Effects Associated with Toxicity and Plant Translocation of Three Phosphate Insecticides12

Abstract

Acaricidal and insecticidal toxicity of octamethylpyrophosphoramide, 0, 0-diethyl O-p-nitrophenyl-phosphate (para-oxon), and O, O-diethyl O-p-nitrophenylthio-phosphate (parathion) were studied. Para-oxon was especially high in initial toxicity to Tetranychus bimaculatus. Both para-oxon and parathion produced fairly high mortality of mites by vapors alone, while octamethylpyrophosphoramide had no significant vapor toxicity. The systemic effect or plant translocation of octamethylpyrophosphoramide was checked quantitatively in the broad bean plant, by use of a bioassay of untreated leaf extracts against larvae of the mosquito Aedes aegypti. An estimated 40% of octamethylpyrophosphoramide or an active toxin formed from it was evident in untreated lower leaves of a growing plant when the chemical was applied to the upper leaves. For para-oxon about 7% activity was evident on the same basis. The toxic effect of octamethylpyrophosphoramide persisted for more than 4 weeks while parathion and para-oxon were effective for 12-14 days in tests with T. bimaculatus. Toxicity (non-translocated tests) of octamethylpyrophosphoramide and para-oxon to Aedes aegypti larvae expressed as L. D. 90 values was 0.95 ppm. and 0.016 ppm., respectively. The translocation of octamethylpyrophosphoramide and para-oxon in plants had many points of similarity with the translocation of the herbicide 2,4-D and related compounds. Some of these points included much greater downward movement than upward movement when a plant is sprayed on its aerial vegetative parts, but an upward movement was detectable. A definite increase in the carbohydrate content of the plant occurred after spray treatment with octamethylpyrophosphoramide, a smaller increase with para-oxon. Such increases were more pronounced in plants placed in sunlight than plants kept in the dark and in vigorously growing plants, but poor in a blooming plant. An increase in nitrate composition of beans and peas was found after spraying the plants with octamethylpyrophosphoramide.