20 January 2005 

Why do some people get bitten by mosquitoes more than others?

Mosquito feeding

Why is it that when you go on holiday some members of your family always seem to get bitten more than others? Scientists at Rothamsted Research in Hertfordshire think they may have found the answer and their work could lead to the development of novel insect repellents.

Research student James Logan has found that some people give off "masking" odours that prevent mosquitoes from finding them. His research builds on earlier studies on cattle, led by Rothamsted's Professor John Pickett, which showed that the number of flies on a herd depended on certain cows being present. The scientists found these key unattractive individuals gave out different chemical signals from the other cows. When these individuals were moved to another field the number of flies afflicting the herd increased.

James, working in collaboration with Professor Jenny Mordue at the University of Aberdeen, tested the behavioural reaction of yellow fever mosquitoes to odour from human volunteers. James said: "The mosquitoes were placed into a y-shaped tube and given the choice of moving upwind down either branch. The air flowing down one branch was laced with odour from the volunteer's hands."

Their results suggest that differential attractiveness is due to compounds in unattractive individuals that switch off attraction either by acting as repellents or by masking the attractant components of human odour. This theory differs from that of other research groups who have suggested that unattractive individuals lack the attractive components. The researchers are now testing these theories further using foil sleeping bags to collect whole body odours from volunteers. James said, "By identifying these key components and understanding how they work we could be closer to new methods of protection from these biting pests that cause losses in livestock and irritation and illness in humans."

James said, "We hope that the work with cattle and mosquitoes will lead to methods of controlling such biting pests that cause losses in livestock and irritation and illness in humans."

Note for editors

1. Rothamsted Research is one of the largest agricultural research institutes in the country and is sponsored by the BBSRC.
2. An article on this research features in the January 2005 issue of Business, the quarterly magazine of the Biotechnology and Biological Sciences Research Council.
3. The original work on Holstein-Frisian heifers was carried out at Rothamsted Research in collaboration with the Danish Institute of Agricultural Sciences and funded by the European Union.
4. The compounds that attracted the mosquitoes were identified using the coupled GC-EAG method. High-resolution gas chromatography is use to split odour extracts into their components parts. These are then passed over the antenna of an insect. Micro-electrodes attached to the antenna detect electrophysiological responses, which indicate that the insect is sensing the compound. Mass spectrometers are then used to identify the compound.

1. For further information, please contact the Rothamsted Research Press Office on 01582 763133 ext 2260 or email Adélia de Paula (adelia.depaula@bbsrc.ac.uk)
2. Rothamsted Research is based in Hertfordshire and is one of the oldest and largest agricultural research institutes in the country. The Applied Crop Science department is based at Broom's Barn, Higham, Bury St. Edmunds. North Wyke Research is located near Okehampton, Devon.