Dry lime-sulfur is made by adding a stabilizer such as cane sugar to liquid lime-sulfur and evaporating to dryncss. Self-boiled lime-sulfur is made by Insecticides utilizing the heat of hydration or slak- ing of quicklime, CaO, to carry on the From Plants reactions with sulfur. Ammonium polysulfide and sodium Louis Feinstein polysulfide are made by passing hydro- gen Sulfide gas, H.^S, into ammonium or sodium hydroxide containing excess More than 2,000 species of plants are sulfur. It is supposed that the chemical said to have some value as insect killers. reactions are similar to those taking They belong to 170-odd families. Com- place in the preparation of lime-sulfur. mercial insecticides of plant origin are Sulfur is used under some conditions found in five families : Nicotine in the for the control of potato leafhopper, Solanaceae family; pyrethrum in Com- the cotton fleahopper, tomato psyllid, positae; derris, cube, and timbo in mites, and plant bugs. Leguminosae; hellebore in Liliaceae; Organic sulfur compounds, includ- and anabasine in Chenopodiaceae. ing thiocyanates, xanthates, and thi- Anabasine is also found in Solanaceae. uram disulfides, have some insecti- Who first discovered the insecticidal cidal properties although they are used value of plants is not known. The Ro- largely as fungicides. mans divided poisons into three groups, Sulfur dioxide, SO2, made by burn- animal, plant, and mineral. They used ing sulfur, is sometimes used to kill in- two species of false hellebore in medi- sects in closed spaces. cines and in rat and mice powders and Thallium sulfate, Tl^SO^, sometimes insecticides. The Chinese discovered is used as the toxic agent in ant poisons. the insecticidal value of derris. Several zinc compounds are in Chemists in the Bureau of Entomol- limited use as insecticides. Zinc sulfate, ogy and Plant Quarantine since 1927 ZnS04, is sometimes used in place of have conducted research on the prin- copper sulfate in reactions with hy- cipal insecticides of plant origin, such drated lime to form a zinc bordeaux as nicotine, nornicotine, anabasine, ro- mixture that has special uses. Zinc tenone, deguelin and related rotenoids, chloride, ZnCl^, is used to protect quassin, and the pyrethrins. They also against termites. have worked on more than 450 plants in an effort to discover new sources of R. H. CARTER is a chemist in the these and other insecticides, as well as Bureau of Entomology and Plant attractants, repellents, and adjuvants. Quarantine, assigned to the division They have learned that many of the of insecticide investigations at the Agri- species in the 170 families do not war- cultural Research Center at Beltsville, rant further investigation and that bo- Md. After graduation from Morning- tanical classification is not a depend- side College and the State University able guide in the search for insecticidal of love a, he was employed in chemical plants. research in the Chemical Warfare Plant insecticides are only a small Service for 10 years. Since joining the fraction of the insecticidal material Department of Agriculture in ig2y, he used each year. Yet in the development has been engaged in research in the of new insecticides they deserve careful development of insecticides, investiga- consideration: Often they are highly tions of spray residue problems, and effective against many insect enemies toxicological investigations of the ef- that are not successfully controlled by fects of insecticide materials on farm inorganic insecticides. The plant insec- animals. ticides often are relatively nontoxic to 222 Insecticides From Plants 223 man and other plants. Poisonous spray of plants grown in Arizona is toxic to residues on fruits and vegetables may adult house flies. The crude alkaloid menace public health. The relative from this plant is effective against most safety of plant insecticides to man insects. It is as toxic as pyrethrum to helps to maintain their continued use. the squash bug. In this article I discuss the commer- Boraginaceae {Borage Family). He- cial plant insecticides and other plants liotropium peruvianum. The borage that appear promising as insecticides. family contains many well-known gar- Included here are plants only of the den plants and often is called the helio- higher orders (phanerogams). They trope family. The compound heliotro- arc listed alphabetically according to pine was one of the best chemicals plant family and genus. The plants are tested against the body louse, being sufficiently promising to warrant inten- apparently nontoxic to the skin and sive chemical and toxicological studies. lasting more than 168 hours when used The lower orders of plants (crypto- in cocoa butter. gams) include the algae, fungi, mosses, Tournefortia hirsutissima is used as ferns, and horsetails. A more complete a general insecticide in Haiti. study of them may also prove to be Cannaceae {Canna Family). Mem- worth while. bers of this family mostly have tuberous ^ Aesculaceae {HOT se chestnut Fam- rootstocks, stately, broad leaves, and ily). Aesculus californica is called the showy flowers. The leaves and stems of California buckeye. The horsechestnut canna plants contain an insecticide that is a highly prized street and lawn shrub gives results similar to tobacco in green- and tree. The common horsechestnut house fumigation. casts the densest shade of almost any Celastraceae {Staff-Tree Family). cultivated tree. George H. Vansell and Tripterygium wilfordii, the thunder- his coworkers in California found that god vine, is a common insecticidal bees feeding on buckeye blossoms be- plant in southern China. The poison in came paralyzed and died. Reports of it has been found in the root bark. Its other investigators, however, show that chemistry has been investigated by the insecticidal value of species of the M. Beroza, who reported that wilfor- horsechestnut family varies. dine is a mixture composed mainly of Annonaceae {Custard-Apple Fam- two similar alkaloids, a- and ^-wilfor- ily) . The genus Annona includes some dine. Both are insecticidally active ester 90 species of trees and shrubs, mainly alkaloids. Powdered fresh small roots in tropical America. S. H. Harper, G. are toxic to first-stage larvae of the Potter, and E. M. Gillham m England codling moth, the diamondback moth, extracted Annona reticulata and A. and the imported cabbageworm. Alco- squamosa seeds and roots with ether. holic extracts of the roots are more The petroleum ether solution of this ex* toxic. Small roots, powdered, are about tract at 0° C. precipitated out an in- half as toxic as pyrethrum to the Amer- secticidal material that was 50 to 100 ican cockroach. The large^and medium times more potent than the original roots are nontoxic. ether extract. Against some insects the Chenopodiaceae {Goosefoot Fam- concentrate had about the same toxic- ily). Anabasis aphyila contains the al- ity as rotenone. More work should be kaloid anabasine, closely related to done with the custard-apple. nicotine. It is the only commercial Apocynaceae {Dogbane Family). source for the alkaloid. It grows mainly Haplophyton cimicidum, the cock- in Russia and is not available in the roach plant, has been used to combat United States. Anabasis aphyila is re- cockroaches, flies, mosquitoes, fleas, lated to the American tumblewecd. In lice, and other insects in Mexico. The this country my coworkers and I ex- dried leaves are toxic to the Mexican tracted anabasine from Nicotiana fruit fly. The water extract of the stems nlauca. 224 Yearbook of Agriculture 1952 Clusiaceae {Balsam Tree Family). curhita pepo commonly is called pump- Mammea americana is known as kin. Freshly cut pumpkin leaves rubbed mamey, "mamey de Santo Domingo." on cattle and horses reputedly repel Harold K. Plank of the Federal Experi- flies. Acetone extracts of pumpkin ment Station at Mayaguez, P. R., be- seeds killed mosquito larvae in experi- lieves that this indigenous West Indian ments conducted by A. Hartzell and tree has greater insecticidal potential- F. Wilcoxon of Boyce Thompson In- ities than any other plant he examined. stitute. The active principle in the mature Euphorbiaceae {Spurge Family), seeds^ the most toxic part, is a type of Crotón tiglium contains crotón oil. substance some^what similar in compo- The plant is cultivated in China, where sition and efTect to pyrethrins. Plank the seeds are the source of a home- found that six of the nine parts of the made insecticide. The plant has insec- plant were appreciably or highly toxic ticidal value against aphids. J. R. Spies, to one or more insects. The bark has a chemist in the Department of Agri- little toxic material. culture, reported that an acetone ex- Cochlospermaceae. Cochlospermum tract of the seeds was more toxic to gossypium. Kutira gum increases the goldfish than der ris extract and that effectiveness of nicotine sulfate sprays. crotón resin was more toxic than ro- The kutira appears to be a synergist to tenone. nicotine sulfate in its action against the Ricinus communis, the castor-bean bean aphid. plant, is said to have some insecticidal Compositae {Thistle or Aster Fam- value. If that is true, the insecticidal ily), This large family of plants in- principle is present only imder certain cludes thousands of herbs, vines, trees, conditions with respect to variety, cul- and shrubs. The dahlia, chrysanthe- tural practice, and environment. A val- mum, coreopsis, mangold, aster, cos- uable synergist is prepared from isobu- mos, and many other garden flowers tylamine and undecylenic acid, which are composites. To the dried flowers of results from the chemical decomposi- Chrysanthemum einerariaefolium the tion by heat of castor oil. By the action name pyrethrum is applied. Pyre- of sulfuric acid on castor oil, we get a thrum, a safe and effective insecticide, useful emulsifier for insecticidal oils. is widely used in household sprays. Flacourtiaceae. Ryania speciosa. The Four compounds exist in pyrethrum— active principles of the plant are alka- pyrethrins I and II and cincrins I and loids and are effective in the control of II.