dynamics of native parasites that ultimately increases disease prevalence in wild bees. Here we review the domestication and deployment of managed bees and explain the evidence for the role of managed bees in causing adverse effects on the health of wild bees. Correlations with the use of managed bees and decreases in wild bee health from territories across the globe are discussed along with suggestions to mitigate further health reductions in wild bees.

No effect of low-level chronic neonicotinoid exposure on bumblebee learning and fecundity

In recent years, many pollinators have declined in abundance and diversity worldwide, presenting a potential threat to agricultural productivity, biodiversity and the functioning of natural ecosystems. One of the most debated factors proposed to be contributing to pollinator declines is exposure to pesticides, particularly neonicotinoids, a widely used class of systemic insecticide. Also, newly emerging parasites and diseases, thought to be spread via contact with managed honeybees, may pose threats to other pollinators such as bumblebees. Compared to honeybees, bumblebees could be particularly vulnerable to the effects of stressors due to their smaller and more short-lived colonies. Here, we studied the effect of field-realistic, chronic clothianidin exposure and inoculation with the parasite Nosema ceranae on survival, fecundity, sugar water collection and learning using queenless Bombus terrestris audax microcolonies in the laboratory. Chronic exposure to 1 ppb clothianidin had no significant effects on the traits studied. Interestingly, pesticide exposure in combination with additional stress caused by harnessing bees for Proboscis Extension Response (PER) learning assays, led to an increase in mortality. In contrast to previous findings, the bees did not become infected by N. ceranae after experimental inoculation with the parasite spores, suggesting variability in host resistance or parasite virulence. However, this treatment induced a slight, short-term reduction in sugar water collection, potentially through stimulation of the immune system of the bees. Our results suggest that chronic exposure to 1 ppb clothianidin does not have adverse effects on bumblebee fecundity or learning ability.

Hygienic food to reduce pathogen risk to bumblebees

Bumblebees are ecologically and economically important pollinators, and the value of bumblebees for crop pollination has led to the commercial production and exportation/importation of colonies on a global scale. Commercially produced bumblebee colonies can carry with them infectious parasites, which can both reduce the health of the colonies and spillover to wild bees, with potentially serious consequences. The presence of parasites in commercially produced bumblebee colonies is in part because colonies are reared on pollen collected from honey bees, which often contains a diversity of microbial parasites. In response to this threat, part of the industry has started to irradiate pollen used for bumblebee rearing. However, to date there is limited data published on the efficacy of this treatment. Here we examine the effect of gamma irradiation and an experimental ozone treatment on the presence and viability of parasites in honey bee pollen. While untreated pollen contained numerous viable parasites, we find that gamma irradiation reduced the viability of parasites in pollen, but did not eliminate parasites entirely. Ozone treatment appeared to be less effective than gamma irradiation, while an artificial pollen substitute was, as expected, entirely free of parasites. The results suggest that the irradiation of pollen before using it to rear bumblebee colonies is a sensible method which will help reduce the incidence of parasite infections in commercially produced bumblebee colonies, but that further optimisation, or the use of a nutritionally equivalent artificial pollen substitute, may be needed to fully eliminate this route of disease entry into factories.

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

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

The effects of single and mixed infections of Apicystis bombi and deformed wing virus in Bombus terrestris

Many pollinators are currently suffering from declines, diminishing their gene pool and increasing their vulnerability to parasites. Recently, an increasing diversity of parasites has been recorded in bumblebees, yet for many, knowledge of their virulence and hence the risk their presence poses, is lacking. The deformed wing virus (DWV), known to be ubiquitous in honey bees, has now been detected in bumblebees. In addition, the neogregarine Apicystis bombi has been discovered to be more prevalent than previously thought. Here, we assess for the first time the lethal and sublethal effects of these parasites during single and mixed infections of worker bumblebees (Bombus terrestris). Fifteen days after experimental exposure, 22% of bees exposed to A. bombi, 50% of bees exposed to DWV and 86% of bees exposed to both parasites had died. Bumblebees that had ingested A. bombi had increased sucrose sensitivity (SS) and a lower lipid:body size ratio than control bees. While dual infected bumblebees showed no increase in SS. Overall, we find that A. bombi exhibits both lethal and sublethal effects. DWV causes lethal effect and may reduce the sub lethal effects imposed by A. bombi. The results show that both parasites have significant, negative effects on bumblebee health, making them potentially of conservation concern.

Large scale patterns of abundance and distribution of parasites in Mexican bumblebees

Bumblebees are highly valued for their pollination services in natural ecosystems as well as for agricultural crops. These precious pollinators are known to be declining worldwide, and one major factor contributing to this decline are infections by parasites. Knowledge about parasites in wild bumblebee populations is thus of paramount importance for conservation purposes. We here report the geographical distribution of Crithidia and Nosema, two common parasites of bumblebees, in a yet poorly investigated country: Mexico. Based on sequence divergence of the Cytochrome b and Glycosomal glyceraldehyde phosphate deshydrogenase (gGPDAH) genes, we discovered the presence of a new Crithidia species, which is mainly distributed in the southern half of the country. It is placed by Bayesian inference as a sister species to C. bombi. We suggest the name Crithidia mexicana for this newly discovered organism. A population of C. expoeki was encountered concentrated on the flanks of the dormant volcanic mountain, Iztaccihuatl, and microsatellite data showed evidence of a bottleneck in this population. This study is the first to provide a large-scale insight into the health status of endemic bumblebees in Mexico, based on a large sample size (n=3,285 bees examined) over a variety of host species and habitats.

Nosema ceranae alters a highly conserved hormonal stress pathway in honeybees

Nosema ceranae, an emerging pathogen of the western honeybee (Apis mellifera), is implicated in recent pollinator losses and causes severe energetic stress. However, whether precocious foraging and accelerated behavioural maturation in infected bees are caused by the infection itself or via indirect energetic stress remains unknown. Using a combination of nutritional and infection treatments, we investigated how starvation and infection alters the regulation of adipokinetic hormone (AKH) and octopamine, two highly conserved physiological pathways that respond to energetic stress by mobilizing fat stores and increasing search activity for food. Although there was no response from AKH when bees were experimentally infected with N. ceranae or starved, supporting the notion that honeybees have lost this pathway, there were significant regulatory changes in the octopamine pathway. Significantly, we found no evidence of acute energetic stress being the only cause of symptoms associated with N. ceranae infection. Therefore, the parasite itself appears to alter regulatory components along a highly conserved physiological pathway in an infection-specific manner. This indicates that pathogen-induced behavioural alteration of chronically infected bees should not just be viewed as a coincidental short-term by-product of pathogenesis (acute energetic stress) and may be a result of a generalist manipulation strategy to obtain energy for reproduction.

Parasites in bloom: flowers aid dispersal and transmission of pollinator parasites within and between bee species

The dispersal of parasites is critical for epidemiology, and the interspecific vectoring of parasites when species share resources may play an underappreciated role in parasite dispersal. One of the best examples of such a situation is the shared use of flowers by pollinators, but the importance of flowers and interspecific vectoring in the dispersal of pollinator parasites is poorly understood and frequently overlooked. Here, we use an experimental approach to show that during even short foraging periods of 3 h, three bumblebee parasites and two honeybee parasites were dispersed effectively onto flowers by their hosts, and then vectored readily between flowers by non-host pollinator species. The results suggest that flowers are likely to be hotspots for the transmission of pollinator parasites and that considering potential vector, as well as host, species will be of general importance for understanding the distribution and transmission of parasites in the environment and between pollinators.

Distribution and diversity of Nosema bombi (Microsporidia: Nosematidae) in the natural populations of bumblebees (Bombus spp.) from West Siberia

Nosema bombi is an obligate intracellular parasite of bumblebees (Hymenoptera, Bombus spp.), which has significant negative effect on individual bumblebees, colony fitness, and development. Recently, several new genetic variants of N. bombi without a defined taxonomic status were identified in natural bumblebee populations from Russia, China, and several European countries, as well as N. ceranae, originally isolated from honey bees, was described in bumblebee species. Thus, it is required to investigate more Nosema variability in bumblebee populations for identifying new genetic Nosema variants. In our study, we used several methods such as total DNA isolation, polymerase chain reaction (PCR) amplification, cloning, sequencing, and comparative and phylogenetic analysis to investigate a prevalence of N. bombi and its diversity in the natural populations of bumblebees across West Siberia. DNA was extracted from intestinal bumblebee tissues. Identification of the parasite was conducted, using PCR with primers specific for the ribosomal RNA gene cluster and methionine aminopeptidase 2 gene of N. bombi followed by sequencing. Seven hundred twenty-seven individual bumblebees belonging to 16 species were tested; 64 specimens revealed presence of the parasite. Prevalence of Nosema bombi infection was different in each region and varied from 4 to 20 %. No infection was found in Bombus agrorum (n = 194) and Bombus equestris (n = 132), both common bumblebees in West Siberia. Three different genetic variants of the same species, N. bombi, were identified. The first variant belonged to N. bombi (AY008373) identified by Fies et al. (J Apicult Res 40:91-96, 2001), second (N. bombi WS2) was identical to the West Siberian variant identified by Szentgyörgyi et al. (Polish Journal of Ecology 59:599-610, 2011), and the last variant, N. bombi WS3, was new. The results led us to suggest that the prevalence of the N. bombi is related to the population structure of bumblebees and distribution of the particular genetic variants of N. bombi.

Bumble Bees (Hymenoptera: Apidae: Bombus spp.) of Interior Alaska: Species Composition, Distribution, Seasonal Biology, and Parasites

Background

Despite the ecological and agricultural significance of bumble bees in Alaska, very little is known and published about this important group at the regional level. The objectives of this study were to provide baseline data on species composition, distribution, seasonal biology, and parasites of the genus Bombus at three major agricultural locations within Alaska: Fairbanks, Delta Junction, and Palmer, to lay the groundwork for future research on bumble bee pollination in Alaska.

New information

A total of 8,250 bumble bees representing 18 species was collected from agricultural settings near Delta Junction, Fairbanks, and Palmer, Alaska in 2009 and 2010. Of the 8,250 specimens, 51% were queens, 32.7% were workers, and 16.2% were males. The species composition and relative abundances varied among sites and years. Delta Junction had the highest relative abundance of bumble bees, representing 51.6% of the specimens collected; the other two locations, Fairbanks and Palmer represented 26.5% and 21.8% of the overall catch respectively. The species collected were: BombusbohemicusSeidl 1837 (= B.ashtoni (Cresson 1864)), B.balteatusDahlbom 1832, B.bifariusCresson 1878, B.centralisCresson 1864, B.cryptarum (Fabricius 1775) (=B.moderatusCresson 1863), B.distinguendusMorawitz 1869, B.flavidusEversmann 1852 (=B.fernaldaeFranklin 1911), B.flavifronsCresson 1863, B.frigidusSmith 1854, B.insularis (Smith 1861), B.jonellus (Kirby 1802), B.melanopygusNylander 1848, B.mixtusCresson 1878, B.neoboreusSladen 1919, B.occidentalisGreene 1858, B.perplexusCresson 1863, B.rufocinctusCresson 1863, and B.sylvicolaKirby 1837. Overall, the most common bumble bees near agricultural lands were B.centralis, B.frigidus, B.jonellus, B.melanopygus, B.mixtus, and B.occidentalis. Species' relative population densities and local diversity were highly variable from year to year. Bombusoccidentalis, believed to be in decline in the Pacific Northwest states, represented 10.4% of the overall specimens collected from the three sites studied. Bumble bees were found to be infected by Nosema and nematodes with infection rates up to 2.1% and 16.7% respectively. Of the eight species infected by parasites, B.occidentalis displayed the highest Nosema infection, while B.centralis was the species with the highest infection of nematodes. To our knowledge this represents the first multi-year study on bumble bees from the main agricultural areas of Alaska to provide baseline data on species composition, distribution, seasonal biology, and parasites of the genus Bombus.

Bee declines driven by combined stress from parasites, pesticides, and lack of flowers

Bees are subject to numerous pressures in the modern world. The abundance and diversity of flowers has declined; bees are chronically exposed to cocktails of agrochemicals, and they are simultaneously exposed to novel parasites accidentally spread by humans. Climate change is likely to exacerbate these problems in the future. Stressors do not act in isolation; for example, pesticide exposure can impair both detoxification mechanisms and immune responses, rendering bees more susceptible to parasites. It seems certain that chronic exposure to multiple interacting stressors is driving honey bee colony losses and declines of wild pollinators, but such interactions are not addressed by current regulatory procedures, and studying these interactions experimentally poses a major challenge. In the meantime, taking steps to reduce stress on bees would seem prudent; incorporating flower-rich habitat into farmland, reducing pesticide use through adopting more sustainable farming methods, and enforcing effective quarantine measures on bee movements are all practical measures that should be adopted. Effective monitoring of wild pollinator populations is urgently needed to inform management strategies into the future.

Identification of candidate agents active against N. ceranae infection in honey bees: establishment of a medium throughput screening assay based on N. ceranae infected cultured cells

Many flowering plants in both natural ecosytems and agriculture are dependent on insect pollination for fruit set and seed production. Managed honey bees (Apis mellifera) and wild bees are key pollinators providing this indispensable eco- and agrosystem service. Like all other organisms, bees are attacked by numerous pathogens and parasites. Nosema apis is a honey bee pathogenic microsporidium which is widely distributed in honey bee populations without causing much harm. Its congener Nosema ceranae was originally described as pathogen of the Eastern honey bee (Apis cerana) but jumped host from A. cerana to A. mellifera about 20 years ago and spilled over from A. mellifera to Bombus spp. quite recently. N. ceranae is now considered a deadly emerging parasite of both Western honey bees and bumblebees. Hence, novel and sustainable treatment strategies against N. ceranae are urgently needed to protect honey and wild bees. We here present the development of an in vitro medium throughput screening assay for the identification of candidate agents active against N. ceranae infections. This novel assay is based on our recently developed cell culture model for N. ceranae and coupled with an RT-PCR-ELISA protocol for quantification of N. ceranae in infected cells. The assay has been adapted to the 96-well microplate format to allow automated analysis. Several substances with known (fumagillin) or presumed (surfactin) or no (paromomycin) activity against N. ceranae were tested as well as substances for which no data concerning N. ceranae inhibition existed. While fumagillin and two nitroimidazoles (metronidazole, tinidazole) totally inhibited N. ceranae proliferation, all other test substances were inactive. In summary, the assay proved suitable for substance screening and demonstrated the activity of two synthetic antibiotics against N. ceranae.

Tubulinosema pampeana sp. n. (Microsporidia, Tubulinosematidae), a pathogen of the South American bumble bee Bombus atratus

An undescribed microsporidium was detected and isolated from the South American bumble bee Bombus atratus collected in the Pampas region of Argentina. Infection intensity in workers averaged 8.2 × 10(7)spores/bee. The main site of infection was adipose tissue where hypertrophy of adipocytes resulted in cyst-like body formation. Mature spores were ovoid and monomorphic. They measured 4.00 μm × 2.37 μm (fresh) or 3.98 μm × 1.88 μm (fixed). All stages were diplokariotic and developed in direct contact with host cytoplasm. Isofilar polar filament was arranged in 16 coils in one or, posteriorly, two layers. Coiling angle was variable, between perpendicular and almost parallel to major spore axis. Late meronts and sporogonial stages were surrounded by vesicles of approximately 60 nm in diameter. Based on both new and already designed primers, a 1827 bp (SSUrRNA, ITS, LSUrRNA) sequence was obtained. Data analyses suggest that this microsporidium is a new species of the genus Tubulinosema. The name Tubulinosema pampeana sp. n. is proposed.

Recent worldwide expansion of Nosema ceranae (Microsporidia) in Apis mellifera populations inferred from multilocus patterns of genetic variation

Nosema ceranae has been found infecting Apismellifera colonies with increasing frequency and it now represents a major threat to the health and long-term survival of these honeybees worldwide. However, so far little is known about the population genetics of this parasite. Here, we describe the patterns of genetic variation at three genomic loci in a collection of isolates from all over the world. Our main findings are: (i) the levels of genetic polymorphism (πS≈1%) do not vary significantly across its distribution range, (ii) there is substantial evidence for recombination among haplotypes, (iii) the best part of the observed genetic variance corresponds to differences within bee colonies (up to 88% of the total variance), (iv) parasites collected from Asian honeybees (Apis cerana and Apis florea) display significant differentiation from those obtained from Apismellifera (8-16% of the total variance, p<0.01) and (v) there is a significant excess of low frequency variants over neutral expectations among samples obtained from A. mellifera, but not from Asian honeybees. Overall these results are consistent with a recent colonization and rapid expansion of N. ceranae throughout A. mellifera colonies.

Evidence for weak genetic recombination at the PTP2 locus of Nosema ceranae

The microsporidian Nosema ceranae is an emergent pathogen that threatens the health of honeybees and other pollinators all over the world. Its recent rapid spread across a wide variety of host species and environments demonstrated an enhanced ability of adaptation, which seems to contradict the lack of evidence for genetic recombination and the absence of a sexual stage in its life cycle. Here we retrieved fresh data of the patterns of genetic variation at the PTP2 locus in naturally infected Apis mellifera colonies, by means of single genome amplification. This technique, designed to prevent the formation of chimeric haplotypes during polymerase chain reaction (PCR), provides more reliable estimates of the diversity levels and haplotype structure than standard PCR-cloning methods. Our results are consistent with low but significant rates of recombination in the history of the haplotypes detected: estimates of the population recombination rate are of the order of 30 and support recent evidence for unexpectedly high levels of variation of the parasites within honeybee colonies. These observations suggest the existence of a diploid stage at some point in the life cycle of this parasite and are relevant for our understanding of the dynamics of its expanding population.

The relationship between managed bees and the prevalence of parasites in bumblebees

Honey bees and, more recently, bumblebees have been domesticated and are now managed commercially primarily for crop pollination, mixing with wild pollinators during foraging on shared flower resources. There is mounting evidence that managed honey bees or commercially produced bumblebees may affect the health of wild pollinators such as bumblebees by increasing competition for resources and the prevalence of parasites in wild bees. Here we screened 764 bumblebees from around five greenhouses that either used commercially produced bumblebees or did not, as well as bumblebees from 10 colonies placed at two sites either close to or far from a honey bee apiary, for the parasites Apicystis bombi, Crithidia bombi, Nosema bombi, N. ceranae, N. apis and deformed wing virus. We found that A. bombi and C. bombi were more prevalent around greenhouses using commercially produced bumblebees, while C. bombi was 18% more prevalent in bumblebees at the site near to the honey bee apiary than those at the site far from the apiary. Whilst these results are from only a limited number of sites, they support previous reports of parasite spillover from commercially produced bumblebees to wild bumblebees, and suggest that the impact of stress from competing with managed bees or the vectoring of parasites by them on parasite prevalence in wild bees needs further investigation. It appears increasingly likely that the use of managed bees comes at a cost of increased parasites in wild bumblebees, which is not only a concern for bumblebee conservation, but which may impact other pollinators as well.

Bee bread increases honeybee haemolymph protein and promote better survival despite of causing higher Nosema ceranae abundance in honeybees

Adequate protein nutrition supports healthy honeybees and reduces the susceptibility to disease. However little is known concerning the effect of the diet on Nosema ceranae development, an obligate intracellular parasite that disturbs the protein metabolism of honeybees (Apis mellifera). Here we tested the effect of natural (bee bread) and non-natural protein diets (substitute) on haemolymph proteins titers of honeybee and N. ceranae spore production. The natural diet induced higher levels of protein and parasite development, but the survival of bees was also higher than with non-natural diets. The data showed that the administration of an artificially high nutritious diet in terms of crude protein content is not sufficient to promote healthy bees; rather the protein ingested should be efficiently assimilated. The overall results support the idea that the physiological condition of the bees is linked to protein levels in the haemolymph, which affects the tolerance to parasite; consequently the negative impact of the parasite on host fitness is not associated only with the level of infection.

Loop-mediated isothermal amplification (LAMP) assays for rapid detection and differentiation of Nosema apis and N. ceranae in honeybees

Nosemosis is a contagious disease of honeybees (Apis mellifera) manifested by increased winter mortality, poor spring build-up and even the total extinction of infected bee colonies. In this paper, loop-mediated isothermal amplifications (LAMP) were used for the first time to identify and differentiate N. apis and N. ceranae, the causative agents of nosemosis. LAMP assays were performed at a constant temperature of 60 °C using two sets of six species-specific primers, recognising eight distinct fragments of 16S rDNA gene and GspSSD polymerase with strand displacement activity. The optimal time for LAMP and its Nosema species sensitivity and specificity were assessed. LAMP only required 30 min for robust identification of the amplicons. Ten-fold serial dilutions of total DNA isolated from bees infected with microsporidia were used to determine the detection limit of N. apis and N. ceranae DNAs by LAMP and standard PCR assays. LAMP appeared to be 10(3) -fold more sensitive than a standard PCR in detecting N. apis and N. ceranae. LAMP methods developed by us are highly Nosema species specific and allow to identify and differentiate N. apis and N. ceranae.

Fumagillin: an overview of recent scientific advances and their significance for apiculture

Fumagillin is a potent fungal metabolite first isolated from Aspergillus fumigatus. It is widely used in apiculture and human medicine against a variety of microsporidian fungal infections. It has been the subject of research in cancer treatments by employing its angiogenesis inhibitory properties. The toxicity of fumagillin has limited its use for human applications and spurred the development of analogues using structure-activity relationships relating to its angiogenesis properties. These discoveries may hold the key to the development of alternative chemical treatments for use in apiculture. The toxicity of fumagillin to humans is important for beekeeping, because any residues remaining in hive products pose a direct risk to the consumer. The analytical methods published to date measure fumagillin and its decomposition products but overlook the dicyclohexylamine counterion of the salt form widely used in apiculture.

The invasion of southern South America by imported bumblebees and associated parasites

The Palaearctic Bombus ruderatus (in 1982/1983) and Bombus terrestris (1998) have both been introduced into South America (Chile) for pollination purposes. We here report on the results of sampling campaigns in 2004, and 2010-2012 showing that both species have established and massively expanded their range. Bombus terrestris, in particular, has spread by some 200 km year(-1) and had reached the Atlantic coast in Argentina by the end of 2011. Both species, and especially B. terrestris, are infected by protozoan parasites that seem to spread along with the imported hosts and spillover to native species. Genetic analyses by polymorphic microsatellite loci suggest that the host population of B. terrestris is genetically diverse, as expected from a large invading founder population, and structured through isolation by distance. Genetically, the populations of the trypanosomatid parasite, Crithidia bombi, sampled in 2004 are less diverse, and distinct from the ones sampled later. Current C. bombi populations are highly heterozygous and also structured through isolation by distance correlating with the genetic distances of B. terrestris, suggesting the latter's expansion to be a main structuring factor for the parasite. Remarkably, wherever B. terrestris spreads, the native Bombus dahlbomii disappears although the reasons remain unclear. Our ecological and genetic data suggest a major invasion event that is currently unfolding in southern South America with disastrous consequences for the native bumblebee species.

First molecular detection of co-infection of honey bee viruses in asymptomatic Bombus atratus in South America

Pollination is critical for food production and has the particularity of linking natural ecosystems with agricultural production systems. Recently, losses of bumblebee species have been reported worldwide. In this study, samples from a commercial exploitation of bumblebees of Argentina with a recent history of deaths were studied using a multiplex PCR for the detection of the honey bee viruses most frequently detected in South America. All samples analysed were positive for co-infections with Deformed wing virus, Black queen cell virus and Sacbrood virus. This is the first report of infection of Bombus atratus with honey bee viruses. A better understanding of viral infections in bumblebees and of the epidemiology of viruses could be of great importance as bumblebees can serve as possible viral reservoirs, resulting in pathogen spillover towards honey bees and native bumblebees.

Apoptosis in the pathogenesis of Nosema ceranae (Microsporidia: Nosematidae) in honey bees (Apis mellifera)

Nosema ceranae is a parasite of the epithelial ventricular cells of the honey bee that belongs to the microsporidian phylum, a biological group of single-cell, spore-forming obligate intracellular parasites found in all major animal lineages. The ability of host cells to accommodate a large parasitic burden for several days suggests that these parasites subvert the normal host cells to ensure optimal environmental conditions for growth and development. Once infected, cells can counteract the invasive pathogen by initiating their own death by apoptosis as a defence strategy. To determine whether N. ceranae blocks apoptosis in infected ventricular cells, cell death was assessed in sections of the ventriculum from experimentally infected honey bees using the TUNEL assay and by immunohistochemistry for caspase-3. Ventricular epithelial cells from infected bees were larger than those in the uninfected control bees, and they contained N. ceranae at both mature and immature stages in the cytoplasm. Apoptotic nuclei were only observed in some restricted areas of the ventriculum, whereas apoptosis was typically observed throughout the epithelium in uninfected bees. Indeed, the apoptotic index was higher in uninfected versus infected ventriculi. Our results suggested that N. ceranae prevents apoptosis in epithelial cells of infected ventriculi, a mechanism possible designed to enhance parasite development.

New insights on the genetic diversity of the honeybee parasiteNosema ceranaebased onmultilocussequence analysis

The microsporidian parasiteNosema ceranaeis a common pathogen of the Western honeybee (Apis mellifera) whose variable virulence could be related to its genetic polymorphism and/or its polyphenism responding to environmental cues. Since the genotyping ofN. ceranaebased on unique marker sequences had been unsuccessful, we tested whether amultilocusapproach, assessing the diversity of ten genetic markers – encoding nine proteins and the small ribosomal RNA subunit – allowed the discrimination betweenN. ceranaevariants isolated from singleA. melliferaindividuals in four distant locations. High nucleotide diversity and allele content were observed for all genes. Most importantly, the diversity was mainly present within parasite populations isolated from single honeybee individuals. In contrast the absence of isolate differentiation precluded anytaxadiscrimination, even through amultilocusapproach, but suggested that similar populations of parasites seem to infect honeybees in distant locations. As statistical evolutionary analyses showed that the allele frequency is under selective pressure, we discuss the origin and consequences ofN. ceranaeheterozygosity in a single host and lack of population divergence in the context of the parasite natural and evolutionary history.

Emerging dangers: deadly effects of an emergent parasite in a new pollinator host

There is growing concern about the threats facing many pollinator populations. Emergent diseases are one of the major threats to biodiversity and a microsporidian parasite, Nosema ceranae, has recently jumped host from the Asian to the Western honeybee, spreading rapidly worldwide, and contributing to dramatic colony losses. Bumblebees are ecologically and economically important pollinators of conservation concern, which are likely exposed to N. ceranae by sharing flowers with honeybees. Whilst a further intergeneric jump by N. ceranae to infect bumblebees would be potentially serious, its capacity to do this is unknown. Here we investigate the prevalence of N. ceranae in wild bumblebees in the UK and determine the infectivity of the parasite under controlled conditions. We found N. ceranae in all seven wild bumblebee species sampled, and at multiple sites, with many of the bees having spores from this parasite in their guts. When we fed N. ceranae spores to bumblebees under controlled conditions, we confirmed that the parasite can infect bumblebees. Infections spread from the midgut to other tissues, reduced bumblebee survival by 48% and had sub-lethal effects on behaviour. Although spore production appeared lower in bumblebees than in honeybees, virulence was greater. The parasite N. ceranae therefore represents a real and emerging threat to bumblebees, with the potential to have devastating consequences for their already vulnerable populations.

Pathogen prevalence in commercially reared bumble bees and evidence of spillover in conspecific populations

Worldwide, wild bumble bees (Bombus spp.) are experiencing marked declines, with potentially up to 11% of species currently under threat. Recent studies from North America suggest that disease transmission from commercially reared bumble bees to wild populations has led to marked range contractions in some species. In Europe, data on the prevalence of pathogen spillover from commercial to wild bumble bee populations is lacking, despite the widespread production and transport of hives within the EU since the early 1980s. We determined the permeability of cropping systems to commercial bumble bees, and quantified the prevalence of four pathogens in commercial Bombus terrestris hives and adjacent conspecific populations at increasing distances from greenhouses in Ireland. Commercial bumble bees collected from 31% to 97% of non-crop pollen, depending on the cropping system, and hives had markedly higher frequencies of two gut parasites, Crithidia spp. and Nosema bombi, compared to adjacent populations, but were free of tracheal mites. The highest prevalence of Crithida was observed within 2 km of greenhouses and the probability of infection declined in a host sex- and pathogen-specific manner up to 10 km. We suggest implementing measures that prevent the interaction of commercially reared and wild bumble bees by integrating the enforcement of national best management practices for users of commercial pollinators with international legislation that regulates the sanitation of commercial hives in production facilities.

Molecular differentiation of Nosema apis and Nosema ceranae based on species-specific sequence differences in a protein coding gene

Nosema apis and Nosema ceranae are two microsporidian pathogens of the European honey bee, Apis mellifera. There is evidence that N. ceranae is more virulent than N. apis subject to environmental factors like climate. This makes N. ceranae one of the suspects in the increasing colony losses recently observed in many regions of the world. Correct differentiation between N. apis and N. ceranae is important and best accomplished by molecular methods. So far only protocols based on species-specific sequence differences in the 16S rRNA gene are available. However, recent studies indicated that these methods may lead to confusing results due to polymorphisms in and recombination between the multi-copy 16S rRNA genes. To solve this problem and to provide a reliable molecular tool for the differentiation between the two bee pathogenic microsporidia we here present and evaluate a duplex-PCR protocol based on species-specific sequence differences in the highly conserved gene coding for the DNA-dependent RNA polymerase II largest subunit. A total of 102 honey bee samples were analyzed by the novel PCR protocol and the results were compared with the results of the originally published PCR-RFLP analysis and two recently published differentiation protocols, based on 16S rRNA sequence differences. Although the novel PCR protocol proved to be as reliable as the 16S rRNA gene based PCR-RFLP it was superior to simple 16S rRNA based PCR protocols which tended to overestimate the rate of N. ceranae infections. Therefore, we propose that species-specific sequence differences of highly conserved protein coding genes should become the preferred molecular tool for differentiation of Nosema spp.

The microsporidian parasites Nosema ceranae and Nosema apis are widespread in honeybee (Apis mellifera) colonies across Scotland

Nosema ceranae is spreading into areas where Nosema apis already exists. N. ceranae has been reported to cause an asymptomatic infection that may lead, ultimately, to colony collapse. It is thought that there may be a temperature barrier to its infiltration into countries in colder climates. In this study, 71 colonies from Scottish Beekeeper's Association members have been screened for the presence of N. apis and N. ceranae across Scotland. We find that only 11 of the 71 colonies tested positive for spores by microscopy. However, 70.4 % of colonies screened by PCR revealed the presence of both N. ceranae and N. apis, with only 4.2 or 7 % having either strain alone and 18.3 % being Nosema free. A range of geographically separated colonies testing positive for N. ceranae were sequenced to confirm their identity. All nine sequences confirmed the presence of N. ceranae and indicated the presence of a single new variant. Furthermore, two of the spore-containing colonies had only N. ceranae present, and these exhibited the presence of smaller spores that could be distinguished from N. apis by the analysis of average spore size. Differential quantification of the PCR product revealed N. ceranae to be the dominant species in all seven samples tested. In conclusion, N. ceranae is widespread in Scotland where it exists in combination with the endemic N. apis. A single variant, identical to that found in France (DQ374655) except for the addition of a single nucleotide polymorphism, is present in Scotland.

Further evidence of an oriental origin for Nosema ceranae (Microsporidia: Nosematidae)

Although Nosema ceranae was first isolated from the Asian honeybee (Apis cerana) in Asia and then subsequently recognized as a widespread gut parasite of the Western honeybee (Apis mellifera), its origins and primary host are yet to be accurately established. In this study we examined the possibility of an Asian origin for the parasite by looking for evidence of its ongoing spread out of Asia. To do this, we surveyed for the presence of N. ceranae in A. cerana and A. mellifera on isolated islands of the Solomon Islands (Pacific region), most of which were inhabited with A. mellifera that had been introduced from Australia and New Zealand at a time when N. ceranae was not present in either country, but on which some had also recently become inhabited with invasive A. cerana that originated from Asia with no prior history of contact with A. mellifera infected with N. ceranae. We also sought to verify previous findings that N. ceranae was widespread in Asian honeybees by surveying for its presence in isolated populations of the Asian honeybees, A. cerana, A. koschevnikovi, A. nigrocincta and A. florea. We obtained evidence that A. cerana introduced N. ceranae to A. mellifera in the Solomon Islands and also confirmed the widespread occurrence of the parasite in Asian honeybees, even reporting it for the first time in A. koschevnikovi from Borneo. Our findings provide further support for the hypothesis that N. ceranae has only recently emerged from Asia to become a parasite of A. mellifera.

Sphaerularia bombi (Nematoda: Sphaerulariidae) parasitizing Bombus atratus (Hymenoptera: Apidae) in southern South America

Bumble bees are some of the most important insect pollinators. However, knowledge on parasites associated to bumble bees in South America is very limited. This study reports the first isolation of a sphaerularid nematode parasitizing queens of the native bumble bee Bombus atratus in Argentina. Measurements and morphological characters of eggs, juveniles, and adults strongly suggest that the species is Sphaerularia bombi, a parasite that affects the reproduction and foraging behavior of the host. The nematode was detected in bumble bees of San Carlos de Bariloche, northwestern Patagonia region, and the surroundings of La Plata, northeastern Pampas region. Prevalence varied between 8% and 20%.

Pervasiveness of parasites in pollinators

Many pollinator populations are declining, with large economic and ecological implications. Parasites are known to be an important factor in the some of the population declines of honey bees and bumblebees, but little is known about the parasites afflicting most other pollinators, or the extent of interspecific transmission or vectoring of parasites. Here we carry out a preliminary screening of pollinators (honey bees, five species of bumblebee, three species of wasp, four species of hoverfly and three genera of other bees) in the UK for parasites. We used molecular methods to screen for six honey bee viruses, Ascosphaera fungi, Microsporidia, and Wolbachia intracellular bacteria. We aimed simply to detect the presence of the parasites, encompassing vectoring as well as actual infections. Many pollinators of all types were positive for Ascosphaera fungi, while Microsporidia were rarer, being most frequently found in bumblebees. We also detected that most pollinators were positive for Wolbachia, most probably indicating infection with this intracellular symbiont, and raising the possibility that it may be an important factor in influencing host sex ratios or fitness in a diversity of pollinators. Importantly, we found that about a third of bumblebees (Bombus pascuorum and Bombus terrestris) and a third of wasps (Vespula vulgaris), as well as all honey bees, were positive for deformed wing virus, but that this virus was not present in other pollinators. Deformed wing virus therefore does not appear to be a general parasite of pollinators, but does interact significantly with at least three species of bumblebee and wasp. Further work is needed to establish the identity of some of the parasites, their spatiotemporal variation, and whether they are infecting the various pollinator species or being vectored. However, these results provide a first insight into the diversity, and potential exchange, of parasites in pollinator communities.

A new threat to honey bees, the parasitic phorid fly Apocephalus borealis

Honey bee colonies are subject to numerous pathogens and parasites. Interaction among multiple pathogens and parasites is the proposed cause for Colony Collapse Disorder (CCD), a syndrome characterized by worker bees abandoning their hive. Here we provide the first documentation that the phorid fly Apocephalus borealis, previously known to parasitize bumble bees, also infects and eventually kills honey bees and may pose an emerging threat to North American apiculture. Parasitized honey bees show hive abandonment behavior, leaving their hives at night and dying shortly thereafter. On average, seven days later up to 13 phorid larvae emerge from each dead bee and pupate away from the bee. Using DNA barcoding, we confirmed that phorids that emerged from honey bees and bumble bees were the same species. Microarray analyses of honey bees from infected hives revealed that these bees are often infected with deformed wing virus and Nosema ceranae. Larvae and adult phorids also tested positive for these pathogens, implicating the fly as a potential vector or reservoir of these honey bee pathogens. Phorid parasitism may affect hive viability since 77% of sites sampled in the San Francisco Bay Area were infected by the fly and microarray analyses detected phorids in commercial hives in South Dakota and California's Central Valley. Understanding details of phorid infection may shed light on similar hive abandonment behaviors seen in CCD.

Microsporidia infecting Apis mellifera: coexistence or competition. Is Nosema ceranae replacing Nosema apis?

Nosema ceranae has been suggested to be replacing Nosema apis in some populations of Apis mellifera honeybees. However, this replacement from one to the other is not supported when studying the distribution and prevalence of both microsporidia in professional apiaries in Spanish territories (transverse study), their seasonal pattern in experimental hives with co-infection or their prevalence at individual level (either in worker bees or drones). Nevertheless, N.ceranae has shown to present a higher prevalence at all the studied levels that could indicate any advantage for its development over N.apis or that it is more adapted to Spanish conditions. Also, both microsporidia show a different pattern of preference for its development according to the prevalence in the different Spanish bioclimatic belts studied. Finally, the fact that all analyses were carried out using an Internal PCR Control (IPC) newly developed guarantees the confidence of the data extracted from the PCR analyses. This IPC provides a useful tool for laboratory detection of honeybee pathogens.

Diversity of Nosema associated with bumblebees (Bombus spp.) from China

Bumblebees (Bombus spp.) are important pollinators of many economically important crops and microsporidia are among the most important infections of these hosts. Using molecular markers, we screened a large sample (n=1,009 bees) of workers of 27 different Bombus spp. from China (Sichuan, Qinghai, Inner Mongolia, and Gansu provinces). The results showed that 62 individuals representing 12 Bombus spp. were infected by microsporidia with an overall prevalence of 6.1%. Based on the haplotypes (ssrRNA sequences), we confirmed the presence of Nosema bombi, Nosema ceranae and (likely) Nosema thomsoni. In addition, four new putatively novel taxa were identified by phylogenetic reconstruction: Nosema A, Nosema B-complex, Nosema C-complex and Nosema D-complex. In many cases, hosts were infected by more than one Nosema taxon. Possible caveats of sequence analyses are discussed.

Apicystis bombi (Apicomplexa: Neogregarinorida) parasitizing Apis mellifera and Bombus terrestris (Hymenoptera: Apidae) in Argentina

The neogregarine Apicystis bombi is considered a low prevalence parasite of Bombus spp. Before our work it has only once been detected in one single specimen of the Western honeybee Apis mellifera. This contribution reports the presence of A. bombi parasitizing both A. mellifera and Bombus terrestris at a site in Northwestern Argentine Patagonia (Bariloche, close to the border with Chile) and analyses its possible absence in the Pampas region, the most important beekeeping region of the country. In Bariloche, prevalence of A. bombi in A. mellifera was 7.6% in 2009, and 13.6% in 2010, whereas in B. terrestris it was 12.1%. Infections were not detected in 302 bee hives periodically prospected along 3 years (almost 400 000 honeybee specimens) in the Pampas. Analysis with the probability program FreeCalc2 suggested a possible absence of A. bombi in this area. Because of high virulence showed in several species of Bombus in the Northern hemisphere, A. bombi should be closely monitored in A. mellifera and in native Bombus species or other Apidae.

Comparative analysis of detection limits and specificity of molecular diagnostic markers for three pathogens (Microsporidia, Nosema spp.) in the key pollinators Apis mellifera and Bombus terrestris

Global pollinator decline has recently been discussed in the context of honey and bumble bee infections from various pathogens including viruses, bacteria, microsporidia and mites. The microsporidian pathogens Nosema apis, Nosema ceranae and Nosema bombi may in fact be major candidates contributing to this decline. Different molecular and non-molecular detection methods have been developed; however, a comparison, especially of the highly sensitive PCR based methods, is currently lacking. Here, we present the first comparative quantitative real-time PCR study of nine Nosema spp. primers within the framework of primer specificity and sensitivity. With the help of dilution series of defined numbers of spores, we reveal six primer pairs amplifying N. apis, six for N. bombi and four for N. ceranae. All appropriate primer pairs detected an amount of at least 10(4) spores, the majority of which were even as sensitive to detect such low amounts as 10(3) to ten spores. Species specificity of primers was observed for N. apis and N. bombi, but not for N. ceranae. Additionally, we did not find any significant correlation for the amplified fragments with PCR efficiency or the limit of detection. We discuss our findings on the background of false positive and negative results using quantitative real-time PCR. On the basis of these results, future research might be based on appropriate primer selection depending on the experimental needs. Primers may be selected on the basis of specificity or sensitivity. Pathogen species and load may be determined with higher precision enhancing all kinds of diagnostic studies.

The growing prevalence of Nosema ceranae in honey bees in Spain, an emerging problem for the last decade

Microsporidiosis caused by infection with Nosema apis or Nosema ceranae has become one of the most widespread diseases of honey bees and can cause important economic losses for beekeepers. Honey can be contaminated by spores of both species and it has been reported as a suitable matrix to study the field prevalence of other honey bee sporulated pathogens. Historical honey sample collections from the CAR laboratory (Centro Apícola Regional) were analyzed by PCR to identify the earliest instance of emergence, and to determine whether the presence of Nosema spp. in honey was linked to the spread of these microsporidia in honey bee apiaries. A total of 240 frozen honey samples were analyzed by PCR and the results compared with rates of Nosema spp. infection in worker bee samples from different years and geographical areas. The presence of Nosema spp. in hive-stored honey from naturally infected honey bee colonies (from an experimental apiary) was also monitored, and although collected honey bees resulted in a more suitable sample to study the presence of microsporidian parasites in the colonies, a high probability of finding Nosema spp. in their hive-stored honey was observed. The first honey sample in which N. ceranae was detected dates back to the year 2000. In subsequent years, the number of samples containing N. ceranae tended to increase, as did the detection of Nosema spp. in adult worker bees. The presence of N. ceranae as early as 2000, long before generalized bee depopulation and colony losses in 2004 may be consistent with a long incubation period for nosemosis type C or related with other unknown factors. The current prevalence of nosemosis, primarily due to N. ceranae, has reached epidemic levels in Spain as confirmed by the analysis of worker honey bees and commercial honey.

Effects of invasive parasites on bumble bee declines

Bumble bees are a group of pollinators that are both ecologically and economically important and declining worldwide. Numerous mechanisms could be behind this decline, and the spread of parasites from commercial colonies into wild populations has been implicated recently in North America. Commercial breeding may lead to declines because commercial colonies may have high parasite loads, which can lead to colonization of native bumble bee populations; commercial rearing may allow higher parasite virulence to evolve; and global movement of commercial colonies may disrupt spatial patterns in local adaptation between hosts and parasites. We assessed parasite virulence, transmission mode, and infectivity. Microparasites and so-called honey bee viruses may pose the greatest threat to native bumble bee populations because certain risk factors are present; for example, the probability of horizontal transmission of the trypanosome parasite Crithidia bombi is high. The microsporidian parasite Nosema bombi may play a role in declines of bumble bees in the United States. Preliminary indications that C. bombi and the neogregarine Apicystis bombi may not be native in parts of South America. We suggest that the development of molecular screening protocols, thorough sanitation efforts, and cooperation among nongovernmental organizations, governments, and commercial breeders might immediately mitigate these threats.

Evaluation of large-scale dissemination of Nosema ceranae spores by European bee-eaters Merops apiaster

Identification of transmission routes and of factors affecting the spatial positions of pathogens, hosts and vectors is basic to an adequate disease management. Nosema ceranae is a Microsporidian recently described as a parasite of Apis mellifera honeybees and is currently considered the aetiological agent of an emergent illness named nosemosis type C. In this article we evaluate the role of a bird species, the European bee-eater, Merops apiaster, as a large-scale dispersive agent of N. ceranae. We found a high prevalence of viable spores of N. ceranae in pellets regurgitated by bee-eaters in different locations in the Iberian Peninsula, Central Europe and central Asia. In contrast, spores of Nosema apis, considered till recently the most common microsporidium infecting honeybees, were detected in a single locality and Nosema bombi spores were not noticed. Since non-viable spores were also found in bee-eater nests from different locations, this bird species could also reduce the fraction of infected insects by withdrawing pathogens from the colonies. We conclude that bee-eater mobility and migration may have played an important role in the transmission of the pathogen N. ceranae.

The differential development of microsporidia infecting worker honey bee (Apis mellifera) at increasing incubation temperature

In the last century, nosemosis caused by Nosema apis is traditionally considered as a low-prevalence disease of Apis mellifera, even though it occurs worldwide. Colonies affected by N. apis display low levels of infection during summer, a small peak in autumn and usually a slow rise during winter. However, nosemosis due to Nosema ceranae is considered as an emergent illness that is posing a major threat to the health of individual honey bees and whole bee colonies. The symptoms of infection by these two pathogens are very different, as are the virulence, spread and pathogenicity. We have carried out experiments in artificially infected worker honey bees maintained in the laboratory at two different temperatures. Both microsporidia developed as expected for up to 4 days after infection at 33.0°C, but when maintained for 5 or 7 days at 37.2°C, only N. ceranae completed its life cycle in infected honey bees, while the development of N. apis was inhibited. This and other published data suggest that N. ceranae is eurythermal whereas N. apis is stenothermal. The higher temperature tolerance recorded may be related to the higher prevalence of N. ceranae reported worldwide.