Effect of Mean Temperatures on the Content of Pyrethrins in Flowers of Chrysanthemum (Pyrethrum) cinerariaefolium

Abstract

Pyrethrum, indigenous to the Adriatic coast of Yugoslavia, is grown on a commercial scale in the highlands of East Africa. Its culture is of major importance to the economy of, for example, Kenya and Tanganyika. The value of the plant lies in the insecticidal properties of four chrysanthemum esters contained in the flower heads, that is, pyrethrin I, pyrethrin II, cinerin I and cinerin II, collectively called the pyrethrins. Their percentage in the whole dry flower head varies from plant to plant, and with the time of season and the climatic conditions prevailing at the time of maturing. While Dalmation flowers on the average possess a pyrethrins content of 1 per cent, that of African flowers is usually 1.3 per cent or higher.