Humans blamed for gypsy moth spread.

The wave of leaf-eating gypsy moths now surging across the eastern United States would slow to a trickle if it weren't for human activities, according to a computer model of the insect scourage.

Since 1966, the moths' tree-destroying larvae have swept into new areas at an average rate of more than 20 kilometers per year. But without hitching rides on recreational vehicles, moving vans and transported plants, the larvae would spread by only 2.5 km per year, predicts a team of entomologists led by Andrew M. Liebhold at the U.S. Forest Service in Morgantown, W. a.

The researchers found that the insect's spread is not due to an expansion into more desirable forests. "The higher observed rates of expansion are probably due to human-caused movement of gypsy moths," they conclude.

Gypsy moths were accidentally introduced into the United States in 1868 by a French naturalist living in Medford, Mass. Today, the bristly caterpillars with red and blue spots live as far south as Virginia and as far west as Michigan. If not halted, the moths will spread southward to Florida and westward to Kansas within 50 years, Liebhold's team predicts. One means to stem the tide, he says, could be a fungal infection that naturally kills the moths. The fungus died off soon after its U.S. introduction in 1910, but has recently begun proliferating in the wild in the Northeast (SN: 8/4/90, p.77).