Relative Toxicities to Insects of Acid Lead Arsenate,Calcium Arsenate and Magnesium Arsenate

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Abstract
Formation of soluble As from acid Pb arsenate, Ca arsenate and Mg arsenate was found to be largely dependent on the pH of the soln., and influenced to a lesser extent by the conc. of acids, bases and salts. The presence of phosphates greatly increased the soluble As formed from acid Pb arsenate in alkaline solns., but influenced that from Ca and Mg arsenates only slightly. 9 spp. of phytophagous insects were selected for toxicity studies, having digestive juices ranging in acidity from pH 5.9 to 9.6. Phosphates were found in these digestive secretions. The relative toxicities of the 3 arsenates to these insects was correlated with the relative amts. of soluble As formed from these arsenates in phosphate solns. having the same pH as was found in the mid-guts of these insects. It appears possible to predict the relative order of toxicity of acid Pb arsenate, Ca arsenate and Mg arsenate to chewing insects if the pH in the insects'' mid-guts is known.

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