Snail control in urban sites in Brazil with slow-release hexabutyldistannoxane and pentachlorophenol.

Slow release formulations of hexabutyldistannoxane (TBTO) and pentachlorophenol (PCP) were tested for the control of Biomphalaria tenagophila in 52 urban sites in Rio de Janeiro. TBTO acted faster and lasted longer than PCP and at 15 g/m(2) it eliminated snails from 76% of the treated sites for 1 year. Water pollution and rate of flow had no significant influence on the molluscicidal properties of either compound, but alkalinity lowered the activity of TBTO. Failure to control snail populations was due mainly to human interference and to the non-treatment of adjacent breeding sites that were temporarily dry and therefore overlooked.

Molluscicidal activity of trifenmorph in field trials.

Trifenmorph granules provided 100% control of Biomphalaria glabrata and B. tenagophila when applied at 2 kg of active ingredient per hectare, except at one site with a pH of 5.6 where the snail population was reduced by only 50%. Granulation was found to facilitate application by either hand or mistblower, and reduces the risk of infection to the spray team. Applied to canal margins the granules had a residual toxic effect.

Field tests of hexabutyldistannoxane (TBTO) in slow-release formulations against Biomphalaria spp.

Hexabutyldistannoxane (TBTO) in an asphalt base was found to retain molluscicidal activity for more than a year in the field. It was not deactivated by immersion in mud or by drying and exposure to the sun. Complete elimination of planorbid snails was achieved and maintained when repopulation pressure was sporadic, but control of a continuously entering population was not practicable. Fixing the product at the site is important, and a formulation in fragments of rubber that floated failed after 1-2 months. TBTO apparently acts cumulatively in snails, but is only initially toxic to aquatic insects and fish, which return to repopulate treated areas that remain snail-free.