Persistence of the molluscicide Bayluscide (clonitralide) emulsifiable concentrate on mud surfaces in the tropics

ABSTRACT

Clonitralide (the active ingredient of the molluscidide Bayluscide) is commonly regarded as non-persistent. It was importnt to determine if this assuption was correct during the development of a programme on St. Lucia to control the intermediate host of Schistosoma mansoni, the snail Biomphalaria glabrata. In 3 separate experiments, aqueous solutions of an emulsifiable concentrate of clonitralide were sprayed onto pans containing dried mud or mud covered with 2.5 cm of water. All snails present at the time of spraying were killed, whether or not water was present. Mortalities were high in similar, unsprayed pans but subsequent chemical and biological assays demonstrated that clonitralide remained active for over a year in tropical conditions, despite several cycles of wetting and drying. Clonitrlide residues from vegetation sprayed in an operational snail control programme remained toxic for 8 weeks exposed to full sunlight, heavy rainfall, temperatures of 20 to 30 degrees C and relative humidities of 70 percent to 95 percent. The implications of these findings for the control of aquatic and amphibious snails are discussed together with some possible mechanisms to explain the persitence of the molluscicide.(AU)