Caddo Lake Giant Salvinia Control Program Updates

It has been a while since the last blog post, but rest assured that the fight against giant salvinia at Caddo Lake has been in high gear. With a relatively mild winter experienced this last year, giant salvinia levels on the lake coming into the spring were already nearing their highest levels in years. One positive of the mild winter was that weevil populations did survive the winter; however, higher water around the first of the year dispersed the remaining weevils widely across the lake.

Extensive giant salvinia coverage during May 2013 along boat road C near Joe Moore Hole

On the biological control front, one weevil release has been made from the Caddo Lake Salvinia Weevil Rearing Facility so far this year and a second release is being planned for the near future. An estimated 34,400 adult weevils were released along with an untold number of larvae and eggs. These weevils were released into backwater areas of the lake where they are least likely to be disturbed.

Weevil research has continued as well and is showing promising results:

- Small frame studies showed that salvinia weevils were able to reduce giant salvinia biomass by 50%

- A "Chill Coma Recovery Test" was conducted to evaluate salvinia weevils resuscitation time following an extended period freezing. Weevils from Australia resuscitated first followed by those from North Texas (Lewisville), South Louisiana (Houma) and from Florida. This suggests that weevils can adapt to localized weather conditions to some extent.

- "Solid Freeze Time Trials" were also conducted to evaluate the weevil's ability to tolerate weather extremes. Weevils were frozen solid for 24, 30 and 36 hours respectively and survival was documented. At 24 hours, survival was good for all weevils; however at 30 hours, Australian weevils survived far better than any weevils from the U.S. At 36 hours of freezing, weevil survival in all samples was greatly reduced.

- Efforts are also underway to collect weevils from higher elevations (cooler areas) in their native ranges in Argentina. Once received, their genetic make up will be evaluated and they will be subjected to "Chill Coma" and "Solid Freeze" tests to determine their ability to tolerate cold weather extremes.