Weevils Enlisted in War Against Giant Salvinia on Caddo Lake

From Staff Reports

Caddo Biocontrol Alliance Project Manager Laura Speight and her Border Terrier, Ghilley, survey the greenhouse in Uncertain where hundreds of thousands of weevils are raised to battle giant salvinia on Caddo Lake.

The Caddo Biocontrol Alliance wages total warfare in a take-no-prisoners battle to stop invasive giant salvinia from choking the waterways on Caddo Lake. Supplementing state herbicide programs, the Alliance musters an army of volunteers to help in the struggle against the invasive weed.

Their greatest allies, however, are hundreds of thousands of weevils they mass produce for the job. Known as the giant salvinia weevil, this tiny creature comes from South America, also the home of the giant salvinia.

The weevils are about the size of the head of a pencil and appear similar to head lice. The Jefferson Jimplecute visited the weevil ranch in Uncertain and met with Laura Speight, project and greenhouse manager for the Alliance, a nonprofit organization.

Launched in 2013, the program runs hand-in-hand with chemical warfare, which involves spraying by the Texas Parks and Wildlife Department. But, as Laura explains, spraying is expensive and it’s difficult in the backwaters. It also has its own downside.

Weevils, on the other hand, are safe with no ecological dangers. “Biocontrol is fairly slow,” says Laura, “whereas spray has a more immediate impact.” Which is why they use an integrated process.” The first weevil greenhouse was built in 2014 and now there are two, with a total of 10 tanks.

Last year alone, the Alliance released more than 200,000 weevils on the lake. “It takes 54 days from egg to egg,” says Laura. “There’s four stages of the weevil: the egg, larva, pupa, and adult. The adult eats the plant and so does the larva.” Which means that two of the four life stages impact the salvinia.

For this reason, they release all life stages in the lake, usually around 40 to 50 kilograms at a time. Evident in at least 20 Texas lakes, giant salvinia had become so bad in Lake Caddo by 2013 that it was starting to choke passageways through the state’s largest natural lake.

While seasonal flooding and freezing helped reduce it, this wasn’t enough.“It’s a tough plant,” says Laura. “One plant in laboratory conditions can cover 40 square miles in three months. But if you bombard it with spray and you bombard it with weevils, the weaker it gets … and the easier it is for Mother Nature’s freeze to hurt it more.”

While Texas Parks and Wildlife and the Corps of Engineers produce some weevils, the Caddo Biocontrol Alliance is the only non-state agency that’s mass producing weevils for biocontrol of salvinia. The success of the operation depends on donations and numerous volunteers.

Fortunately they get both, with people from Dallas, Atlanta, Jefferson, and Marshall joining those from Uncertain and Karnack. They also get a subsidy from Texas Parks Wildlife.

A recent donation through AEP SWEPCO got them some big vegetation booms, so now, for the first time, they’ll be able to count the weevils and see how they multiply when out on the lake. They also hope for the kind of results Texas Parks Wildlife had when they boomed off Pine Island Pond several years ago.

“They put weevils in there, and it went from a mat to clear open water,” says Laura. “So they do work, but it’s not an overnight thing.” But weevils cost more than most people might think. It costs 25 cents to raise just one weevil for release on the lake.

This makes fundraising a vital factor in the success of the project.

Two fundraisers are planned for this year:

1. East Texas Giving Day online on April 30.

2. The Weevil Wobble 5K on October 5 in Uncertain. They also need sponsors for this race.

So how else can you help? First of all, if you take your boat out on the lake, clean it, drain it, and dry it when you get back. That’s the best way to stop salvinia from spreading. You can also donate time and money.


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