Sometime after making a star appearance at Halloween, bats in the Mid-Atlantic region will fly into caves for their annual winter hibernation. And if a disturbing trend holds, most won’t fly back out in the spring.

Bats have been nearly wiped out in states including Virginia, West Virginia, Pennsylvania, New York and Vermont by white-nose syndrome. A survey of six species at 42 sites in those states found that their numbers have declined by almost 90 percent.

The long suspected culprit, an aggressive fungus called Geomyces destructans, has been definitively linked to the disease, according to a study published last week in the journal Nature. It gives hope that a treatment could be found that would slow the progress of the disease, wildlife biologists said.

But it might already be too late to save some bats in the Northeast. Two species could become extinct in Mid-Atlantic states in as few as seven years, scientists said. In 2009, biologists said at least 1 million bats had dropped dead over three years.

“And it’s absolutely gotten worse since then,” said Mylea Bayless, a conservation biologist for Bat Conservation International in Austin.

“Easily, the number of states and sites where it’s been found has doubled,” she said. “It’s probably far more than a million, or likely millions” of dead bats.

The significant loss of insect-eating bats could lead to greater damage to agricultural crops and force farmers to spend more on pesticides.

Gudrun Wibbelt, a veterinary pathologist in wildlife diseases for the Leibniz Institute for Zoo and Wildlife Research in Berlin, called it “a horrible death.”

Bats plummet into a deep sleep during their winter-to-spring hibernation, driving their heart rates down, causing their bodies to cool.

That’s when the disease, which covets low temperatures, strikes.