Honey bee winter mortality in France in 1999 and 2000

The Epidemiological Situation of the Managed Honey Bee (Apis mellifera) Colonies in the Italian Region Emilia-Romagna

The recent decades witnessed the collapse of honey bee colonies at a global level. The major drivers of this collapse include both individual and synergic pathogen actions, threatening the colonies’ survival. The need to define the epidemiological pattern of the pathogens that are involved has led to the establishment of monitoring programs in many countries, Italy included. In this framework, the health status of managed honey bees in the Emilia–Romagna region (northern Italy) was assessed, throughout the year 2021, on workers from 31 apiaries to investigate the presence of major known and emerging honey bee pathogens. The prevalence and abundance of DWV, KBV, ABPV, CBPV, Nosema ceranae, and trypanosomatids (Lotmaria passim, Crithidia mellificae, Crithidia bombi) were assessed by molecular methods. The most prevalent pathogen was DWV, followed by CBPV and N. ceranae. Trypanosomatids were not found in any of the samples. Pathogens had different peaks in abundance over the months, showing seasonal trends that were related to the dynamics of both bee colonies and Varroa destructor infestation. For some of the pathogens, a weak but significant correlation was observed between abundance and geographical longitude. The information obtained in this study increases our understanding of the epidemiological situation of bee colonies in Emilia–Romagna and helps us to implement better disease prevention and improved territorial management of honey bee health.

A derived honey bee stock confers resistance to Varroa destructor and associated viral transmission

The ectoparasite Varroa destructor is the greatest threat to managed honey bee (Apis mellifera) colonies globally. Despite significant efforts, novel treatments to control the mite and its vectored pathogens have shown limited efficacy, as the host remains naïve. A prospective solution lies in the development of Varroa-resistant honey bee stocks, but a paucity of rigorous selection data restricts widespread adoption. Here, we characterise the parasite and viral dynamics of a Varroa-resistant honey bee stock, designated ‘Pol-line’, using a large-scale longitudinal study. Results demonstrate markedly reduced Varroa levels in this stock, diminished titres of three major viruses (DWV-A, DWV-B, and CBPV), and a two-fold increase in survival. Levels of a fourth virus that is not associated with Varroa—BQCV—do not differ between stocks, supporting a disruption of the transmission pathway. Further, we show that when decoupled from the influence of Varroa levels, viral titres do not constitute strong independent predictors of colony mortality risk. These findings highlight the need for a reassessment of Varroa etiology, and suggest that derived stocks represent a tractable solution to the Varroa pandemic.

The Comparison of Honeybee Viral Loads for Six Honeybee Viruses (ABPV, BQCV, CBPV, DWV, LSV3 and SBV) in Healthy and Clinically Affected Honeybees with TaqMan Quantitative Real-Time RT-PCR Assays

The viral loads of acute bee paralysis virus (ABPV), black queen cell virus (BQCV), chronic bee paralysis virus (CBPV), deformed wing virus (DWV), Lake Sinai virus 3 (LSV3), and sacbrood bee virus (SBV) were determined in samples with the use of quantitative TaqMan real-time reverse transcription and polymerase chain reaction (RT-qPCR). A total of 108 samples of healthy adult honeybees from four differently located apiaries and samples of honeybees showing different clinical signs of viral infections from 89 apiaries were collected throughout Slovenia. The aim of this study was to discover correlations between viral loads and clinical signs in adult honeybees and confirm previously set threshold viral load levels between healthy and clinically affected honeybees. Within this study, two new RT-qPCR assays for quantification of LSV3 and SBV were developed. Statistically significant differences in viral loads of positive samples were identified between healthy and clinically affected honeybees for ABPV, CBPV, DWV, and SBV, while for BQCV and LSV3, no statistical differences were observed between both groups. Despite high detected LSV3 prevalence and viral loads around 6.00 log₁₀ viral copies/bee, this lineage probably has a limited impact on the health status of honeybee colonies. The determined viral loads between 3.94 log₁₀ and 13.17 log₁₀ in positive samples for six viruses, collected over 10 consecutive months, including winter, present additional information of high viral load variations in healthy honeybee colonies.

A Pesticide Residues Insight on Honeybees, Bumblebees and Olive Oil after Pesticidal Applications against the Olive Fruit Fly Bactrocera oleae (Diptera: Tephritidae)

In 2017 and 2018, a field survey was initiated on Greek olive orchards to investigate the attractiveness of bait spray applications and the impact of cover and bait sprays applied against the olive fruit fly Bactrocera oleae (Diptera: Tephritidae), on the honeybee, Apis mellifera L. and bumblebees Bombus terrestris, by investigating the pesticides' residual prevalence. Bee colonies were evenly distributed in three sites located on coastal areas of Western Crete and visited almost weekly between July and October. Samples collected, were analyzed using existing or developed-optimized liquid and gas chromatographic methods. In bee samples, concentrations varied from 0.0013 to 2.3 mg/kg for dimethoate, from 0.0013-0.059 mg/kg for its metabolite omethoate, and from 0.0035 to 0.63 mg/kg regarding the pyrethroids, β-cyfluthrin and λ-cyhalothrin. In one bee sample dimethoate concentration exceeded both acute oral and contact median lethal dose (LD50). Residue findings in bees, along with verified olive oil residues corroborated that those insecticides had been applied in the olive orchards and transferred to bees. The possibility of non-target effects of the bait sprays to the bees, as well as the impact of the contaminated olive to the bees are discussed.

On the Importance of the Sound Emitted by Honey Bee Hives

Recent years have seen a worsening in the decline of honey bees (Apis mellifera L.) colonies. This phenomenon has sparked a great amount of attention regarding the need for intense bee hive monitoring, in order to identify possible causes, and design corresponding countermeasures. Honey bees have a key role in pollination services of both cultivated and spontaneous flora, and the increase in bee mortality could lead to an ecological and economical damage. Despite many smart monitoring systems for honey bees and bee hives, relying on different sensors and measured quantities, have been proposed over the years, the most promising ones are based on sound analysis. Sounds are used by the bees to communicate within the hive, and their analysis can reveal useful information to understand the colony health status and to detect sudden variations, just by using a simple microphone and an acquisition system. The work here presented aims to provide a review of the most interesting approaches proposed over the years for honey bees sound analysis and the type of knowledge about bees that can be extracted from sounds.

A Smart Sensor-Based Measurement System for Advanced Bee Hive Monitoring

The widespread decline of honey bee (Apis mellifera L.) colonies registered in recent years has raised great attention to the need of gathering deeper knowledge about this phenomenon, by observing the colonies' activity to identify possible causes, and design corresponding countermeasures. In fact, honey bees have well-known positive effects on both the environment and human life, and their preservation becomes critical not only for ecological reasons, but also for the social and economic development of rural communities. Smart sensor systems are being developed for real-time and long-term measurement of relevant parameters related to beehive conditions, such as the hive weight, sounds emitted by the bees, temperature, humidity, and CO 2 inside the beehive, as well as weather conditions outside. This paper presents a multisensor platform designed to measure the aforementioned parameters from beehives deployed in the field, and shows how the fusion of different sensor measurements may provide insights on the status of the colony, its interaction with the surrounding environment, and the influence of climatic conditions.

Acute oral and contact toxicity of new ethyl-carbamates on the mortality and acetylcholinesterase activity of honey bee (Apis mellifera)

The effects produced by the ethyl-carbamates: ethyl-4-bromophenyl carbamate (LQM 919) and ethyl-4-chlorophenyl carbamate (LQM 996) on the mortality and behavior of Apis mellifera were evaluated by the acute oral toxicity test and the acute contact toxicity test. The oral lethal dose, 50% of the ethyl-carbamates was >145.24 μg per bee, and the oral lethal dose, 50% of propoxur was 0.072 μg per bee. Therefore, according to the OECD criteria, the ethyl-carbamates were classified as relatively nontoxic orally; meanwhile, propoxur was classified as highly toxic orally. In the contact test, lethal concentrations 50% of the ethyl-carbamates were 4.83 and 2.23 μg/cm² for LQM 919 and LQM 996, respectively; therefore, they were at least 10-fold less lethal (p < 0.05) than propoxur (0.22 μg/cm²). The ethyl-carbamates reduced the activity of A. mellifera acetylcholinesterase by up to 30%. The k_i and k_d values of both ethyl-carbamates were lower (p < 0.05) than those of propoxur and indicated that they are weak inhibitors and with low affinity to A. mellifera acetylcholinesterase, which along with the absence of behavioral alterations suggests that the mortality caused by ethyl carbamates is not related to damage to the nervous system. According to these results, the evaluated ethyl-carbamates can be considered a low ecotoxic risk for A. mellifera.

Transcriptional response of honey bee (Apis mellifera) to differential nutritional status and Nosema infection

Background

Bees are confronting several environmental challenges, including the intermingled effects of malnutrition and disease. Intuitively, pollen is the healthiest nutritional choice, however, commercial substitutes, such as Bee-Pro and MegaBee, are widely used. Herein we examined how feeding natural and artificial diets shapes transcription in the abdomen of the honey bee, and how transcription shifts in combination with Nosema parasitism.

Results

Gene ontology enrichment revealed that, compared with poor diet (carbohydrates [C]), bees fed pollen (P > C), Bee-Pro (B > C), and MegaBee (M > C) showed a broad upregulation of metabolic processes, especially lipids; however, pollen feeding promoted more functions, and superior proteolysis. The superiority of the pollen diet was also evident through the remarkable overexpression of vitellogenin in bees fed pollen instead of MegaBee or Bee-Pro. Upregulation of bioprocesses under carbohydrates feeding compared to pollen (C > P) provided a clear poor nutritional status, uncovering stark expression changes that were slight or absent relatively to Bee-Pro (C > B) or MegaBee (C > M). Poor diet feeding (C > P) induced starvation response genes and hippo signaling pathway, while it repressed growth through different mechanisms. Carbohydrate feeding (C > P) also elicited ‘adult behavior’, and developmental processes suggesting transition to foraging. Finally, it altered the ‘circadian rhythm’, reflecting the role of this mechanism in the adaptation to nutritional stress in mammals.

Nosema-infected bees fed pollen compared to carbohydrates (PN > CN) upheld certain bioprocesses of uninfected bees (P > C). Poor nutritional status was more apparent against pollen (CN > PN) than Bee-Pro (CN > BN) or MegaBee (CN > MN). Nosema accentuated the effects of malnutrition since more starvation-response genes and stress response mechanisms were upregulated in CN > PN compared to C > P. The bioprocess ‘Macromolecular complex assembly’ was also enriched in CN > PN, and involved genes associated with human HIV and/or influenza, thus providing potential candidates for bee-Nosema interactions. Finally, the enzyme Duox emerged as essential for guts defense in bees, similarly to Drosophila.

Conclusions

These results provide evidence of the superior nutritional status of bees fed pollen instead of artificial substitutes in terms of overall health, even in the presence of a pathogen.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5007-0) contains supplementary material, which is available to authorized users.

The exposure of honey bees (Apis mellifera; Hymenoptera: Apidae) to pesticides: Room for improvement in research

Losses of honey bees have been repeatedly reported from many places worldwide. The widespread use of synthetic pesticides has led to concerns regarding their environmental fate and their effects on pollinators. Based on a standardised review, we report the use of a wide variety of honey bee matrices and sampling methods in the scientific papers studying pesticide exposure. Matrices such as beeswax and beebread were very little analysed despite their capacities for long-term pesticide storage. Moreover, bioavailability and transfer between in-hive matrices were poorly understood and explored. Many pesticides were studied but interactions between molecules or with other stressors were lacking. Sampling methods, targeted matrices and units of measure should have been, to some extent, standardised between publications to ease comparison and cross checking. Data on honey bee exposure to pesticides would have also benefit from the use of commercial formulations in experiments instead of active ingredients, with a special assessment of co-formulants (quantitative exposure and effects). Finally, the air matrix within the colony must be explored in order to complete current knowledge on honey bee pesticide exposure.

Assessment of chronic sublethal effects of imidacloprid on honey bee colony health

Here we present results of a three-year study to determine the fate of imidacloprid residues in hive matrices and to assess chronic sublethal effects on whole honey bee colonies fed supplemental pollen diet containing imidacloprid at 5, 20 and 100 μg/kg over multiple brood cycles. Various endpoints of colony performance and foraging behavior were measured during and after exposure, including winter survival. Imidacloprid residues became diluted or non-detectable within colonies due to the processing of beebread and honey and the rapid metabolism of the chemical. Imidacloprid exposure doses up to 100 μg/kg had no significant effects on foraging activity or other colony performance indicators during and shortly after exposure. Diseases and pest species did not affect colony health but infestations of Varroa mites were significantly higher in exposed colonies. Honey stores indicated that exposed colonies may have avoided the contaminated food. Imidacloprid dose effects was delayed later in the summer, when colonies exposed to 20 and 100 μg/kg experienced higher rates of queen failure and broodless periods, which led to weaker colonies going into the winter. Pooled over two years, winter survival of colonies averaged 85.7, 72.4, 61.2 and 59.2% in the control, 5, 20 and 100 μg/kg treatment groups, respectively. Analysis of colony survival data showed a significant dose effect, and all contrast tests comparing survival between control and treatment groups were significant, except for colonies exposed to 5 μg/kg. Given the weight of evidence, chronic exposure to imidacloprid at the higher range of field doses (20 to 100 μg/kg) in pollen of certain treated crops could cause negative impacts on honey bee colony health and reduced overwintering success, but the most likely encountered high range of field doses relevant for seed-treated crops (5 μg/kg) had negligible effects on colony health and are unlikely a sole cause of colony declines.

Holistic screening of collapsing honey bee colonies in Spain: a case study

Background

Here we present a holistic screening of collapsing colonies from three professional apiaries in Spain. Colonies with typical honey bee depopulation symptoms were selected for multiple possible factors to reveal the causes of collapse.

Results

Omnipresent were Nosema ceranae and Lake Sinai Virus. Moderate prevalences were found for Black Queen Cell Virus and trypanosomatids, whereas Deformed Wing Virus, Aphid Lethal Paralysis Virus strain Brookings and neogregarines were rarely detected. Other viruses, Nosema apis, Acarapis woodi and Varroa destructor were not detected. Palinologic study of pollen demonstrated that all colonies were foraging on wild vegetation. Consequently, the pesticide residue analysis was negative for neonicotinoids. The genetic analysis of trypanosomatids GAPDH gene, showed that there is a large genetic distance between Crithidia mellificae ATCC30254, an authenticated cell strain since 1974, and the rest of the presumed C. mellificae sequences obtained in our study or published. This means that the latter group corresponds to a highly differentiated taxon that should be renamed accordingly.

Conclusion

The results of this study demonstrate that the drivers of colony collapse may differ between geographic regions with different environmental conditions, or with different beekeeping and agricultural practices. The role of other pathogens in colony collapse has to bee studied in future, especially trypanosomatids and neogregarines. Beside their pathological effect on honey bees, classification and taxonomy of these protozoan parasites should also be clarified.

Electronic supplementary material

The online version of this article (doi:10.1186/1756-0500-7-649) contains supplementary material, which is available to authorized users.

Evaluation of the distribution and impacts of parasites, pathogens, and pesticides on honey bee (Apis mellifera) populations in East Africa

In East Africa, honey bees (Apis mellifera) provide critical pollination services and income for small-holder farmers and rural families. While honey bee populations in North America and Europe are in decline, little is known about the status of honey bee populations in Africa. We initiated a nationwide survey encompassing 24 locations across Kenya in 2010 to evaluate the numbers and sizes of honey bee colonies, assess the presence of parasites (Varroa mites and Nosema microsporidia) and viruses, identify and quantify pesticide contaminants in hives, and assay for levels of hygienic behavior. Varroa mites were present throughout Kenya, except in the remote north. Levels of Varroa were positively correlated with elevation, suggesting that environmental factors may play a role in honey bee host-parasite interactions. Levels of Varroa were negatively correlated with levels of hygienic behavior: however, while Varroa infestation dramatically reduces honey bee colony survival in the US and Europe, in Kenya Varroa presence alone does not appear to impact colony size. Nosema apis was found at three sites along the coast and one interior site. Only a small number of pesticides at low concentrations were found. Of the seven common US/European honey bee viruses, only three were identified but, like Varroa, were absent from northern Kenya. The number of viruses present was positively correlated with Varroa levels, but was not correlated with colony size or hygienic behavior. Our results suggest that Varroa, the three viruses, and Nosema have been relatively recently introduced into Kenya, but these factors do not yet appear to be impacting Kenyan bee populations. Thus chemical control for Varroa and Nosema are not necessary for Kenyan bees at this time. This study provides baseline data for future analyses of the possible mechanisms underlying resistance to and the long-term impacts of these factors on African bee populations.

Biphasic responses of the honeybee heart to nanomolar concentrations of amitraz

Amitraz is a pesticide targeting the octopaminergic receptors. In a previous study, octopamine, a biogenic amine, was found to induce a biphasic effect on the honeybee heart, inhibition at low concentrations and excitation at high concentrations. Furthermore, the honeybee heart was found to be far more sensitive to octopamine compared to other insect hearts. The objective of the present study was to investigate the effects of amitraz on the electrical and mechanical properties of the honeybee heart ex vivo and on the heart rate in vivo. In ex vivo conditions, amitraz at 10(-12) M caused a significant inhibition in the mechanical (p<0.05, n=4) and electrical properties (p<0.05, n=4). Higher concentrations such as 10(-9) and 10(-6) M induced a biphasic effect, with total inhibition for 7.86±1.26 min (n=7), followed by strong excitation of spontaneously-generated contractions (n=7). The initial elimination of heart activity was caused by strong hyperpolarization, while the subsequent excitation was caused by a depolarization in the membrane potential of pacemaker cells at 10(-9) M (n=8). In the in vivo experiments, abdominal injection or oral application of 0.20 ng of amitraz per bee induced a persistent increase of 134.28±4.07% (p<0.05, n=4) in the frequency of the cardiac action potentials. The above responses clearly show that the heart of the honeybee is extremely vulnerable to amitraz, which is nevertheless still used inside beehives, ostensibly to "protect" the honeybees against their main parasite, Varroa destructor.

Direct effect of acaricides on pathogen loads and gene expression levels in honey bees Apis mellifera

The effect of using acaricides to control varroa mites has long been a concern to the beekeeping industry due to unintended negative impacts on honey bee health. Irregular ontogenesis, suppression of immune defenses, and impairment of normal behavior have been linked to pesticide use. External stressors, including parasites and the pathogens they vector, can confound studies on the effects of pesticides on the metabolism of honey bees. This is the case of Varroa destructor, a mite that negatively affects honey bee health on many levels, from direct parasitism, which diminishes honey bee productivity, to vectoring and/or activating other pathogens, including many viruses. Here we present a gene expression profile comprising genes acting on diverse metabolic levels (detoxification, immunity, and development) in a honey bee population that lacks the influence of varroa mites. We present data for hives treated with five different acaricides; Apiguard (thymol), Apistan (tau-fluvalinate), Checkmite (coumaphos), Miteaway (formic acid) and ApiVar (amitraz). The results indicate that thymol, coumaphos and formic acid are able to alter some metabolic responses. These include detoxification gene expression pathways, components of the immune system responsible for cellular response and the c-Jun amino-terminal kinase (JNK) pathway, and developmental genes. These could potentially interfere with the health of individual honey bees and entire colonies.

An exposure study to assess the potential impact of fipronil in treated sunflower seeds on honey bee colony losses in Spain

BACKGROUND

There is great concern about the high losses and strong depopulation of honey bee colonies in some areas of Spain. Some beekeepers have suggested that sunflower seeds treated with the insecticide fipronil could be an important factor in causing those losses. Therefore, an in-depth field study has been carried out in two regions of Spain where sunflower production is intense (Cuenca and Andalucía) and where, for some crops and varieties, fipronil has been used as seed insecticide.

RESULTS

Samples of adult bees and pollen were analysed for bee pathogens and pesticide residues respectively. Neither fipronil residues nor its metabolites were detected in any of the samples analysed, indicating that short-term or chronic exposure of bees to fipronil and/or its metabolites can be ruled out in the apiaries surveyed. Varroa destructor and Nosema ceranae were found to be very prevalent.

CONCLUSION

The combination of the two pathogens could augment the risk of colony death in infected colonies, without fipronil residues exerting a significant effect in the given field conditions. Indeed, in this study the losses observed in apiaries located close to sunflower crops were similar to those in apiaries situated in forested areas with wild vegetation.

Genetic variation and widespread dispersal of Nosema ceranae in Apis mellifera apiaries from Argentina

Using molecular techniques, we documented the presence of Nosema ceranae in honeybees (Apis mellífera) from Argentina. Samples were collected from A. mellifera colonies in 38 districts of Buenos Aires province, Argentina. Molecular characterization was achieved with a multiplex PCR-based method, which allows parallel diagnosis of N. ceranae and N. osema apis. N. ceranae was identified in all the samples analyzed. Moreover, coinfections with N. apis were detected in Balcarce and Maipú districts. We identified three rRNA sequence variants of N. ceranae, which may represent diverse sources of bee importation. The results suggest that N. ceranae is widely distributed in Argentina and that the genetic variation observed between the different isolates could be related with the difference in the symptomatology found previously by our work group. Our results highlight the need to re-assess the health protocols currently in force so that they recognize N. ceranae as the main causal agent of Nosemosis in this country.

A preliminary study of the epidemiological factors related to honey bee colony loss in Spain

In recent years, a worldwide decline in the Apis mellifera populations has been detected in many regions, including Spain. This decline is thought to be related to the effects of pathogens or pesticides, although to what extent these factors are implicated is still not clear. In this study, we estimated the prevalence of honey bee colony depopulation symptoms in a random selected sample (n = 61) and we explored the implication of different pathogens, pesticides and the flora visited in the area under study. The prevalence of colony depopulation symptoms in the professional apiaries studied was 67.2% [95% confidence interval (CI) = 54.6-79.8; P < 0.0001]. The most prevalent pathogen found in the worker honey bee samples was Nosema ceranae[65.6%; 95% CI = 52.8-78.3; P < 0.0001], followed by Varroa destructor[32.7%; 95% CI = 20.2-45.4; P < 0.0001] and 97.5% of the colonies infected by N. ceranae were unhealthy (depopulated). Co-infection by V. destructor and N. ceranae was evident in 22.9% (95% CI = 11.6-34.3; P < 0.0001) of the samples and only in unhealthy colonies. Of the 40 pesticides studied, only nine were detected in 49% of the stored pollen samples analysed. Fipronil was detected in only three of 61 stored pollen samples and imidacloprid was not detected in any. Acaricides like fluvalinate, and chlorfenvinphos used to control Varroa mite were the most predominant residues in the stored pollen, probably as a result of their application in homemade formulae. None of the pesticides identified were statistically associated to colony depopulated. This preliminary study of epidemiological factors suggests that N. ceranae is a key factor in the colony losses detected over recent years in Spain. However, more detailed studies that permit subgroup analyses will be necessary to contrast these findings.

Interactions between Nosema microspores and a neonicotinoid weaken honeybees (Apis mellifera)

Global pollinators, like honeybees, are declining in abundance and diversity, which can adversely affect natural ecosystems and agriculture. Therefore, we tested the current hypotheses describing honeybee losses as a multifactorial syndrome, by investigating integrative effects of an infectious organism and an insecticide on honeybee health. We demonstrated that the interaction between the microsporidia Nosema and a neonicotinoid (imidacloprid) significantly weakened honeybees. In the short term, the combination of both agents caused the highest individual mortality rates and energetic stress. By quantifying the strength of immunity at both the individual and social levels, we showed that neither the haemocyte number nor the phenoloxidase activity of individuals was affected by the different treatments. However, the activity of glucose oxidase, enabling bees to sterilize colony and brood food, was significantly decreased only by the combination of both factors compared with control, Nosema or imidacloprid groups, suggesting a synergistic interaction and in the long term a higher susceptibility of the colony to pathogens. This provides the first evidences that interaction between an infectious organism and a chemical can also threaten pollinators, interactions that are widely used to eliminate insect pests in integrative pest management.

The Acute bee paralysis virus-Kashmir bee virus-Israeli acute paralysis virus complex

Acute bee paralysis virus (ABPV), Kashmir bee virus (KBV) and Israeli acute paralysis virus (IAPV) are part of a complex of closely related viruses from the Family Dicistroviridae. These viruses have a widespread prevalence in honey bee (Apis mellifera) colonies and a predominantly sub-clinical etiology that contrasts sharply with the extremely virulent pathology encountered at elevated titres, either artificially induced or encountered naturally. These viruses are frequently implicated in honey bee colony losses, especially when the colonies are infested with the parasitic mite Varroa destructor. Here we review the historical and recent literature of this virus complex, covering history and origins; the geographic, host and tissue distribution; pathology and transmission; genetics and variation; diagnostics, and discuss these within the context of the molecular and biological similarities and differences between the viruses. We also briefly discuss three recent developments relating specifically to IAPV, concerning its association with Colony Collapse Disorder, treatment of IAPV infection with siRNA and possible honey bee resistance to IAPV.

Asymmetrical coexistence of Nosema ceranae and Nosema apis in honey bees

Globalization has provided opportunities for parasites/pathogens to cross geographic boundaries and expand to new hosts. Recent studies showed that Nosema ceranae, originally considered a microsporidian parasite of Eastern honey bees, Apis cerana, is a disease agent of nosemosis in European honey bees, Apis mellifera, along with the resident species, Nosema apis. Further studies indicated that disease caused by N. ceranae in European honey bees is far more prevalent than that caused by N. apis. In order to gain more insight into the epidemiology of Nosema parasitism in honey bees, we conducted studies to investigate infection of Nosema in its original host, Eastern honey bees, using conventional PCR and duplex real time quantitative PCR methods. Our results showed that A. cerana was infected not only with N. ceranae as previously reported [Fries, I., Feng, F., Silva, A.D., Slemenda, S.B., Pieniazek, N.J., 1996. Nosema ceranae n. sp. (Microspora, Nosematidae), morphological and molecular characterization of a microsporidian parasite of the Asian honey bee Apis cerana (Hymenoptera, Apidae). Eur. J. Protistol. 32, 356-365], but also with N. apis. Both microsporidia produced single and mixed infections. Overall and at each location alone, the prevalence of N. ceranae was higher than that of N. apis. In all cases of mixed infections, the number of N. ceranae gene copies (corresponding to the parasite load) significantly out numbered those of N. apis. Phylogenetic analysis based on a variable region of small subunit ribosomal RNA (SSUrRNA) showed four distinct clades of N. apis and five clades of N. ceranae and that geographical distance does not appear to influence the genetic diversity of Nosema populations. The results from this study demonstrated that duplex real-time qPCR assay developed in this study is a valuable tool for quantitative measurement of Nosema and can be used to monitor the progression of microsprodian infections of honey bees in a timely and cost efficient manner.

Widespread dispersal of the microsporidian Nosema ceranae, an emergent pathogen of the western honey bee, Apis mellifera

The economically most important honey bee species, Apis mellifera, was formerly considered to be parasitized by one microsporidian, Nosema apis. Recently, [Higes, M., Martín, R., Meana, A., 2006. Nosema ceranae, a new microsporidian parasite in honeybees in Europe, J. Invertebr. Pathol. 92, 93-95] and [Huang, W.-F., Jiang, J.-H., Chen, Y.-W., Wang, C.-H., 2007. A Nosema ceranae isolate from the honeybee Apis mellifera. Apidologie 38, 30-37] used 16S (SSU) rRNA gene sequences to demonstrate the presence of Nosema ceranae in A. mellifera from Spain and Taiwan, respectively. We developed a rapid method to differentiate between N. apis and N. ceranae based on PCR-RFLPs of partial SSU rRNA. The reliability of the method was confirmed by sequencing 29 isolates from across the world (N =9 isolates gave N. apis RFLPs and sequences, N =20 isolates gave N. ceranae RFLPs and sequences; 100% correct classification). We then employed the method to analyze N =115 isolates from across the world. Our data, combined with N =36 additional published sequences demonstrate that (i) N. ceranae most likely jumped host to A. mellifera, probably within the last decade, (ii) that host colonies and individuals may be co-infected by both microsporidia species, and that (iii) N. ceranae is now a parasite of A. mellifera across most of the world. The rapid, long-distance dispersal of N. ceranae is likely due to transport of infected honey bees by commercial or hobbyist beekeepers. We discuss the implications of this emergent pathogen for worldwide beekeeping.

Outcome of colonization of Apis mellifera by Nosema ceranae

A multiplex PCR-based method, in which two small-subunit rRNA regions are simultaneously amplified in a single reaction, was designed for parallel detection of honeybee microsporidians (Nosema apis and Nosema ceranae). Each of two pairs of primers exclusively amplified the 16S rRNA targeted gene of a specific microsporidian. The multiplex PCR assay was useful for specific detection of the two species of microsporidians related to bee nosemosis, not only in purified spores but also in honeybee homogenates and in naturally infected bees. The multiplex PCR assay was also able to detect coinfections by the two species. Screening of bee samples from Spain, Switzerland, France, and Germany using the PCR technique revealed a greater presence of N. ceranae than of N. apis in Europe, although both species are widely distributed. From the year 2000 onward, statistically significant differences have been found in the proportions of Nosema spp. spore-positive samples collected between and within years. In the first period examined (1999 to 2002), the smallest number of samples diagnosed as Nosema positive was found during the summer months, showing clear seasonality in the diagnosis, which is characteristic of N. apis. From 2003 onward a change in the tendency resulted in an increase in Nosema-positive samples in all months until 2005, when a total absence of seasonality was detected. A significant causative association between the presence of N. ceranae and hive depopulation clearly indicates that the colonization of Apis mellifera by N. ceranae is related to bee losses.

Nosema ceranae, a new microsporidian parasite in honeybees in Europe

Twelve samples of adult honey bees from different regions of Spain from colonies with clear signs of population depletion, positive to microsporidian spores using light microscopy (1% of total positive samples analysed), were selected for molecular diagnosis. PCR specific primers for a region of the 16S rRNA gene of Microsporidia were developed and the PCR products were sequenced and compared to GenBank entries. The sequenced products of 11 out of the 12 samples were identical to the corresponding Nosema ceranae sequence. This is the first report of N. ceranae in colonies of Apis mellifera in Europe. The suggested link of the infections to clinical disease symptoms makes imperative a study of the virulence of N. ceranae in European races of honey bees.

Experimental study on the toxicity of imidacloprid given in syrup to honey bee (Apis mellifera) colonies

Two groups of eight honey bee colonies were fed with two different concentrations of imidacloprid in saccharose syrup during summer (each colony was given 1 litre of saccharose syrup containing 0.5 microg litre(-1) or 5 microg litre(-1) of imidacloprid on 13 occasions). Their development and survival were followed in parallel with control hives (unfed or fed with saccharose syrup) until the end of the following winter. The parameters followed were: adult bee activity (number of bee entering the hive and pollen carrying activity), adult bee population level, capped brood area, frequency of parasitic and other diseases, mortality, number of frames with brood after wintering and a global score of colonies after wintering. The only parameters linked to feeding with imidacloprid-supplemented saccharose syrup when compared with feeding with non-supplemented syrup were: a statistically non-significant higher activity index of adult bees, a significantly higher frequency of pollen carrying during the feeding period and a larger number of capped brood cells. When imidacloprid was no longer applied, activity and pollen carrying were re-established at a similar level for all groups. Repeated feeding with syrup supplemented with imidacloprid did not provoke any immediate or any delayed mortality before, during or following the next winter, whereas such severe effects are described by several French bee keepers as a consequence of imidacloprid use for seed dressing in neighbouring cultures. In any case, during the whole study, mortality was very low in all groups, with no difference between imidacloprid-fed and control colonies. Further research should now address several hypotheses: the troubles described by bee keepers have causes other than imidacloprid; if such troubles are really due to this insecticide, they may only be observed either when bees consume contaminated pollen, when no other sources of food are available, in the presence of synergic factors (that still need to be identified), with some particular races of bees or when colonies are not strong and healthy.