Friday, 24 June 2011

Buzzing bees in poppies

ResearchBlogging.orgThere were lots of poppies around today, and they buzzed with a high pitch produced by the bees and bumblebees inside, often more than one, gathering their almost black pollen. Poppies are unusual flowers, bright red, bowl shaped, with black centers and radial symmetry, and they do not produce nectar, just lots and lots of edible, protein-rich pollen. Poppies open at dawn, and before they do, their anthers start to release pollen. By the following day, fully fertilised and depleted of pollen, the flower loses its petals. Although the red and black colour combination of poppies - like some tulips and other Mediterranean flowers - is through to have evolved to be fertilised by beetles, bees and bumblebees take advantage of the pollen bonanza offered by these short-lived flowers. Bumblebees do not need much time to learn how to collect nectar, even from complex flowers, but pollen collecting is much trickier. The powdery pollen needs to be released from the anthers, brushed from the bees hairy body, mixed with nectar to make it sticky, packed into pellets and fixed to their corbicula, the specialized area on their legs adapted to carry the pollen. Nigel Raine and Lars Chittka, from Queen Mary University of London, carried out some experiments in a greenhouse to investigate how bumblebees learn to collect pollen. They used freshly collected poppy flowers from a field nearby before each bumblebee foraging trip, and tested six Bombus terrestris bumblebees that had never collected pollen before.
The figure above shows how pollen from the wild collected poppies drastically decreased along the morning - as the wild bees outside collected it - by 9:00 am there wasn't much left. The researchers then computed the rate at which their bumblebees collected pollen from the poppies, related to the available pollen at each foraging bout, by removing and counting one of the pollen pellets brough to the colony after each foraging trip by each bee.
 Bumblebee pollen collection behaviour markedly changed with experience:
During their first few visits, all bees were surprisingly clumsy, one bee even failed to collect any pollen during its first foraging bout despite making 56 flower visits. In the early stages of their foraging career, bees were observed to collect pollen loads that fell apart, or were so large that they fell from the bee’s corbiculae (pollen baskets) before reaching the nest. As each bee gained foraging experience, the frequency of such events rapidly declined. Bees also changed how they used ‘buzzing’, a technique of holding the anthers in their mandibles while vibrating their flight muscles, to facilitate pollen collection. While naïve bees typically buzzed either all or no flowers, skilled foragers would selectively ‘buzz’ flowers containing less pollen.
The following graph shows how foraging efficiency increases with foraging trip, indicating that bees learn to be more adept at collecting pollen. Despite this, the bees seemed to forget most of what they had learn overnight, as efficiency was much lower in the first trip of the second day than in the last trip of the previous day. :

A honeybee and a bumblebee share an Opium poppy
Raine, N., & Chittka, L. (2006). Pollen foraging: learning a complex motor skill by bumblebees (Bombus terrestris) Naturwissenschaften, 94 (6), 459-464. DOI: 10.1007/s00114-006-0184-0
Dafni, A.; Bernhardt, P., Shmida, A., Ivri, Y. and Greenbaum, S. (1990). Red bowl-shaped flowers: convergence for beetle pollination in the Mediterranean region. Israel Journal of Botany, 39, no1-2, pp. 81-92, 81-92 Other: 0021-213X

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