Extrapolation of acute toxicity across bee species

Abstract

In applying cross-species extrapolation safety factors from honeybees to other bee species, some basic principles of toxicity have not been included, for example, the importance of body mass in determining a toxic dose. The present study re-analyzed published toxicity data, taking into account the reported mass of the individuals in the identified species. The analysis demonstrated a shift to the left in the distribution of sensitivity of honeybees relative to 20 other bee species when body size is taken into account, with the 95 th percentile for contact and oral toxicity reducing from 10.7 (based on mg/individual bee) to 5.0 (based on mg/g bodyweight). Such an approach results in the real drivers of species differences in sensitivity-such as variability in absorption, distribution, metabolism, and excretion in and target-receptor binding-being more realistically reflected in the revised safety factor. Body mass can also be used to underpin the other parameter of first-tier risk assessment, that is, exposure. However, the key exposure factors that cannot be predicted from bodyweight are the effects of ecology and behavior of the different species on exposure to a treated crop. Further data are required to understand the biology of species associated with agricultural crops and the potential consequences of effects on individuals at the levels of the colony or bee populations. This information will allow the development of appropriate higher-tier refinement of risk assessments and testing strategies rather than extensive additional toxicity testing at Tier 1. Integr Environ Assess Manag 2016;12:622-626.

Are honeybees suitable surrogates for use in pesticide risk assessment for non‐Apisbees?

“…The fundamental nature of scaling laws also influences toxicology with the sensitivity of organisms towards a range of xenobiotics exhibiting compound‐specific scaling relationships . A conserved scaling relationship for the acute toxicity (LD 50 ) of bees towards the acetylcholinesterase‐inhibiting insecticides (organophosphorus and carbamate classes) has also been suggested with A. mellifera as a sensitive bee species on a per bee and even more so on a per weight bee basis, even when compared with the smallest bees of the data set, Brazilian stingless bees (Tribe Meliponini) . In this case, the LD 50 values for these acetylcholinesterase inhibitors scaled proportionally with body weight (i.e.…”

“…by an order of magnitude for Bombus impatiens . Therefore, if meaningful comparisons between species are to be made, we need to move away from expressing toxicity on a per‐bee basis and towards a size/weight‐corrected expression following current regulatory ecotoxicological and toxicological norms …”

“…the confidence intervals of the regression slope overlap with 1). Because we do not know the scaling relationships for other classes of xenobiotics in bees, a simple linear scaling approach could be an appropriate first attempt to account for body weight. However, care must be taken when comparing bees on the far ends of the size spectrum because these comparisons will be most susceptible to nonlinear properties of scaling relationships.…”

“…30 Therefore, if meaningful comparisons between species are to be made, we need to move away from expressing toxicity on a per-bee basis and towards a size/weight-corrected expression following current regulatory ecotoxicological and toxicological norms. 28 How exactly the correction for size should be undertaken in bees is an open question. Utilising allometric scaling relationships would be one option to more accurately account for the expected effects of body size on bee sensitivity.…”

Advancing environmental risk assessment of regulated products under EFSA's remit

“…represent an excellent model and case study for the implementation of an integrated ERA of multiple stressors. Honeybees are typically used as a surrogate species for other bees in ERAs, but they cannot be considered representative of all bee taxa because populations of wild bees usually comprise different functional and life-history characteristics and exhibit different sensitivities (Arena and Sgolastra, 2014;Thompson, 2015). Many crops depend directly on insect pollination and the honeybee is considered to be one of the most important pollinators, although other insect taxa contribute to pollination (Rader et al, 2016).…”