BES Facebook pageBritish Ecological Society Press Release
1 February 2011
Secret life of bees now a little less secret
Many plants produce toxic chemicals to protect themselves against plant-eating animals, and many flowering plants have evolved flower structures that prevent pollinators such as bees from taking too much pollen. Now ecologists have produced experimental evidence that flowering plants might also use chemical defences to protect their pollen from some bees. The results are published next week in the British Ecological Society's journal Functional Ecology.
In an elegant experiment, Claudio Sedivy and colleagues from ETH Zurich in Switzerland collected pollen from four plant species – buttercup, viper's bugloss, wild mustard and tansy – using an ingenious method. Instead of themselves collecting pollen from plants, the researchers let bees do the leg work, harvesting pollen from the nests of specialist bees which only feed on one type of plant.
They then fed the pollen from each of the four plants to different broods of the larvae of two closely-related generalist species of mason bee (Osmia bicornis and Osmia cornuta) to see how well the larvae developed.
They found that despite the fact that the two generalist mason bees have a wide diet of different pollens, they showed striking differences in their ability to develop on pollen from the same plant species.
According to Claudio Sedivy: “While the larvae of Osmia cornuta were able to develop on viper's bugloss pollen, more than 90% died within days on buttercup pollen. Amazingly, the situation was exactly the opposite with the larvae of Osmia bicornis. And both bee species performed well on wild mustard pollen, while neither managed to develop on tansy pollen.”
“As far as we know, this is the first clear experimental evidence that bees need physiological adaptations to cope with the unfavourable chemical properties of certain pollen,” he says.
Plants would have good reason to protect their pollen against bees. Bees need enormous amounts of pollen to feed their young, pollen that could otherwise be used by the plants for pollination. The pollen of up to several hundred flowers is needed to rear one single larva, and bees are very efficient gatherers of pollen, often taking 70-90% of a flower's pollen in one visit. Because they store this pollen in special hairbrushes or in their gut, this means the pollen is not used to pollinate the flower.
Sedivy explains: “Bees and plants have conflicting interests when it comes to pollen. While most plants offer nectar to visiting insects as a bait for insects to transport the pollen from flower to flower, bees are very efficient pollen collectors. Therefore, plants have evolved a great variety of morphological adaptations to impede bees from depleting all their pollen. This study provides strong evidence that pollen chemistry might be at least as important as flower morphology to constrain pollen loss to bees.”
Claudio Sedivy et al (2011), 'Closely related pollen generalist bees differ in their ability to develop on the same pollen diet: evidence for physiological adaptations to digest pollen', doi: doi: 10.1111/j.1365-2435.2010.01828.x, is published in Functional Ecology on 1 February 2011.
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Notes for editors
1. For further information please contact Claudio Sedivy, tel: +41 44 632 39 05; +41 76 575 18 78, email: claudio.sedivy@ipw.agrl.ethz.ch
2. Copies of the paper and photographs are available from Becky Allen, British Ecological Society Press Officer, tel: +44 (0)1223 570016, mob: +44 (0)7949 804317, email: beckyallen@ntlworld.com
3. Most flowering plants attract animals to distribute their pollen. Bees, of which there are 20,000 to 30,000 species worldwide, are the primary pollen vectors in most ecosystems. Bees differ from all other pollinators except masarid wasps in that both adults and larvae eat pollen and nectar. Rearing one single bee larva often requires pollen from several hundred flowers.
4. Functional Ecology is published by Wiley-Blackwell for the British Ecological Society. Contents lists are available at www.functionalecology.org
5. The British Ecological Society is a learned society, a registered charity and a company limited by guarantee. Established in 1913 by academics to promote and foster the study of ecology in its widest sense, the Society has 4,000 members in the UK and abroad. Further information is available at www.britishecologicalsociety.org
