Baseball is a durable sport. It survived the Black Sox scandal, the players' strike and the steroids era, not to mention one-man distractions like Pete Rose, John Rocker and Ozzie Guillen. But now a different kind of dilemma has emerged, and instead of hurting baseball's public image, it's quietly eating at the sport from within.

No one knows exactly when or where emerald ash borers arrived in America, but the first report came in 2002 from Canton, Mich. A decade later, the diminutive Asian beetles have invaded 15 states and two Canadian provinces, killing tens of millions of ash trees in Michigan alone, plus tens of millions more from Kentucky to Quebec. On April 18, researchers reported the first sighting east of the Hudson River, suggesting the bugs are now dangerously close to the vast ash forests of New England.

Emerald ash borers eat trees' innards and then leave them to die, a tactic that can wreak havoc without natural predators or immunities to mitigate it. It's not just ecological havoc, either: The U.S. Department of Agriculture has already spent more than $200 million battling the bugs, and it estimates they'll ultimately rob billions from the national economy. Ash wood is popular in lots of U.S. products, from guitars and archer's bows to tool handles and bar stools. And one of the most iconic uses for ash is at the core of America's national pastime: the wooden baseball bat.

Of course, it's unlikely EABs will eat baseball out of business entirely — even if they killed every ash tree in America, major leaguers could still use maple, and many amateurs could simply stick with aluminum. But lots of high-profile players swear by ash, including New York Yankees stars Derek Jeter and Alex Rodriguez, arguing it's lighter, more flexible and safer than other options. And with their tastes in timber now shared by ravenous invaders from Asia, the issue has grown to symbolize exotic pests nationwide. It has also provided a crash course in how not to contain them.

Meet the beetles

The emerald ash borer may be a big problem for North America, but the bug itself is tiny — as the photo at right shows. Its small size likely helped it sneak onto the continent undetected, possibly even years before its official discovery in June 2002. The USDA suspects it was hidden in wooden pallets, or some other type of lumber, that was shipped into southeast Michigan through the Great Lakes. But however it got here, the EAB clearly liked what it found.

Female EABs lay eggs on the bark of ash trees in summer, and after hatching, the larvae chew into the inner bark, known as the cambial layer. They feed there during fall and winter, making S-shaped tunnels as they burrow (see photo below).

BORED TO DEATH: An EAB larva bores through the inner bark of an ash tree. (Photo: USDA)

This can easily kill the tree, since the cambial layer is not only where it produces new wood and bark, but also where it transports water and nutrients through its trunk. The larvae finally pupate in late spring, and adults emerge in summer from D-shaped holes in the bark. They'll live for just three weeks after this, but that's long enough to fly somewhere new, mate and lay eggs, starting the process all over again.

Home-field disadvantage

"EAB adults are strong fliers, yet most only fly short distances," says Sharon Lucik, spokeswoman for the USDA's Animal and Plant Health Inspection Service, which deals with EABs and other non-native species. "However, under certain conditions, individual beetles are capable of flying up to several miles to infest new trees. This is the natural spread of the pest." The unnatural spread, she adds, is when people move around infested timber, namely firewood. "It's this human-assisted spread that is the wild card and is the source of the widespread dispersal of the pest," she says.

While North America's main EAB population is only spreading by 2 to 3 miles per year, transportation of firewood has helped satellite colonies jump much farther afield. Federal and state public-awareness campaigns now warn people to stick with local kindling, and Lucik already notices at least a small difference. "Certainly a portion of the public has changed their behavior about transporting firewood," she says, noting that many campgrounds now forbid campers from bringing in firewood.

Growing public awareness may slow the beetles' spread, but it can't do much to save forests already on the frontlines. And since EAB damage isn't immediately obvious, it's not always clear where those frontlines are. Here's a map of the 15 states, colored green, where EAB invasions are known to be under way:

Knock on wood

Lucik's guarded optimism is shared by Brian Boltz, general manager for Larimer & Norton, the company that makes Louisville Slugger baseball bats. His business relies heavily on ash forests in eastern Pennsylvania and New York, which have yet to show signs of EAB infestation. And even though EABs were found about 100 miles away in 2007, he says their initial five-year explosion has slowed down in the past five years.

"It's still spreading, but from 2003 to 2006, when I was following it out of Michigan to Ohio, you'd hear about another county [being infested] almost every month in the summer," Boltz says. "The findings in Pennsylvania now are kind of spread out ... so I feel a little bit better. We've at least got more time."

Production of ash bats is actually up lately, he adds, since people are cutting trees earlier in hopes of beating beetles to the punch. Still, he can't help but wonder how long that strategy will work: "There is more harvesting now, but how that affects us five, 10, 15 years from now, I am a little worried about that."

SWING THEORY: L.A. Angels second baseman Howie Kendrick has advocated for ash bats, telling ESPN in 2008 that he likes "how the ash has some give." (Photo: Lisa Blumenfeld/Getty Images)

Boltz's concern is understandable, even with the recent surge of harder, heavier maple bats. Ash has been used in Major League Baseball since 1884, while maple dates back only to the 1990s — popularized largely by slugger Barry Bonds, whose own popularity later fell amid doping accusations. The MLB banned certain types of maple in 2010, citing its tendency to shatter dangerously when a bat breaks, rather than flaking like ash. Many players also praise ash's flexibility, Boltz adds. "It's kind of like in golf, where you have a metal versus a graphite shaft. When you're swinging a bat, you get a little more flex with ash than you would with maple."

Since EABs don't eat whole trees, bats could still be made from their victims. Larimer & Norton hasn't tested that yet, but Boltz says the company tries to avoid wasting cut timber. "We have a philosophy that if someone brings in a weakened tree, we will use it — but for souvenir bats, little league maybe. We will not use it to make professional bats. We just don't want to take a chance on our highest quality product."

Boltz does have backup plans, though, if his current ash stocks vanish. "Long term, if it's all gone, we'll have to look at different areas," including New England, he says. "New England ash is heavier than Pennsylvania ash, not quite as flexible, but it will still satisfy the majority of players." Yet EABs are also nearing New England, and Boltz admits other tree types may be needed. "We did try a beech bat, also yellow birch," he says. "At this point, those are the only two other species we've worked with."

Battle of the bugs

EABs have run amok in America mainly due to a lack of natural predators. But they still have enemies back in Asia, and if one bug can travel the world, why not the other? That's the idea behind a promising EAB-control plan in which the borers' natural predators — parasitic, stingless wasps — are being released into U.S. forests.

In their native habitat, the wasps walk on the outer bark of ash trees, tapping their antennae to listen for the vibrations of EAB larvae chewing. Once they find one, they use their long "ovipositor" to penetrate the bark and lay a clutch of eggs. Up to a dozen wasps will later hatch and eat the larva — all while it's still inside the tree. Although their effectiveness remains unproven in America, these wasps can kill 60 to 90 percent of EAB larvae and eggs in Asia, according to the USDA.

Researchers began limited tests of this in 2007, proving at least that the wasps can survive a Michigan winter. More tests have since followed in five additional states, with some wasps later found half a mile away from their release points, confirming "parasitoid dispersal." The USDA is now testing several wasp species, one of which is already established at three release sites in Michigan and attacking EAB larvae. The agency is about halfway through a five-year implementation of this strategy.

WASP WARS: The parasitic wasp Tetrastichus planipennisi, native to China, is one of several species being released in U.S. forests to control invasive ash borers. (Photo: Stephen Ausmus/USDA)

While the wasp idea is intriguing, it's not the USDA's only trick pitch. The fungus Beauveria bassiana, for example, is being tested as a biocontrol agent to complement the wasps. It's already sold commercially as an insecticide, and scientists think it could be applied to infested trees before wasps are released, hitting EAB larvae with a one-two punch. (Preliminary studies suggest it doesn't kill the wasps.)

Aside from killing EABs, researchers have found clever ways to attract them, too. Purple traps are used in many states, capitalizing on EABs' odd fixation with that color. Scientists are also "girdling" some trees, cutting away a 6-inch-wide ring of bark that lures EABs into a trap. These trees become "population sinks," drawing in lots of EABs from the surrounding area, and are then cut down the next winter or spring. Along with various chemical baits, these tactics can help diagnose an invasion, but they aren't considered practical means of pest control.

Boltz is encouraged by initial results of the USDA's efforts, although his experience over the past 10 years has left him with a certain respect for his enemy.

"This is the critical time for us," he says, since the flurry of ash borers in late spring and summer offers updates on their conquest. "If I can get to the end of the summer and they haven't found any EABs in the harvest areas — that doesn't mean they're not there, but then I can at least breathe a sigh of relief until this time next year."

Also on MNN:

Russell McLendon ( @russmclendon ) writes about humans and other wildlife.

Emerald ash borer: The real 'Green Monster'
Exotic beetles are killing America's ash trees, a popular source of wood for baseball bats. And as these verdant invaders spread into the Northeast, their grow