How to stop the invasion of insects in Louisiana wetlands? Maybe confuse them to death | Environment

The mysterious insect that has been devouring Louisiana’s coastal marshes for the past six years likely came aboard a ship from Beijing, new research suggests. And the solution to this insect invasion could also come from China.

A study by the US Department of Agriculture traced the stink bug, a tiny sap-sucking insect known as the mealy bug, to the region of northeastern China that surrounds Beijing. Genetic analysis of scales that have spread through Gulf Coast swamps since 2016 shows they are likely descended from a small group that traveled to Louisiana in a single event, likely via infected plants that are somehow found on a ship while it was docked in Beijing.

The study, published last month in the scientific journal Biological Invasions, suggests enlisting the help of the mealybug’s natural enemies in southern China, where the mealybug’s predators and parasites may be better adapted to the subtropical climate. of Louisiana.






A stand of reed cane dies, converting to bare ground and open water in the lower Mississippi River delta in February 2018.




This rice grain-sized insect feeds almost exclusively on Phragmites australis, a hardy, thick-rooted reed known locally as reed cane. Reed is considered the lower Mississippi Delta’s best natural defense against storms, sea level rise, and other factors contributing to Louisiana’s land loss crisis.

But reed is dying at a rate not seen since the insect’s appearance. In the reed-dominated marshes of the parish of Plaquemines south of Venice, the land was reduced to open water within months. Reed weakening and death is most pronounced on the eastern side of the delta, along the Main Pass, Otter Pass and South Pass – areas that are part of the Otter Pass Wildlife Management Area of state and the nearby Delta National Wildlife Refuge, which together total 165,000 acres. Scientists estimated that the scale damaged more than 80 percent of the land in the two wildlife areas.

It’s unclear how much land has disappeared, but some reed marshes have retreated nearly 1,000 feet over a 16-month period, according to an analysis by the state Department of Wildlife and Fisheries.







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LSU Professor Andy Nyman removes layers of reed to reveal Scale, a plant pest, at the Pass-a-Otter Wildlife Management Area at the bottom of the Mississippi River on June 14, 2021.




The dismantling of reed swamps can hamper river navigation, harm various coastal fisheries and expose hundreds of oil wells to waves and storms, state officials say.

In 2017, the scale was mostly confined to Plaquemines, but by December the scale was found along every reed stand surveyed on the Louisiana coast, according to Rodrigo Diaz, an entomologist at LSU AgCenter. The scale has also appeared in the swamps of Mississippi and eastern Texas.

Scientists still don’t know how to fight the spread of the scale. They cannot spray pesticides because the insect-killing chemicals would harm other animals in sensitive Louisiana wetlands. In China, scale outbreaks are fought with fire, but burns in humid environments require large doses of toxic accelerators, and the presence of oil wells and pipelines on the coast raise safety concerns.

One of the cochineal’s natural enemies is already found in Louisiana – a parasitic wasp that apparently crossed the Pacific Ocean with the cochineal. The tiny black wasp uses the cochineal body as a kind of edible nursery. The larvae that the wasp injects into the scales grow into adolescence while feeding on the inside of the scale.

As nightmarish as the wasp’s methods are, they haven’t been very effective in curbing the explosive growth of the cochineal in Louisiana, perhaps because the wasp does better in the cooler temperatures of northern China.

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The study suggests looking for a hot-weather enemy of scales, perhaps one that likes to eat scales and could thrive, as the scale did, in Louisiana’s hot, humid climate. Ecological niche modeling conducted by the USDA suggests that southern China, Malaysia or Indonesia might have what it takes.

“This means the search for natural enemies could be optimized,” Diaz said. “Natural enemies found in these regions may have the best chance of attacking reed mealybug in Louisiana (and) adapting to our climate.”

The study recommends “foreign exploration efforts” to find predators and parasites on a South Asian scale. The study did not indicate when or how these efforts would be undertaken.

Introducing more alien species to control a problem could have unintended consequences. It’s unclear how the USDA would handle a potential blowback. The study’s lead author could not discuss the study.

The fight against the scale began in earnest in 2019, when Congress appropriated $1 million to fund reed and scale research. State and other federal resources brought the total to $2.4 million, allowing for the expansion of a small research team that includes Diaz and other LSU scientists. This funding is expected to run out this summer.







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A glossy ibis flies over unhealthy reed reeds at the Pass-a-Loutre Wildlife Management Area at the bottom of the Mississippi River on June 14, 2021.




One potential remedy identified in the research is to promote the growth of a European strain of reed that is much more resistant to mealybug than varieties already present in Louisiana. But the European reed is, like the tortoiseshell, an aggressive invader. On the East Coast and along the Great Lakes, European reed pushes out native plants, clogs waterways and has been the subject of costly eradication efforts for decades.

On the positive side, the European reed could prevent large sections of the Mississippi Delta from being washed away. European reed could be strategically planted where landraces are rapidly receding and then successfully control its spread, said LSU conservationist Jim Cronin.

However, recent test plantings in scale-damaged marshes have not offered much hope. While the European reed manages to keep the scales at bay, the plant doesn’t seem to like the marshes of Louisiana. Cronin admits the results came as a surprise, but he stressed that more research and time is needed to determine the European reed’s potential to revive Louisiana swamps, possibly in combination with the scale’s natural enemies. and other solutions.

“It’s a complicated problem, and we’re attacking it from many different directions,” he said.

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