PLANTS TO KILL INSECTS
[To the Editor of THE SPECTATOR]
Sta,—In his notes of April 15th, Sir W. Beach Thomas suggests that plants used for fish poisoning in the Amazon Valley might prove of insecticidal value. It may be of interest to mention that the American tropics have already yielded quite a number of plants, Cube, Timbo, &c. (species of Lonchocarpus), which like Derris contain rotenone and are of commercial value as sources of insecticides.
Official Trade Returns show that in i937 the imports into the U.S.A. of rotenone-containing materials were valued at $325,481, of which 898,051 represented Derris from the East, and $227,430 Cube and Timbo from South America and mostly from Brazil. They are now cultivated in the Amazon Valley. Primitive races have been very thorough in their search for these plants, as witness the statement made in 5935 by Dr. R. Le G. Worsley of the East African Research Station at Amani • "My usual basis for considering a plant as a possible source of insecticides is a report that the natives use it as a fish poison, and it is astonishing how very many plants are claimed to be effective as such."—Yours faithfully,
W. G. FREEMAN.