This section is from the book "The Gardener's Monthly And Horticulturist V20", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
Why the flowers of the composite plants Pyrethrum carneum and P. roseum, when pulverized to form the well-known "Persian Insect Powder, " should prove so destructive to insects, while perfectly innocuous to other forms of animal life, has not hitherto been understood. Rother, who has investigated the chemical composition of P. roseum, ascribes its active powers to the presence of an acid, or, more properly, of a glycoside, which he terms Persicin. It is a brown non-crystallizable substance, having the odor of honey, and when boiled with hydrochloric acid is converted into sugar and Persiretin. With alkalies it forms a neutral amorphous salt, as well as an acid crystallizable one. Persiretin also behaves like an acid. The plant contains, in addition, an oily resin-like acid, Persi-cein. No alkaloid was found by Rother. Bel-lesone, however, obtained from the plant a crystallizable substance which exhibited exceedingly acetic properties. Hager, who has examined the flowers of both P. carneum and P. roseum, attributes their insecticide effects to the presence of two substances, one of which, a body allied to trimethylamine, is combined with an acid in the flower. This powder as well as the pollen has a peculiarly powerful effect as an irritant.
Hager finds that aqueous or alcoholic extracts of the powdered flowers contain little of these ingredients, and consequently to be of no value as insecticides. - Scientific American.