INSECTICIDAL‐ACTION STUDIES WITH BISDIMETHYLAMINOPHOSPHONOUS ANHYDRIDE CONTAINING 32PHOSPHORUS

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Abstract
Bisdimethylaminophosphonous anhydride containing 32P has been used to study the absorption of this systemic insecticide into plants and its action on aphids.The radio‐anhydride is absorbed by the roots of broad beans placed in culture solutions containing it. The level of radio‐activity in the plant increases as the solution is absorbed and is higher in the washed roots than in the rest of the plant. The activity of the remaining culture solution increases as more is absorbed showing that the roots selectively reject the radio‐anhydride. The material is absorbed more slowly from soil than from sand. In both cases the concentration per gram of tissue is highest in the leaves on the middle part of the stem.By introducing the insecticide by the cut tap‐root technique it can be shown that about 50% of the radio‐anhydride is decomposed within the plant in 8 days. The concentration of undecomposed anhydride in the plant necessary to give a complete kill of Aphis fabae Scop. is about 50 mg./kg. of beans. Dead aphids were found to contain about 15–20 mg./kg. of radioactive material calculated on the assumption that it was undecomposed anhydride. The honey‐dew of aphids feeding on treated plants is also radioactive.Absorption and translocation of radioactive material occurs following the application of the radio‐anhydride to the leaves of the broad bean, cabbage, hop, pea and strawberry. In the broad bean radioactive material can be detected within the leaf a few hours after it has been applied to the surface. In all plants there is evidence that radioactive material is translocated to untreated parts. Much more is translocated to leaves younger than those treated than to leaves older than those treated. In favourable cases, where a large number of leaves on the plant are treated, where the plant holds a large quantity of the anhydride applied or where a heavy dose is given, either by repeated treatments or the use of high concentrations, it is found that insecticidal quantities of what is presumed to be the anhydride are translocated to untreated young growing parts of the plants.No measurable quantity of radioactive material is transpired by plants taking up the radio‐anhydride by the roots.
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