J. Green

A study of a small tropical lake treated with the molluscicide Frescon.

Ntritylmorpholine was applied, as the 16·5 w/v emulsificable concentrate in tetrachloroethylene, to parts of the shores of two lakes in West Cameroon aagainst the vectors of schistosomiasis. The concentrations of N-tritylmorpholine, with its breakdown product, triphenylcarbinol, in the lakes just after spraying ranged from 0·9 to 8·0 ppm. The treatment killed many cichlid fishes, particularly the young that live close inshore, and the higher concentrations killed or immobilised several species of aquatic insects, crustaceans and rotifers. Ostracods and hydracarines survived 4·8 ppm. There were no obvious long-term effects on the populations of fishes or invertebrates, probably because these animals quickly recolonise the treated beaches from unsprayed areas nearby. n nThe use of an alternative, granular, formulation of N-tritylmorpholine may prove less harmful to fishes and invertebrates other than snails.