Lethal effects and sex-specific tolerance of copper and cadmium in the buff-tailed bumble bee

Abstract

Exposure to environmental pollutants, including trace metals, is a major driver of bee decline worldwide. While pesticides undergo standardised risk assessments (i.e., LD₅₀) and the implementation of online databases, no such approaches exist for trace metals. Here, using acute oral exposure, we determined the LC₅₀, LD₅₀, and mass-standardised LD₅₀ of copper and cadmium, essential and non-essential metals, respectively, in workers and males of the buff-tailed bumble bee. We also evaluated gut damage and sucrose consumption in workers post-exposure. Cadmium was more toxic than copper for workers at same doses, although both metals induced severe gut melanisation and reduced sucrose consumption at high concentrations. Males displayed higher tolerance to cadmium, but it was correlated to their higher body mass, emphasising the necessity for reporting mass-standardised LD₅₀ for genuine sex comparisons in risk assessments. Our findings advocate for the establishment of databases focusing on metal-induced lethal effects on model bee species.