Within an egg shell, the rapidly developing embryo needs plenty of oxygen. Using an oil to kill eggs by impeding oxygen transfer through the shell is nothing new. For instance, the USFWS has recommended mineral oil for use on nuisance geese nests. Why not use vegetable oil to kill apple snail eggs?
I spoke my old friend Dr. Bill Haller this morning about his team’s work with the use of oil as an oocide on apple snail eggs. At the University of Florida’s Center for Aquatic Invasive Plants’ laboratory, they have tried castor oil, Crisco oil, peanut oil, Pam Spray, corn oil, and even Mobil oil!
“Just about any oil will work,” Bill said, “but corn oil is the way to go because it is most likely exempt from EPA regulations. Technically, however, we need a company to submit a label to EPA to get the EPA review and an exemption letter. A company hasn’t stepped up because a patented product is doubtful. The ingredients are just too generic.”
Bill discussed the nuances of effectively treating snail eggs. First, the fresher the better – – Recently laid eggs are more vulnerable to the smothering effects of an oil barrier. Secondly, straight oil is the way to go. Diluting the oil and adding surfactants didn’t work as well as 100% oil. Finally, a thorough application is necessary to kill the eggs. This was made apparent in the discrepancy between the efficacy of dipping the eggs in oil versus spraying. Dipping clearly worked better in the lab tests.
Is it practical to load up a 50 gallon sprayer with oil on an airboat and treat the perimeter of an infested lake? “In reality, vegetable oil is tough to use,” Bill noted. And, it’s not cheap. Vegetable oils range from $3.00 to $6.00/gallon.
My bench tests using an emulsion of Crisco oil (50%) and Yucca saponins (3%) provided mixed results (see image above). The idea was to reduce costs via dilution of the oil with water, while adding a saponin with possible molluscicidal properties. Hatching numbers were reduced, but the cost/benefit wasn’t that appealing. I also tried hand-spraying vegetable oil on some egg clusters Wellman Lake and found it to be almost as time consuming as simply hand-picking the eggs, plus some of the “slick eggs” eventually hatched.
This is not to say we should all give up on this avenue. A student project in the Philippines recently revealed the great promise of coconut oil as an oocide on Pomacea canaliculata (See Recent Publications, June, 2008): “Results showed that coconut oil could inhibit the hatching of 82.2% of the golden snail eggs.” So, let’s keep working on it. After all, “the weak point of the invasive apple snails are the egg clutches,” as Dr. Haller put it. Posted by Jess Van Dyke
Dr. Wm. T. Haller: email@example.com
The Center for Aquatic & Invasive Plants: