INSECT Poison Called Rotenone Highly Toxic But Costly at Present

Man has always been obliged to share his crops with worms and insects. In order to control these pests he has had to resort to the use of insect poisons.

The ideal insecticide kills all insects but is neither injurious to plants nor toxic to animals. Substances which are very effective as insecticides and not injurious to plants are found in the plant world.  Among these are the pyrethrins, two similar but highly complicated chemical compounds found in the flower of a species of pyrethrum.  Unfortunately they are too expensive to use on a large scale and there is little hope of preparing these or related substances artificially.

The root of a vine (Derris elliptica) that grows in the East Indies contains a substance called rotenone, which may be easily extracted and purified and which is extremely toxic to fish and to some insects. It has long been a practice in Borneo to throw the crushed roots of the Derris plant into rivers and then pick up the fish that it has killed or stunned.

Preparations of rotenone have lately appeared on the market in the form of a semisolid solution in fish oil. For use as an insecticide this is emulsified with soap and sprayed on plants or trees. In a few days, in contact with the soap and air, according to Japanese investigations the rotenone is completely decomposed, but in the meantime it destroys most, soft-bodied insects with which it comes in contact or insects which eat the sprayed foliage or fruit, for rotenone is both a contact and a stomach poison. Its toxicity seems to be of about the same order as that of the pyrethrins or nicotine. Unlike arsenic and other mineral poisons, the toxic effect of which can not be destroyed and which are removed with difficulty, this natural organic insecticide automatically disappears.

Rotenone at present is too expensive for wide use, but there is some hope of producing it artificially or at least of developing a similar chemical product.