A bug from China is destroying our marshes. How do we stop it?
The mysterious bug that’s been devouring coastal marshes in Louisiana over the last six years likely came aboard a ship from Beijing, new research has found. And the solution to this insect invasion may also come from China. A study led by the U.S. Department of Agriculture traced the bug, a tiny, sap-sucking insect known as a scale, to the region in northeast China that surrounds Beijing. Genetic analysis of the scales that have been spreading across Gulf Coast marshlands since 2016 shows they likely descended from a small group that traveled to Louisiana in a single event, probably via infected plants that somehow ended up on a ship while it was docked in Beijing. The study, published last month in the scientific journal Biological Invasions, suggests recruiting help from the scale’s natural enemies in south China, where scale predators and parasites may be better suited to Louisiana’s subtropical climate.nola.com
It, of course, chose to attack the main part of the marsh that defends us.
The rice-grain-sized insect feeds almost exclusively on Phragmites australis,a hardy, thick-rooted reed known locally as roseau cane. Roseau is considered the lower Mississippi River Delta’s best natural defense against storms, sea level rise and other factors contributing to Louisiana’s land loss crisis. But roseau has been dying at an unprecedented rate since the insect appeared. In the roseau-dominated marshlands of Plaquemines Parish south of Venice, land has been reduced to open water in a matter of months. Weakening and dying roseau is most pronounced on the delta’s east side, along Main Pass, Pass a Loutre and South Pass – areas that are part of the state’s Pass a Loutre Wildlife Management Area and the neighboring Delta National Wildlife Refuge, which are a combined 165,000 acres. Scientists have estimated the scale has damaged more than 80 percent of land in both wildlife areas. It’s unclear how much land has disappeared, but some roseau marshes showed nearly 1,000 feet of retreat over a 16-month period, according to an analysis by the state Department of Wildlife and Fisheries. Unraveling roseau marshes may impede river shipping, harm various near-shore fisheries, and expose hundreds of oil wells to waves and storms, state officials say.
It was contained locally but now has spread all along the coast.
In 2017, the scale was mostly confined to Plaquemines, but as of December, the scale was found along every stand of roseau surveyed in coastal Louisiana, according to Rodrigo Diaz, an LSU AgCenter entomologist. The scale has also popped up in Mississippi and east Texas marshlands. Scientists still aren’t sure how to combat the scale’s spread. They can’t spray pesticides because bug-killing chemicals would harm other animals in Louisiana’s sensitive wetlands. In China, scale outbreaks are battled with fire, but burns in wet environments require large doses of toxic accelerants, and the presence of oil wells and pipelines on the coast raises safety concerns. One of the scale’s natural enemies is already in Louisiana – a parasitic wasp that apparently crossed the Pacific Ocean with the scale. The tiny black wasp uses the scale’s body as a sort of edible nursery. The larvae the wasp injects into scales grow into adolescence while feeding on the scale’s insides. As nightmarish as the wasp’s methods are, they haven’t been very effective at curbing the scale’s explosive growth in Louisiana, possibly because the wasp does best in the cooler temperatures of north China. The study suggests looking for a warmer-weather scale enemy, perhaps one that likes to eat scales and could thrive, as the scale has, in Louisiana’s hot and humid climate. Ecological niche modeling conducted by the USDA suggests southern China, Malaysia or Indonesia might have just the thing. “This means the search for natural enemies could be optimized,” Diaz said. “Natural enemies found in these regions could have the best chance to attack the roseau cane scale in Louisiana (and) adapt to our climate.”
Go find a solution but the study neglects to say how.
The study recommends “foreign exploration efforts” to find south Asian scale predators and parasites. The study didn’t indicate when or how these efforts would be undertaken. Introducing more foreign species to combat a problematic one could have unforeseen consequences. It’s unclear how the USDA would manage potential blowback. The study’s lead author was unable to discuss the study. The fight against the scale began in earnest in 2019, when Congress appropriated $1 million to fund roseau and scale research. State and other federal resources brought the total to $2.4 million, allowing the expansion of a small research team that includes Diaz and other LSU scientists. That funding is set to run out this summer.
There is one possible solution that is in this country already.
One potential remedy identified in the research is to foster the growth of a European strain of roseau that is much more resistant to the scale than the varieties already in Louisiana. But European roseau is, like the scale, an aggressive invader. On the East Coast and along the Great Lakes, European roseau pushes out native plants, clogs waterways and has been the target of expensive removal efforts for decades. On the positive side, the European roseau might prevent large sections of the Mississippi Delta from washing away. European roseau could be strategically planted where local varieties are in rapid retreat and then managed to control its spread, said Jim Cronin, an LSU ecologist. Recent trial plantings in scale-damaged marshes haven’t offered much hope, though. While the European roseau manages to keep scales at bay, the plant doesn’t appear to like Louisiana marshes. Cronin admits the results were a surprise, but he stressed more research and time is needed to determine European roseau’s potential to revive Louisiana’s marshes, possibly in combination with the scale’s natural enemies and other solutions. “It’s a complicated problem, and we’re attacking it from a lot of different directions,” he said.
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