Long-term protection from termites.

Minute quantities of an insecticide used in Europe, but not the United States, to kill certain crop pests can provide slow, yet effective protection against subterranean termites.

In the soil, millions of these termites build nests that extend over an area the size of a football field. To protect houses, builders often put several kilograms of pesticides on the soil, says Nan-Yao Su, an entomologist at the University of Florida research center in Ft. Lauderdale. "It forms a chemical barrier but [doesn't] do anything to the population in the soil," he adds.

Consequently, researchers have been investigating other control strategies, many of which use growth inhibitors such as a chemical called juvenile hormone to try to reduce the number of termites in the soil. In coming up with one such control strategy, Su and his colleagues have discovered that, over time, a chemical called Hexaflumuron will wipe out these termites. This chemical inhibits the production of chitin, the material that makes the insect's outer coat strong.

Su mixed up to 1.5 grams of this pesticide in with bait, which termites retrieved and ate with no apparent ill effects. But weeks later, the ingested chemical prevented the insects from molting properly "It's a time bomb, so to speak," Su explains.

For two years, he and his colleagues monitored the termite populations living near a group of infested houses. They placed wooden stakes around six houses and, once the stakes had become infested, placed bait-filled plastic tubes near them.

Within two months, the termites had disappeared completely from the ground near four of the infested houses and have not returned, even after two years, says Su. The ground near the other two houses still has a small number of termites.

A company called DowElanco in Indianapolis is developing the chemical for use against termites, says Su. But he expects it wiil take several years for a commercial product to appear.