Ecologists have found a new pattern in the gypsy moth invasion across the Northeastern United States that might be useful in battling the moths.

The gypsy moth invasion is arguably the most intensively studied species invasion in history. Since the moths' accidental release near Boston in 1869, the species has swarmed across more than 1 million square miles of the United States, defoliating up to 12 million acres of forest each year.

By analyzing more than four decades' worth of data, Derek Johnson and colleagues at the University of Louisiana at Lafayette discovered the moths' spread occurs in pulses roughly four years apart.

That, say the scientists, is probably because moths that spread far beyond the current frontier cannot establish breeding populations unless they colonize in sufficient numbers.

Thus, says Johnson, moths can spread only at times when their populations are high and so targeting large groups of moths near the edges of the current distribution could help to slow their advance.

The study appears in the current issue of the journal Nature.

Copyright 2006 by United Press International