The salvinia weevil has been successful at helping to control the aquatic weed giant salvinia in waterways across the southern portion of the state for nearly seven years. The LSU AgCenter has been working with the Louisiana Department of Wildlife and Fisheries to release weevils into lakes and streams clogged with salvinia.

But researchers aren’t seeing the same results in north Louisiana. Cold winters have killed off the weevils working to remove the salvinia from waterways in that area.

“We did a huge release in north Louisiana in 2009, but the weevils were wiped out in 2010 by cold weather,” said Seth Johnson, a retired LSU AgCenter entomologist, who will continue working on the salvinia weevil project.

Johnson collaborates with LSU AgCenter weed scientist Dearl Sanders and entomologist Steve Micinski to rid Louisiana of salvinia. The salvinia weevils can do it, if they can survive.

Sanders said every other year temperatures have been cold enough to kill the weevils in waterways such as Lake Bisteneau in northwest Louisiana.

“Of the 22 main lakes in north Louisiana, 19 of them have a bad salvinia problem,” Sanders said.

The Department of Wildlife and Fisheries has given AgCenter researchers a three-year grant for $450,000 to find or create a weevil that can survive a cold winter in the northern part of the state.

“The goal is to find one that already exists somewhere in the world, or try to develop one by taking a population and selecting out for cold tolerance,” Sanders said.The weevils used in Louisiana originate from South America. Johnson said he has put in a request for a permit to import weevils from Australia to see if they will have the cold tolerance needed to survive.

“The weevils have been in Australia for 30 years,” Johnson said. “Winters in Southern Australia are comparable to the winters we experience in north Louisiana.”

Johnson hopes to have Australian weevils by March. Once here, he will test their cold tolerance compared to the weevils that have survived north Louisiana temperatures.

Sanders said in 2010 most weevils died at temperatures below 14 degrees. That same year, weevils survived cold temperatures in Toledo Bend where temperatures were only a few degrees higher.

“We’re not looking for a huge difference, just a degree or two,” Sanders said.

Johnson will expose the weevils to different low temperatures for different lengths of time and determine the lethal temperature and lethal time for the different populations.

The researchers are also looking at bringing in another weevil population from South America. Johnson said a new LSU AgCenter assistant professor, Rodrigo Diaz, will conduct research on invasive species and will assist with the salvinia project.

“We will scour the world to find a cold-tolerant weevil,” Sanders said.

Micinski, who is located at the AgCenter Red River Research Station in Bossier City, is conducting experiments on the current weevil population in north Louisiana. He wants to see if mulch placed over the salvinia will raise the temperature of the weevils and help them survive the winter.

“The leaves fall off of the existing cypress trees, and if you pile those leaves over the salvinia, it’s going to insulate it,” Sanders said.

Sanders said a major outbreak of giant salvinia in southwest Louisiana is now under control with help from the weevil. The researchers have been releasing weevils in the area for two years. A recent survey showed good weevil survival with increases in weevil numbers and a reduction in the amount of salvinia there.

“We’re doing well with the weevil we’ve got in south Louisiana, and we are optimistic that we will get a cold-tolerant one for north Louisiana,” Sanders said.

Tobie Blanchard is an associate specialist with LSU AgCenter Communications and communication coordinator for the College of Agriculture.

This article was published in the winter 2015 issue of Louisiana Agriculture Magazine.