Tephrosia Vogelii Research Articles

THE INSECTICIDAL PROPERTIES OF SOME EAST AFRICAN PLANTS. I

Summary.A number of East African plants, mostly indigenous, has been tested for insecticidal value as contact poisons.No new insecticide equal in toxicity to nicotine has been discovered.Two plants, Cassia didymobotrya and Barringtonia racemosa, have toxic properties slightly less than half that of nicotine used as sulphate. The plants, which grow dd, should be of value for making insecticides on those farms where they are already growing: they would not, however, be worth cultivating. No definite chemical compounds were obtained from these two plants.The toxicity of extracts of Tephrosia vogelii has been found to be of the same order as that of nicotine in the form of sulphate, and these extracts should be able to replace nicotine in all sprays against soft‐bodied insects such as aphis and thrips.Nearly all parts of this plant contain tephrosin, the seeds having the largest content at 0.35 per cent., whilst the leaves contain 0.18 per cent. Methods are given for the easy extraction of tephrosin from the various parts of the plant. The product obtained has been called “crude tephrosin ” by the author, and in this form is suitable for the preparation of insecticides.Crude tephrosin contains about 20 per cent. of a substance crystallising in he yellow needles with a melting‐point of 227° C., which is probably dehydrodeguelin and is non‐toxic. The remaining 80 per cent, forms white tabular crystals with a melting‐point of 187° C., and is undoubtedly identical with Hanriot's tephrosin. So far it has resisted separation into two or more constituents, either by repeated recrystal‐lisation or by oxidation. This crystalline substance accounts for the toxicity of the crude tephrosin and of the plant itself.Resins were obtained from most parts of the plant but, contrary to Tattersfield's results, they were found to be only slightly toz.It is considered that in view of the fact that Tephrosia vogelii grows both widely spread and vigorously in East Africa it should be able to replace the use of nicotine almost entirely. On a small scale home‐made solutions could be easily and cheaply prepared, and the extraction of crude tephrosin on a larger scale is also worth consideration.9. As a paraffin spray agarnst Antestia and Lygus, Tephrosia vogelii extracts proved useless compared with pyrethrum, but as a domestic spray against flies, mosquitoes, etc., paraffin extracts were found to be as effective as pyrethrum and should be able to replace it, at least for local use.10. The finely powdered pod of T. vogelii has some value as an insect powder, due probably to the tephrosal in it, but cannot compare with pyrethrum powders.11. The seeds contain 12 per cent. of fixed oil from which a soft soap can be made, suitable, according to preliminary tests, for a spreader but not for domestic purposes. The oil is a non‐drying one.12. Further work on many of these points is continuing.

STUDIES ON CONTACT INSECTICIDES

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.

STUDIES ON CONTACT INSECTICIDES: PART I. INTRODUCTION AND METHODS. PART II. A QUANTITATIVE EXAMINATION OF THE TOXICITY OF TEPHROSIA VOGELII HOOK. TO APHIS RUMICIS L. (THE BEAN APHIS).

SUMMARY.1. The first part of this paper forms a general introduction to investigations carried out on contact insecticides. The methods used are briefly described and some consideration is given to the mode of expressing results.2. The second part deals in detail with the insecticidal properties of Tephrosia Vogelii Hook. which, with other species of this genus, occurs abundantly in many parts of the world. The aqueous and alcoholic extracts of the leaves and seeds of T. Vogelii are shown to be highly toxic to Aphis rumicis L., the toxicity being of the same order as that of nicotine. Extracts of the stems have not proved so poisonous.3. The plants of the genus Tephrosia seem to offer possibilities for practical use as insecticides and it is hoped to extend the work in this direction.