Caddo Lake Weevil Overwintering Study

Beginning in early fall of 2010, a study to document how well salvinia weevils (Cyrtobagous salviniae) can tolerate a Caddo Lake winter was designed by research entomologist Dr. Allen Knutson of the Texas AgriLife Extension Service . To do this, fifty "weevil cages" were built and placed in a densely infested area of giant salvinia in the backwaters of Caddo Lake. In each cage, exactly ten weevils were placed along with a clump of green giant salvinia for them to feed upon. In addition, temperature loggers are recording the surface water temperature at the cage location.

Every two weeks, from fall till early spring, four cages are removed and taken to a lab where the cages are searched for the ten weevils. Alive and dead weevils are counted and recorded to give a complete picture of weevil mortality coinciding with the changing water temperature through winter. Preliminary results show that weevil survival was high until the last week of December 2010 when overall survival plummeted (likely due to the first major cold spell of the winter season). At the end of the study, we'll be able to match the temperature logs with the weevil count data. Results and findings will be published on this blog and the facebook page.

Our next study will use these same cages to monitor the date and temperature in which weevils start laying eggs during a Caddo Lake spring.

So, if you're in the backwaters of Caddo Lake and you see numerous pink, floating styrofoam squares (with wedding veil tulle coming off the top of each square), don't throw it away because it's probably not trash! (or at least not yet)

Small-Scale Weevil Release on Caddo (Sept. 2010)

This past September 2010, approximately 1,000 salvinia weevils were released into a designated are for research purposes. Weevils were raised at the Lewisville Aquatic Ecosystem Research Facility (LAERF). On a side note, we were totally unprepared for the mud and muck that is Caddo Lake's bottom. The stains did wash out of my jeans, but the Caddo Lake aroma is still there. We now have several good pairs of chest waders to tackle the lake with.

Three months later, in December 2010, area was sampled to see if weevils persisted through the initial cold weather of the season. Out of the twelve hand-sized samples, ten living weevils were found alive. That's not that many, but very encouraging that some living weevils were actually found! The area will be sampled again in mid-February to see if any weevils can be found after the series of cold snaps the region has experienced in January and February of 2011.

Blog and Facebook page online for the Caddo Lake Giant Salvinia Eradication Project

We're online!! The Caddo Lake Giant Salvinia Eradication Project is now being prominently displayed on the web. With the addition of this blog and a new facebook page up and running, we hope to better spread the word to the masses about the efforts to kill giant salvinia at Caddo Lake. If you are reading this, then you know how to get to the blog. You can look us up on facebook by searching for "Caddo Lake Giant Salvinia Eradication Project." You can probably find us just by searching for Caddo Lake, but you never know.


If you have been by the Caddo Lake National Wildlife Refuge lately, you may have noticed two really big greenhouses out behind the headquarters. These greenhouses are being used to grow giant salvinia and salvinia weevils year round so that live weevils can be released on Caddo Lake early this spring while giant salvinia is still recovering from the winter.


Each greenhouse has 2 large tanks inside that are 15ft x 48 ft and hold about 6,000 gallons of water. The Karnack Volunteer Fire Department has been great and helped us out with obtaining water from Caddo Lake to fill these tanks. Believe it or not, giant salvinia is actually hard to grow. It just so happens that it really likes the conditions in Caddo Lake.


Salvinia weevils (Crytobagous salviniae) are a biological control agent used to kill giant salvinia. The weevils currently being grown at this facility will be released on to Caddo Lake this spring providing a cost effective mechanism for controlling giant salvinia in those parts of the lake that are off the beaten path.


The weevils themselves are tiny little critters that are barely longer than 2 millimeters or about the width of 2 pennies stacked together. The weevils feed on and lay their eggs in giant salvinia causing damage to the plant. When the eggs hatch, the larve eat their way out of the plant causing further damage to the plant and its eventual demise.


So now that you know what is going on in those greenhouses, stop by the main office and ask for Patrick. If he is there, he will be glad to give you a tour.


Don't forget, you can also check out the project website at: http://cise.tamu.edu/caddo