(08/27/19) BATON ROUGE, La. — After working a week with U.S. Department of Agriculture and Puerto Rican government officials, the LSU AgCenter has received permission to bring salvinia weevils to the island territory. The weevils will be a major part of a comprehensive management plan to help fight a giant salvinia infestation.

Charlie Wahl, an entomology research associate with the AgCenter, spent seven days in Puerto Rico documenting the magnitude of the salvinia problem and collecting baseline data such as oxygen levels and nutrients in waterbodies having salvinia.

“We found oxygen levels were virtually nonexistent in Lago Las Curias,” Wahl said, referring to a lake just southeast of San Juan. “Nutrient levels were also very low.”

Lago Las Curias is a 12-acre lake, and it has been entirely covered in giant salvinia for the past two years. The invasive plant from South America is so thick that sunlight is unable to penetrate the mat and has turned the lake into a virtual aquatic desert.

“The salvinia is up to 28 centimeters thick,” Wahl said. “It is strong enough to support small shrubs or other plants that are actually growing in the mat.”

The baseline data collected by Wahl will be used to compare with data collected after the weevil release, which is expected to happen in September or October.

Wahl spent part of his time discussing with officials how to develop a control plan, which included weevils. This plan included components such as how to manage a weevil nursery, how to release the weevils at specific sites to get the best results and develop a monitoring program to gauge the success of the weevils.

“Once we were able to speak with the officials and alleviate some of their concerns, the process picked up steam and moved really quickly,” Wahl said.

Wahl said this is a good year to do this because Louisiana’s mild winter allowed for higher survival in Louisiana waters. Only a small number of weevils will be brought to Puerto Rico, and they will be the basis for starting the nursery there.

In Puerto Rico, the tropical climate would help in the rearing of the weevils because they are not extremely cold-hardy insects. Louisiana’s harsh winter weather in January 2018 caused high mortality of weevil populations.

Like Louisiana before the importation of salvinia weevils, no insects provide effective biological control in Puerto Rico. Samea moths are found in both Puerto Rico and Louisiana, and while they do feed on giant salvinia, they do not feed to the point the plant is killed. Research in Australia also indicates samea moths are not good biological control agents.

Puerto Rico suffered a great deal of damage from Hurricane Maria in 2018 and has limited resources to dedicate to projects such as this. Help provided by the AgCenter in dealing with the salvinia problem can help accelerate the recovery of freshwater habitat on the island.

Giant salvinia has overtaken Lago Las Curias, an inland lake southeast of San Juan, Puerto Rico. In some places, the salvinia is more than 10 inches thick and is supporting the growth of other plants. Scientists with the LSU AgCenter will bring salvinia weevils from Louisiana to start a weevil nursery. The weevils will be used as a biological control for the salvinia. Photo by Charlie Wahl/LSU AgCenter

Near San Juan, Puerto Rico, giant salvinia clogs the Canal La Malaria. The LSU AgCenter is working with Puerto Rican officials and representatives of the U.S. Department of Agriculture to bring salvinia weevils to provide biological control of the invasive aquatic plant. The weevils are expected to be delivered in September or October. Photo by Charlie Wahl/LSU AgCenter