To counter this threat, the pest control technician leaves the stations in place and periodically checks them for signs of new infestation.

When the eggs hatch, a new infestation begins.

"You don't want to tear your house apart and put it back together," he said, "only to have a new infestation six months down the road."

No evidence of new infestation was found.

Flea soaps and shampoos can kill adult fleas on the animal, but they provide no lasting protection against new infestations.

In recent years, a new infestation of a hazardous moth has effected the population of oak trees in London.

"The bad news is that we have found a new infestation in Central Park," Mr. Benepe said.

Controlling new infestations is more effective, and oftentimes more feasible, than trying to control large infestations.

Because of the shortfall, only 25 percent, or 2.2 million acres, of the areas that need to sprayed to prevent new infestation have been treated.

Despite the treatment, Dr. Parker said he found a new infestation in the reading room on Dec. 24, and the room was treated again.