Good critters, bad critters

Jonathan Lundgren, an entomologist at the North Central Agricultural Research Laboratory near Brookings, looks at part of an ash tree that was infested with the emerald ash borer. The insect has not hit South Dakota yet, but it could “hitchhike” in on firewood.

• Predator might control emerald ash borer



BROOKINGS – Mother Nature plays no favorites in the insect world. Survival is the name of the game, and oft times the little bugs beat and defeat the bigger bugs.

And sometimes people take sides in the bug battles.

Humankind is not above manipulating nature when it comes to controlling insects it considers detrimental to its habitat or agricultural endeavors.

That might be the key to controlling the emerald ash borer – a beetle aka the EAB – should the nasty little critter that kills ash trees ever get to South Dakota.

The borer’s larvae destroy the water- and nutrient-conducting tissues under the bark of ash trees, eventually starving and killing them.

One of the most destructive non-native insect in the United States is not here now – but it's headed this way.

"Not yet," said Jonathan Lundgren, an entomologist at the North Central Agricultural Research Laboratory just due north of Brookings on Medary Avenue. He's not a pessimist; he is a realist about the possibility of the EAB getting into our state.

Lundgren explained, "The way this thing moves, as many invasive pests do, it's adapted to living under conditions that are favorable in South Dakota.

"It can survive our winters; it can survive our summers. That means it's only a matter of time. We have its host tree in abundance. Many of us have replaced a lot of the elm trees, that have been killed over the years by Dutch elm disease, with ash trees.

"So it was only a matter of time before something came in that would handle the ash." That's the emerald ash borer, the beetle whose name pretty well describes its brilliant color and what it does to certain trees.



Trees not 'sitting ducks'

But why do some insects only develop a taste for a particular piece of plant life? For example, EAB only for ash trees?

Lundgren explained, "That is a deeper question. Insects, especially herbivorous insects, tend to specialize on specific plants."

Continuing, he added, "The reason is, even though a tree can't get up and run away, it's not a sitting duck, either. It has all kinds of different chemical defenses that it uses to resist critters that like to eat it. Ash is no exception."

Think of the insects vs. plants as an ongoing war. Lundgren went back in history and geography: to Asia, where the EAB lived and "co-evolved with ash trees over there. Some of the only resistant ash trees that we know of live in Asia.

"So there's probably this arms race: as the pests got better, the trees figured out new defenses. And then the insects had to find a way around those – the law of progression."

In addition to Asia, the EAB is now found in North America. About 10 years ago the EAB was found around Michigan – and well ahead in the arms race.

"It found itself amidst all these ash trees," Lundgren said. "And the ash trees hadn't figured out how to live with this pest yet. It just found all this food and went really crazy."

He added that when EAB "first arrived in Michigan, they cut down millions and millions of trees, tens of millions of trees. Whole neighborhoods were laid bare."



Insects notorious hitchhikers

Since Asia is a long way from North America and the EAB is not a long-range flyer, how did these beetles get there?

Bugs don't have thumbs; but that doesn't keep them from being very successful hitchhikers, ironically with the unwitting help of humans who then have to turn around and do battle with them.

Laughing, Lundgren said, "'We’ are how they got here, probably through trade or possibly a nursery industry, most likely through solid wood packing material."

He's sympathetic to agents of the U.S. Department of Agriculture, Animal and Plant Health Inspection Service (APHIS), whose job of keeping critters like the EAB from getting into the country is a "terribly difficult one."

He knows: he's been there, done that.

Lundgren, who once worked for APHIS at the Minneapolis-St. Paul International Airport, said, "Every day we would see dozens of insects just coming in on passengers, in their luggage, stuff like that. I mean, just strange things, things that we'd never experienced before from international locations. The United States is constantly being inundated by these things."

Check any of several maps of the United States available online that show the presence of emerald ash borers and where they are being quarantined, and it reveals what Lundgren points out: "South Dakota is really on the invasion front. They're coming in from all sides."

Pretty much to the all the way from South Dakota's eastern border to the Atlantic Ocean there are pockets of infestation.

Lundgren added, "I haven't heard any tales told out of Iowa, but it wouldn't surprise me at all. Illinois has it. Wisconsin's got it, and all the way out to the East Coast."



Too little, too late

"How does this thing disperse?" is a rhetorical question posed by the entomologist.

Lundgren said, "Once it arrives in an area, these things aren't really good flyers, they just kind of hang out within the area."

How the EAB "gets long distances is critical to places like South Dakota, where most of our ash trees are found in little communities like Brookings or any the small towns around here."

Back to hitchhiking: "The way it's going to get in is not through flying; it's going to get in through people bringing in infested wood."

One way that could happen – that is a great cause for concern by those battling EAB and looking to stop its spread – is through infested firewood being brought out of an area that is infested and quarantined and taken into an area that is not infested – South Dakota, for example.

By the time it is discovered, the battle against EAB is already well on the way to being lost.

Lundgren explained, "By the time we can see the symptoms of an attack, it's been there three to five years. And you can bet that the surrounding area is also infested."

The beetles can be fought by getting insecticide into a tree's root system in a sort-of chemotherapy fashion; but that rarely proves effective.



Good bug vs. bad bug

A more effective weapon is the introduction of a "good" bug to fight the bad bug.

"We need to introduce a natural enemy,” Lundgren said. “This is an ongoing thing. What kinds of critters like to eat emerald ash borers, getting those into the country and making sure that they're safe and not eating insects that they're not supposed to."

A small parasitic wasp is now being studied by USDA Agricultural Research Service entomologists as a possible predator to the EAB beetles. Additionally, trying to find resistant ash trees is under way; that could be followed by their introduction into neighborhoods.

But Lundgren cautions that the introduction of one predator bug to battle another can be a two-edged sword.

Laughing, he said, "There are some instances where some cowboys have come in and decided they are going to save the world, and they've released predators that weren't safe. We need to be very careful about what we're doing."

Lundgren noted that for "invasive species, one of the key characteristics that makes them so successful is that they've found a way to live in and around humans."

There is no short-term solution to the challenge posed by the emerald ash borer. But everybody can help in a small way – don't pick up hitchhikers.

Don't bring firewood into South Dakota from infested areas that have been quarantined.

Lundgren stressed that "we need to make sure we are not the ones that are helping this thing get through."



Contact John Kubal at jkubal@brookingsregister.com.