Plants That Help Kill Nicotine is the chief insecticidal principle in tobacco. It belongs to the class of compounds known as alkaloids, Insects which are basic, nitrogen-containing plant products having a marked physi- ological action. Other related alkaloids, Ruth L. Bushey notably nornicotine, also may be pres- ent in tobacco. Nicotine derives its name from Nico- tiajia, the genus of plants to which to- In June 1943, DDT was revealed to bacco belongs. The genus was named the American public. Floods of pub- for Jean Nicot, who introduced tobac- licity told of its amazing powers as an co into France in 1560. Chemically, insect killer. Announcements of other nicotine is 1 -methyl-2- ( 3-pyridyl) pyr- synthetic insecticides have followed in rolidine. Most preparations that con- rapid succession. It is not surprising tain it have a strong tobaccolike smell. that many who read those accounts as- Its boiling point is 477° F., yet it evap- sumed that insecticides of natural oi'ates rather rapidly at ordinary room origin, derived from plants, arc out- or outdoor summer temperatures. It is moded and of little importance now- peculiar in that between 140° and adays. The assumption is far from true. 248° F. it is soluble in water in all pro- As each new synthetic ins(x:ticide is portions, but above and below those studied and the ramifications of its temperatures its solubility is limited. It toxicity to man and animals explored, is highly toxic to warm-blooded ani- the problems of removing its residues mals and to most insects, but because of from foods encountered, and its pos- its volatility it disappears rapidly from sible injurious effects on plants exam- products that have been sprayed or ined, we appreciate the value of insecti- dusted with it. Its freezing point has cides, like pyrethrum and rotenone, not been determined, but it is a liquid which are nontoxic to warm-blooded even at -110°F. animals in the small quantities needed Nicotine has been isolated from at for insect control, are safe for plants, least 18 species of Nicotian a and from and leave no harmful residues. a few species in other plant genera. In Within the plant kingdom are many this country it is produced commer- species, known or yet untried, whose cially from Nicoiiana tahacum, the insecticida 1 properties are worth a ordinary tobacco used for smoking and careful search by chemists and ento- chewing. From the woody stems and leaf midribs, which are not suitable for mologists. Today nicotine, pyrethrum, smoking or chewing, we extract the derris, and cube are by far the best nicotine. A coarser species of tobacco, known and most commonly used in- Nicotiana rustica, of higher alkaloid secticides of plant origin, but a few content, is cultivated in Soviet Russia, others are utilized for specific purposes Germany, Kenya, and Hungary as a or in a few localities. Others still in source of nicotine. experimental stages have been found to contain substances highly toxic to THE ALKALOID is obtained by treat- insects. The indications arc that many ing the plant material with an alkali plant insecticides await discovery. solution and distilling by passing steam 765 766 1950-1951 YEARBOOK OF AGRICULTURE through the mixture. The nicotine is Anabasine, a compound isomeric volatilized and carried off by the steam with nicotine (that is, containing the and afterwards condensed by cooling. same proportions of carbon, hydrogen, All parts of the plant contain the alka- and nitrogen), is like it in chemical, loid, but it is chiefly in the leaves. The physical, and insecticidal properties. proportion of nicotine present varies Russian chemists in 1929 isolated from from almost none in high-grade smok- the Asiatic shrub Anabasis aphylla an ing tobacco to as much as 12 percent in alkaloid that they identified as 2-(3- leaves of N. rustica. pyridyl) piperidine and called anaba- Most of the nicotine used as an in- sine because of its source. The year secticide in the United States is sold in before, C. R. Smith, who was synthe- the form of the sulfate, in a water solu- sizing a number of compounds related tion, containing 40 percent of the alka- to nicotine in order to study their toxic- loid. Free nicotine also is available, but ity to insects, found one that appeared it is not so widely used in spraying be- to be equal to nicotine. The compound, cause it evaporates too quickly and be- which he named neonicotine, was iden- cause it is much more toxic to man tical with anabasine. It was unique in than the sulfate. The spray is greatly being first prepared synthetically and diluted for use, as concentrations of later found to occur as a natural plant 0.05 to 0.1 percent of nicotine are constituent. In 1935 Mr. Smith found enough to control most aphids and anabasine in Nicotiana glauca, the wild other soft-bodied insects. tree tobacco native to our Southwest- Many attempts have been made to ern States and Mexico. fix the alkaloid and lengthen its period The Russians have produced anab- of effectiveness. One of the most efiPec- asine sulfate commercially as an in- tive forms is nicotine bentonite, which secticide from Anabasis aphylla, which was developed by a Department of is a salt-loving perennial plant of Agriculture chemist, C. R. Smith, in the family Chenopodiaceae, grow- 1934. It is made by adding nicotine to ing in the semiarid steppes of Trans- a suspension of bentonite (a kind of caucasia, Russian Turkestan, and clay) in water, then drying and grind- neighboring parts of Central Asia. A ing the mixture. The nicotine combines Russian commercial product that was with acidic constituents of the benton- marketed in the United States for a ite and the product, when properly few years before 1934 contained about made, is effective for several weeks 40 percent of anabasine and associated after it is sprayed. It has been used alkaloids. Anabasine has been used ex- especially to control the codling moth tensively in the Soviet Union in the on apple trees. form of insecticidal dusts. Finely ground tobacco, or nicotine The production of anabasine has not sulfate diluted with a carrier, such as been developed commercially in the clay, pyrophyllite, fuller's earth, or talc, United States. Small-scale tests by en- often is used as a dust on vegetable tomologists of the Department of Agri- crops. If a quick-acting dust is desired, culture have shown that it is of the alkaline diluents such as hydrated lime same order of toxicity as nicotine to a are useful. number of species of aphids and other For the fumigation of greenhouses, insects. H. H. Smith, a geneticist in the nicotine is ordinarily used as the free Department of Agriculture, and C. R. alkaloid in concentrated form to be Smith in 1942 studied the alkaloid con- volatilized by heating, or as a mixture tent of several species and interspecific with a combustible organic material hybrids of Nicotiana. They found and an oxidizing agent, like potassium that anabasine was the predominant nitrate, to be applied by burning. alkaloid in N. debneyi, N. glauca, and Further details about nicotine are the hybrid N. tabacum x A^. glauca. given in the chapter that follows. Russian workers have reported as much PLANTS THAT HELP KILL INSECTS 767 as 8 percent of anabasinc in hybrids of dichloridc, and then removing the sol- A^ glauca and A', rustica. De})artraent vent by evaporation to leave a semi- chemists in 1948 began to investigate solid residue, w^hich can b(^ diluted N, ¿llanca as a source of anabasinc for with kerosene or other solvent. insecticidal use and to study methods Many chemists, beginning wath an that might be feasible for extracting Italian named Ragazzini in 1.854, tried the aikaioid on a com.mercial basis. without success to isolate the active Wild plants, collected in Texas, which princi])les of pyrethrum flowers. In contained 1 percent or less of the alka- 1924 two Swiss chemists, H. Staudin- loid were used in the studies. L. Fein- ger and L. Ruzicka, obtained two in- stein and P. J. Hannan developed secticidally active esters, which they methods of extraction that arc satis- called ])yrethrin I and pyrethrin II. factory on a laboratory scale, A plant- A group of De]:>artmcnt chemists, breeding program to develop strains or headed by F. B. LaForge, finally estab- hybrids of N. glauca of higher alkaloid lished the exact chemical structure of content is necessary before develop- the pyrethrins in 1947. They dis- ment as a cultivated croj) can bi^ under- co\'ered that twx:) other very similar in- taken profitably. secticidal esters also are present in jjyrethrum, and they named them EARLY IN THE NINETEENTH CEN- cinerin I and cinerin II. TURY an insecticide jDowder was intro- duced into Europe by an Armenian METHOD^ of making highly purified, trader, who learned its secret while standardized concentrates from pyre- traveling in the Caucasus. The prepa- thrum have been so successful that ration consisted of jDow^dered dried extracts containing 20 percent of pyre- pyrethrum flowers, w^hich had been ob- thrins now arc commercially available. tained from certain species of Chrysan- The extracts are especially useful in themum and probably had been used insecticidal aerosols, w^hich contain the as an insecticide in Persia for a long pyrethrum concentrate and a liquefied- time. The trader's son began to make gas i^ropellent, like Freon-12 (dichlo- it on a commercial scale in 1.828. rodiiluoromethane). Usually the aero- Pyrethrum ])owder w^as introduced into sols also contain one of a number of the United States about .1860.