Authors: Theodorou, Panagiotis; Kühn, Olga;Baltz, Lucie ;Wil, Christopher ;Rasti, Sirus;Bucksch, Carolina ;Strohm, Erhard ;Paxton, Robert ;Kurze, Christoph ;

Urbanisation can affect fitness and challenge the persistence of many species, including wild bees. Yet, how and which urban environmental features affect bee health and fitness remain unclear. Here, we placed experimental Bombus terrestris colonies in sites spanning from the edge into a city’s core to investigate bee parasitism, foraging behaviour, energetic stress, colony growth and reproductive output. In each site, ambient temperature was recorded, floral resources were evaluated and landscape heterogeneity was characterized. We found that Bombus terrestris parasitism levels increased across the season in line with colony growth but was negatively related to the proportion of impervious surfaces. Bombus terrestris foraging trip duration decreased with increasing ecotones but increased in sites with honey bee hives present. Energetic stress increased with the proportion of impervious surfaces. Furthermore, high ambient temperature reduced colony growth and indirectly the production of gynes. Our results highlight the importance of ecotones as well as minimizing the intensity of urbanisation and urban honey bee beekeeping for bumblebee colony health and foraging behaviour. They also point to the importance of microclimate for bumblebee colony performance and suggest that increasing temperatures could have a negative impact in slowing colony weight gain, and indirectly in reducing colony reproduction.