Invasive Bugs, Plants Prefer Summer Plane Flights, Study Finds

Kate Ravilious
for National Geographic News

April 11, 2007

Humans aren't the only ones to take a summer holiday, a new study has revealed.

Creepy-crawlies, flies, and plants also join the vacation rush by hitching long-haul rides inside airline baggage.

The research reveals that—as for people in many countries—June, July, and August are the peak months for long-distance travel.

Jet-Setting Beetles

Previous studies have shown that international flights are a significant factor in unwelcome insect invasion. Some 73 percent of recorded pest interceptions in the U.S., in fact, occur at airports. (Related: "It's Invaders vs. Invaders as Scientists Target Alien Species" [February 22, 2006].)

Curious to determine when insects pack their bags and where the bugs are most likely to go, Andrew Tatem and Simon Hay of the University of Oxford in England studied global flight patterns for the 12-month period from May 1, 2005 to April 30, 2006.

Pest transfer between far-flung locations is more likely when the weather is similar in both regions, making it easy for the pests to settle into their new home.

So the researchers used rainfall, temperature, and humidity data from each region to work out which places linked by the global flight network had the most similar climates at various times of the year.

"Hawaii, with its moderate year-round climate, is a hot spot for pest invasions," Tatem said. "It is linked to a similar climate in Central America in April, Asia in July, and the Caribbean in October."

In general, though, June, July, and August are the peak months for insect travel.

"There are more airports in the Northern Hemisphere, and the major Southern Hemisphere airports tend to be closer to the Equator," Tatem said. "The June-to-August period stood out as the time when, overall, the busiest flight routes connect geographically distant but climatically similar locations."

The new study appears in the Proceedings of the Royal Society B.

Ecological, Economic Damage

Invasive insects—from Asian longhorned beetles to South American fire ants—are a big and costly problem for North America. (Related: "Alien Beetles Tracked with "Ray Guns," Dental Floss" [October 16, 2006].)

"The Mediterranean fruit fly is one of the most destructive pests and has frequently invaded California," Tatem said. "It decimates fruit crops and is very expensive to eradicate."

And a beetle called the emerald ash borer, which hails from eastern Asia, is currently munching its way through forests near Detroit, Michigan.

"There is now nothing we can do to stop it, and eventually it is likely to kill most of the ash trees in North America," said Sandy Liebhold, a specialist on forest insects from the Forestry Sciences Laboratory in Morgantown, West Virginia.

Hopefully, though, the new findings will help stop the foreign pests from arriving in the first place.

"One way this analysis could be used immediately would be for agencies to target limited resources on the airports and times of the year when the risk of invasions is highest," said biologist David M. Lodge of the University of Notre Dame in Indiana.

Australia and New Zealand already have strict fumigation and control policies at their airports, and this may soon become common elsewhere.

"It is much more effective to prevent something from arriving in the first place," Liebhold said, "than to try and deal with it after it has arrived."

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