Researchers at the University of Cambridge have shown that viruses 'use' aphids as pawns, discouraging the insects from permanently settling on already-infected crops and using this forced migration to spread infection to healthy plants.

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Aphids are sap-sucking insects that attack many different types of plants. They are a major agricultural pest and frequently transmit crop-infecting viruses. By altering infected plants' biochemistry, crop-infecting viruses cause those plants to smell and taste unpleasant to visiting aphids. This repels the insects, causing them to move swiftly away to healthier plants, unwittingly transporting and spreading the virus they carry.

This research could have significant impact on African agriculture, in particular, the authors said on Wednesday. Working with various agencies, Dr John Carr and colleagues aim to help resource-poor farmers by deploying plants to act as aphid-decoys, drawing the insects away from crucial crops and halting the spread of infection through these farmers' livelihoods.

Dr Carr commented, "The work started almost accidentally when about five years ago a student and I noticed that aphids became sick or died when confined on a virus-infected plant. It's an illustration of how research driven by curiosity can lead to findings that could have a positive impact in the real world – in this case in combating crop-damaging insects and the viruses they transmit."

The Cambridge team collaborated with researchers at Imperial College, London, using Arabidopsis plants – a model organism for research – as hosts and monitoring the effect that the crop-infecting cucumber mosaic virus had. It was observed that the virus launched a concerted attack on both the plant's immune system and its biochemistry, meaning it was unable to fight off either the disease or aphid pests.

The aphids, instantly repelled by the smell and taste of the plant, left for healthier plants, but not before landing on the plant and contracting the virus. The scientists said this meant the mosaic virus could ensure that the spread of the infection would be self-sustaining and highly efficient.

This research focuses on an example of what evolutionary biologist Richard Dawkins has called the 'extended phenotype'. For Dawkins, the word 'phenotype' (the traits of an organism) should not be limited solely to biological processes, but should also be used to describe all effects that a gene has on the organism or environment in which it exists, or other organisms nearby. In this case, it was discovered that a virus influences the infected host, the Arabidopsis plant, and forces the host to change in a way that is beneficial to the parasite.