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The emergence of agricultural land use change creates a number of challenges that insect pollinators, such as eusocial bees, must overcome. Resultant fragmentation and loss of suitable foraging habitats, combined with pesticide exposure, may increase demands on foraging, specifically the ability to collect or reach sufficient resources under such stress. Understanding effects that pesticides have on flight performance is therefore vital if we are to assess colony success in these changing landscapes. Neonicotinoids are one of the most widely used classes of pesticide across the globe, and exposure to bees has been associated with reduced foraging efficiency and homing ability. One explanation for these effects could be that elements of flight are being affected, but apart from a couple of studies on the honeybee (Apis mellifera), this has scarcely been tested. Here, we used flight mills to investigate how exposure to a field realistic (10 ppb) acute dose of imidacloprid affected flight performance of a wild insect pollinator—the bumblebee, Bombus terrestris audax. Intriguingly, observations showed exposed workers flew at a significantly higher velocity over the first ¾ km of flight. This apparent hyperactivity, however, may have a cost because exposed workers showed reduced flight distance and duration to around a third of what control workers were capable of achieving. Given that bumblebees are central place foragers, impairment to flight endurance could translate to a decline in potential forage area, decreasing the abundance, diversity, and nutritional quality of available food, while potentially diminishing pollination service capabilities.

Global biodiversity is threatened by multiple anthropogenic stressors but little is known about the combined effects of environmental warming and invasive species on ecosystem functioning. We quantified thermal preferences and then compared leaf-litter processing rates at eight different temperatures (5.0–22.5 °C) by the invasive freshwater crustacean Dikerogammarus villosus and the Great Britain native Gammarus pulex at a range of body sizes. D. villosus preferred warmer temperatures but there was considerable overlap in the range of temperatures that the two species occupied during preference trials. When matched for size, G. pulex had a greater leaf shredding efficiency than D. villosus, suggesting that invasion and subsequent displacement of the native amphipod will result in reduced ecosystem functioning. However, D. villosus is an inherently larger species and interspecific variation in shredding was reduced when animals of a representative size range were compared. D. villosus shredding rates increased at a faster rate than G. pulex with increasing temperature suggesting that climate change may offset some of the reduction in function. D. villosus, but not G. pulex, showed evidence of an ability to select those temperatures at which its shredding rate was maximised, and the activation energy for shredding in D. villosus was more similar to predictions from metabolic theory. While per capita and mass-corrected shredding rates were lower in the invasive D. villosus than the native G. pulex, our study provides novel insights in to how the interactive effects of metabolic function, body size, behavioural thermoregulation, and density produce antagonistic effects between anthropogenic stressors.Electronic supplementary materialThe online version of this article (doi:10.1007/s00442-016-3796-x) contains supplementary material, which is available to authorized users.

Climate change and agricultural intensification are exposing insect pollinators to temperature extremes and increasing pesticide usage. Yet, we lack good quantification of how temperature modulates the sublethal effects of pesticides on behaviours vital for fitness and pollination performance. Consequently, we are uncertain if warming de-

23The emergence of agricultural land use change creates a number of challenges that insect pollinators, such as 24 eusocial bees, must overcome. Resultant fragmentation and loss of suitable foraging habitats, combined with 25 pesticide exposure, may increase demands on foraging, specifically the ability to reach resources under such 26 stress. Understanding the effect that pesticides have on flight performance is therefore vital if we are to assess 27 colony success in these changing landscapes. Neonicotinoids are one of the most widely used classes of pesticide 28 across the globe, and exposure to bees has been associated with reduced foraging efficiency and homing ability. 29One explanation for these effects could be that elements of flight are being affected, but apart from a couple of 30 studies on the honeybee, this has scarcely been tested. Here we used flight mills to investigate how exposure to 31 a field realistic (10ppb) acute dose of imidacloprid affected flight performance of a wild insect pollinator -the 32 bumblebee, Bombus terrestris audax. Intriguingly, intial observations showed exposed workers flew at a 33 significantly higher velocity over the first ¾ km of flight. This apparent hyperactivity, however, may have a cost 34 as exposed workers showed reduced flight distance and duration to around a third of what control workers were 35 capable of achieving. Given that bumblebees are central place foragers, impairment to flight endurance could 36 translate to a decline in potential forage area, decreasing the abundance, diversity and nutritional quality of 37 available food, whilst potentially diminishing pollination service capabilities.