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  The Daily Telegraph 11 Apr 07
Air travel threatens biodiversity
Alien species and diseases are invading new habitats, reports Roger Highfield

An analysis has examined how global air travel has made it easier than ever for hitchhiking pests to move from one part of the planet to another to reduce biodiversity and create havoc, as occurred when the Mediterranean fruit fly attacked American fruit crops.

For centuries the distances that potential pests and diseases had to cover was a natural barrier. But in the age of low cost air travel nowhere in the world is more than a few days away and the chances of bringing in new species by accident are so much higher.

The research has identified an 'invasion window' across the global air network from June to August when climatic conditions at regions linked by long haul routes are most similar to one another and the higher number of flights increases the chances of exotic species hitching a ride to somewhere new.

It is the far-flung regions with similar climates that have in the past half century been linked by a busy flight route that are at most increased risk of an invasion of foreign species, according to the analysis by Dr Andy Tatem and Dr Simon Hay at Oxford University, published in the Proceedings of the Royal Society B.

While the spread of invading species in a new area has been extensively studied, relatively little work has been done on how such organisms might initially be dispersed and survive.

Recently, international air travel has been pinpointed as a significant factor in the movement of economically damaging pest species, with 73 per cent of recorded pest interceptions in the US occurring at airports.

From the 1980s, the Mediterranean fruit fly has been consistently imported through the transport of fruit, triggering eradication campaigns in America that have cost tens of millions of pounds.

"There is evidence for sustained introduction to the US of the world's biggest fruit production pest, the Mediterranean fruit fly, through passenger baggage and cargo," said Dr Tatem.

Another hitchhiker is its cousin, the peach fruit fly, from India and Southeast Asia. Plant pathogens are often found in air cargo, such as Asian citrus canker which can kill trees. Travellers carrying fruit for an in-flight snack may unknowingly bring with them fly larvae or a plant disease.

A native of Australia, Indonesia, Papua New Guinea, and the Solomon Islands, the brown tree snake is thought to have hitchhiked to Guam on military aircraft in the late 1940s or early 1950s. The lack of natural predators and ample prey allowed the snake population to explode, exterminating Guam's native forest birds.

Disease-carrying mosquitoes have also survived long haul flights in aircraft cabins, which is why they are sprayed with insecticide.

"There also exists the (very rare) phenomenon of 'airport malaria' where a mosquito carrying malaria hitches a lift on a plane, and then flies off to bite and give malaria to people who have never even travelled to a malarious area," said Dr Tatem.

To weigh up the risk that the explosion of air travel is making it easier for such alien species to invade, the team analysed data from over 800 airlines for 12 months (from 1 May 2005 to 30 April 2006) detailing overt three million flights. They then examined the mean temperature, rainfall and humidity at each region linked by a flight route to see how the global air network provides seasonal links to places with similar climates.

"When we combined this monthly climate data with information on how busy flight routes were in particular months the results were striking," said Dr Tatem, "the June to August period stood out as the time when the busiest flight routes connect geographically distant but climatically similar locations. This combination potentially increases the overall chances of dispersal and successful invasion of foreign species."

The research will help airport and government biosecurity experts to identify where and when a heightened risk of an invasion of foreign species may occur; enabling them to target their surveillance and control efforts more effectively.
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Related articles on Global issues: biodiversity loss and Exotic Species
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