Levels Of Deformed Wing Virus Research Articles

Alcohol extract of the gypsy mushroom (Cortinarius caperatus) inhibits the development of Deformed wing virus infection in western honey bee (Apis mellifera)

Deformed wing virus (DWV) transmitted by the parasitic mite Varroa destructor is one of the most significant factors contributing to massive losses of managed colonies of western honey bee (Apis mellifera) subspecies of European origin reported worldwide in recent decades. Despite this fact, no antiviral treatment against honey bee viruses is currently available for practical applications and the level of viral infection can only be controlled indirectly by reducing the number of Varroa mites in honey bee colonies. In this study, we investigated the antiviral potential of the gypsy mushroom (Cortinarius caperatus) to reduce DWV infection in honey bees. Our results indicate that the alcohol extract of C. caperatus prevented the development of DWV infection in cage experiments as well as after direct application to honey bee colonies in a field experiment. The applied doses did not shorten the lifespan of honey bees. The reduced levels of DWV in C. caperatus-treated honey bees in cage experiments were accompanied by significant changes in the gene expression of Tep7, Bap1, and Vago. The C. caperatus treatment was not effective against the trypanosomatid Lotmaria passim. No residues of C.caperatus were found in honey harvested in the spring from colonies supplemented with the mushroom extract for their winter feeding. These findings suggest that C. caperatus alcohol extract could be a potential natural remedy to treat DWV infection in honey bees.

Genotype, but Not Climate, Affects the Resistance of Honey Bees (Apis mellifera) to Viral Infections and to the Mite Varroa destructor.

This study was conducted to analyze the effect of genotype and climate on the resistance of honey bee (Apis mellifera) colonies to parasitic and viral diseases. The prevalence and intensity of parasitism by Varroa destructor, or infection by Nosema spp., and four honey bee viruses were determined in 365 colonies of predominantly European or African ancestry (descendants of A. m. scutellata) in subtropical and temperate regions of Mexico. Varroa destructor was the most prevalent parasite (95%), whilst N. ceranae was the least prevalent parasite (15%). Deformed wing virus (DWV) and black queen cell virus (BQCV) were the only viruses detected, at frequencies of 38% and 66%, respectively. Varroa destructor was significantly more prevalent in colonies of European ancestry (p < 0.05), and the intensity of parasitism by V. destructor or infection by DWV and BQCV was also significantly higher in colonies of European descent than in African descent colonies (p < 0.01), although no genotype-parasite associations were found for N. ceranae. Additionally, significant and positive correlations were found between V. destructor and DWV levels, and the abundance of these pathogens was negatively correlated with the African ancestry of colonies (p < 0.01). However, there were no significant effects of environment on parasitism or infection intensity for the colonies of both genotypes. Therefore, it is concluded that the genotype of honey bee colonies, but not climate, influences their resistance to DWV, BQCV, and V. destructor.

Honey Bee Genetic Stock Determines Deformed Wing Virus Symptom Severity but not Viral Load or Dissemination Following Pupal Exposure.

Honey bees exposed to Varroa mites incur substantial physical damage in addition to potential exposure to vectored viruses such as Deformed wing virus (DWV) that exists as three master variants (DWV-A, DWV-B, and DWV-C) and recombinants. Although mite-resistant bees have been primarily bred to mitigate the impacts of Varroa mites, mite resistance may be associated with increased tolerance or resistance to the vectored viruses. The goal of our study is to determine if five honey bee stocks (Carniolan, Italian, Pol-Line, Russian, and Saskatraz) differ in their resistance or tolerance to DWV based on prior breeding for mite resistance. We injected white-eyed pupae with a sublethal dose (105) of DWV or exposed them to mites and then evaluated DWV levels and dissemination and morphological symptoms upon adult emergence. While we found no evidence of DWV resistance across stocks (i.e., similar rates of viral replication and dissemination), we observed that some stocks exhibited reduced symptom severity suggestive of differential tolerance. However, DWV tolerance was not consistent across mite-resistant stocks as Russian bees were most tolerant, while Pol-Line exhibited the most severe symptoms. DWV variants A and B exhibited differential dissemination patterns that interacted significantly with the treatment group but not bee stock. Furthermore, elevated DWV-B levels reduced adult emergence time, while both DWV variants were associated with symptom likelihood and severity. These data indicate that the genetic differences underlying bee resistance to Varroa mites are not necessarily correlated with DWV tolerance and may interact differentially with DWV variants, highlighting the need for further work on mechanisms of tolerance and bee stock–specific physiological interactions with pathogen variants.

Combined effects of oxalic acid sublimation and brood breaks on Varroa mite (Varroa destructor) and deformed wing virus levels in newly established honey bee (Apis mellifera) colonies

Annual losses of honey bee colonies are high in the United States, with losses often attributed to the effects of the ectoparasitic mite, Varroa destructor, and its associated viruses (e.g., Deformed Wing Virus, DWV). In the spring, beekeepers rely on package bees to replace lost colonies. However, these packages often come with high levels of mites and are treated with miticides upon installation. Oxalic acid (OA) is a popular miticide used in spring, but little is known about its long-term efficacy for mite control. On the other hand, natural behavior that helps with mite control is swarming, which results in a break in the production of brood in a colony. In this study, we investigated the effect of spring OA sublimation and summer swarming on colony health and productivity. We found that OA sublimation is an effective method to increase mite drop from the colony in the first three days after treatment. However, mite populations recovered quickly leading to high mite levels in the fall for colonies that did not swarm during the summer. OA applications had a marginally significant negative effect on honey yield. Mid-season swarming was correlated with lower levels of Varroa mites suggesting that implementing a brood break in the middle of the summer could play an important role in reducing mite populations for colonies originating from packages. However, the combination of OA applications to packages in the spring and summer brood break had a significant effect on reducing mite levels for colonies entering the winter. We conclude that treating packages with OA in the spring in combination with summer mite treatments are powerful tools for beekeepers to keep colonies with lower pest loads entering the winter.

Pupal cannibalism by worker honey bees contributes to the spread of deformed wing virus

Transmission routes impact pathogen virulence and genetics, therefore comprehensive knowledge of these routes and their contribution to pathogen circulation is essential for understanding host–pathogen interactions and designing control strategies. Deformed wing virus (DWV), a principal viral pathogen of honey bees associated with increased honey bee mortality and colony losses, became highly virulent with the spread of its vector, the ectoparasitic mite Varroa destructor. Reproduction of Varroa mites occurs in capped brood cells and mite-infested pupae from these cells usually have high levels of DWV. The removal of mite-infested pupae by worker bees, Varroa Sensitive Hygiene (VSH), leads to cannibalization of pupae with high DWV loads, thereby offering an alternative route for virus transmission. We used genetically tagged DWV to investigate virus transmission to and between worker bees following pupal cannibalisation under experimental conditions. We demonstrated that cannibalization of DWV-infected pupae resulted in high levels of this virus in worker bees and that the acquired virus was then transmitted between bees via trophallaxis, allowing circulation of Varroa-vectored DWV variants without the mites. Despite the known benefits of hygienic behaviour, it is possible that higher levels of VSH activity may result in increased transmission of DWV via cannibalism and trophallaxis.

The Role of Pathogen Dynamics and Immune Gene Expression in the Survival of Feral Honey Bees

Studies of the ecoimmunology of feral organisms can provide valuable insight into how host–pathogen dynamics change as organisms transition from human-managed conditions back into the wild. Honey bees (Apis mellifera Linnaeus) offer an ideal system to investigate these questions as colonies of these social insects often escape management and establish in the wild. While managed honey bee colonies have low probability of survival in the absence of disease treatments, feral colonies commonly survive in the wild, where pathogen pressures are expected to be higher due to the absence of disease treatments. Here, we investigate the role of pathogen infections [Deformed wing virus (DWV), Black queen cell virus (BQCV), and Nosema ceranae] and immune gene expression (defensin-1, hymenoptaecin, pgrp-lc, pgrp-s2, argonaute-2, vago) in the survival of feral and managed honey bee colonies. We surveyed a total of 25 pairs of feral and managed colonies over a 2-year period (2017–2018), recorded overwintering survival, and measured pathogen levels and immune gene expression using quantitative polymerase chain reaction (qPCR). Our results showed that feral colonies had higher levels of DWV but it was variable over time compared to managed colonies. Higher pathogen levels were associated with increased immune gene expression, with feral colonies showing higher expression in five out of the six examined immune genes for at least one sampling period. Further analysis revealed that differential expression of the genes hymenoptaecin and vago increased the odds of overwintering survival in managed and feral colonies. Our results revealed that feral colonies express immune genes at higher levels in response to high pathogen burdens, providing evidence for the role of feralization in altering pathogen landscapes and host immune responses.

Can supplementary pollen feeding reduce varroa mite and virus levels and improve honey bee colony survival?

Varroa destructor is an ectoparasitic mite of immature and adult honey bees that can transmit several single-stranded RNA viruses to its host. Varroa reproduce in brood cells, and mite populations increase as colonies produce brood in spring and summer. Mite numbers also can sharply rise, particularly in the fall, by the migration of varroa into hives on foragers. Colonies with high levels of varroa and viruses often die over the winter. Feeding colonies pollen might keep virus levels low and improve survival because of the positive effects of pollen on immunity and colony growth. We compared varroa and virus levels and overwinter survival in colonies with (fed) and without (unfed) supplemental pollen. We also measured the frequency of capturing foragers with mites (FWM) at colony entrances to determine its relationship to varroa and virus levels. Colonies fed supplemental pollen were larger than unfed colonies and survived longer. Varroa populations and levels of Deformed wing virus (DWV) rose throughout the season, and were similar between fed and unfed colonies. The growth of varroa populations was correlated with FWM in fed and unfed colonies, and significantly affected DWV levels. Increasing frequencies of FWM and the effects on varroa populations might reduce the positive influence of supplemental pollen on immune function. However, pollen feeding can stimulate colony growth and this can improve colony survival.

Interaction of Varroa destructor and Sublethal Clothianidin Doses during the Larval Stage on Subsequent Adult Honey Bee (Apis mellifera L.) Health, Cellular Immunity, Deformed Wing Virus Levels and Differential Gene Expression.

Honeybees (Apis mellifera L.) are exposed to many parasites, but little is known about interactions with abiotic stressors on their health, particularly when affected as larvae. Larvae were exposed singly and in combination to the parasitic mite Varroa destructor and three sublethal doses of the neonicotinoid insecticide clothianidin to evaluate their effects on survivorship, weight, haemocyte counts, deformed wing virus (DWV) levels and gene expression of the adult bees that subsequently developed. Clothianidin significantly reduced bee weight at the highest dose and was associated with an increase in haemocyte counts at the lowest dose, whereas V. destructor parasitism increased DWV levels, reduced bee emergence, lowered weight and reduced haemocyte counts. An interaction between the two stressors was observed for weight at emergence. Among the differentially expressed genes (DEGs), V. destructor infestation resulted in broader down-regulatory effects related to immunity that was often shared with the combined stressors, while clothianidin resulted in a broader up-regulatory effect more related to central metabolic pathways that was often shared with the combined stressors. Parasites and abiotic stressors can have complex interactions, including additive effects on reduced weight, number of up-regulated DEGs and biological pathways associated with metabolism.

Interaction of field realistic doses of clothianidin and Varroa destructor parasitism on adult honey bee (Apis mellifera L.)health and neural gene expression, and antagonistic effects on differentially expressed genes.

While many studies have examined the effects of neonicotinoid insecticides and the parasitic mite Varroa destructor on honey bees (Apis mellifera), more information on the combined effects of such stressors on gene expression, including neural related genes, and their impact on biological pathways is needed. This study analyzed the effects of field realistic concentrations of the neonicotinoid clothianidin on adult bees infested and not infested with V. destructor over 21 consecutive days and then determined bee survivorship, weight, deformed wing virus (DWV) levels and gene expression. V. destructor parasitism with or without clothianidin exposure was significantly associated with decreased survivorship, weight loss and higher DWV levels, while clothianidin exposure was only associated with higher levels of DWV. Expression analysis of the neural genes AmNlg-1, BlCh and AmAChE-2 showed that V. destructor caused a significant down-regulation of all of them, whereas clothianidin caused a significant down-regulation of only AmNrx-1 and BlCh. An interaction was only detected for AmNrx-1 expression. RNAseq analysis showed that clothianidin exposure resulted in 6.5 times more up-regulated differentially expressed genes (DEGs) than V. destructor alone and 123 times more than clothianidin combined with V. destructor. Similar results were obtained with down-regulated DEGs, except for a higher number of DEGs shared between V. destructor and the combined stressors. KEGG (Kyoto Encyclopedia of Genes and Genomes) biological pathway analysis of the DEGs showed that the stressor linked to the highest number of KEGG pathways was clothianidin, followed by V. destructor, and then considerably fewer number of KEGG pathways with the combined stressors. The reduced numbers of DEGs and KEGG pathways associated with the DEGs for the combined stressors compared to the stressors alone indicates that the interaction of the stressors is not additive or synergistic, but antagonistic. The possible implications of the antagonistic effect on the number of DEGs are discussed.

Deformed wing virus type A, a major honey bee pathogen, is vectored by the mite Varroa destructor in a non-propagative manner

Honey bees, the primary managed insect pollinator, suffer considerable losses due to Deformed wing virus (DWV), an RNA virus vectored by the mite Varroa destructor. Mite vectoring has resulted in the emergence of virulent DWV variants. The basis for such changes in DWV is poorly understood. Most importantly, it remains unclear whether replication of DWV occurs in the mite. In this study, we exposed Varroa mites to DWV type A via feeding on artificially infected honey bees. A significant, 357-fold increase in DWV load was observed in these mites after 2 days. However, after 8 additional days of passage on honey bee pupae with low viral loads, the DWV load dropped by 29-fold. This decrease significantly reduced the mites’ ability to transmit DWV to honey bees. Notably, negative-strand DWV RNA, which could indicate viral replication, was detected only in mites collected from pupae with high DWV levels but not in the passaged mites. We also found that Varroa mites contain honey bee mRNAs, consistent with the acquisition of honey bee cells which would additionally contain DWV replication complexes with negative-strand DWV RNA. We propose that transmission of DWV type A by Varroa mites occurs in a non-propagative manner.

Effects of sublethal doses of clothianidin and/or V. destructor on honey bee (Apis mellifera) self-grooming behavior and associated gene expression

Little is known about the combined effects of stressors on social immunity of honey bees (Apis mellifera) and related gene expression. The interaction between sublethal doses of a neurotoxin, clothianidin, and the ectoparasite, Varroa destructor, was examined by measuring differentially expressed genes (DEGs) in brains, deformed wing virus (DWV) and the proportion and intensity of self-grooming. Evidence for an interaction was observed between the stressors in a reduction in the proportion of intense groomers. Only the lowest dose of clothianidin alone reduced the proportion of self-groomers and increased DWV levels. V. destructor shared a higher proportion of DEGs with the combined stressors compared to clothianidin, indicating that the effects of V. destructor were more pervasive than those of clothianidin when they were combined. The number of up-regulated DEGs were reduced with the combined stressors compared to clothianidin alone, suggesting an interference with the impacts of clothianidin. Clothianidin and V. destructor affected DEGs from different biological pathways but shared impacts on pathways related to neurodegenerative disorders, like Alzheimer’s, which could be related to neurological dysfunction and may explain their negative impacts on grooming. This study shows that the combination of clothianidin and V. destructor resulted in a complex and non-additive interaction.

Direct transmission by injection affects competition among RNA viruses in honeybees.

The arrival of the ectoparasitic mite Varroa destructor on the western honeybee Apis mellifera saw a change in the diversity and prevalence of honeybee RNA viruses. One virus in particular, deformed wing virus (DWV) has become closely associated with V. destructor, leading many to conclude that V. destructor has affected viral virulence by changing the mode of transmission. While DWV is normally transmitted via feeding and faeces, V. destructor transmits viruses by direct injection. This change could have resulted in higher viral prevalence causing increased damage to the bees. Here we test the effect of a change in the mode of transmission on the composition and levels of honeybee RNA viruses in the absence of V. destructor. We find a rapid increase in levels of two viruses, sacbrood virus (SBV) and black queen cell virus (BQCV) after direct injection of viral extracts into honeybee pupae. In pupae injected with high levels of DWV extracted from symptomatic adult bees, DWV levels rapidly decline in the presence of SBV and BQCV. Further, we observe high mortality in honeybee pupae when injected with SBV and BQCV, whereas injecting pupae with high levels of DWV results in near 100% survival. Our results suggest a different explanation for the observed association between V. destructor and DWV. Instead of V. destructor causing an increase in DWV virulence, we hypothesize that direct virus inoculation, such as that mediated by a vector, quickly eliminates the most virulent honeybee viruses resulting in an association with less virulent viruses such as DWV.

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

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

Comb Irradiation Has Limited, Interactive Effects on Colony Performance or Pathogens in Bees, Varroa destructor and Wax Based on Two Honey Bee Stocks.

Parasitic mites and pathogens compromise honey bee health. Development of sustainable and integrative methods of managing these problems will minimize their detrimental impact on honey bees. Here, we aimed to determine if the combination of using mite-resistant stocks along with gamma-irradiated combs influences colony health and productivity. The major finding concerned honey bee genotype confirming that Russian honey bees are more resistant to Varroa destructor than Italian honey bees. The effect of comb irradiation was inconsistent showing a significant increase in adult bee population and amount of stored pollen in 2015, but not in 2016. The increased amount of stored pollen was probably associated with larger adult population in colonies with irradiated combs in September 2015 regardless of honey bee stock. Nevertheless, the ability of bees to collect and store more pollen in the irradiated group does not appear to compensate the negative impacts of mite parasitism on honey bees especially in the Italian bees, which consistently suffered significant colony losses during both years. Results of viral analyses of wax, newly emerged bees, and Varroa and their pupal hosts showed common detections of Deformed wing virus (DWV), Varroa destructor virus (VDV-1), Chronic bee paralysis virus (CBPV), and Black queen cell virus (BQCV). Wax samples had on average ~4 viruses or pathogens detected in both irradiated and non-irradiated combs. Although pathogen levels varied by month, some interesting effects of honey bee stock and irradiation treatment were notable, indicating how traits of mite resistance and alternative treatments may have additive effects. Further, this study indicates that wax may be a transmission route of viral infection. In addition, pupae and their infesting mites from Italian colonies exhibited higher levels of DWV than those from Russian colonies suggesting potential DWV resistance by Russian honey bees. CBPV levels were also reduced in mites from Russian colonies in general and in mites, mite-infested pupae, and newly emerged bees that were collected from irradiated combs. However, BQCV levels were not reduced by comb irradiation. Overall, the contribution of irradiating comb in improving honey bee health and colony survival appears to be subtle, but may be useful as part of an integrated pest management strategy with the addition of using mite-resistant stocks.

Comparative Flight Activities and Pathogen Load of Two Stocks of Honey Bees Reared in Gamma-Irradiated Combs.

Gamma irradiation is known to inactivate various pathogens that negatively affect honey bee health. Bee pathogens, such as Deformed wing virus (DWV) and Nosema spp., have a deleterious impact on foraging activities and bee survival, and have been detected in combs. In this study, we assessed the effects of gamma irradiation on the flight activities, pathogen load, and survival of two honey bee stocks that were reared in irradiated and non-irradiated combs. Overall, bee genotype influenced the average number of daily flights, the total number of foraging flights, and total flight duration, in which the Russian honey bees outperformed the Italian honey bees. Exposing combs to gamma irradiation only affected the age at first flight, with worker bees that were reared in non-irradiated combs foraging prematurely compared to those reared in irradiated combs. Precocious foraging may be associated with the higher levels of DWV in bees reared in non-irradiated combs and also with the lower amount of pollen stores in colonies that used non-irradiated combs. These data suggest that gamma irradiation of combs can help minimize the negative impact of DWV in honey bees. Since colonies with irradiated combs stored more pollen than those with non-irradiated combs, crop pollination efficiency may be further improved when mite-resistant stocks are used, since they performed more flights and had longer flight durations.

Responses of Varroa-resistant honey bees (Apis mellifera L.) to Deformed wingvirus

The negative impact of Deformed wing virus (DWV) on European honey bees Apis mellifera is magnified by Varroa destructor parasitism. This study compared the responses of two Varroa-resistant honey bee stocks, pure Russian honey bees (RHB) and out-crossed Varroa Sensitive Hygienic bees, Pol-line (POL) to DWV infection to that of Varroa- susceptible stock, Italian honey bees (IHB). Two-day-old larvae were fed with DWV lysate in different concentrations: undiluted DWV lysate (D1), D1:100, and D1:1000. The unfed larvae served as negative control. Combs containing test larvae were exposed to a common environment during their development using host colonies. Our results showed that only POL displayed variation in DWV levels when fed different DWV concentrations. POL fed highest concentration of DWV inoculum had the highest increase in DWV level than those fed low concentrations and unfed POL. This high increase in DWV level probably contributed to the decrease in the survival and median longevity (LT50) of D1-fed POL. Weights of newly eclosed D1-fed POL were similar to those of the two controls and DWV-fed bees. However, within IHB, D1-fed bees showed significant reductions in weight, days of survival and LT50. Regardless of the concentrations of DWV inoculum, the DWV levels were similarly low within RHB; adult bees had similar weights. Overall, larvae fed D1 had the highest rate of wing deformation. POL and RHB had numerically lower proportions of bees with deformed wings. This study suggests that RHB showed some degree of resistant to DWV as shown by no reduction on weight and numerically lower proportion of wing deformity when compared with the other bee stocks.

The ectoparasitic mite Tropilaelaps mercedesae reduces western honey bee, Apis mellifera, longevity and emergence weight, and promotes Deformed wing virus infections

Historically an ectoparasite of the native Giant honey bee Apis dorsata, the mite Tropilaelaps mercedesae has switched hosts to the introduced western honey bee Apis mellifera throughout much of Asia. Few data regarding lethal and sub-lethal effects of T. mercedesae on A. mellifera exist, despite its similarity to the devastating mite Varroa destructor. Here we artificially infested worker brood of A. mellifera with T. mercedesae to investigate lethal (longevity) and sub-lethal (emergence weight, Deformed wing virus (DWV) levels and clinical symptoms of DWV) effects of the mite on its new host. The data show that T. mercedesae infestation significantly reduced host longevity and emergence weight, and promoted both DWV levels and associated clinical symptoms. Our results suggest that T. mercedesae is a potentially important parasite to the economically important A. mellifera honey bee.

The Iflaviruses Sacbrood virus and Deformed wing virus evoke different transcriptional responses in the honeybee which may facilitate their horizontal or vertical transmission.

Sacbrood virus (SBV) and Deformed wing virus (DWV) are evolutionarily related positive-strand RNA viruses, members of the Iflavirus group. They both infect the honeybee Apis mellifera but have strikingly different levels of virulence when transmitted orally. Honeybee larvae orally infected with SBV usually accumulate high levels of the virus, which halts larval development and causes insect death. In contrast, oral DWV infection at the larval stage usually causes asymptomatic infection with low levels of the virus, although high doses of ingested DWV could lead to DWV replicating to high levels. We investigated effects of DWV and SBV infection on the transcriptome of honeybee larvae and pupae using global RNA-Seq and real-time PCR analysis. This showed that high levels of SBV replication resulted in down-regulation of the genes involved in cuticle and muscle development, together with changes in expression of putative immune-related genes. In particular, honeybee larvae with high levels of SBV replication, with and without high levels of DWV replication, showed concerted up-regulated expression of antimicrobial peptides (AMPs), and down-regulated expression of the prophenoloxidase activating enzyme (PPAE) together with up-regulation of the expression of a putative serpin, which could lead to the suppression of the melanisation pathway. The effects of high SBV levels on expression of these immune genes were unlikely to be a consequence of SBV-induced developmental changes, because similar effects were observed in honeybee pupae infected by injection. In the orally infected larvae with high levels of DWV replication alone we observed no changes of AMPs or of gene expression in the melanisation pathway. In the injected pupae, high levels of DWV alone did not alter expression of the tested melanisation pathway genes, but resulted in up-regulation of the AMPs, which could be attributed to the effect of DWV on the regulation of AMP expression in response to wounding. We propose that the difference in expression of the honeybee immune genes induced by SBV and DWV may be an evolutionary adaptation to the different predominant transmission routes used by these viruses.

Varroa destructor (Mesostigmata: Varroidae) Parasitism and Climate Differentially Influence the Prevalence, Levels, and Overt Infections of Deformed Wing Virus in Honey Bees (Hymenoptera: Apidae).

The prevalence and loads of deformed wing virus (DWV) between honey bee (Apis mellifera L.) colonies from a tropical and a temperate environment were compared. The interaction between these environments and the mite Varroa destructor in relation to DWV prevalence, levels, and overt infections, was also analyzed. V. destructor rates were determined, and samples of mites, adult bees, brood parasitized with varroa mites and brood not infested by mites were analyzed. DWV was detected in 100% of the mites and its prevalence and loads in honey bees were significantly higher in colonies from the temperate climate than in colonies from the tropical climate. Significant interactions were found between climate and type of sample, with the highest levels of DWV found in varroa-parasitized brood from temperate climate colonies. Additionally, overt infections were observed only in the temperate climate. Varroa parasitism and DWV loads in bees from colonies with overt infections were significantly higher than in bees from colonies with covert infections. These results suggest that interactions between climate, V. destructor, and possibly other factors, may play a significant role in the prevalence and levels of DWV in honey bee colonies, as well as in the development of overt infections. Several hypotheses are discussed to explain these results.

Virus Status, Varroa Levels, and Survival of 20 Managed Honey Bee Colonies Monitored in Luxembourg Between the Summer of 2011 and the Spring of 2013

Abstract Twenty managed honey bee colonies, split between 5 apiaries with 4 hives each, were monitored between the summer of 2011 and spring of 2013. Living bees were sampled in July 2011, July 2012, and August 2012. Twenty-five, medium-aged bees, free of varroa mites, were pooled per colony and date, to form one sample. Unlike in France and Belgium, Chronic Bee Paralysis Virus (CBPV) has not been found in Luxembourg. Slow Bee Paralysis Virus (SBPV) and Israeli Acute Paralysis Virus (IAPV) levels were below detection limits. Traces of Kashmir Bee Virus (KBV) were amplified. Black Queen Cell Virus (BQCV), Varroa destructor Virus-1 (VDV-1), and SacBrood Virus (SBV) were detected in all samples and are reported from Luxembourg for the first time. Varroa destructor Macula- Like Virus (VdMLV), Deformed Wing Virus (DWV), and Acute Bee Paralysis Virus (ABPV) were detected at all locations, and in most but not all samples. There was a significant increase in VDV-1 and DWV levels within the observation period. A principal component analysis was unable to separate the bees of colonies that survived the following winter from bees that died, based on their virus contents in summer. The number of dead varroa mites found below colonies was elevated in colonies that died in the following winter. Significant positive relationships were found between the log-transformed virus levels of the bees and the log-transformed number of mites found below the colonies per week, for VDV-1 and DWV. Sacbrood virus levels were independent of varroa levels, suggesting a neutral or competitive relationship between this virus and varroa.