Abstract
BackgroundForaging bumblebees are normally associated with spring and summer in northern Europe. However, there have been sightings of the bumblebee Bombus terrestris during the warmer winters in recent years in southern England. But what floral resources are they relying upon during winter and how much winter forage can they collect?Methodology/Principal FindingsTo test if urban areas in the UK provide a rich foraging niche for bees we set up colonies of B. terrestris in the field during two late winter periods (2005/6 & 2006/7) in London, UK, and measured their foraging performance. Fully automatic radio-frequency identification (RFID) technology was used in 2006/7 to enable us to record the complete foraging activity of individually tagged bees. The number of bumblebees present during winter (October 2007 to March 2008) and the main plants they visited were also recorded during transect walks. Queens and workers were observed throughout the winter, suggesting a second generation of bee colonies active during the winter months. Mass flowering shrubs such as Mahonia spp. were identified as important food resources. The foraging experiments showed that bees active during the winter can attain nectar and pollen foraging rates that match, and even surpass, those recorded during summer.Conclusions/Significance B. terrestris in the UK are now able to utilise a rich winter foraging resource in urban parks and gardens that might at present still be under-exploited, opening up the possibility of further changes in pollinator phenology.
Highlights
Bumblebees in northern Europe typically have one, or in a few species, two generations that are active during the spring and summer [1,2]
A mean of 100.367.5 mg of nectar were collected per foraging bout, which took on average 21.561.9 minutes. This resulted in a mean nectar foraging rate of 457.1654.3 mg h21 (Fig. 3). This is substantially above the range that has been recorded for B. t. dalmatinus in previous experiments at the same location and other locations in southern England in spring/summer (Fig. 3; 12 colonies at Queen Mary with NFRs ranging from 8768 to 257618 mg h21, see [25] for details; five colonies tested near Egham, Surrey with NFRs ranging from 146.5627.9 to 440.0651.3, see [17] for details)
Our data show that urban areas can represent a rich winter foraging resource for B. terrestris and other pollinators
Summary
Bumblebees in northern Europe typically have one, or in a few species, two generations that are active during the spring and summer [1,2]. In recent years, foraging bumblebees, Bombus terrestris (L.), have been repeatedly observed during winters in southern England [1,3,4]. Queens of B. terrestris emerging from hibernation during midwinter are not uncommon after warm spells, even in otherwise colder winters [6], recent observations of bees in the winter include workers as well as males and nest-founding (collecting pollen) queens [1,7]. These ad hoc sightings suggest that B. terrestris may be establishing a second generation during the autumn/winter in southern Britain. What floral resources are they relying upon during winter and how much winter forage can they collect?
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