A new technique is described for studying the reactions of Simulium larvae to insecticides in the laboratory. By means of a constant stream of air bubbles directed against the inner walls of a large glass test jar, submerged larvae are induced to leave the vegetation on which they were fixed and to become attached to the inner wall of the jar at the point of maximum turbulence. In this position they can be counted and observed throughout the experiment.
The larvae receive no handling at all, and mortality in untreated controls remains low for at least 48 hours after larvae have been collected from the field. The water in the experimental jars is replaced with fresh stream water 2 or 3 times during the course of each experiment, and there is no need for a constant supply of untreated and unfiltered running water.
The technique has been worked out with particular reference to Simulium damnosum, which react well to these experimental conditions.