Herding aphids – how 'farmer' ants keep control of their food

New study shows how ants use chemical footprints to keep ready supply of aphids nearby<em> - News Release</em>

A joint news release from Imperial College London, Royal Holloway University of London, and the University of Reading

Strictly embargoed for
00.01 hours British Summer Time
Wednesday 10 October 2007

Chemicals on ants' feet tranquilise and subdue colonies of aphids, keeping them close-by as a ready source of food, says new research published today (10 October). The study throws new light on the complex relationship between ants and the colonies of aphids whose sugary secretions the ants eat.

Scientists had previously established that certain types of aphids live in colonies where they are used as a food source by a neighbouring colony of ants. The ants have been known to bite the wings off the aphids in order to stop them from getting away and depriving the ants of one of their staple foods: the sugar-rich sticky honeydew which is excreted by aphids when they eat plants. Chemicals produced in the glands of ants can also sabotage the growth of aphid wings. The new study shows, for the first time, that ants' chemical footprints – which are already known to be used by ants to mark out their territory - also play a key role in manipulating the aphid colony, and keeping it nearby.

The research, which was carried out by a team from Imperial College London, Royal Holloway University of London, and the University of Reading, used a digital camera and specially modified software to measure the walking speed of aphids when they were placed on filter paper that had previously been walked over by ants. The data showed that the aphids' movement was much slower when they were on paper that had been walked on by ants, than on plain paper.

Furthermore, when placed on a dead leaf, where the aphid's instinct is to walk off in search of healthy leaves for food, the scientists found that the presence of ants significantly slowed the aphids' dispersal from the leaf. Lead author Tom Oliver from Imperial's Department of Life Sciences explains how ants could use this manipulation in a real-life scenario:

"We believe that ants could use the tranquillising chemicals in their footprints to maintain a populous 'farm' of aphids close their colony, to provide honeydew on tap. Ants have even been known to occasionally eat some of the aphids themselves, so subduing them in this way is obviously a great way to keep renewable honeydew and prey easily available."

However, Tom points out that the relationship between the ants and the aphids might not be that straightforward: "There are some definite advantages for aphids being 'farmed' like this by ants for their honeydew. Ants have been documented attacking and fighting off ladybirds and other predators that have tried to eat their aphids. It's possible that the aphids are using this chemical footprint as a way of staying within the protection of the ants."

Professor Vincent Jansen of Royal Holloway's School of Biological Sciences, concludes: "Although both parties benefit from the interaction, this research shows is that all is not well in the world of aphids and ants. The aphids are manipulated to their disadvantage: for aphids the ants are a dangerous liaison."

-Ends-

For further information please contact:

Danielle Reeves, press officer, Imperial College London
Tel: +44 (0)20 7594 2198
Mob: +44 (0)7803 886248
Email: Danielle.reeves@imperial.ac.uk

Notes to Editors:

1. 'Ant semiochemicals limit apterous aphid dispersal' Proceedings of the Royal Society B: Biological Sciences, Wednesday 10 October 2007.

Thomas H Oliver (1), Alla Mashanova (2), James M Cook (3), Simon R Leather (1), Vincent AA Jansen (2)

(1) Division of Biology, Imperial College London, Silwood Park Campus, Ascot, Berkshire, SL5 7PY
(2) School of Biological Sciences, Royal Holloway University of London, Egham, Surrey, TW20 0EX
(3) School of Biological Sciences, University of Reading, Reading RG6 6AS.

2. About Imperial College London

Rated as the world's ninth best university in the 2006 Times Higher Education Supplement University Rankings, Imperial College London is a science-based institution with a reputation for excellence in teaching and research that attracts 11,500 students and 6,000 staff of the highest international quality.

Innovative research at the College explores the interface between science, medicine, engineering and management and delivers practical solutions that improve quality of life and the environment - underpinned by a dynamic enterprise culture.

With 66 Fellows of the Royal Society among our current academic staff and distinguished past members of the College including 14 Nobel Laureates and two Fields Medallists, Imperial's contribution to society has been immense. Inventions and innovations include the discovery of penicillin, the development of holography and the foundations of fibre optics. This commitment to the application of our research for the benefit of all continues today with current focuses including interdisciplinary collaborations to tackle climate change and mathematical modelling to predict and control the spread of infectious diseases.

The College's 100 years of living science will be celebrated throughout 2007 with a range of events to mark the Centenary of the signing of Imperial's founding charter on 8 July 1907.

Website: www.imperial.ac.uk

3. About Royal Holloway University of London

Royal Holloway, University of London is globally recognised as one of the UK's leading teaching and research institutions - ranking among the top 10 elite research-intensive UK universities (in the most recent Research Assessment Exercise) and 5th in a league table of UK universities in the 2005 'National Survey of Student Satisfaction.' Located in 135 acres of parkland and with easy access to central London, the College offers challenging and innovative courses for a vibrant community of 7,000 undergraduate and postgraduate students from more than 120 countries. Royal Holloway also has strong links with business and the local community. Through its Research & Enterprise team the College offers high-quality support for start-up businesses, actively promotes entrepreneurship and collaboration, and is a key contributor to the regional economy.

4. About the University of Reading

The University of Reading is one of the foremost research-led universities in the UK. Founded in the nineteenth century and gaining a Royal Charter in 1926, we offer a wide range of programmes from the pure and applied sciences to languages, social sciences and fine art. New research and the latest thinking continually feed into undergraduate teaching, with our academic staff working at the forefront of their fields of expertise.