Resource supplementation later in the colony cycle improves real‐world bumblebee colony survival

Abstract Global agricultural expansion has led to the deterioration of much key foraging habitat for bees, but the impacts of nutritional stress caused by temporal gaps in food availability can be hard to isolate from other agricultural stressors. For bumblebee colonies ( Bombus spp.), which have an annual lifecycle culminating in a summer reproductive period, this issue is further complicated by potential variation in vulnerability over the colony lifecycle. Isolating the effects of nutritional stress on bumblebee colonies could therefore direct agricultural interventions that seek to mitigate against further decline. We assayed whether available food resources are limiting colony productivity and survival by supplementing post‐worker emergence Bombus terrestris colonies with ad libitum food during mid‐spring or early summer on 20 farms across south‐east England (‘earlier’ vs. ‘later’ treatments). In mid‐spring, forage is potentially more abundant but colonies are at an earlier developmental stage, while in early summer colonies are more established when forage is potentially sparser. Later‐supplemented colonies survived for significantly longer than both unsupplemented controls and earlier‐supplemented colonies. We found no detectable effects of supplementary feeding on reproductive output, which was minimal overall. Colonies in areas dominated by non‐flowering arable crops failed soonest and had fewer workers irrespective of feeding regime, and colonies experiencing higher weekly precipitation produced fewer workers. Synthesis and applications . Our findings suggest that B. terrestris colonies became food‐limited towards the end of their colony cycle in early summer. We suggest ecological intensification through planting native wildflower species may be more effective if it targets this flowering period, particularly within heavily arable areas, and that a staggered patchwork of mowing or grazing could be important in ensuring seasonal resource continuity.