PYRETHRUM Powder as Insecticide
The use of insecticides, particularly arsenical preparations, for destroying potato bugs, grasshoppers, and fruit and cotton insects is well known, but few realize the enormous amount of money spent annually in the United States for materials used in the fight against household insects. One of the oldest and most extensively employed of these insecticides is insect (pyrethrum) powder, which consists of the finely powdered dried flower heads of certain species of Pyrethrum. We depend almost entirely for our supply of these flowers on foreign countries. Previous to 1914 most of the flowers came from Dalmatia, but during the World War this supply was cut off and Japan became our principal source of supply. Large quantities of Dalmatian flowers are again being imported, however, through the Italian port Trieste.
In 1920, the year of the maximum importation of insect flowers, nearly 7,000,000 pounds, valued at over $2,600,000, was brought in. During 1925 slightly over 3,800,000 pounds, valued at more than $1,000,000, was imported. The importation in 1926 will undoubtedly exceed that of 1920; during the first six months nearly 5,000,000 pounds, valued at about $700,000, was brought in. ® The price of these flowers has varied greatly. "In March, 1920, it reached $1 a pound, while in December, 1926, the wholesale quotations for insect powder were from 23 to 27 cents a pound and the import prices for the flowers decidedly lower. The present low prices may be accounted for by the fact that the 1925 crop, both in Japan and in Dalmatia, was very large.
The dried whole Pyrethrum flowers are shipped into the United States in bales and ground into insect powder in American mills. The powder has frequently been subjected to adulteration. The most common adulterants have been powdered Pyrethrum stems and powdered flowers of the oxeye daisy, which resembles closely the species of Pyrethrum flowers from which most of the insect powder is produced. Owing largely to the activities of the Insecticide and Fungicide Board of the United States Department of Agriculture, both of these forms of adulteration are practiced very much less extensively than they formerly were. This accounts in large measure for the great increase in the use of this product during the past 10 years.
Notwithstanding the fact that insect powder has been used for more than 100 years and has engaged the attention of chemists for more than 50 years, it was not until 1924 that the exact chemical composition of the constituents which are toxic to insects was announced. In 1924 two Swiss chemists reported that they had found that Pyrethrum flowers contain two highly toxic compounds. As these compounds are exceedingly complex in their structure and constitute only about 0.2 to 0.3 per cent of the flowers, it is not surprising that scientists were baffled for a long time. Efforts to synthesize these compounds have been unsuccessful.
Experiments conducted in the Department of Agriculture and reported in 1920 showed that certain organic solvents, including the lighter fraction of petroleum, completely extract the active principles of Pyrethrum flowers. Since that time there have been placed on the market many commercial preparations consisting essentially of light mineral oil, of the nature of kerosene, containing the active principles of Pyrethrum flowers. The sale of these products, used as sprays in the control of insects, particularly house flies, has reached extensive proportions, amounting, it is estimated, to several million dollars annually.
The Department of Agriculture is frequently asked why the United States does not grow its own Pyrethrum flowers, as the plant which bears these flowers is closely related to our common oxeye daisy. In former years insect flowers were produced commercially in California, and field experiments are now being made by the department to determine whether insect flowers of the required potency can be grown elsewhere in the United States at a cost which would permit their cultivation on a commercial scale.