Growing Magazine - February, 2012
Widespread Bat Deaths Mean Higher Insect Populations
As millions die, growers will see more crop pests
When bats turned up with little snouts that looked like they were snorting cocaine, biologists took notice. Upon closer inspection, the bats had foamy white froth on their noses. The disease quickly became known as white nose syndrome. WNS promises to cause as much concern and upheaval for growers as it does for any other group.
Depending on which source you believe, bats eat roughly the equivalent of their body weight in insects each day. That means bats, along with birds, represent one of the best natural pesticides available to fruit, vegetable and other farmers.
Without bats, horticulturalists say, growers are likely to see a major upturn in insect infestations. This could lead to production problems or a need for more insecticides, neither of which is great news for producers.
First noticed in northern New York state, WNS quickly spread east into New England and down the backbone of the Appalachians. WNS is associated with high bat mortality.
Soon, officials with state and federal agriculture departments, the U.S. Fish and Wildlife Service (USFWS) and other agencies began to field reports from abandoned mines, caves, barns and other places where bats normally congregate. The concern for growers is whether this will mean a jump in insect problems come summer.
"If you take out a top predator, it will have an impact," says Christina Kocer, assistant national coordinator for WNS with the USFWS in Hadley, Mass. She notes that insects have their own patterns, influenced by weather and population cycles. However, the loss of bats is likely to mean more insects in orchards and groves.
"I don't see anything stopping WNS," says DeeAnn Reeder, associate professor of biology at Bucknell University, Lewisburg, Pa. "I try not to be a 'sky is falling' person, but the outlook is bleak."
She figures that every million bats in a region consume 692 tons of insects per summer. She puts the number of dead bats at 2 million. So something like 2.8 million pounds of live insects will not be taken out of the sky this summer. "That is tractor trailer loads of insects," she says.
According to wildlife biologist John DePue with the Maine Department of Inland Fisheries and Wildlife, the little brown bats that have already died due to WNS would have eaten between 660 and 1,320 metric tons of insects in one year. That is one species. WNS might affect as many as 25 bat species.
He notes a recent study published in Science magazine estimates that insect-eating bats save the U.S. agricultural industry $3.7 billion a year. A similar study in Texas, using local bat figures, said that bats save farmers anywhere from $12 to $173 an acre a year in pesticide costs, depending on the crops grown and the pesticide program followed. That study in Science magazine is the best look at the impact of the bat die-off.
The agent that causes WNS is thought to be a cold-loving fungus, Geomyces destructans. Dead bats with the white nose have exhausted their fat reserves, and the fungus is thought to be a causal agent. Recent research shows that during hibernation WNS-affected bats awake as often as every three or four days as opposed to the normal stirring every 10 to 20 days. A study from The Ohio State University found that bats need to eat three moths per night just to maintain their ability to echolocate - the way bats "see" their environment. It takes many more bugs to support their metabolism. Needless to say, in the dead of winter there are few moths, or any other insects, flying around for bats to eat. So, about 90 percent of the bats infected with WNS perish due to starvation.
Should growers plan to spray more frequently or at higher rates? Most extension experts say "no," but do caution that insect scouting will be even more critical in the near term.
"I don't want to promote using more chemical pesticides," Kocer says, adding that chemicals will also affect bat health. "Bats are having a hard enough time as it is," she says. "Increasing the use of pesticides will decrease the quantity and quality of their food. They are dealing with enough stress."
Reeder says the fungus has not yet been proven to kill the bats. "Typically fungal infections don't kill animals," she says. "Typically animals get fungal infections when they are immune-compromised. We know a fair amount about what white nose syndrome is doing to the bats, but we don't know exactly why they die. We know their hibernation patterns are altered in a way that would cause them to lose weight. We know that in many cases they appear to have starved to death. What we don't know is how you go from a fungal infection in your skin to starving to death."
The good news, Reeder says, is that the spread of the disease has slowed as it moves across the country. "I think it is slowing down since the population of bats is thinner," she speculates. "But I don't see anything stopping it. This is a wildlife disease of unprecedented size." Unlike the elimination of a species like passenger pigeons, WNS has the potential to take out 25 species.
How it happened
Sport cavers - people who explore caves for fun - first noticed bats dying off in 2006 in the Albany, N.Y., area. According to the Organization for Bat Conservation (OBC), about 10,000 bats were found dead in several New York caves in 2007. That represented more than half of the wintering bat population in those caves. Many of the dead bats had a white ring of fungus around their nose. Most affected hibernating bats in the region have white fungal growth on their ears, wings or nose.
To date, the fungus is estimated to have killed millions of hibernating bats in 17 states and four Canadian provinces. Little brown bats, once a common bat in the area, are sustaining the largest number of deaths. States as far from the East Coast as Wyoming are developing plans to monitor WNS. Nobody seems optimistic that a cure is in the offing.
A recent N.Y. Department of Environmental Conservation survey shows a 93 percent decline of little brown bats in 23 caves at the epicenter of WNS. Five other hibernating bat species are currently affected by the fungus: big brown bat, northern myotis, tricolored bat, eastern small-footed myotis and Indiana bat. The federally endangered Indiana bat has shown a decline of 53 percent in the epicenter caves.
Reeder says a nursing big brown bat with two pups will eat 110 percent of her body weight in insects. "That's like me eating 550 Quarter Pounders each night," she says.
The bats eat agriculturally important insects like corn moths. "That's a big, juicy meal for them," Reeder says. "It's a lot better than having to work to catch lots of tiny mosquitoes."
In an effort to stop the spread of WNS, the government banned sport cavers from entering caves on federal and state land. The fear was that cavers were spreading the disease. That has been shown to be quite unlikely. At the same time, it removed those most knowledgeable about local caves, and the bats therein, from providing more information to scientists. Ironically, the federal government kept all of its own show caves open to visitors from everywhere. It soon became apparent, however, that humans are not the vector spreading WNS.
The USDA has not done a lot with WNS. Reeder thinks that the USDA has not yet made the farm connection. She notes that honeybee colony collapse got a lot of attention since there was a direct connection between bees and pollination. Interestingly, most of the work done by the USDA on WNS revolves around forestry rather than fruit tree crops. That may be because many caves are found in the forest. However, a huge number - more than half - of all wild caves are on privately held land, often farms.
The USFWS has taken the lead in researching the situation. In December, they began evaluation of research grants, and the USFWS says it expects to pour over $1 million into grants in an effort to define and remedy the problem. Despite the continuing search to find the source of this condition by numerous laboratories and state and federal biologists, the cause of the bat deaths remains unknown (see sidebar).
Six species of bats have been affected so far. "I think that one of those species, the big brown bat, will probably be OK," Reeder says. However, she feels the other species - the little brown bat, tricolored bat, small-footed myotis, northern long-eared myotis and the Indiana bat, which is critically endangered already - are all equally highly susceptible. She would also add the Virginia big-eared bat and the gray bat, which are endangered, to that list.
Ironically, two species of tree-dwelling bats do not appear to be susceptible to WNS.
Big brown bats are somewhat less susceptible to WNS than other species like the little browns. "Big brown bats might survive in decent numbers," Reeder says. "Little brown bats may be extirpated from the Northeast in the next 10 to 15 years."
"I think within several years there will be practically no bats left in Pennsylvania," Reeder worries. "New York is empty. Massachusetts is empty. There are just handfuls," she says.
"One of our sites that we study heavily, the Shindle Iron Mine, normally has over 1,000 bats. Now it has six. Even if there are survivors, these bats may become functionally extinct, meaning that we might have some small populations, but they will be below a viable population size," Reeder says.
There is some hope, albeit distant. Geomyces destructans has been detected on bats in several European countries including Spain, France, the Netherlands, Switzerland, Romania and Hungary. European bats are not dying from WNS in the mass numbers observed in the U.S. and Canada. In fact, not many are dying at all. Nobody yet knows why.
Kocer says the fungus appears to be the same, but geneticists are working to see whether there is some miniscule genetic difference between Europe's fungus and America's that allows their bats to deal with it.
Did the European bats go through a bout with WNS and those that survived are basically immune to its ravages? Are the European bats experiencing milder winters or better insect crops to harvest on their nightly flights and thus are less prone to starvation? Some note that European bats roost in small groups where many American bats roost in large colonies. Perhaps the European bats do not spend as much time underground. Or is something else at work?
Tree-roosting bats in America do well, too. "We have no idea why," Kocer says. "They are tough to study since they are migratory." Researchers hope to have answers to these questions soon. In the meantime, growers are advised to ramp up insect scouting programs and be alert for devastating insect population booms in their local region.
What growers can do
Kocer says the best thing to do is to be "bat friendly." That means helping bats out by not destroying their roosts. "A lot of people have that fear of bats," she says. "Give them a safe place to roost."
Some growers build purple martin houses for insect control. Bat conservation groups promote bat houses - structures that bats can use for roosting or hibernation. However, given the reduced number of bats out there, it is less likely that a new bat house will attract new residents, but it's worth a try.
More to the point, leave old snag trees that are exfoliating where they are, Kocer suggests. If you do need to remove trees, wait until fall or winter, when bats are in caves.
Tree-roosting bats have fewer problems with WNS. Kocer says she thinks it is because they spend so little time underground. "They don't have the exposure to the fungus," she says. They do, however, have exposure to wind farms, and that adds another mortality factor for bats.
"Above all, protect their maternity colonies," Kocer encourages.
Curt Harler is a freelance writer and a frequent contributor. He resides in Strongsville, Ohio.