A Brazilian weevil that feeds on giant salvinia is a biological control for the invasive species that has been taking over water bodies in Louisiana since it was first discovered in the state in the Toledo Bend reservoir in 1999.
Dearl Sanders, an invasive species specialist for the LSU AgCenter, explained how the weevil works at a Congressional Natural Resources Subcommittee hearing led by U.S. Rep. John Fleming, R-La., and U.S. Rep. Louis Gohmert, R-Texas, at LSU-Shreveport on June 27.
Sanders, who has reared weevils that have been used to control giant salvinia on local water bodies, and other witnesses were invited to offer their ideas for control or eradication strategies of the invasive species and costs involved.
Giant salvinia is native to Brazil and spread to many areas of the world in the 1950s and 1960s. Experts have employed several control measures, including herbicide sprays, mechanical control, booms, drawdowns, educating the general public and weevils.
The LSU AgCenter has been involved in investigating and implementing control measures for giant salvinia since 1999.
The larvae of the weevils ease some of the problem by burrowing into the rhizomes of salvinia. Adults eat leaves and buds, inhibiting plant growth. Larval feeding causes the leaves to first darken and then drop off. The combined feeding by larvae and adults kills the plant.
In partnership with the Louisiana Department of Wildlife and Fisheries, the LSU AgCenter helped collect and transport more than 30 tons of weevil-infested giant salvinia with approximately one million weevils to Lake Bistineau near Bossier City and four other north Louisiana lakes in 2009.
Sanders said the weevils have reduced salvinia 90 percent in some areas in south Louisiana, but they have not survived the cold winters in the Shreveport area. He said research needs to be directed on finding a strain that can accommodate low winter temperatures.
The LSU AgCenter has helped establish weevil nurseries in Lafourche, Terrebonne and St. Charles parishes. The initial weevil nursery in Gheens was used to develop the protocol for salvinia and weevil production, the timeline for weevil population growth and the optimum times for weevil harvest and distribution.
Sanders noted that weevils don’t fly. “This is important in planning a distribution system, since any movement of weevils from one place to another that is not directly connected by water is unlikely. Man has to move them from point A to point B, and it is labor intensive.”
Sanders has also conducted an extensive grass carp biological control study that confirmed that grass carp will not eat giant salvinia even when it is the only plant available. “Grass carp only eating giant salvinia died,” Sanders said. “Giant salvinia contains a metabolic toxin.”
Sanders said it was “the nastiest trial I ever ran in my life.”
“Being a member of Congress is a lot easier than what you gentlemen do every day,” Fleming said.
Various panel members explained that giant salvinia grows in thick mats and blocks sunlight, deoxygenates the water and leads to fish kills. It clings to boat motors and trailers and doubles surface area covered every day and a half.
One treatment chemical costs $1,851 a gallon, according to Robert Barham, secretary of the Louisiana Department of Wildlife and Fisheries. He called giant salvinia a “science fiction challenge” and named Lake Bistineau the poster location.
“All the help you can give us we can use,” Barham said.
State Rep. Henry Burns said residents along Lake Bistineau have had broken dreams because their real estate values, retirement homes and waterfront amenities are being taken from them due to giant salvinia. “The Number One question I’m asked is ‘when are we going to get our lake back?’”
“We will continue to contain this invasive species by utilizing a number of different strategies, including simple things like making absolutely sure that once a boat is removed from a lake, the boat owner does not allow giant salvinia to hitchhike home,” Fleming said.
Ross Melinchuk, deputy executive director, natural resources in the Texas Parks and Wildlife Department, said a media program of radio, TV, print, online, billboards and gas pump toppers that focused on four bodies of water showed 96 percent of boaters surveyed reported that the campaign made them more likely to clean their boat and trailer.
Damon Waitt, senior director and botanist at the Lady Bird Johnson Wildflower Center at the University of Texas at Austin, said he camped, caught his first fish, skied and met girls at Lake Bistineau.
“Nature deficit disorder did not exist at Bistineau. It is sad to think these kinds of experiences are no longer available to the 11-year-olds of 2011,” Waitt said. “Bistineau helped define me and started me on a path that led to a Ph.D. in botany, the Wildflower Center and a passion to protect ecosystems from invasive species.
“You have in this room all the ingredients to address the threat of giant salvinia – research, biocontrol, herbicide programs, volunteer support, a management plan. What seems to be lacking is the recipe that combines these ingredients into a coordinated effort that will solve the giant salvinia problem.”
Waitt recommended integrated management resources across jurisdictional boundaries.