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.

Wildlife biologists who’ve sounded an alarm about the disease since it was discovered at Howes Cave near Albany, N.Y., five years ago seem resigned to losing several species in the Mid-Atlantic region, starting with the once abundant little brown bat.

It “has the potential to become extinct in the northeast in only 7-30 years; a similar fate may await Indiana, northern long-eared, and tri-colored bats,” according to a report completed in June and later published in Bat Research News.

Geomyces destructans has been called athlete’s foot on steroids. It burns holes in the membrane that allows bats to flap their wings. Bats found alive amid hundreds of corpses in caves are often experiencing death spasms.

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. Lesions develop on the hair and exposed skin of bats and a cotton-like fuzz often covers their noses. Small bodies plop on damp cave floors along the Appalachian trail from North Carolina to Vermont.

A similar fungus exists in Europe, but scientists aren’t certain that the American fungus is related — or how it crossed the Atlantic if it is. European bats aren’t dying en masse.

The survey conducted last year of the 42 sites focused on caves where bats have been dying for at least two years. It found that the little brown bat population fell from nearly 385,000 before white-nose syndrome to 30,000, a 91 percent decline. The northern bat’s numbers fell from about 1,700 to 31, a 98 percent drop.

A separate study released in April said the loss of so many insect-eating bats could force farmers to pay tens of millions of dollars more for pesticides to protect crops. The U.S. Fish and Wildlife Services recently offered $1 million in grants to study white-nose syndrome, bringing the total to $9 million since 2008.

The fungus is traveling south and west, but Bayless said scientists aren’t sure it can survive without cool Mid-Atlantic cave temperatures. In those regions, its growth could slow and it might not be as lethal. The fungus has been found in Oklahoma but bats there have not been sickened.

Farmers rely on bats to dine on beetles and gypsy moths that lay eggs that produce worms in corn and other crops. Each bat eats half its weight in insects every night, according to Wildlife Magazine, published by Defenders of Wildlife. They especially crave big crunchy moths that lay worm-producing eggs in corn.

The April study, Economic Importance of Bats in Agriculture, published in the journal Science, said a single colony of 150 bats in Indiana ate about 1.3 million insect pests in a year.

Drawing on that number, the study’s authors — Justin G. Broyles, Paul M. Cryan, Gary F. McCracken and Thomas H. Kunz — estimated that up to 1,320 metric tons of insects were not eaten due to the disappearance of a million bats.

The economic impact on agriculture was hard to predict, the authors said, but they gave it a shot. Using estimates that insect-chomping bats lessen damage to crops, they calculated that their worth to farmers is about $3.7 billion or more per year.

Moths, which also burrow into trees, will threaten more acres of forests because of the absence of bats.

The economic study raised both awareness and controversy. “They’re making some assumptions, clearly,” Bayless said. “But it’s the first time anyone has tried to quantify those kinds of economics. It’s a good first look at what those impacts might be.”