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

Abstract

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.

Intra-specific variation in sensitivity of Bombus terrestris and Osmia bicornis to three pesticides

“…Products containing glyphosate may be applied to flowering weeds 73 and contaminate their pollen and nectar 54 , thus driving bee contact and oral exposure. Glyphosate showed low lethal hazards in regulatory-ready laboratory 74 and semi-field designs when dosed as pure active substance or as MON 52276 (SL formulation containing 360 g glyphosate/L) 75 . A recent study found ready-to-use consumer products containing glyphosate to be lethally hazardous to bumble bees 73 .…”

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

“…The reduced mortality in the Amistar + C. bombi treatment is likely stochastic, as there is little reason C. bombi would ameliorate the impacts of the pesticide. It is worth noting that this work pre-dates the experiments in Straw and Brown (2021) [ 52 ], so the mortality was unexpected, hence the sample size for the haemoproteome analysis is reduced as only living bees had haemolymph extracted.…”

“…Finally, (iii) glyphosate, a herbicide that is the world’s most used pesticide [ 49 , 50 ]. The impacts of glyphosate on bees are hotly contested [ 51 , 52 ], with the most rigorous evidence pointing to potential sublethal impacts on the microbiome [ 53 ], with conflicting evidence as to lethal effects [ 54 , 55 , 56 ]. To represent the most likely co-exposure situation in the field, we used the trypanosome gut parasite C. bombi , which is the most prevalent parasite of bumble bees across Europe [ 41 , 42 , 43 , 44 ].…”

Do pesticide and pathogen interactions drive wild bee declines?

“…As our results and previous studies show (e.g., Siviter et al, 2021a ), most of these experiments have used viruses and Nosema spp. In honey bees (e.g., Doublet et al, 2014 ; Harwood and Dolezal, 2020 ; Paris et al, 2020 , 2018 ; Retschnig et al, 2015 ; Vidau et al, 2011 ), and Crithidia bombi in bumble bees ( Baron et al, 2014 , 2017 ; Fauser-Misslin et al, 2014 ; Fauser et al, 2017 ; Straw and Brown, 2021a ). While important parasites, these are only a tiny subset of the parasites and pathogens known to infect these two groups of social bees ( Schmid-Hempel, 1998 ).…”

“…However, insecticides are not the only agrochemical group that could impact bee health. Herbicides and fungicides are heavily used around the globe, and have been shown to have negative effects on bee health (e.g., Belsky and Joshi, 2020 ), as have other ingredients within agrochemical applications (e.g., Straw and Brown, 2021a ). Given this, studies of interactions between stressors need to incorporate a more balanced approach, which recognizes the potential importance of other agrochemicals ( Straw et al, 2022 ).…”