Preliminary investigations of Island Applesnails (Pomacea insularum) control methods applicable for natural areas in Louisiana

Background/Question/Methods and Results/Conclusions The Island Applesnail (Pomacea insularum) is a new invasive species in South Louisiana. First reported in 2005 in a canal south of New Orleans, Louisiana, there are now 3 know watersheds where they exist. Each site is very different. One is a system residential water retention ponds; another is a series of drainage canals; and the third is a swamp and associated river system. Each population seems to be a separate introduction based on location, habitat type and distance from other known populations. Applesnails have been documented to have devastating impacts on wetland agricultural crops such as rice and taro. They also have been shown to shift swamp ecosystems in Southeast Asia from macrophyte to algae based systems by overgrazing. Furthermore they are an intermediate host for the rat lungworm (Angiostrongylus cantonensis) a nematode that can infect and cause meningitis in humans. Most control efforts have focused on agricultural systems. We are exploring tools that are applicable in more naturally managed areas such as wildlife refuges, national parks, and private swamplands managed for crawfish productions. Techniques we have investigated include biological, chemical, and mechanical control. Biological Control- we investigated the use of the native red swamp crayfish (Procambarus clarkii). They will eat small applesnails, but do not have a high preference for them. However, since they are native and are raised commercially, they have a high potential as an acceptable option in this region. Chemical Control- we tested two classes of chemicals, a saponins, and a niclosamides. Both were effective against applesnails and did not affect crawfish, an important consideration if we want to combine techniques. However, both are toxic to fish. Mechanical Control- through experimentation we showed that a common control method (knocking eggs into the water) was not completely effective and now recommend smashing the egg masses. An applesnail trap and bait are currently being tested. Field inspection of the three know populations indicates that a healthy and diverse predator community may be important in keeping applesnails in check. These may include ducks that eat the eggs, otters that eat adult snails, and a variety of fish and reptiles that may take out various size classes of applesnails. A combination of control techniques and management of habitat to encourage natural predation may prove a successful strategy for south Louisiana.