STUDIES ON CONTACT INSECTICIDES

Abstract

SUMMARY An account is given of laboratory experiments on the toxicity to Aphis rumicis L. of extracts of a considerable number of plants, including some tropical fish‐poisons, Lupins, Broom, Gorse, Lobelia and others. Alcoholic extracts of certain tropical plants used as fish‐poisons are shown to have a high toxicity under the conditions of the experiments. The roots and stems of White Haiari, and the stems of Black Haiari (both species of Lonchocarpus from British Guiana), the roots of Tephrosia toxicaria and the leaves of T. Vogelii all possess notable insecticidal properties. The roots and stems of T. Candida are less toxic. Preliminary experiments indicate that the Haiaris and T. Vogelii and T. toxicaria, when tested as stomach poisons, exert both a repellent and toxic action to caterpillars. Certain derivatives isolated from these plants were tested. The most toxic substance obtained from the Haiaris is shown to be identical with tubatoxin, the crystalline poison found in Derris elliptica. Tubatoxin proved to be several times more toxic than nicotine. In the case of Tephrosia Vogelii and T. toxicaria, the most toxic substances isolated were resinous in nature. Crystals closely corresponding to tephrosin, as isolated by Hanriot, were less toxic. A number of alkaloids was also investigated. Cytisine and lobeline, known to have a physiological action on higher animals similar to that of nicotine, were found somewhat less toxic than nicotine to aphides. Eserine was the only other alkaloid tested which approached nicotine in toxicity.