Determining the Efficacy of Agricultural Oils for Suppressing Applesnail Egg Mass Hatch-out

Science Center Objects

Maculata applesnails (Pomacea maculata) are exotic freshwater snails that have been widely introduced along the Gulf of Mexico coast. The snails can significantly impact freshwater macrophytes and reduce the quality of water bodies.

Self-documenting envelope method for quantifying egg mass hatch-out
Self-documenting envelope method for quantifying egg mass hatch-out

The Science Issue and Relevance: Maculata applesnails (Pomacea maculata) are exotic freshwater snails that have been widely introduced along the Gulf of Mexico coast. The snails can significantly impact freshwater macrophytes and reduce the quality of water bodies. Applesnails are fairly easy to detect due to their distinctive egg masses; however, controlling their movement and distribution has been a problem. While smashing egg masses can be an effective tool in reducing their population, in many cases egg masses are inaccessible, even from a boat. A pilot study in which a molluscicide was applied directly to egg masses did not prove effective.

Methodologies for Addressing the Issue: In this study, with support from the USGS Invasive Species Program and funding for pilot studies from the U.S. Fish and Wildlife Service on aquatic nuisance species, the efficacy of using agricultural oils to suppress egg mass hatch-out is being tested. It is hoped that by coating the egg masses with oil – spraying the mass from a convenient distance – the eggs will suffocate and not hatch. Because the oil itself is not toxic and is biodegradable, it does not present an environmental hazard or permitting difficulties.

The study site is at Langan Municipal Park in Mobile, Alabama. In April-July 2015 oil application methods, two differing oil formulations, and a new method developed by the principal investigator for quantifying hatching success were tested. The experiment used two different treatments with one control. The egg masses were age assessed using their color and their measured length before treatment. The egg masses were observed over the course of four weeks for signs of hatch-out. Snails were captured in envelopes and used to quantify the impact of the treatments.

Future Steps: The oil concentrations used in the 2015 field season had little effect on hatch-out. From May through July 2016 undiluted coconut oil and Pam™ applied to egg masses were tested at Langan Park and in a laboratory system to determine if they prevented egg hatch-out. Preliminary analysis indicate that both were effective under some circumstances, however further analysis is needed.