In a hungry little insect, a big threat to Louisiana’s coast

Science Friday
The silhouette of roseau cane during a sunset on the Louisiana coast.

Louisiana’s coast is disappearing for a few reasons: the natural sinking of the land, saltwater intrusion and sea level rise. Now there’s another threat: a little tiny bug from the other side of the ocean. It’s killing plants and destroying marshes at the mouth of the river, worrying the state and the shipping industry.

Down in the marsh near the mouth of the Mississippi River, roseau cane is everywhere. It grows tall and bright green as far as the eye can see. But suddenly, a lot of it is dying. That has state officials worried, so they’re sending biologists like Todd Baker, with the Louisiana Department of Wildlife and Fisheries, to check it out.

From the front of a boat, Baker bends over and grabs a long, slender cane. It’s brown and half-dead. He peels it apart to reveal the killer — a tiny insect.

“So, if you look at your fingernail on your pinky,” he says, “the adult version can get almost that big.”

It’s sometimes called a scale, sometimes called a mealybug. But no matter what you call it, Baker says it’s an invasive species — it comes from either China or Japan. He’s not sure how it got here. Maybe by boat. Regardless, they’re hungry, and they love roseau cane.

“It burrows, or puts a little nose, into the cane and withdraws the sap,” Baker says, “and that’s what kills it.”

And when the cane dies, so do its roots.

“It takes a lot to kill it,” he says. “The fact that it’s been dying off this quickly is alarming. I’ve never seen anything like this.”

And when the roots die, the soil loosens and can easily be washed away into the main river channel. Lots of land has been lost already.

“Thousands of acres over a short period of time,” Baker says.

The Army Corps of Engineers — which dredges the river — and the state found out about the problem about a year ago. From the stern of his huge ship, a pilot looked down at the marsh as he made his way up the river. He noticed that the cane looked a little patchy and reported it.

Captain Michael Miller says it’s “a big big big big issue for Louisiana.” He’s the president of the Associated Branch Pilots, a group that pilots ships on the Mississippi. He worries the dying cane will make the job harder.

Roseau cane is what holds the riverbanks together. So if the banks start to disintegrate, that could require more maintenance for the Army Corps.

“It’ll have to be constant dredging to keep that channel open,” Miller says. “Because it’ll be — the sands from the Gulf of Mexico and mud and whatnot will be able to wash back and forth.”

So, what can be done to control it? That’s what Dr. Rodrigo Diaz is trying to figure that out. He’s an entomologist at LSU — he studies insects — and he’s leading the team looking for solutions. He says there are a couple initial ideas, but they all have drawbacks.

In China, for example, they burn the cane to get rid of the bug. But that’s not an option here — burning a bunch of dead grass next to oil pipelines isn’t a good idea. They could use pesticides, but that might hurt fish and shrimp. Before they propose any kind of solution, Diaz says they just need to know more. They’re not sure, for example, if the insect is entirely to blame.

“Seems to be, it’s a combination of stressors that’s actually resulted in the die-offs,” Diaz says.

Stressors like saltwater intrusion and erosion. So Diaz and his research team are going to run some experiments to figure that out. He says it’ll be at least six months before they get their first results. If you’re thinking that sounds like a long time for such a fast-moving problem, Diaz says he gets it. But good science takes time.

“We want to do it properly,” he says, “rather than going in and spending millions of dollars to do something that may do more harm, you know?”

Which is why they don’t want to just spray pesticides or burn all the dead cane off right away. In the meantime, though, the bugs aren’t losing their appetite.

This story and interview were featured on Science Friday’s series The State of Science, which showcases science stories from public radio stations across the United States. A version of this story was originally published by WWNO in New Orleans.

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