The Greater Caddo Lake Association


The Giant Salvinia Weevil.
Can it help control giant salvinia at Caddo Lake?


The diminutive salvinia weevil, (Cyrtobagous salviniae) is only 1/10th-inch long. This highly specific insect feeds only on salvinia species from South America. In some areas, researchers have shown it to be an effective biocontrol agent for giant salvinia.


Adult females lay their eggs in cavities they create by chewing into the plants' rhizomes and petioles, the structures that attach the leaves to the rhizomes. The larvae that hatch feed on buds before tunneling into the rhizomes, where the most serious damage to the plant is inflicted.



Giant salvinia weevils are not a magic bullet. Weevil cultivation & deployment is but one tool in salvinia control.
For weevils to be successful in reducing giant salvinia in Caddo Lake, they will have to survive winters and increase their populations dramatically. It is estimated it will take a minimum of five years before any significant reduction in giant salvinia can be obtained from weevils.

1st introduction of weevils at Caddo Lake by Texas Parks & Wildlife.
November 7, 2007

Weed Warden Mike Turner scouted several locations suitable for the initial release. TPW crews will monitor these initial releases, which will be isolated in a floating enclosure.



Two locations were selected in heavily infested areas that are well sheltered and not likely to be routinely encountered by boaters. Such floating structures should never be disturbed any time you see them on the lake.

In addition to giant salvinia research & control measures, other studies underway at Caddo often use similar floating structures to identify and contain a sample area that is being monitored by TPW crews or other researchers.


TPWs Howard Elder, Carl Boatman, & Jacob Green assemble the floating structure on the study site, creating a frame out of PVC pipe. Note that they are completely surrounded by a very large infestation of giant salvinia.

Below, Weed Warden Dale Renkenburger & TPWs Howard Elder check out the structure before adding weevils.

RECIPE FOR HOPEadd giant salvinia weevils, stir vigorously, & pray.

Below, crew adds giant salvinia weevils at second location again, in a large infestation of salvinia in a sheltered cypress brake.

WEEVILS are grown in giant salvinia and must be transported to the site and introduced along with the salvinia plants they are established in. Ideally, the weevils will move into the fresh salvinia and over time reproduce in sufficient numbers that new weevil populations migrate out of the introduction site and continue to spread throughout the infestation.

The floating frame used for these initial insertions is not intended as a barricade, but is instead a marker and a means by which TPW can monitor these sites to determine how the weevils are doing.

The initial introduction of giant salvinia weevils by TPW at Caddo Lake consisted of approximately 8,500 weevils. Additional weevils will be introduced at other locations at the lake beginning early in 2008.


Copyright 2007 Caddo Lake News