Two years from a compound to repel the dreaded midge

Published on Wednesday 28 July 2010 14:40

THE lucky few are about to come to the rescue of the suffering majority.

Within the next two years scientists hope to have a commercially available answer to the dreaded midge, inspired by the small number of people who naturally repel the biting beasts.

A survey of more than 300 competitors taking part in an endurance race have supported experts' views that one in ten people has an in-built resistance to the insect which causes misery to thousands of residents and visitors.

The research showed that taller and larger people are more susceptible to midge attack and that women are more likely to react badly to bites. Vulnerability to the insects is also hereditary with children likely to inherit a tendency to be bitten from their parents.

The study was conducted by researchers at the University of Aberdeen and Rothamsted Research and involved competitors taking part in the 2008 First Monster Challenge, a 120km team relay duathlon around the shores of Loch Ness.

Professor Jenny Mordue, a retired professor in the university's department of zoology and an expert on midges, was joint leader of the study.

She said: "Just over one in ten are not bitten at all and that substantiates our more detailed work on volunteers. We know these people produce one or two compounds, or volatiles, from their skin - out of the 300 that everyone produces - in slightly higher amounts than the rest of us and these act as natural repellents."

She said the compounds alter the human scent which, along with carbon dioxide in the breath, is one of the ways midges recognise people.

"The small compounds are floating in the air, we know what they are and they are under patent as we develop them into a new repellent," she said. "We hope to have that natural, human-derived repellent on the market within the next two years."

Prof Mordue said size matters when it comes to midge attack.

She added: "We think this relates to the overall quantity of these volatiles coming off our skin, so the more you are releasing, the more midges you attract.

"The preference for the insects to target taller people could be associated with midge behaviour and flight patterns, as they have a preferred flight height of about two metres.

"So as they come towards a group of people they would meet the tall ones first and we think that's why they are getting bitten more frequently. Larger people would provide a more substantial visual target for host-seeking midges as well as greater amounts of heat, moisture and attractant semiochemicals (behaviour modifying chemicals), such as carbon dioxide, which encourage midges to bite."

However it is unclear why women suffer more after being bitten. Professor Mordue said: "We don't know if women are more sensitive about what's happening on their skin or men try to ignore things and be manly about it."

The peak midge season, around June to September, directly matches the Scottish tourist season. It has been estimated that the insects cost the industry 286 million a year.

Midges are most active at temperatures between 15-30C, with August seeing the biters at their most ferocious.

A swarm of midges can deliver approximately 3,000 bites an hour. Only the females bite. It gives them protein and energy to produce their eggs.

It was hoped that the harsh winter would have killed off many of the insects this year but experts say populations are no different from previous years.