The Pathogens Spillover and Incidence Correlation in Bumblebees and Honeybees in Slovenia

Slovenia has a long tradition of beekeeping and a high density of honeybee colonies, but less is known about bumblebees and their pathogens. Therefore, a study was conducted to define the incidence and prevalence of pathogens in bumblebees and to determine whether there are links between infections in bumblebees and honeybees. In 2017 and 2018, clinically healthy workers of bumblebees (Bombus spp.) and honeybees (Apis mellifera) were collected on flowers at four different locations in Slovenia. In addition, bumblebee queens were also collected in 2018. Several pathogens were detected in the bumblebee workers using PCR and RT-PCR methods: 8.8% on acute bee paralysis virus (ABPV), 58.5% on black queen cell virus (BQCV), 6.8% on deformed wing virus (DWV), 24.5% on sacbrood bee virus (SBV), 15.6% on Lake Sinai virus (LSV), 16.3% on Nosema bombi, 8.2% on Nosema ceranae, 15.0% on Apicystis bombi and 17.0% on Crithidia bombi. In bumblebee queens, only the presence of BQCV, A. bombi and C. bombi was detected with 73.3, 26.3 and 33.3% positive samples, respectively. This study confirmed that several pathogens are regularly detected in both bumblebees and honeybees. Further studies on the pathogen transmission routes are required.

Testing the multiple stressor hypothesis: chlorothalonil exposure alters transmission potential of a bumblebee pathogen but not individual host health

Numerous threats are putting pollinator health and essential ecosystem pollination services in jeopardy. Although individual threats are widely studied, their co-occurrence may exacerbate negative effects, as posited by the multiple stressor hypothesis. A prominent branch of this hypothesis concerns pesticide–pathogen co-exposure. A landscape analysis demonstrated a positive association between local chlorothalonil fungicide use and microsporidian pathogen ( Nosema bombi ) prevalence in declining bumblebee species ( Bombus spp.), suggesting an interaction deserving further investigation. We tested the multiple stressor hypothesis with field-realistic chlorothalonil and N. bombi exposures in worker-produced B. impatiens microcolonies. Chlorothalonil was not avoided in preference assays, setting the stage for pesticide–pathogen co-exposure. However, contrary to the multiple stressor hypothesis, co-exposure did not affect survival. Bees showed surprising tolerance to Nosema infection, which was also unaffected by chlorothalonil exposure. However, previously fungicide-exposed infected bees carried more transmission-ready spores. Our use of a non-declining bumblebee and potential higher chlorothalonil exposures under some scenarios could mean stronger individual or interactive effects in certain field settings. Yet, our results alone suggest consequences of pesticide co-exposure for pathogen dynamics in host communities. This underlies the importance of considering both within- and between-host processes when addressing the multiple stressor hypothesis in relation to pathogens.

Agri-environment nectar chemistry suppresses parasite social epidemiology in an important pollinator

Emergent infectious diseases are a principal driver of biodiversity loss globally. The population and range declines of a suite of North American bumblebees, a group of important pollinators, have been linked to emergent infection with the microsporidian Nosema bombi. Previous work has shown that phytochemicals in pollen and nectar can negatively impact parasites in individual bumblebees, but how this relates to social epidemiology and by extension whether plants can be effectively used as disease management strategies remains unexplored. Here we show that caffeine, identified in the nectar of Sainfoin, a constituent of agri-environment schemes, significantly reduced N. bombi infection intensity in individual bumblebees and, for the first time, that such effects impact social epidemiology, with colonies reared from wild caught queens having lower prevalence and intensity of infection. Furthermore, infection prevalence was lower in foraging bumblebees from these colonies, suggesting a likely reduction in population-level transmission. Our results demonstrate that phytochemicals can impact pollinator disease epidemiology and that planting strategies, which increase floral abundance to support biodiversity could be co-opted as disease management strategies.

Assessment of intestinal parasites in the coexisting Bombus terrestris (Apidae) and Xylocopa augusti (Apidae) in central Chile

Bombus terrestris is a European bumblebee extensively commercialized worldwide for crop pollination. In Chile, this species was introduced in 1997 and after confinement escape, it has spread and established in several localities of central-southern Chile and in the Argentine Patagonia. The South American carpenter bee Xylocopa augusti, in turn, has been recently reported in central Chile, and as B. terrestris, this species has become increasingly common, often found in sympatry with B. terrestris in some localities. While intestinal parasites such as the flagellate trypanosome Crithidia bombi, the microsporidium Nosema bombi, and the neogregarine protozoan Apicystis bombi, show high levels of specialization on the Bombus genus, parasites often increase their host range, especially after invading novel habitats, hence creating new infection disease scenarios. In this work, we used molecular techniques to detect the presence of the intestinal pathogens of B. terrestris in coexisting X. augusti from different localities in the Metropolitan Region of Chile. Our results revealed the presence of the three pathogens in B. terrestris only, with population prevalence broadly similar to that reported in other studies. The carpenter bee X. augusti did not show evidence of any of the three parasites examined, indicating that this invader species is not recipient of any of the parasite species present in B. terrestris.

Individual and combined impacts of sulfoxaflor and Nosema bombi on bumblebee ( Bombus terrestris ) larval growth

Sulfoxaflor is a globally important novel insecticide that can have negative impacts on the reproductive output of bumblebee ( Bombus terrestris ) colonies. However, it remains unclear as to which life-history stage is critically affected by exposure. One hypothesis is that sulfoxaflor exposure early in the colony's life cycle can impair larval development, reducing the number of workers produced and ultimately lowering colony reproductive output. Here we assess the influence of sulfoxaflor exposure on bumblebee larval mortality and growth both when tested in insolation and when in combination with the common fungal parasite Nosema bombi, following a pre-registered design. We found no significant impact of sulfoxaflor (5 ppb) or N. bombi exposure (50 000 spores) on larval mortality when tested in isolation but found an additive, negative effect when larvae received both stressors in combination. Individually, sulfoxaflor and N. bombi exposure each impaired larval growth, although the impact of combined exposure fell significantly short of the predicted sum of the individual effects (i.e. they interacted antagonistically). Ultimately, our results suggest that colony-level consequences of sulfoxaflor exposure for bumblebees may be mediated through direct effects on larvae. As sulfoxaflor is licensed for use globally, our findings highlight the need to understand how novel insecticides impact non-target insects at various stages of their development.

Observations of native bumble bees inside of commercial colonies ofBombus impatiens(Hymenoptera: Apidae) and the potential for pathogen spillover

Many fruit producers use commercial colonies ofBombus impatiensCresson (Hymenoptera: Apidae) to supplement crop pollination by native bees. A small number of Newfoundland (Newfoundland and Labrador, Canada) farmers forego purchasing new colonies and, instead, purchase previously used colonies from crops in other provinces. This practice has potentially dangerous implications that may adversely affect future native bee diversity in Newfoundland. This study is the first to record the presence of native bumble bee species inside the colonies of new and pre-used commercialB. impatiensand the first to look at diseases in native bumble bees from Newfoundland. Polymerase chain reaction and taxon-specific oligonucleotides were used to screen the commercial and native bumble bee species for pathogens.Crithidia bombi(Lipa and Triggiani), Apicystis bombi(Liu, Macfarlane, and Pengelly),Nosema bombiFantham and Porter, Nosema ceranaeFrieset al., and species ofAscosphaeraOlive and Spiltoir, were detected in native bumble bees that were collected from inside the new and pre-used commercialB. impatiens.Crithidia bombi,A. bombi, andN. bombiwere also detected among native bees that were collected away from the commercial colonies.Nosema apis(Zander) andMelissococcus plutonius(White) were not detected in any of the bees tested. The mixing of native bumble bees inB. impatienscolonies increases the potential for pathogen spillover and spillback that may threaten the small and vulnerable island bee fauna.

Landscape predictors of pathogen prevalence and range contractions in US bumblebees

Several species of bumblebees have recently experienced range contractions and possible extinctions. While threats to bees are numerous, few analyses have attempted to understand the relative importance of multiple stressors. Such analyses are critical for prioritizing conservation strategies. Here, we describe a landscape analysis of factors predicted to cause bumblebee declines in the USA. We quantified 24 habitat, land-use and pesticide usage variables across 284 sampling locations, assessing which variables predicted pathogen prevalence and range contractions via machine learning model selection techniques. We found that greater usage of the fungicide chlorothalonil was the best predictor of pathogen ( Nosema bombi ) prevalence in four declining species of bumblebees. Nosema bombi has previously been found in greater prevalence in some declining US bumblebee species compared to stable species. Greater usage of total fungicides was the strongest predictor of range contractions in declining species, with bumblebees in the northern USA experiencing greater likelihood of loss from previously occupied areas. These results extend several recent laboratory and semi-field studies that have found surprising links between fungicide exposure and bee health. Specifically, our data suggest landscape-scale connections between fungicide usage, pathogen prevalence and declines of threatened and endangered bumblebees.

Short communication: First data on the prevalence and distribution of pathogens in bumblebees (Bombus terrestris and Bombus pascuorum) from Spain

Bumblebees provide pollination services not only to wildflowers but also to economically important crops. In the context of the global decline of pollinators, there is an increasing interest in determining the pathogen diversity of bumblebee species. In this work, wild bumblebees of the species Bombus terrestris and Bombus pascuorum from northern and southern Spain were molecularly screened to detect and estimate prevalence of pathogens. One third of bumblebees were infected: while viruses only infected B. pascuorum, B. terrestris was infected by Apicystis bombi, Crithidia bombi and Nosema bombi. Ecological differences between host species might affect the success of the pathogens biological cycle and consequently infection prevalence. Furthermore, sex of the bumblebees (workers or males), sampling area (north or south) and altitude were important predictors of pathogen prevalence. Understanding how these factors affect pathogens distribution is essential for future conservation of bumblebee wild populations.