Rodrigo Diaz, Steven Woodley and Charlie Wahl
Freshwater wetlands are beautiful as well as economically important habitats. They lie at the core of culture and history in Louisiana, and they also contain vast natural resources and are home to many wildlife species. Transportation among these bodies of water relies on clean navigation channels or canals. However, freshwater wetlands in Louisiana and other countries have been under threat by the invasion of giant salvinia, a fast-growing floating fern from South America. Since its detection in the Toledo Bend Reservoir in northwest Louisiana in 1999, giant salvinia has spread exponentially and now is in every parish in the state.
In 2004, LSU AgCenter scientists began implementing biological control of giant salvinia in Louisiana using the salvinia weevil, which has been imported from South America. This weevil feeds exclusively on giant salvinia buds and stems, causing massive damage to salvinia and allowing the recovery of wetlands. The AgCenter has since established two facilities where the salvinia weevil is mass reared for distribution (Photo 1).
In the past two years, AgCenter scientists have been assisting in other areas of the world where giant salvinia is causing problems, which helps provide additional scientific information for the control of this plant pest here at home. AgCenter entomologists have been helping plant managers in Lake Ossa in Cameroon, where the salvinia has limited access to fishing by the local residents and reduced the habitat quality for an endangered manatee. In addition, Hurricane Maria in Puerto Rico facilitated the dispersal of giant salvinia on the island. Lake Las Curias near San Juan became completely covered with the plant by 2018 (Photo 2). Because of the rapid growth of giant salvinia during the warm months, lake managers rely heavily on periodic applications of herbicides, which are not always economically or logistically feasible. This creates a massive need for more tools to control giant salvinia.
In 2019, AgCenter entomologists implemented the biological control program in Cameroon and Puerto Rico by training local personnel in the handling and monitoring of weevils. The AgCenter shipped more than 1,000 weevils to each destination, and personnel released the weevils and initiated the rearing process. In addition, a critical aspect of the implementation of biological control of giant salvinia was the education of stakeholders in Puerto Rico and Cameroon using on-site demonstrations, fact sheets, how-to manuals, workshops and YouTube videos.
Results of the initial releases of weevils in Cameroon and Puerto Rico look promising. Two shipments of weevils have been sent to Cameroon, where a local nongovernmental organization is rearing the weevils on the shores of Lake Ossa. After the release of weevils in Lake Las Curias in Puerto Rico in November 2019, AgCenter entomologists confirmed the establishment and dispersal of weevils at the release locations (Photo 3). With the help of community leaders, this local “weevil nursery” will be used to accelerate the dispersal of weevil-infested salvinia to new locations in the lake. To monitor the recovery of the ecological functions of the lake, scientists from the University of Puerto Rico are measuring the coverage and thickness of salvinia and water quality parameters, including dissolved oxygen.
The expectation is that the tropical climate in Cameroon and Puerto Rico will accelerate the growth of the salvinia weevil, thus having a faster control of the salvinia plant. If successful, the implementation of the biological control program at these locations will result in the recovery of native plants and animals and improve water quality and ecological services provided by the lakes. Moreover, economic benefits will result from the reduction in control costs involved in the use of herbicides or mechanical harvesters and from the increase in revenue because of the improved navigation and access to fishing and tourism.
For more information about the LSU AgCenter biological control program of giant salvinia, visit the AgCenter giant salvinia webpage at www.lsuagcenter.com/giantsalvinia.
Rodrigo Diaz is an assistant professor, and Steven Woodley and Charlie Wahl are research associates in the Department of Entomology.
(This article appears in the spring 2020 issue of Louisiana Agriculture magazine, which focuses on entomology.)
Here is a link to a 50-sec video to help identify giant salvinia: https://www.youtube.com/watch?v=KsLmOXLwus4
Photo 1. Harvest of giant salvinia infested with weevils at the LSU AgCenter Reproductive Biology ponds in St. Gabriel, Louisiana. Photo by Rodrigo Diaz
Photo 2. Lake Las Curias in Puerto Rico completely infested with giant salvinia in July 2019. Photo by Tito Castro
Photo 3. Graduate student Giovana Matos Franco collects samples of giant salvinia at a weevil releases site in Lake Las Curias in December 2019. Photo by Manuel Godinez