In late March of 2011, we released approximately 1,500-2,000 weevils into a small area (less than an acre) of semi-green giant salvinia that persisted through the cold winter. We are closely monitoring this release site in hopes of collecting valuable data regarding early season weevil reproduction, weevil feeding activity, as well as environmental variables that may affect overall weevil success.
As of early May, there appears to be few, if any mats of giant salvinia that appear large and green enough for a large scale weevil release (however, the water hyacinth seems to be recovering rapidly). We know this situation will change quickly as we progress into May and early-June; as summer approaches, it's quite possible we'll have many covered areas that will be ideal for weevil releases.
Based upon the preliminary results of our ongoing "weevil egg-laying and larvae cage study", it's clear that lake temperatures are within range for weevil reproduction. This is critical because the larvae (pictured on the right), not the adults, are the most effective in controlling giant salvinia. These 1-2 mm larvae tunnel through the plant rhizome (rhizome is basically the stem connecting the leaves of the plant) causing massive damage to the plant. By dissecting the plants in our cage study, we are finding lots of these larvae doing their work. In fact, the giant salvinia in our weevil tanks are starting to show this larvae-induced damage (shown in the yellow/brown coloration in the bottom picture). Thus, the sooner we can get these bugs out and reproducing, the better.
We are hoping to do our first large scale release in the next 2-3 weeks. Of course, this is anticipating that we have some spots with adequate giant salvinia on the lake. If you are interested in assisting with this and other weevil releases, please email
paireland@ag.tamu.edu to receive more information. As giant salvinia growth increases and CISE efforts ramp up, look for more updates on the blog and facebook page.
In late March of 2011, we released approximately 1,500-2,000 weevils into a small area (less than an acre) of semi-green giant salvinia that persisted through the cold winter. We are closely monitoring this release site in hopes of collecting valuable data regarding early season weevil reproduction, weevil feeding activity, as well as environmental variables that may affect overall weevil success.
Based upon the preliminary results of our ongoing "weevil egg-laying and larvae cage study", it's clear that lake temperatures are within range for weevil reproduction. This is critical because the larvae (pictured on the right), not the adults, are the most effective in controlling giant salvinia. These 1-2 mm larvae tunnel through the plant rhizome (rhizome is basically the stem connecting the leaves of the plant) causing massive damage to the plant. By dissecting the plants in our cage study, we are finding lots of these larvae doing their work. In fact, the giant salvinia in our weevil tanks are starting to show this larvae-induced damage (shown in the yellow/brown coloration in the bottom picture). Thus, the sooner we can get these bugs out and reproducing, the better.
It's documented that correct water temperature is critical for the development of salvinia weevils. As the water temperature increases from 62.6 F to 69.9 F many activities such as feeding, oviposition (egg-laying), and egg-hatch begin. However, spring temperatures (in a water body such as Caddo) at which these activities begin have apparently not been reported. Therefore, a study has begun to determine the temperature and date in which egg-laying occurs on Caddo Lake. It's hoped that the results will help further guide our efforts to control giant salvinia using weevils.
We've been fortunate this winter to have had a series of cold spells that knocked back the giant salvinia a great deal. It's expected that much of the dead, brown material that is floating will take several weeks to sink out of sight.
These strange looking contraptions with lights on top are known as "Berlese Funnels". For our purposes, these funnels are used to estimate the density of weevils (numbers present per amount of giant salvina) located either on the lake or in our weevil rearing tanks.
