Field Studies on Larval Control of Black Flies in Guatemala1

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Abstract
Tests were made to determine the relationship of insecticide material, concn., application period, and stream volume to the distance of kill of black fly larvae attainable with a single treatment. It was found that for DDT at the rates of 0.1 ppm for 3 min., 0.1 ppm. for 60 min., and 2 ppm. for 3 min., the greater the stream-volume at the point of treatment the farther the insecticide would be effective in a stream. However, DDT at 0.1 ppm for 3 min., which was effective for about 2 miles at a vol. of 5000 gal. per min., appeared to have reached the limit of its effectiveness at that vol., for beyond it, the distance of kill showed relatively little increase. Such a limit to the effective distance of control was never reached with DDT at the 0.1 ppm concn. applied over a 1-hour period, the largest river so treated having a vol. of 90,000 gallons per min. In any future larvicid-ing program treatment with 0.1 ppm DDT for 3 min. in the short rivulets and most intermediate size streams (100-1000 gal. per min.), which constitute 90% of the breeding streams in the area, would make possible important savings in man-hours spent in making applications as well as reducing the amount of material which would have to be transported in the field over rugged terrain. In streams over 5000 gallons per min. either 2.0 ppm DDT for 3 min. or 0.1 ppm for 60 min. should be used.

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