Data from: Individual and combined impacts of sulfoxaflor and Nosema bombi on bumblebee (Bombus terrestris) larval growth

Sulfoxaflor is a globally important novel insecticide that can have negative impacts on the reproductive output of bumblebee (Bombus terrestris) colonies. However, it remains unclear as to which life-history stage is critically affected by exposure. One hypothesis is that sulfoxaflor exposure early in the colony's life cycle can impair larval development, reducing the number of workers produced, and ultimately lowering colony reproductive output. Here we assess the influence of sulfoxaflor exposure on bumblebee larval mortality and growth both when tested in insolation and when in combination with the common fungal parasite Nosema bombi, following a pre-registered design. We found no impact of sulfoxaflor (5ppb) or N. bombi exposure (50,000 spores) on larval mortality when tested in isolation but found an additive, negative effect when larvae received both stressors in combination. Furthermore, we found that sulfoxaflor and N. bombi exposure individually impaired larval growth but also found possible antagonistic effects when used in combination. Ultimately, our results suggest that colony-level consequences of sulfoxaflor exposure for bumblebees may be mediated through direct effects on larvae. As sulfoxaflor is licenced for use globally, our findings highlight the need to understand how novel insecticides impact non-target insects at various stages of their development.