Naled/diesel oil (1:99), applied as a thermal fog, was tested against the biting midge Culicoides furens. The insects were confined in small cages suspended at 4 heights on poles at progressively greater distances from the fog release point. In terms of population survival 24 hr after treatment, a parabolic equation accurately described the regression of percent survival on distance from the release point. If 10% survival is considered as the maximum acceptable, then the equation predicts adequate control up to 19.6 m (64.3 ft) from the fog release point.