Do pesticide and pathogen interactions drive wild bee declines?

There is clear evidence for wild insect declines globally. Habitat loss, climate change, pests, pathogens and environmental pollution have all been shown to cause detrimental effects on insects. However, interactive effects between these stressors may be the key to understanding reported declines. Here, we review the literature on pesticide and pathogen interactions for wild bees, identify knowledge gaps, and suggest avenues for future research fostering mitigation of the observed declines. The limited studies available suggest that effects of pesticides most likely override effects of pathogens. Bees feeding on flowers and building sheltered nests, are likely less adapted to toxins compared to other insects, which potential susceptibility is enhanced by the reduced number of genes encoding detoxifying enzymes compared with other insect species. However, to date all 10 studies using a fully-crossed design have been conducted in the laboratory on social bees using Crithidia spp. or Nosema spp., identifying an urgent need to test solitary bees and other pathogens. Similarly, since laboratory studies do not necessarily reflect field conditions, semi-field and field studies are essential if we are to understand these interactions and their potential effects in the real-world. In conclusion, there is a clear need for empirical (semi-)field studies on a range of pesticides, pathogens, and insect species to better understand the pathways and mechanisms underlying their potential interactions, in particular their relevance for insect fitness and population dynamics. Such data are indispensable to drive forward robust modelling of interactive effects in different environmental settings and foster predictive science. This will enable pesticide and pathogen interactions to be put into the context of other stressors more broadly, evaluating their relative importance in driving the observed declines of wild bees and other insects. Ultimately, this will enable the development of more effective mitigation measures to protect bees and the ecosystem services they supply

Buffered fitness components: Antagonism between malnutrition and an insecticide in bumble bees.

Global insect biodiversity declines due to reduced fitness are linked to interactions between environmental stressors. In social insects, inclusive fitness depends on successful mating of reproductives, i.e. males and queens, and efficient collaborative brood care by workers. Therefore, interactive effects between malnutrition and environmental pollution on sperm and feeding glands (hypopharyngeal glands (HPGs)) would provide mechanisms for population declines, unless buffered against due to their fitness relevance. However, while negative effects for bumble bee colony fitness are known, the effects of malnutrition and insecticide exposure singly and in combination on individuals are poorly understood. Here we show, in a fully-crossed laboratory experiment, that malnutrition and insecticide exposure result in neutral or antagonistic interactions for spermatozoa and HPGs of bumble bees, Bombus terrestris, suggesting strong selection to buffer key colony fitness components. No significant effects were observed for mortality and consumption, but significant negative effects were revealed for spermatozoa traits and HPGs. The combined effects on these parameters were not higher than the individual stressor effects, which indicates an antagonistic interaction between both. Despite the clear potential for additive effects, due to the individual stressors impairing muscle quality and neurological control, simultaneous malnutrition and insecticide exposure surprisingly did not reveal an increased impact compared to individual stressors, probably due to key fitness traits being resilient. Our data support that stressor interactions require empirical tests on a case-by-case basis and need to be regarded in context to understand underlying mechanisms and so adequately mitigate the ongoing decline of the entomofauna

From antagonism to synergism: Extreme differences in stressor interactions in one species

Interactions between stressors are involved in the decline of wild species and losses of managed ones. Those interactions are often assumed to be synergistic, and per se of the same nature, even though susceptibility can vary within a single species. However, empirical measures of interaction effects across levels of susceptibility remain scarce. Here, we show clear evidence for extreme differences in stressor interactions ranging from antagonism to synergism within honeybees, Apis mellifera. While female honeybee workers exposed to both malnutrition and the pathogen Nosema ceranae showed synergistic interactions and increased stress, male drones showed antagonistic interactions and decreased stress. Most likely sex and division of labour in the social insects underlie these findings. It appears inevitable to empirically test the actual nature of stressor interactions across a range of susceptibility factors within a single species, before drawing general conclusions

Pan-european assessment, monitoring, and mitigation of stressors on the health of bees

Within the PoshBee Project, we have worked out precise protocols for testing the toxicological endpoints and metabolisation rate of agrochemicals on and in bees. Three agrochemical classes (insecticides, fungicides and herbicides) were tested on three bee groups (honey bees, bumble bees and solitary mason bees). The specific protocols, different for each combination of the pesticide class and bee group, were designed based on the existing toxicity testing methods and modified according to the specificities of the different bee groups, their castes and the different exotoxicological features of the compounds. Sulfoxaflor, Azoxystrobin, and Glyphosate were used respectively as examples of the three pesticide classes. Apis mellifera, Bombus terrestris and Osmia bicornis were chosen as the examples of the three bee groups. The protocols for honey bees and bumble bees were designed based on the official existing guidelines edited by OECD. Nevertheless, given that the OECD guidelines provide recommendations to fit with most agrochemicals, many of the parameters are defined with low precision in order to be flexible and adapt to different categories of molecules. While OECD has no guidelines for testing solitary bees, we used information from the unpublished ring test protocols for Osmia bicornis by the ICPPR non- Apis working group.Prepared under contract from the European Commission; Grant agreement No. 773921; EU Horizon 2020 Research and Innovation action.Prepared under contract from the European Commission; Grant agreement No. 773921; EU Horizon 2020 Research and Innovation action

Pan-european assessment, monitoring, and mitigation of stressors on the health of bees

Inter-individual differences in pesticide sensitivity may trigger variability in the risk posed by pesticides. Therefore, to better inform pesticide risk assessment for bees, we studied the variability of responses to several pesticides based on endogenous (developmental stage, genetic background, caste) and exogenous factors (pesticide co-exposure). We mainly investigated the toxicity of the insecticide sulfoxaflor, the fungicide azoxystrobin and the herbicide glyphosate. We first used LD50 tests to determine the acute oral and contact toxicity of these pesticides across the different bee species, developmental stages (larva vs adult in honey bees), castes (honey bee and bumble bee workers, queens and drones), and genetic backgrounds (honey bee subspecies). We then considered the risks posed by chronic and sublethal exposures to pesticides by implementing behavioural and reproductive endpoints in the screening of pesticide toxicity. Data showed that azoxystrobin and glyphosate under the test conditions were mildly toxic to bees. However, a large variability in bee sensitivity to sulfoxaflor was found, especially across species and individuals of different castes or sex. This variability is therefore important to consider for increasing the safety margin of the risk posed by insecticides in bees. Several effects induced by sublethal concentrations or doses of pesticides are also described, such as the occurrence of a Non-Monotonic Dose-Response (NMDR) and delayed effects in honey bees, impairment of reproductive performances in bumble bees, and a decreased longevity of Osmia adult females (although no effects were found on larval development). Finally, an interaction between pesticides was found when exposure was by contact, but not under oral exposure. In conclusion, the range of effects described here provides very useful insights for better understanding the toxicity of pesticides and therefore the risks they might pose to bees.Prepared under contract from the European Commission; Grant agreement No. 773921; EU Horizon 2020 Research and Innovation action.Prepared under contract from the European Commission; Grant agreement No. 773921; EU Horizon 2020 Research and Innovation action

Pan-european assessment, monitoring, and mitigation of stressors on the health of bees

Within the PoshBee Project we have tested three bee species – honey bees Apis mellifera, bumble bees Bombus terrestris and solitary bees Osmia bicornis – for their sensitivity to pesticides and analysed the clearance of pesticides from bees. For each species, all castes and sexes were studied. We synthesised the mortality data (LD50 or results of limit tests) with the toxicokinetic patterns and analysed this against the background of inter- and intraspecific variation in life-histories of the tested bees. The clearance of sulfoxaflor is relatively similar across all bee species tested and in females after contact treatment it tends to be retained. The toxicity increases over time independently of the clearance from the body. The clearance of azoxystrobin was rapid in Osmia and bumble bees, as well as in honey bee queens, but in honey bee workers there was very little clearance. Similar to sulfoxaflor the toxicity increased over time, although the residues were detected at very low levels. Glyphosate tended to be retained in bumble bees after contact treatment but cleared rapidly after oral treatment. For Osmia bees only in males after contact treatment was the glyphosate almost lost. The toxicity of a pesticide is dependent on the exact dosage, but also the exposure route and time, as well as the speed of detoxification and clearance from a body. The assessment for the hazard that a less toxic pesticide might pose, can be largely dependent on the exposure route. The effects of pesticide toxicity can increase even after the molecules have been cleared out of the body.Prepared under contract from the European Commission; Grant agreement No. 773921; EU Horizon 2020 Research and Innovation action.Prepared under contract from the European Commission; Grant agreement No. 773921; EU Horizon 2020 Research and Innovation action

Adoptive transfer of allergen-expressing B cells prevents IgE-mediated allergy

IntroductionProphylactic strategies to prevent the development of allergies by establishing tolerance remain an unmet medical need. We previously reported that the transfer of autologous hematopoietic stem cells (HSC) expressing the major timothy grass pollen allergen, Phl p 5, on their cell surface induced allergen-specific tolerance in mice. In this study, we investigated the ability of allergen-expressing immune cells (dendritic cells, CD4+ T cells, CD8+ T cells, and CD19+ B cells) to induce allergen-specific tolerance in naive mice and identified CD19+ B cells as promising candidates for allergen-specific cell therapy.MethodsFor this purpose, CD19+ B cells were isolated from Phl p 5-transgenic BALB/c mice and transferred to naive BALB/c mice, pre-treated with a short course of rapamycin and an anti-CD40L antibody. Subsequently, the mice were subcutaneously sensitized three times at 4-week intervals to Phl p 5 and Bet v 1 as an unrelated control allergen. Allergen-expressing cells were followed in the blood to monitor molecular chimerism, and sera were analyzed for Phl p 5- and Bet v 1-specific IgE and IgG1 levels by RBL assay and ELISA, respectively. In vivo allergen-induced lung inflammation was measured by whole-body plethysmography, and mast cell degranulation was determined by skin testing.ResultsThe transfer of purified Phl p 5-expressing CD19+ B cells to naive BALB/c mice induced B cell chimerism for up to three months and prevented the development of Phl p 5-specific IgE and IgG1 antibody responses for a follow-up period of 26 weeks. Since Bet v 1 but not Phl p 5-specific antibodies were detected, the induction of tolerance was specific for Phl p 5. Whole-body plethysmography revealed preserved lung function in CD19+ B cell-treated mice in contrast to sensitized mice, and there was no Phl p 5-induced mast cell degranulation in treated mice.DiscussionThus, we demonstrated that the transfer of Phl p 5-expressing CD19+ B cells induces allergen-specific tolerance in a mouse model of grass pollen allergy. This approach could be further translated into a prophylactic regimen for the prevention of IgE-mediated allergy in humans

Emerging threats and opportunities to managed bee species in European agricultural systems: a horizon scan

peer reviewedManaged bee species provide essential pollination services that contribute to food security worldwide. However, managed bees face a diverse array of threats and anticipating these, and potential opportunities to reduce risks, is essential for the sustainable management of pollination services. We conducted a horizon scanning exercise with 20 experts from across Europe to identify emerging threats and opportunities for managed bees in European agricultural systems. An initial 63 issues were identified, and this was shortlisted to 21 issues through the horizon scanning process. These ranged from local landscape-level management to geopolitical issues on a continental and global scale across seven broad themes-Pesticides & pollutants, Technology, Management practices, Predators & parasites, Environmental stressors, Crop modification, and Political & trade influences. While we conducted this horizon scan within a European context, the opportunities and threats identified will likely be relevant to other regions. A renewed research and policy focus, especially on the highest-ranking issues, is required to maximise the value of these opportunities and mitigate threats to maintain sustainable and healthy managed bee pollinators within agricultural systems

Emerging threats and opportunities to managed bee species in European agricultural systems: a horizon scan

Managed bee species provide essential pollination services that contribute to food security worldwide. However, managed bees face a diverse array of threats and anticipating these, and potential opportunities to reduce risks, is essential for the sustainable management of pollination services. We conducted a horizon scanning exercise with 20 experts from across Europe to identify emerging threats and opportunities for managed bees in European agricultural systems. An initial 63 issues were identified, and this was shortlisted to 21 issues through the Horizon Scanning process. These ranged from local landscape-level management to geopolitical issues on a continental and global scale across seven broad themes - Pesticides & pollutants, Technology, Management practices, Predators & parasites, Environmental stressors, Crop modification, and Political & trade influences. While we conducted this Horizon Scan within a European context, the opportunities and threats identified will likely be relevant to other regions. A renewed research and policy focus, especially on the highest-ranking issues, is required to maximise the value of these opportunities and mitigate threats to maintain sustainable and healthy managed bee pollinators within agricultural systems

Conditional Stat1 Ablation Reveals the Importance of Interferon Signaling for Immunity to Listeria monocytogenes Infection

Signal transducer and activator of transcription 1 (Stat1) is a key player in responses to interferons (IFN). Mutations of Stat1 cause severe immune deficiencies in humans and mice. Here we investigate the importance of Stat1 signaling for the innate and secondary immune response to the intracellular bacterial pathogen Listeria monocytogenes (Lm). Cell type-restricted ablation of the Stat1 gene in naïve animals revealed unique roles in three cell types: macrophage Stat1 signaling protected against lethal Lm infection, whereas Stat1 ablation in dendritic cells (DC) did not affect survival. T lymphocyte Stat1 reduced survival. Type I IFN (IFN-I) signaling in T lymphocytes reportedly weakens innate resistance to Lm. Surprisingly, the effect of Stat1 signaling was much more pronounced, indicating a contribution of Stat1 to pathways other than the IFN-I pathway. In stark contrast, Stat1 activity in both DC and T cells contributed positively to secondary immune responses against Lm in immunized animals, while macrophage Stat1 was dispensable. Our findings provide the first genetic evidence that Stat1 signaling in different cell types produces antagonistic effects on innate protection against Lm that are obscured in mice with complete Stat1 deficiency. They further demonstrate a drastic change in the cell type-dependent Stat1 requirement for memory responses to Lm infection