Abstract
There is now considerable evidence that climate change is disrupting the phenology of key pollinator species. The recently reported UK winter activity of the bumblebee Bombus terrestris brings a novel set of thermal challenges to bumblebee workers that would typically only be exposed to summer conditions. Here we assess the ability of workers to survive acute and chronic cold stress (via lower lethal temperatures and lower lethal times at 0°C), the capacity for rapid cold hardening (RCH) and the influence of diet (pollen versus nectar consumption) on supercooling points (SCP). Comparisons are made with chronic cold stress indices and SCPs in queen bumblebees. Results showed worker bees were able to survive acute temperatures likely to be experienced in a mild winter, with queens significantly more tolerant to chronic cold temperature stress. The first evidence of RCH in any Hymenoptera is shown. In addition, dietary manipulation indicated the consumption of pollen significantly increased SCP temperature. These results are discussed in the light of winter active bumblebees and climate change.
Highlights
Climate change has resulted in changes to the physiology, survival, abundance and range of many organisms [1]
This study has identified that B. t. audax is a freeze avoiding species, with limited supercooling ability
This is in contrast to several other bee species, e.g. Osmia cornuta and O. rufa, both with supercooling points (SCP) typically below 224uC [37], but is comparable with Megachile rotundata with SCPs of 28uC [38]
Summary
Climate change has resulted in changes to the physiology, survival, abundance and range of many organisms [1]. Spring advancement, extended growing seasons, milder winters and the availability of winter forage [1] have all combined to allow some normally univoltine species to become bivoltine, as evidenced by winter active bumblebees, Bombus terrestris, in the southern UK [8] This raises a number of new challenges, in particular the survival of life stages previously unexposed to winter conditions. The issue in the UK, and in other parts of Northern Europe, is that B. terrestris queens appear to be averting diapause, or have a greatly curtailed diapause, under warmer conditions and so are establishing new colonies in late Summer/Autumn [8] This is in stark contrast to a previous study [18], that reported a period of dormancy spanning 6–9 months in the UK
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