Prevalence and Seasonal Variations of Six Bee Viruses in Apis mellifera L. and Varroa destructor Mite Populations in France

A survey of six bee viruses on a large geographic scale was undertaken by using seemingly healthy bee colonies and the PCR technique. Samples of adult bees and pupae were collected from 36 apiaries in the spring, summer, and autumn during 2002. Varroa destructor samples were collected at the end of summer following acaricide treatment. In adult bees, during the year deformed wing virus (DWV) was found at least once in 97% of the apiaries, sacbrood virus (SBV) was found in 86% of the apiaries, chronic bee paralysis virus (CBPV) was found in 28% of the apiaries, acute bee paralysis virus (ABPV) was found in 58% of the apiaries, black queen cell virus (BQCV) was found in 86% of the apiaries, and Kashmir bee virus (KBV) was found in 17% of the apiaries. For pupae, the following frequencies were obtained: DWV, 94% of the apiaries; SBV, 80% of the apiaries; CBPV, none of the apiaries; ABPV, 23% of the apiaries; BQCV, 23% of the apiaries; and KBV, 6% of the apiaries. In Varroa samples, the following four viruses were identified: DWV (100% of the apiaries), SBV (45% of the apiaries), ABPV (36% of the apiaries), and KBV (5% of the apiaries). The latter findings support the putative role of mites in transmitting these viruses. Taken together, these data indicate that bee virus infections occur persistently in bee populations despite the lack of clinical signs, suggesting that colony disease outbreaks might result from environmental factors that lead to activation of viral replication in bees.     

Effects of Imidacloprid and Varroa destructor on survival and health of European honey bees,Apis mellifera

There has been growing concern over declines in populations of honey bees and other pollinators which are a vital part to our food security. It is imperative to identify factors responsible for accelerated declines in bee populations and develop solutions for reversing bee losses. While exact causes of colony losses remain elusive, risk factors thought to play key roles are ectoparasitic mites Varroa destructor and neonicotinoid pesticides. The present study aims to investigate effects of a neonicotinoid pesticide Imidacloprid and Varroa mites individually on survivorship, growth, physiology, virus dynamics and immunity of honey bee workers. Our study provides clear evidence that the exposure to sublethal doses of Imidacloprid could exert a significantly negative effect on health and survival of honey bees. We observed a significant reduction in the titer of vitellogenin (Vg), an egg yolk precursor that regulates the honey bees development and behavior and often are linked to energy homeostasis, in bees exposed to Imidacloprid. This result indicates that sublethal exposure to neonicotinoid could lead to increased energy usage in honey bees as detoxification is a energy‐consuming metabolic process and suggests that Vg could be a useful biomarker for measuring levels of energy stress and sublethal effects of pesticides on honey bees. Measurement of the quantitative effects of different levels of Varroa mite infestation on the replication dynamic of Deformed wing virus (DWV), an RNA virus associated with Varroa infestation, and expression level of immune genes yields unique insights into how honey bees respond to stressors under laboratory conditions.     

Prospective Large-Scale Field Study Generates Predictive Model Identifying Major Contributors to Colony Losses

Over the last decade, unusually high losses of colonies have been reported by beekeepers across the USA. Multiple factors such as Varroa destructor, bee viruses, Nosema ceranae, weather, beekeeping practices, nutrition, and pesticides have been shown to contribute to colony losses. Here we describe a large-scale controlled trial, in which different bee pathogens, bee population, and weather conditions across winter were monitored at three locations across the USA. In order to minimize influence of various known contributing factors and their interaction, the hives in the study were not treated with antibiotics or miticides. Additionally, the hives were kept at one location and were not exposed to potential stress factors associated with migration. Our results show that a linear association between load of viruses (DWV or IAPV) in Varroa and bees is present at high Varroa infestation levels (>3 mites per 100 bees). The collection of comprehensive data allowed us to draw a predictive model of colony losses and to show that Varroa destructor, along with bee viruses, mainly DWV replication, contributes to approximately 70% of colony losses. This correlation further supports the claim that insufficient control of the virus-vectoring Varroa mite would result in increased hive loss. The predictive model also indicates that a single factor may not be sufficient to trigger colony losses, whereas a combination of stressors appears to impact hive health.     

Biology and control of Varroa destructor

The ectoparasitic honey bee mite Varroa destructor was originally confined to the Eastern honey bee Apis cerana. After a shift to the new host Apis mellifera during the first half of the last century, the parasite dispersed world wide and is currently considered the major threat for apiculture. The damage caused by Varroosis is thought to be a crucial driver for the periodical colony losses in Europe and the USA and regular Varroa treatments are essential in these countries. Therefore, Varroa research not only deals with a fascinating host–parasite relationship but also has a responsibility to find sustainable solutions for the beekeeping.This review provides a survey of the current knowledge in the main fields of Varroa research including the biology of the mite, damage to the host, host tolerance, tolerance breeding and Varroa treatment. We first present a general view on the functional morphology and on the biology of the Varroa mite with special emphasis on host–parasite interactions during reproduction of the female mite. The pathology section describes host damage at the individual and colony level including the problem of transmission of secondary infections by the mite. Knowledge of both the biology and the pathology of Varroa mites is essential for understanding possible tolerance mechanisms in the honey bee host. We comment on the few examples of natural tolerance in A. mellifera and evaluate recent approaches to the selection of Varroa tolerant honey bees. Finally, an extensive listing and critical evaluation of chemical and biological methods of Varroa treatments is given.This compilation of present-day knowledge on Varroa honey bee interactions emphasizes that we are still far from a solution for Varroa infestation and that, therefore, further research on mite biology, tolerance breeding, and Varroa treatment is urgently needed.     

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.     

Evidence for emerging parasites and pathogens influencing outbreaks of stress-related diseases like chalkbrood

In agriculture, honey bees play a critical role as commercial pollinators of crop monocultures which depend on insect pollination. Hence, the demise of honey bee colonies in Europe, USA, and Asia caused much concern and initiated many studies and research programmes aiming at elucidating the factors negatively affecting honey bee health and survival. Most of these studies look at individual factors related to colony losses. In contrast, we here present our data on the interaction of pathogens and parasites in honey bee colonies. We performed a longitudinal cohort study over 6 years by closely monitoring 220 honey bee colonies kept in 22 apiaries (ten randomly selected colonies per apiary). Observed winter colony losses varied between 4.8% and 22.4%; lost colonies were replaced to ensure a constant number of monitored colonies over the study period. Data on mite infestation levels, infection with viruses, Nosema apis and Nosema ceranae, and recorded outbreaks of chalkbrood were continuously collected. We now provide statistical evidence (i) that Varroa destructor infestation in summer is related to DWV infections in autumn, (ii) that V. destructor infestation in autumn is related to N. apis infection in the following spring, and most importantly (iii) that chalkbrood outbreaks in summer are related to N. ceranae infection in the preceding spring and to V. destructor infestation in the same season. These highly significant links between emerging parasites/pathogens and established pathogens need further experimental proof but they already illustrate the complexity of the host–pathogen-interactions in honey bee colonies.     

Honey bees and wild pollinators differ in their preference for and use of introduced floral resources

Introduced plants may be important foraging resources for honey bees and wild pollinators, but how often and why pollinators visit introduced plants across an entire plant community is not well understood. Understanding the importance of introduced plants for pollinators could help guide management of these plants and conservation of pollinator habitat. We assessed how floral abundance and pollinator preference influence pollinator visitation rate and diversity on 30 introduced versus 24 native plants in central New York. Honey bees visited introduced and native plants at similar rates regardless of floral abundance. In contrast, as floral abundance increased, wild pollinator visitation rate decreased more strongly for introduced plants than native plants. Introduced plants as a group and native plants as a group did not differ in bee diversity or preference, but honey bees and wild pollinators preferred different plant species. As a case study, we then focused on knapweed (Centaurea spp.), an introduced plant that was the most preferred plant by honey bees, and that beekeepers value as a late‐summer foraging resource. We compared the extent to which honey bees versus wild pollinators visited knapweed relative to coflowering plants, and we quantified knapweed pollen and nectar collection by honey bees across 22 New York apiaries. Honey bees visited knapweed more frequently than coflowering plants and at a similar rate as all wild pollinators combined. All apiaries contained knapweed pollen in nectar, 86% of apiaries contained knapweed pollen in bee bread, and knapweed was sometimes a main pollen or nectar source for honey bees in late summer. Our results suggest that because of diverging responses to floral abundance and preferences for different plants, honey bees and wild pollinators differ in their use of introduced plants. Depending on the plant and its abundance, removing an introduced plant may impact honey bees more than wild pollinators.     

The effect of the ectoparasitic mite, Varroa destructor on adult worker honeybee (Apis mellifera) emergence weights, water, protein, carbohydrate, and lipid levels

Wet weight, dry weight and water contents of emerging honeybees (Apis mellifera L. [Hymenoptera: Apidae]) infested with the ectoparasitic mite Varroa destructor (Anderson) (Acari: Varroidae) were all negatively correlated with increasing numbers of mites. It was estimated that for every female mite present during the bees' development, the host would lose three percent of its body water. Parasitised bees also emerged with lower head and abdomen concentrations of protein and with lower abdominal carbohydrate concentrations. Lipid concentrations were not detectably affected by V. destructor infestation. The losses of metabolic reserves were not, however, judged to be serious enough to be directly responsible for the high bee mortality and ultimate colony collapse that are associated with the arrival of Varroa in a hive. Some 8.5% of the emerging bees exhibited morphological deformities and deformity was positively correlated with increasing numbers of mites in brood cells. Deformed bees were, however, found in all categories of parasitosis, suggesting that other factors, such as infectious agents, may be involved. Mites that fed on either live or dead U¹⁴C- labelled bees acquired the label within 24 h and it was calculated that an adult female mite consumes 0.67 l haemolymph 24 h^–1. It was also demonstrated that ¹⁴C was transmitted to a previously non-radio-labelled bee when a mite that had been feeding on a labelled bee changed hosts. The level of transfer was above that which could have arisen through contamination of the mites' mouthparts and supports the suggestion that Varroa is an important vector of pathogens such as viruses.     

Prevalence,intensity and associated factor analysis of <Emphasis Type="Italic">Tropilaelaps</Emphasis><Emphasis Type="Italic">mercedesae</Emphasis> infesting <Emphasis Type="Italic">Apis</Emphasis><Emphasis Type="Italic">mellifera</Emphasis> in China

Tropilaelaps mercedesae is a serious ectoparasite of Apis mellifera in China. The aim of this study was to investigate the infestation rates and intensity of T. mercedesae in A. mellifera in China, and to explore the relative importance of climate, district, management practices and beekeeper characteristics that are assumed to be associated with the intensity of T. mercedesae. Of the 410 participating apiaries, 379 apiaries were included in analyses of seasonal infestation rates and 352 apiaries were included in multivariable regression analysis. The highest infestation rate (86.3%) of T. mercedesae was encountered in autumn, followed by summer (66.5%), spring (17.2%) and winter (14.8%). In autumn, 28.9% (93) of the infested apiaries were in the north (including the northeast and northwest of China), 71.1% (229) were in the central and south (including east, southeast and southwest China), and 306 apiaries (82.9%) were co-infested by both T. mercedesae and Varroa. Multivariable regression analysis showed that geographical location, season, royal jelly collection and Varroa infestation were the factors that influence the intensity of T. mercedesae. The influence of beekeeper’s education, time of beekeeping, operation size, and hive migration on the intensity of T. mercedesa was not statistically significant. This study provided information about the establishment of the linkage of the environment and the parasite and could lead to better timing and methods of control.     

Prevalence and seasonal variations of six bee viruses in Apis mellifera L. and Varroa destructor mite populations in France

A survey of six bee viruses on a large geographic scale was undertaken by using seemingly healthy bee colonies and the PCR technique. Samples of adult bees and pupae were collected from 36 apiaries in the spring, summer, and autumn during 2002. Varroa destructor samples were collected at the end of summer following acaricide treatment. In adult bees, during the year deformed wing virus (DWV) was found at least once in 97% of the apiaries, sacbrood virus (SBV) was found in 86% of the apiaries, chronic bee paralysis virus (CBPV) was found in 28% of the apiaries, acute bee paralysis virus (ABPV) was found in 58% of the apiaries, black queen cell virus (BQCV) was found in 86% of the apiaries, and Kashmir bee virus (KBV) was found in 17% of the apiaries. For pupae, the following frequencies were obtained: DWV, 94% of the apiaries; SBV, 80% of the apiaries; CBPV, none of the apiaries; ABPV, 23% of the apiaries; BQCV, 23% of the apiaries; and KBV, 6% of the apiaries. In Varroa samples, the following four viruses were identified: DWV (100% of the apiaries), SBV (45% of the apiaries), ABPV (36% of the apiaries), and KBV (5% of the apiaries). The latter findings support the putative role of mites in transmitting these viruses. Taken together, these data indicate that bee virus infections occur persistently in bee populations despite the lack of clinical signs, suggesting that colony disease outbreaks might result from environmental factors that lead to activation of viral replication in bees.     

Do competing honey bees matter? Dynamics and abundance of native bees before and after honey bee invasion

To provide replicate samples of local bee populations in a nature preserve, light traps operated continuously on Barro Colorado Island (BCI), Panama, collected bees for 17 years, including 10 years following invasion by African Apis mellifera. Honey bees appeared in light traps as the first swarms colonized the Panama Canal area. Their numbers followed seasonal trends shown in inde-pendent studies, thus indicating bee abundance and activity in a large area. No measurable population-level impact of competition between this invading honey bee and native bees, despite many demonstrations of resource competition at flower patch and colony levels, changed annual abundances of all 15 native bee species. Native bee abundance did not decrease, nor did native bees show substantial reciprocal yearly change with honey bee abundance. One strong negative correlation of bee catches with an extremely rainy year was found. However, multiple regression using rainfall and honey bee abundance as the independent variables showed that neither was responsible for bee population change over 17 years. Nearly half the native species declined during a year that displayed peak honey bee number. That competition from honey bees on an island the size of BCI was necessarily reduced below impact levels expected on the mainland is discussed using a model of resource and consumer density, foraging range, and island size.     

A gene for resistance to the Varroa mite (Acari) in honey bee (Apis mellifera) pupae

Social insect colonies possess a range of defences which protect them against highly virulent parasites and colony collapse. The host–parasite interaction between honey bees (Apis mellifera) and the mite Varroa destructor is unusual, as honey bee colonies are relatively poorly defended against this parasite. The interaction has existed since the mid‐20th Century, when Varroa switched host to parasitize A. mellifera. The combination of a virulent parasite and relatively naïve host means that, without acaricides, honey bee colonies typically die within 3 years of Varroa infestation. A consequence of acaricide use has been a reduced selective pressure for the evolution of Varroa resistance in honey bee colonies. However, in the past 20 years, several natural‐selection‐based breeding programmes have resulted in the evolution of Varroa‐resistant populations. In these populations, the inhibition of Varroa's reproduction is a common trait. Using a high‐density genome‐wide association analysis in a Varroa‐resistant honey bee population, we identify an ecdysone‐induced gene significantly linked to resistance. Ecdysone both initiates metamorphosis in insects and reproduction in Varroa. Previously, using a less dense genetic map and a quantitative trait loci analysis, we have identified Ecdysone‐related genes at resistance loci in an independently evolved resistant population. Varroa cannot biosynthesize ecdysone but can acquire it from its diet. Using qPCR, we are able to link the expression of ecdysone‐linked resistance genes to Varroa's meals and reproduction. If Varroa co‐opts pupal compounds to initiate and time its own reproduction, mutations in the host's ecdysone pathway may represent a key selection tool for honey bee resistance and breeding.     

On the Front Line: Quantitative Virus Dynamics in Honeybee (Apis mellifera L.) Colonies along a New Expansion Front of the Parasite Varroa destructor

Over the past fifty years, annual honeybee (Apis mellifera) colony losses have been steadily increasing worldwide. These losses have occurred in parallel with the global spread of the honeybee parasite Varroa destructor. Indeed, Varroa mite infestations are considered to be a key explanatory factor for the widespread increase in annual honeybee colony mortality. The host-parasite relationship between honeybees and Varroa is complicated by the mite''s close association with a range of honeybee viral pathogens. The 10-year history of the expanding front of Varroa infestation in New Zealand offered a rare opportunity to assess the dynamic quantitative and qualitative changes in honeybee viral landscapes in response to the arrival, spread and level of Varroa infestation. We studied the impact of de novo infestation of bee colonies by Varroa on the prevalence and titres of seven well-characterised honeybee viruses in both bees and mites, using a large-scale molecular ecology approach. We also examined the effect of the number of years since Varroa arrival on honeybee and mite viral titres. The dynamic shifts in the viral titres of black queen cell virus and Kashmir bee virus mirrored the patterns of change in Varroa infestation rates along the Varroa expansion front. The deformed wing virus (DWV) titres in bees continued to increase with Varroa infestation history, despite dropping infestation rates, which could be linked to increasing DWV titres in the mites. This suggests that the DWV titres in mites, perhaps boosted by virus replication, may be a major factor in maintaining the DWV epidemic after initial establishment. Both positive and negative associations were identified for several pairs of viruses, in response to the arrival of Varroa. These findings provide important new insights into the role of the parasitic mite Varroa destructor in influencing the viral landscape that affects honeybee colonies.     

Parasite Pressures on Feral Honey Bees (Apis mellifera sp.)

Feral honey bee populations have been reported to be in decline due to the spread of Varroa destructor, an ectoparasitic mite that when left uncontrolled leads to virus build-up and colony death. While pests and diseases are known causes of large-scale managed honey bee colony losses, no studies to date have considered the wider pathogen burden in feral colonies, primarily due to the difficulty in locating and sampling colonies, which often nest in inaccessible locations such as church spires and tree tops. In addition, little is known about the provenance of feral colonies and whether they represent a reservoir of Varroa tolerant material that could be used in apiculture. Samples of forager bees were collected from paired feral and managed honey bee colonies and screened for the presence of ten honey bee pathogens and pests using qPCR. Prevalence and quantity was similar between the two groups for the majority of pathogens, however feral honey bees contained a significantly higher level of deformed wing virus than managed honey bee colonies. An assessment of the honey bee race was completed for each colony using three measures of wing venation. There were no apparent differences in wing morphometry between feral and managed colonies, suggesting feral colonies could simply be escapees from the managed population. Interestingly, managed honey bee colonies not treated for Varroa showed similar, potentially lethal levels of deformed wing virus to that of feral colonies. The potential for such findings to explain the large fall in the feral population and the wider context of the importance of feral colonies as potential pathogen reservoirs is discussed.     

Activity and abundance of bumble bees near Crested Butte,Colorado: diel,seasonal, and elevation effects

1. We revisited bumble bee survey data collected by Pyke in 1974 (Pyke, Ecology, 63 , 555–573, 1982) to evaluate seasonal changes in abundances of bumble bees and their floral resources, diel patterns of bumble bee activity, and elevation effects on plant and bumble bee phenology. 2. Bumble bee abundance increased during summer as spring queens founded colonies that produced workers, followed by males and autumn queens. The number of plant species visited by bumble bees increased to a peak in midsummer, then declined. 3. The number of bumble bees recorded per person‐hour peaked later than the number of flowering plant species used by the bees. Few autumn queens were observed. 4. Despite species differences in emergence times of spring queens, there were no apparent phenological differences among species in worker abundances. 5. Because flowering commences later at higher elevation, abundances of workers and males are also shifted later; therefore elevational comparisons must be seasonally adjusted. 6. These analyses provide basic information about important pollinating insects, and permit future investigations of elevational shifts over time to be properly adjusted for phenological and elevation effects in survey data.     

Molecular Prevalence of Acarapis Mite Infestations in Honey Bees in Korea

Acarapis mites, including Acarapis woodi, Acarapis externus, and Acarapis dorsalis, are parasites of bees which can cause severe damage to the bee industry by destroying colonies and decreasing honey production. All 3 species are prevalent throughout many countries including UK, USA, Iran, Turkey, China, and Japan. Based on previous reports of Acarapis mites occurring in northeast Asia, including China and Japan, we investigated a survey of Acarapis mite infestations in honey bees in Korean apiaries. A total of 99 colonies of Apis mellifera were sampled from 5 provinces. The head and thorax of 20 bees from each colony were removed for DNA extraction. PCR assays were performed with 3 primer sets, including T, A, and K primers. Results indicated that 42.4% (42/99) of samples were Acarapis-positive by PCR assay which were sequenced to identify species. Each sequence showed 92.6-99.3% homology with reference sequences. Based on the homology, the number of colonies infected with A. dorsalis was 32 which showed the highest infection rate among the 3 species, while the number of colonies infected with A. externus and A. woodi was 9 and 1, respectively. However, none of the Acarapis mites were morphologically detected. This result could be explained that all apiaries in the survey used acaricides against bee mites such as Varroa destructor and Tropilaelaps clareae which also affect against Acarapis mites. Based on this study, it is highly probable that Acarapis mites as well as Varroa and Tropilaelaps could be prevalent in Korean apiaries.     

Oxalic acid: a prospective tool for reducing <Emphasis Type="Italic">Varroa</Emphasis> mite populations in package bees

Numerous studies have investigated using oxalic acid (OA) to control Varroa mites in honey bee colonies. In contrast, techniques for treating package bees with OA have not been investigated. The goal of this study was to develop a protocol for using OA to reduce mite infestation in package bees. We made 97 mini packages of Varroa-infested adult bees. Each package contained 1,613 ± 18 bees and 92 ± 3 mites, and represented an experimental unit. We prepared a 2.8% solution of OA by mixing 35 g OA with 1 l of sugar water (sugar:water = 1:1; w:w). Eight treatments were assigned to the packages based on previous laboratory bioassays that characterized the acute contact toxicity of OA to mites and bees. We administered the treatments by spraying the OA solution directly on the bees through the mesh screen cage using a pressurized air brush and quantified mite and bee mortality over a 10-day period. Our results support applying an optimum volume of 3.0 ml of a 2.8% OA solution per 1,000 bees to packages for effective mite control with minimal adult bee mortality. The outcome of our research provides beekeepers and package bee shippers guidance for using OA to reduce mite populations in package bees.     

Non-reproducing Varroa jacobsoni Oud. in honey bee worker cells—status of mites or effect of brood cells?

The parasitic mite Varroa jacobsoni Oud. reproduces in sealed honey bee brood cells. Within worker cells a considerable fraction of the mites do not produce offspring. It is investigated whether variation in the ratio of cells without reproduction is caused by properties of the worker brood, or by the state of the mites entering cells. Pieces of brood comb were taken from colonies of 12 different bee lines and were placed simultaneously into highly infested colonies. Non-reproduction was independent of the origin of the brood pieces, indicating a minor role of a variation due to different brood origin. Between colonies used for infestation, however, it differed considerably. A comparison of the proportion of cells without reproduction when infested by one Varroa mite or when infested by two or three Varroa mites showed, that non-reproduction was mainly related to the state of the mites entering cells, and only to a minor degree to an influence of the brood cells. A high ratio of worker cells without reproduction was consistently reported in bee lines which survive the disease without treatment, and a high level of non-reproduction is thus regarded to be a key factor in breeding bees for high Varroa tolerance. The current results indicate, that differences in this trait are only to a minor degree related to differences between bee lines in the ability of the bee brood to induce oviposition. These differences seem rather to depend on other, unknown colony factors influencing the reproductive state of Varroa when they enter cells for reproduction.     

Host brood traits,independent of adult behaviours,reduce Varroa destructor mite reproduction in resistant honeybee populations

The ectoparasitic mite Varroa destructor is an invasive species of Western honey bees (Apis mellifera) and the largest pathogenic threat to their health world-wide. Its successful invasion and expansion is related to its ability to exploit the worker brood for reproduction, which results in an exponential population growth rate in the new host. With invasion of the mite, wild honeybee populations have been nearly eradicated from Europe and North America, and the survival of managed honeybee populations relies on mite population control treatments. However, there are a few documented honeybee populations surviving extended periods without control treatments due to adapted host traits that directly impact Varroa mite fitness. The aim of this study was to investigate if Varroa mite reproductive success was affected by traits of adult bee behaviours or by traits of the worker brood, in three mite-resistant honey bee populations from Sweden, France and Norway. The mite’s reproductive success was measured and compared in broods that were either exposed to, or excluded from, adult bee access. Mite-resistant bee populations were also compared with a local mite-susceptible population, as a control group. Our results show that mite reproductive success rates and mite fecundity in the three mite-resistant populations were significantly different from the control population, with the French and Swedish populations having significantly lower reproductive rates than the Norwegian population. When comparing mite reproduction in exposed or excluded brood treatments, no differences were observed, regardless of population. This result clearly demonstrates that Varroa mite reproductive success can be suppressed by traits of the brood, independent of adult worker bees.     

Deformed wing virus associated with <Emphasis Type="Italic">Tropilaelaps mercedesae</Emphasis> infesting European honey bees (<Emphasis Type="Italic">Apis mellifera</Emphasis>)

Mites in the genus Tropilaelaps (Acari: Laelapidae) are ectoparasites of the brood of honey bees (Apis spp.). Different Tropilaelaps subspecies were originally described from Apis dorsata, but a host switch occurred to the Western honey bee, Apis mellifera, for which infestations can rapidly lead to colony death. Tropilaelaps is hence considered more dangerous to A. mellifera than the parasitic mite Varroa destructor. Honey bees are also infected by many different viruses, some of them associated with and vectored by V. destructor. In recent years, deformed wing virus (DWV) has become the most prevalent virus infection in honey bees associated with V. destructor. DWV is distributed world-wide, and found wherever the Varroa mite is found, although low levels of the virus can also be found in Varroa free colonies. The Varroa mite transmits viral particles when feeding on the haemolymph of pupae or adult bees. Both the Tropilaelaps mite and the Varroa mite feed on honey bee brood, but no observations of DWV in Tropilaelaps have so far been reported. In this study, quantitative real-time RT-PCR was used to show the presence of DWV in infested brood and Tropilaelaps mercedesae mites collected in China, and to demonstrate a close quantitative association between mite-infested pupae of A. mellifera and DWV infections. Phylogenetic analysis of the DWV sequences recovered from matching pupae and mites revealed considerable DWV sequence heterogeneity and polymorphism. These polymorphisms appeared to be associated with the individual brood cell, rather than with a particular host.