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.
Adult parasitoids Lysiphlebus testaceipes Cresson (Hymenoptera: Aphidiidae) lose locomotory function and enter chill coma at significantly lower temperatures (−0.1 and −8.0 • C, respectively) than their second-instar hosts, the black bean aphid Aphis fabae Scop. (Hemiptera: Aphididae) (5.6 and 2.3 • C, respectively). Parasitoids are also more heat tolerant, stop walking at 41.4 • C, with heat coma at 44.1 • C, than the aphid (39.1 and 43.0 • C, respectively). Furthermore, across a range of temperatures (0-20 • C), L. testaceipes has considerably faster walking speeds than A. fabae. These data are discussed in relation to the climatic conditions under which L. testaceipes would be an effective control agent, and the likelihood of establishment and spread in northern European climates.
Bumblebees are regularly exported to countries outside their native range for the purposes of commercial pollination. In contrast to the tight regulations imposed on biological control introductions, the movement of bumblebees has largely been without risk assessment. This study represents the first formal assessment of establishment risk for Bombus terrestris dalmatinus in the UK. The ability of workers to survive winter conditions is seen as the primary barrier to establishment, given the year-round colony activity of this sub-species. We use standardised cold tolerance indices as outlined by the EU policy support action ‘REBECA’ as well as assessing rapid cold hardening (RCH) ability. Cold tolerance was comparable to that of the UK-native Bombus terrestris audax, including a strong RCH response. Results suggest that B. t. dalmatinus could survive mild UK winters in southern areas and potentially displace B. t. audax. The implications of ongoing climate change on establishment risks are discussed.
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