Comparative toxicity of pesticides and environmental contaminants in bees: Are honey bees a useful proxy for wild bee species?

Abstract

Threats to wild and managed insect pollinators in Europe are cause for both ecological and socio-economic concern. Multiple anthropogenic pressures may be exacerbating pollinator declines. One key pressure is exposure to chemicals including pesticides and other contaminants. Historically the honey bee (Apis mellifera spp.) has been used as an 'indicator' species for 'standard' ecotoxicological testing but it has been suggested that it is not always a good proxy for other types of eusocial and solitary bees because of species differences in autecology and sensitivity to various stressors. We developed a common toxicity test system to conduct acute and chronic exposures of up to 240h of similar doses of seven chemicals, targeting different metabolic pathways, on three bee species (Apis mellifera spp., Bombus terrestris and Osmia bicornis). We compared the relative sensitivity between species in terms of potency between the chemicals and the influence of exposure time on toxicity. While there were significant interspecific differences that varied through time, overall the magnitude of these differences (in terms of treatment effect ratios) was generally comparable (<2 fold) although there were some large divergences from this pattern. Our results suggest that A. mellifera spp. could be used as a proxy for other bee species provided a reasonable assessment factor is used to cover interspecific variation. Perhaps more importantly our results show significant and large time dependency of toxicity across all three tested species that greatly exceeds species differences (>25 fold within test). These are rarely considered in standard regulatory testing but may have severe environmental consequences, especially when coupled with the likelihood of differential species exposures in the wild. These insights indicate that further work is required to understand how differences in toxicokinetics vary between species and mixtures of chemicals.

Osmia bicornis is rarely an adequate regulatory surrogate species. Comparing its acute sensitivity towards multiple insecticides with regulatory Apis mellifera endpoints

“…We therefore agree with Heard et al (2017) that A. mellifera is a sufficient 258 proxy for wild bee species in laboratory acute mortality testing [17]. However, it is still 259 necessary to investigate less well-known issues such as effects of pesticides mixtures [32,33], prolonged pesticides exposure [17] or effects of pesticide adjuvants [34].…”

“…This approach proofed to be protective in 52 95% of cases in the meta-analysis by Arena & Sgolastra (2014) [14]. It is unclear, 53 however, if this factor would be protective for both proposed test species due to the slim 54 database of their sensitivity [16,17].…”

“…herbicides, fungicides, insecticides [7,8]. They are not 16 only contaminated during foraging on crops but also from visitations of field-adjacent 17 wild flowers [9]. Bees are exposed to pesticides by direct overspray as well as oral uptake 18 of and contact to nectar and pollen while foraging.…”

Comparing bee species responses to chemical mixtures: Common response patterns?

“…Different mechanistic categories including similar and dissimilar combinations were also tested. All six mixtures were tested for Apis mellifera , with three combinations also tested in Bombus terrestris and Osmia bicornis (see summary Table 1) for which clear concentration response curves were already available [20, 21]. Mixtures tested included both cases where the two chemicals had an effect on the same physiological effect (e.g.…”

“…[20, 21]) showed one or both chemicals to have an effect on survival at the tested concentrations. Controls containing only 50% w/v sucrose were included in all experiments.…”