The consequences for wildlife of living in radiologically contaminated environments are uncertain. Previous laboratory studies suggest insects are relatively radiation-resistant; however, some field studies from the Chernobyl Exclusion Zone report severe adverse effects at substantially lower radiation dose rates than expected. Here we present the first laboratory investigation to study how environmentally-relevant radiation exposure affects bumblebee life-history, assessing the shape of the relationship between radiation exposure and fitness-loss. Dose rates comparable to the Chernobyl Exclusion Zone (50-400 µGy h-1) impaired bumblebee reproduction and delayed colony growth but did not affect colony weight or longevity. Our best-fitting model for the effect of radiation dose rate on colony queen production had a strongly non-linear concave relationship: exposure to only 100 µGy h-1 impaired reproduction by 30-45%, while further dose rate increases caused more modest additional reproductive impairment. Our data indicate that the practice of estimating effects of environmentally-relevant low dose rate exposure by extrapolating from high dose rates may have considerably underestimated the effects of radiation. If our data can be generalised, they suggest insects suffer significant negative consequences at dose rates previously thought safe; we therefore advocate relevant revisions to the international framework for radiological protection of the environment.

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