Abstract
Field and laboratory studies on the rôle of oxygen concentration and speed of current on larvae of Simulium ornatum Mg. show that current speed is more important than oxygen concentration in governing their distribution.The larvae prefer waters with a velocity range of 50 to 120 cm./sec., the greatest numbers occurring between 80 and 90 cm./sec.Larvae move independently of oxygen in concentrations above 50 per cent, saturation level.