The Relative Toxicity of Trisodium Arsenite and Arsenious Acid to the House Fly, Musca Domestica L.1

Abstract

Solutions of arsenious acid and trisodium arsenite of various pH values were fed quantitatively to newly-emerged adult house flies. The solutions contained 15 grams of sucrose per 100 cc. Under these conditions, the toxicity of arsenious acid (pH 6.58 to 6.96) was indistinct from that of trisodium arsenite (pH 11.3 to 11.4), possibly the result of buffer action within the digestive tract. The M. L. D. for the two forms of trivalent arsenic was 0.14 mg. arsenic per gram of body weight. This is comparatively a large M. L. D. for an insect. Arsenious acid solutions were not repellent at any arsenic or hydrogen-ion concentration used; trisodium arsenite solutions of equivalent As concentration were not repellent at pH 11.3 and 11.4, but were distinctly repellent at higher pH values. In practice, no more alkali should be added to a house fly bait than is necessary to hold the trivalent arsenic in solution.