Intra-specific variation in sensitivity of <i>Bombus terrestris</i> and <i>Osmia bicornis</i> to three pesticides

There is growing evidence that pesticides may be among the causes of worldwide bee declines, which has resulted in repeated calls for their increased scrutiny in regulatory assessments. One recurring concern is that the current frameworks may be biased towards assessing risks to the honey bee. This paradigm requires extrapolating toxicity information across bee species. Most research effort has therefore focused on quantifying differences in sensitivity across species. However, our understanding of how responses to pesticides may vary within a species is still very poor. Here we take the first steps towards filling this knowledge gap by comparing acute, lethal hazards in sexes and castes of the eusocial bee Bombus terrestris and in sexes of the solitary bee Osmia bicornis after oral and contact exposure to the pesticides sulfoxaflor, Amistar (azoxystrobin) and glyphosate. We show that sensitivity towards pesticides varies significantly both within and across species. Bee weight was a meaningful predictor of pesticide susceptibility. However, weight could not fully explain the observed differences, which suggests the existence of unexplored mechanisms regulating pesticide sensitivity across bee sexes and castes. Our data show that intra-specific responses are an overlooked yet important aspect of the risk assessment of pesticides in bees

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

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

No evidence of effects or interaction between the widely used herbicide, glyphosate, and a common parasite in bumble bees

Background Glyphosate is the world’s most used pesticide and it is used without the mitigation measures that could reduce the exposure of pollinators to it. However, studies are starting to suggest negative impacts of this pesticide on bees, an essential group of pollinators. Accordingly, whether glyphosate, alone or alongside other stressors, is detrimental to bee health is a vital question. Bees are suffering declines across the globe, and pesticides, including glyphosate, have been suggested as being factors in these declines. Methods Here we test, across a range of experimental paradigms, whether glyphosate impacts a wild bumble bee species, Bombus terrestris. In addition, we build upon existing work with honey bees testing glyphosate-parasite interactions by conducting fully crossed experiments with glyphosate and a common bumble bee trypanosome gut parasite, Crithidia bombi. We utilised regulatory acute toxicity testing protocols, modified to allow for exposure to multiple stressors. These protocols are expanded upon to test for effects on long term survival (20 days). Microcolony testing, using unmated workers, was employed to measure the impacts of either stressor on a proxy of reproductive success. This microcolony testing was conducted with both acute and chronic exposure to cover a range of exposure scenarios. Results We found no effects of acute or chronic exposure to glyphosate, over a range of timespans post-exposure, on mortality or a range of sublethal metrics. We also found no interaction between glyphosate and Crithidia bombi in any metric, although there was conflicting evidence of increased parasite intensity after an acute exposure to glyphosate. In contrast to published literature, we found no direct impacts of this parasite on bee health. Our testing focussed on mortality and worker reproduction, so impacts of either or both of these stressors on other sublethal metrics could still exist. Conclusions Our results expand the current knowledge on glyphosate by testing a previously untested species, Bombus terrestris, using acute exposure, and by incorporating a parasite never before tested alongside glyphosate. In conclusion our results find that glyphosate, as an active ingredient, is unlikely to be harmful to bumble bees either alone, or alongside Crithidia bombi

No impacts of glyphosate or Crithidia bombi, or their combination, on the bumblebee microbiome

Abstract Pesticides are recognised as a key threat to pollinators, impacting their health in many ways. One route through which pesticides can affect pollinators like bumblebees is through the gut microbiome, with knock-on effects on their immune system and parasite resistance. We tested the impacts of a high acute oral dose of glyphosate on the gut microbiome of the buff tailed bumblebee (Bombus terrestris), and glyphosate’s interaction with the gut parasite (Crithidia bombi). We used a fully crossed design measuring bee mortality, parasite intensity and the bacterial composition in the gut microbiome estimated from the relative abundance of 16S rRNA amplicons. We found no impact of either glyphosate, C. bombi, or their combination on any metric, including bacterial composition. This result differs from studies on honeybees, which have consistently found an impact of glyphosate on gut bacterial composition. This is potentially explained by the use of an acute exposure, rather than a chronic exposure, and the difference in test species. Since A. mellifera is used as a model species to represent pollinators more broadly in risk assessment, our results highlight that caution is needed in extrapolating gut microbiome results from A. mellifera to other bee species

Parasite and Pesticide Impacts on the Bumblebee (Bombus terrestris) Haemolymph Proteome

International audiencePesticides pose a potential threat to bee health, especially in combination with other stressors, such as parasites. However, pesticide risk assessment tests pesticides in isolation from other stresses, i.e., on otherwise healthy bees. Through molecular analysis, the specific impacts of a pesticide or its interaction with another stressor can be elucidated. Molecular mass profiling by MALDI BeeTyping ® was used on bee haemolymph to explore the signature of pesticidal and parasitic stressor impacts. This approach was complemented by bottom-up proteomics to investigate the modulation of the haemoproteome. We tested acute oral doses of three pesticides-glyphosate, Amistar and sulfoxaflor-on the bumblebee Bombus terrestris, alongside the gut parasite Crithidia bombi. We found no impact of any pesticide on parasite intensity and no impact of sulfoxaflor or glyphosate on survival or weight change. Amistar caused weight loss and 19-41% mortality. Haemoproteome analysis showed various protein dysregulations. The major pathways dysregulated were those involved in insect defences and immune responses, with Amistar having the strongest impact on these dysregulated pathways. Our results show that even when no response can be seen at a whole organism level, MALDI BeeTyping ® can detect effects. Mass spectrometry analysis of bee haemolymph provides a pertinent tool to evaluate stressor impacts on bee health, even at the level of individuals

Improving pesticide-use data for the EU

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