Longitudinal analysis on parasite diversity in honeybee colonies: new taxa, high frequency of mixed infections and seasonal patterns of variation

Current status of Nosema spp. infection cases in apis mellifera in eurasian countries and Ptp3 gene haplotypes in the Republic of Tatarstan, Russia

The current status of Nosema spp. infections in A. mellifera throughout Eurasia was characterized using electronic databases. Although N. ceranae was predominantly detected in southwestern and south-central regions and N. apis in northwestern and north-central areas, most studies reported the occurrence of both species in Eurasia. In addition, the occurrence of Nosema spp. and Ptp3 gene haplotypes was investigated in the Republic of Tatarstan, Russia. Most of the examined honey bees were infected with both N. apis and N. ceranae. N. apis and N. ceranae isolates were either heterozygous or belonged to different strains and showed infection with more than one strain. New haplotypes were found for N. apis and N. ceranae in the Republic of Tatarstan, Russia. This study expands the data regarding existing haplotypes of Nosema species: there are currently 9 shared and 56 unique Ptp3 nucleotide sequence haplotypes of N. ceranae, and 2 shared and 7 unique haplotypes of N. apis, respectively.

A tale of two parasites: Responses of honey bees infected with Nosema ceranae and Lotmaria passim

Nosema ceranae and Lotmaria passim are two commonly encountered digestive tract parasites of the honey bee that have been associated with colony losses in Canada, the United States, and Europe. Though honey bees can be co-infected with these parasites, we still lack basic information regarding how they impact bee health at the individual and colony level. Using locally-isolated parasite strains, we investigated the effect of single and co-infections of these parasites on individual honey bee survival, and their responsiveness to sucrose. Results showed that a single N. ceranae infection is more virulent than both single L. passim infections and co-infections. Honey bees singly infected with N. ceranae reached < 50% survival eight days earlier than those inoculated with L. passim alone, and four days earlier than those inoculated with both parasites. Honey bees infected with either one, or both, parasites had increased responsiveness to sucrose compared to uninfected bees, which could correspond to higher levels of hunger and increased energetic stress. Together, these findings suggest that N. ceranae and L. passim pose threats to bee health, and that the beekeeping industry should monitor for both parasites in an effort correlate pathogen status with changes in colony-level productivity and survival.

Frequent Parasitism of Apis mellifera by Trypanosomatids in Geographically Isolated Areas with Restricted Beekeeping Movements

Trypanosomatids form a group of high prevalence protozoa that parasitise honey bees, with Lotmaria passim as the predominant species worldwide. However, the knowledge about the ecology of trypanosomatids in isolated areas is limited. The Portuguese archipelagos of Madeira and Azores provide an interesting setting to investigate these parasites because of their geographic isolation, and because they harbour honey bee populations devoid of two major enemies: Varroa destructor and Nosema ceranae. Hence, a total of 661 honey bee colonies from Madeira and the Azores were analysed using different molecular techniques, through which we found a high prevalence of trypanosomatids despite the isolation of these islands. L. passim was the predominant species and, in most colonies, was the only one found, even on islands free of V. destructor and/or N. ceranae with severe restrictions on colony movements to prevent the spread of them. However, islands with V. destructor had a significantly higher prevalence of L. passim and, conversely, islands with N. ceranae did not shown any significant correlation with the trypanosomatid. Crithidia bombi was detected in Madeira and on three islands of the Azores, almost always coincident with L. passim. By contrast, Crithidia mellificae was not detected in any sample. A high-throughput sequencing analysis distinguished two main haplotypes of L. passim, which accounted for 98% of the total sequence reads. This work suggests that L. passim and C. bombi are parasites that have been associated with honey bees predating the spread of V. destructor and N. ceranae.

Trypanosomatids in honey bee colonies in Spain: A new specific qPCR method for specific quantification of Lotmaria passim, Crithidia mellificae and Crithidia bombi

Bee trypanosomatids have not been widely studied due to the original belief that these organisms were not pathogenic to honey bees. However, trypanosomatids have been linked to increased winter mortality in honey bee colonies in recent years and it has been shown that these pathogens can shorten a honey bee worker's lifespan in laboratory conditions. These studies found that this mortality corresponded to dose-dependent infection. Although Lotmaria passim is the most prevalent species worldwide, the natural load in colonies remains poorly investigated. Here we describe a new highly specific and sensitive qPCR method that allows the differentiation and quantification of the parasitic load of each of the three most common trypanosomatid species described to date in honey bee colonies: L. passim, Crithidia mellificae, and Crithidia bombi. We have used this new method to analyze honey bee colonies in central Spain and confirm that L. passim is the most common species and the one with higher parasitic loads in the colonies, which increased over the years, being higher in spring than in autumn. Crithidia mellificae was present along the study, with the highest prevalence in autumn 2019 and lately it was only found in non-quantifiable loads. Crithidia bombi was not detected in any of the colonies analyzed.

RNA viruses of Crithidia bombi, a parasite of bumblebees

Leishbuviridae (Bunyavirales) are a diverse monophyletic group of negative-sense single-stranded RNA virus infecting parasitic flagellates of the family Trypanosomatidae. The presence of RNA viruses in trypanosomatids can influence the virulence of the latter. Here, we performed a screening for viruses in Crithidia bombi - a common parasite of important pollinators Bombus spp. (bumblebees) that negatively affects its host in stressful conditions. The majority (8/10) of C. bombi isolates collected in Europe and North America were positive for a virus that we named Crithidia bombi leishbuvirus 1 with high conservation of amino acid sequences between isolates. The results of our comparative phylogenetic analyses of the trypanosomatids and their viruses suggest that the high mobility of bumblebees and frequent coinfections by different strains of C. bombi determine an extensive viral exchange between the latter.

Bee Trypanosomatids: First Steps in the Analysis of the Genetic Variation and Population Structure of Lotmaria passim, Crithidia bombi and Crithidia mellificae

Trypanosomatids are among the most prevalent parasites in bees but, despite the fact that their impact on the colonies can be quite important and that their infectivity may potentially depend on their genotypes, little is known about the population diversity of these pathogens. Here we cloned and sequenced three non-repetitive single copy loci (DNA topoisomerase II, glyceraldehyde-3-phosphate dehydrogenase and RNA polymerase II large subunit, RPB1) to produce new genetic data from Crithidia bombi, C. mellificae and Lotmaria passim isolated from honeybees and bumblebees. These were analysed by applying population genetic tools in order to quantify and compare their variability within and between species, and to obtain information on their demography and population structure. The general pattern for the three species was that (1) they were subject to the action of purifying selection on nonsynonymous variants, (2) the levels of within species diversity were similar irrespective of the host, (3) there was evidence of recombination among haplotypes and (4) they showed no haplotype structuring according to the host. C. bombi exhibited the lowest levels of synonymous variation (π_S= 0.06 ± 0.04 %) - and a mutation frequency distribution compatible with a population expansion after a bottleneck - that contrasted with the extensive polymorphism displayed by C. mellificae (π_S= 2.24 ± 1.00 %), which likely has a more ancient origin. L. passim showed intermediate values (π_S= 0.40 ± 0.28 %) and an excess of variants a low frequencies probably linked to the spread of this species to new geographical areas.

Antiparasitic effects of three floral volatiles on trypanosomatid infection in honey bees

Trypanosomatid gut parasites are common in pollinators and costly for social bees. The recently described honey bee trypanosomatid Lotmaria passim is widespread, abundant, and correlated with colony losses in some studies. The potential for amelioration of infection by antimicrobial plant compounds has been thoroughly studied for closely related trypanosomatids of humans and is an area of active research in bumble bees, but remains relatively unexplored in honey bees. We recently identified several floral volatiles that inhibited growth of L. passim in vitro. Here, we tested the dose-dependent effects of four such compounds on infection, mortality, and food consumption in parasite-inoculated honey bees. We found that diets containing the monoterpenoid carvacrol and the phenylpropanoids cinnamaldehyde and eugenol at >10-fold the inhibitory concentrations for cell cultures reduced infection, with parasite numbers decreased by >90% for carvacrol and cinnamaldehyde and >99% for eugenol; effects of the carvacrol isomer thymol were non-significant. However, both carvacrol and eugenol also reduced bee survival, whereas parasite inoculation did not, indicating costs of phytochemical exposure that could exceed those of infection itself. To our knowledge, this is the first controlled screening of phytochemicals for effects on honey bee trypanosomatid infection, identifying potential treatments for managed bees afflicted with a newly characterized, cosmopolitan intestinal parasite.

Detection of Lotmaria passim and Crithidia mellificae in Selected Bumblebee Species

Bumblebees (Bombus spp.) are an essential element of the ecosystem and the global economy. They are valued pollinators in many countries around the word. Unfortunately, there has been a decline in the bumblebee population, which is attributed to, among others, pathogens and reduced access to food due to the loss of natural nesting sites. Lotmaria passim and Crithidia mellificae, protozoan pathogens of the family Trypanosomatidae, commonly infect bumblebees, including in Poland. In this study, a Polish population of bumblebees was screened for L. passim and C. mellificae. The experiment was performed on 13 adult bumblebees belonging to 4 species: B. lapidarius, B. lucorum, B. pascuorum, and B. terrestris. Protozoa of the family Trypanosomatidae were identified by PCR. Only L. passim was identified in one B. pascuorum individual. Further research is needed to confirm the effect of concurrent pathogens on the decline of bumblebee populations.

The Haptomonad Stage of Crithidia acanthocephali in Apis mellifera Hindgut

Crithidia acanthocephali is a trypanosomatid species that was initially described in the digestive tract of Hemiptera. However, this parasite was recently detected in honey bee colonies in Spain, raising the question as to whether bees can act as true hosts for this species. To address this issue, worker bees were experimentally infected with choanomastigotes from the early stationary growth phase and after 12 days, their hindgut was extracted for analysis by light microscopy and TEM. Although no cellular lesions were observed in the honey bee’s tissue, trypanosomatids had differentiated and adopted a haptomonad morphology, transforming their flagella into an attachment pad. This structure allows the protozoa to remain attached to the gut walls via hemidesmosomes-such as junctions. The impact of this species on honey bee health, as well as the pathogenic mechanisms involved, remains unknown. Nevertheless, these results suggest that insect trypanosomatids may have a broader range of hosts than initially thought.

Molecular Detection and Differentiation of Arthropod, Fungal, Protozoan, Bacterial and Viral Pathogens of Honeybees

The honeybee Apis mellifera is highly appreciated worldwide because of its products, but also as it is a pollinator of crops and wild plants. The beehive is vulnerable to infections due to arthropods, fungi, protozoa, bacteria and/or viruses that manage to by-pass the individual and social immune mechanisms of bees. Due to the close proximity of bees in the beehive and their foraging habits, infections easily spread within and between beehives. Moreover, international trade of bees has caused the global spread of infections, several of which result in significant losses for apiculture. Only in a few cases can infections be diagnosed with the naked eye, by direct observation of the pathogen in the case of some arthropods, or by pathogen-associated distinctive traits. Development of molecular methods based on the amplification and analysis of one or more genes or genomic segments has brought significant progress to the study of bee pathogens, allowing for: (i) the precise and sensitive identification of the infectious agent; (ii) the analysis of co-infections; (iii) the description of novel species; (iv) associations between geno- and pheno-types and (v) population structure studies. Sequencing of bee pathogen genomes has allowed for the identification of new molecular targets and the development of specific genotypification strategies.

Punch in the gut: Parasite tolerance of phytochemicals reflects host diet

Gut parasites of plant-eating insects are exposed to antimicrobial phytochemicals that can reduce infection. Trypanosomatid gut parasites infect insects of diverse nutritional ecologies as well as mammals and plants, raising the question of how host diet-associated phytochemicals shape parasite evolution and host specificity. To test the hypothesis that phytochemical tolerance of trypanosomatids reflects the chemical ecology of their hosts, we compared related parasites from honey bees and mosquitoes-hosts that differ in phytochemical consumption-and contrasted our results with previous studies on phylogenetically related, human-parasitic Leishmania. We identified one bacterial and ten plant-derived substances with known antileishmanial activity that also inhibited honey bee parasites associated with colony collapse. Bee parasites exhibited greater tolerance of chrysin-a flavonoid found in nectar, pollen, and plant resin-derived propolis. In contrast, mosquito parasites were more tolerant of cinnamic acid-a product of lignin decomposition present in woody debris-rich larval habitats. Parasites from both hosts tolerated many compounds that inhibit Leishmania, hinting at possible trade-offs between phytochemical tolerance and mammalian infection. Our results implicate the phytochemistry of host diets as a potential driver of insect-trypanosomatid associations, and identify compounds that could be incorporated into colony diets or floral landscapes to ameliorate infection in bees. This article is protected by copyright. All rights reserved.

Hot and sour: parasite adaptations to honeybee body temperature and pH

Host temperature and gut chemistry can shape resistance to parasite infection. Heat and acidity can limit trypanosomatid infection in warm-blooded hosts and could shape infection resistance in insects as well. The colony-level endothermy and acidic guts of social bees provide unique opportunities to study how temperature and acidity shape insect-parasite associations. We compared temperature and pH tolerance between three trypanosomatid parasites from social bees and a related trypanosomatid from poikilothermic mosquitoes, which have alkaline guts. Relative to the mosquito parasites, all three bee parasites had higher heat tolerance that reflected body temperatures of hosts. Heat tolerance of the honeybee parasite Crithidia mellificae was exceptional for its genus, implicating honeybee endothermy as a plausible filter of parasite establishment. The lesser heat tolerance of the emerging Lotmaria passim suggests possible spillover from a less endothermic host. Whereas both honeybee parasites tolerated the acidic pH found in bee intestines, mosquito parasites tolerated the alkaline conditions found in mosquito midguts, suggesting that both gut pH and temperature could structure host-parasite specificity. Elucidating how host temperature and gut pH affect infection-and corresponding parasite adaptations to these factors-could help explain trypanosomatids' distribution among insects and invasion of mammals.

First description of Lotmaria passim and Crithidia mellificae haptomonad stages in the honeybee hindgut

The remodelling of flagella into attachment structures is a common and important event in the trypanosomatid life cycle. Lotmaria passim and Crithidia mellificae can parasitize Apis mellifera, and as a result they might have a significant impact on honeybee health. However, there are details of their life cycle and the mechanisms underlying their pathogenicity in this host that remain unclear. Here we show that both L. passim promastigotes and C. mellificae choanomastigotes differentiate into haptomonad stages covering the ileum and rectum of honeybees. These haptomonad cells remain attached to the host surface via zonular hemidesmosome-like structures, as revealed by transmission electron microscopy. This work describes for the first known time the haptomonad morphotype of these species and their hemidesmosome-like attachments in A. mellifera, a key trait used by other trypanosomatid species to proliferate in the insect host hindgut.

Identification of pathogens in the invasive hornet Vespa velutina and in native Hymenoptera (Apidae, Vespidae) from SW-Europe

Invasive species contribute to deteriorate the health of ecosystems due to their direct effects on native fauna and the local parasite-host dynamics. We studied the potential impact of the invasive hornet Vespa velutina on the European parasite-host system by comparing the patterns of diversity and abundance of pathogens (i.e. Microsporidia: Nosematidae; Euglenozoa: Trypanosomatidae and Apicomplexa: Lipotrophidae) in European V. velutina specimens with those in the native European hornet Vespa crabro, as well as other common Hymenoptera (genera Vespula, Polistes and Bombus). We show that (i) V. velutina harbours most common hymenopteran enteropathogens as well as several new parasitic taxa. (ii) Parasite diversity in V. velutina is most similar to that of V. crabro. (iii) No unambiguous evidence of pathogen release by V. velutina was detected. This evidence together with the extraordinary population densities that V. velutina reaches in Europe (around of 100,000 individuals per km² per year), mean that this invasive species could severely alter the native pathogen-host dynamics either by actively contributing to the dispersal of the parasites and/or by directly interacting with them, which could have unexpected long-term harmful consequences on the native entomofauna.

Workflow of Lotmaria passim isolation: Experimental infection with a low-passage strain causes higher honeybee mortality rates than the PRA-403 reference strain

The impact of trypanosomatid parasites on honeybee health may represent a major threat to bee colonies worldwide. However, few axenic isolates have been generated to date and with no details on cell culture passages, a parameter that could influence parasite virulence. To address this question, a trypanosomatid isolation protocol was developed and a new strain was obtained, named L. passim C1. Using experimental infection of worker honeybees, we compared the virulence and mortality rates of the ATCC PRA-403 reference strain and C1 strain, the latter showing higher virulence from 10 days post-infection onward. This study highlights the impact of cell culture passages on the pathogenicity of L. passim in honeybees, providing new evidence of its negative effects on honeybee health.

Wide diversity of parasites in Bombus terrestris (Linnaeus, 1758) revealed by a high-throughput sequencing approach

Assessing the extent of parasite diversity requires the application of appropriate molecular tools, especially given the growing evidence of multiple parasite co-occurrence. Here, we compared the performance of a next-generation sequencing technology (Ion PGM ™ System) in 12 Bombus terrestris specimens that were PCR-identified as positive for trypanosomatids (Leishmaniinae) in a previous study. These bumblebees were also screened for the occurrence of Nosematidae and Neogregarinorida parasites using both classical protocols (either specific PCR amplification or amplification with broad-range primers plus Sanger sequencing) and Ion PGM sequencing. The latter revealed higher parasite diversity within individuals, especially among Leishmaniinae (which were present as a combination of Lotmaria passim, Crithidia mellificae and Crithidia bombi), and the occurrence of taxa never reported in these hosts: Crithidia acanthocephali and a novel neogregarinorida species. Furthermore, the complementary results produced by the different sets of primers highlighted the convenience of using multiple markers to minimize the chance of some target organisms going unnoticed. Altogether, the deep sequencing methodology offered a more comprehensive way to investigate parasite diversity than the usual identification methods and provided new insights whose importance for bumblebee health should be further analysed.

Lotmaria passim (Kinetoplastea: Trypanosomatidae) in honey bees from Argentina

Lotmaria passim (Kinetoplastea) is considered the most prevalent as well as the most virulent trypanosomatid associated to the European honey bee Apis mellifera. We used qPCR to screen for the presence of this parasite in 57 samples from ten Argentinian provinces, and were able to detect its presence throughout most of the country with 41% of the samples testing positive. In a retrospective analysis, we detected L. passim in 73% of honey bee samples from 2006 showing that this flagellate has been widely present in Argentina for at least ~15 years. Additionally, three primer sets for L. passim detection were compared, with the pair that produced smallest PCR product having the best detection capability. Finally, we also found L. passim DNA in 100% (n = 6) of samples of the mite Varroa destructor. The role of this ectoparasite in the lifecycle of Lotmaria, if any, remains unrevealed.