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of opaque rosin is seen. This property is due to the presence of water or rosin acid crystals. Sometimes the rosin, as such, shows no signs of crystalline opacity. But when used in the manufacture of gloss and core oils or adhesives, the finished product does solidify as a result of the crystallization of the rosin acids. The oil or adhesive is thus rendered useless. Studies are being made to recognize this procrystallizing tendency in rosin and to prevent its occurrenceby proper processing. Methods for the production of a noncrystallizing rosin have been the subjects of many patents. The methods usually add foreign substances to the rosin, either as chemical reagents or from pyrolytic decomposition of the rosin. By separating through fractional crystallization the resin acids in the oleoresin, Palkin and Smith (4) produced a noncrystallizing rosin. When available in commercial quantities, this product should be of interest to the industrial user. Color is today the predominating, if not the only, property
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used to grade rosin. Improved methods of production, possibly by modern central stills, of gum rosin will make available more nearly standardized rosin of that type. With the prospect of an increasing rather than a decreasing supply of this raw material and a better knowledge of its properties and components, there should be a wider field of use in many industries.
Literature Cited Am, SOC.Testhg Materials, 37, Part 11, 574 (1937). (2) Fleck, E. E , and Palkin, S., J . Am. Chem. SOC.,59, 1593 (1937). (3) Palkin, S., Chadwick, T. C.,and Matlack, M. B.. U. S. DeDt. Agr.. Tech. Bull. 596 (1937). (4) Pal&, S., and Smith,’W. C., Oil & Soap, 15, 120-2 (May, 1938). (1) Chadwick, T. C., and Palkin, S., Proc.
RECEIVED September 12 1938.
AGRICULTURAL PRODUCTS AS INSECTICIDES R. C. ROARIC Bureau of Entomology and Plant Quarantine, U, S. Departmeqt of Agriculture, Washington, D. C.
N‘JURIOUS insects in the United States are estimated to cause an annual loss of 2 billion dollars. B a c t e r i a and fungi damage crops to the extent of an additional billion dollars. To combat these pests about 100 million dollars’ worth of insecticides and fungicides are used each year. I n the past, arsenicals have been relied upon to control most iniurious insects, and copper and sulfur compounds have been the principal fungicides, but now organic products are used to an increasing extent. Farmers are turning to organic insecticides to avoid poisonous residues of lead, arsenic, antimony, fluorine, selenium, mercury, and other elements on foodstuffs, and also because certain organic compounds are more effective than the commonly used inorganic ones. Organic insecticides may be of natural or of synthetic origin. With the exception of petroleum oils, which may be derived from either plant or animal life of former geological periods, most organic insecticidal materials of natural origin are derived from the vegetable rather than the animal kingdom. Insecticides derived from plants may be divided into three categories: (a) those from crops such as tobacco, (a) those from forest products, and (c) those from weeds, which a t present have no economic value.
Insecticides from Crops Insecticides derived from cultivated plants include nicotine from tobacco, pyrethrins from pyrethrum flowers, and rotenone from Derris, Lonkhocarpus, Tephrosia, Mundulea, and other genera of Fabaceae (the bean family). The farm value of tobacco produced in the United States in 1936 was $250,364,000. From the stems and sweepings from cigar factories and off-grade and refuse tobacco there were produced about a million pounds of nicotine, equivalent to 2.5 million pounds of the commonly used 40 per cent solution sold as nicotine sulfate solution. Nicotine is one of our most valuable insecticides. It can be used as a contact poison, as a stomach poison, and as a fumigant. Nicotine in certain fixed forms-for example, nicotine bentoniteshows promise of becoming a successful substitute for lead arsenate in the control of the codling moth. Pyrethrum flowers were imported into the United States to the extent of 20 million pounds in 1937. Nearly all the world’s supply comes from Japan, but significant quantities are now being grown in Jugoslavia, Kenya Colony, and Brazil. Pyrethrum flowers of satisfactory toxic content have been grown in several localities in the United States. During 1937 the United States imported 570,341 pounds of Derris from British Malaya, the Netherlands Indies, and the Philippine Islands, and 1,591,604 pounds of Lonchocurpus root from Peru and Brazil. These plants contain the powerful insecticide rotenone. An idea of the potency of rotenone may be had when it is realized that as a stomach poison on silkworms it is thirty times as poisonous as lead arsenate, and as a contact poison upon bean aphids it is fifteen times as toxic as nicotine. Goldfish are killed by rotenone a t a concentration of 1 part in 13 million parts of water, but to
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(Right) TWO-MULE, Form-Row TRACTION DUSTERm ACTION AGAINST THE MEXICAN BEAN BEETLE
rats rotenone is only one one-hundredth as poisonous as lead arsenate. Rotenone possesses many of the properties of the hypothetical ideal insecticide. It is toxic to insects at an economical dosage, it is not injurious to the host plant or animal sprayed or dusted with it, and the residues left on foodstuffs are not poisonous to man or domestic animals. In addition to these plants which are useful primarily or exclusively as insecticides, other agricultural products have distinct value for this purpose. Reference is made to the oils of corn, cotton, soybean, linseed, peanut, and many other plants. These oils may be used in the same way as petroleum oils. They may be applied undiluted in the form of a very fine spray, or they may be emulsified in water and the emulsion then sprayed. Recent work in the Bureau of Entomology and Plant Quarantine by Cressman and Dawsey (1) has shown that certain plant oils are more toxic to mealy bugs than are the usual petroleum hydrocarbon oils used for this purpose. Moreover, the plant oils possess a decided advantage over petroleum oils in that they are better solvents for other insecticides of greater potency, especially rotenone. The use of rotenone and various synthetic compounds of high insecticidal value dissolved in oils is rapidly increasing. Steiner and Sazama (6)in 1938 reported that soybean oil added to nicotine bentonite in the spray tank increases the deposit of nicotine on apples and thus ensures better control of the codling moth. There appears to be a promising field
for drying and semidrying plant oils as adhesives for use with insecticides. Still another utilization for plant oils is indicated by the recent work of Fulton and Howard (3). They reported that the toxicity to certain insects of derris, nicotine, nicotine sulfate, and anabasine sulfate is markedly increased by the addition of certain oils, especially peanut oil. Vegetable oils increased the toxicity much more than did mineral oil. Soaps made from corn oil, cottonseed oil, soybean oil, etc.. possess high insecticidal value. These soaps may be made with sodium or potassium hydroxide or triethanolamine. The triethanolamine soaps, as pointed out by Cupples (6), have certain properties which make them valuable for use in agricultural sprays. The fatty acids derived from plant oils may be used in place of acetic acid in Paris green, and the resulting compounds have greater insecticidal value and are less phytocidsl. A compound analogous to Paris green prepared from peanut oil appears particularly promising as a poison for the control of leaf-eating insects and yet does not harm the most delicate foliage. About 3 million pounds of Paris green are consumed annually in the United States. Paris green is recognized as a valuable insecticide, but its use is limited because in contact with water it is readily hydrolyzed, and the soluble arsenic formed is very injurious to growing plants. These greens prepared from the fatty acids from plant oils are safe
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gives particularly good results, especially in arsenical cattle dips. Rosin has recently been used as a sticking agent for derris powder and phenothiazine, for when used alone they are easily washed off the foliage by a light rain. Goodhue and Fleming (4) in 1936 found that rosin residue also is an excellent adhesive. Rosin residue is a sticky resinous material that remains in the stills after the distillation of rosin. For ease in handling it is used in the form of an emulsion made with ammonium caseinate, and the concentrated emulsion is now commercially available. Pine-tar oil is a very effective repellent for certain species of blow flies, especially the destructive screwworm fly (Cochliomyia americana C. and P.), and large quantities are consumed annually in the southern states for protectinglivestock. Hardwood oils have been less studied than pine products as insecticides. They do possess insecticidal value and are also useful as solAIRPLANE FLYING OVER LEVELLANDIN MAINEAND DUSTING BLUEBERRIES vents for rotenone and FORCONTROLOFTHE BLUEBERRY MAGGOT synthetic insecticides.
to use on foliage, and yet retain the well-known insecticidal and fungicidal elements, copper and arsenic. I n addition to oils, other constituents found in cultivated crops are useful as insecticides or as adjuvants for use with agricultural sprays. For example, the lecithin in soybeans has valuable properties as a wetting and spreading agent, and has given encouraging results in orchard tests. Gums
found in many plants are excellent emulsifiers of both petroleum and plant oils used as insecticides. Tobacco contains gums that should be tested both as emulsifiers and as adhesives for use with insecticides.
Insecticides from Forest Products I
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Products derived from coniferous trees and used as insecticides include turpentine, pine oil, rosin, and pine-tar oil. Turpentine is employed only to a limited extent as an agricultural insecticide because of its injurious effect upon growing plants, but it is valuable for the control of bedbugs and other household insects. Pine oil is utilized to an increasing extent as an ingredient of cattle sprays and household fly sprays. The advantage of pine oil in liquid insecticides is that it has a greater solvent power for rotenone than the paraffi hydrocarbons have. Sprays consisting of a petroleum hydrocarbon oil, a small proportion of pine oil, together with pyrethrum extract, derris extract, or synthetics, are growing in favor. Rosin has many uses as an insecticide. It is employed in making sticky flypaper and adhesives for banding trees. In the form of rosin soap it is utilized in arsenical cattle dips, as an emulsifier, and as a wetting and spreading agent for use with nicotine and other insecticides. Practically all formulas for sticky flypaper include rosin as one of the ingredients; a common one specifies two parts of rosin and one part of castor oil. These sticky materials also find extensive use for banding the trunks of trees to keep caterpillars from ascending and eating the foliage. Rosin soap has certain physical and chemical properties which make it extremely valuable for use in emulsifying oils and as a wetting and spreading agent. A mixture of rosin soap with fish oil soap
Insecticides from Weeds Many species of plants contain constituents that have marked insecticidal value. Most of theBe plants are not produced as crops and their potential economic value is ignored; yet they can be cultivated without competing with other crops. Some of them can be grown on land poorly adapted for general agricultural use. A striking example is the devil’s shoestring, a plant belonging to the bean family (Fabaceae or Leguminosae), technically known as Tephrosia uirginiana. This weed grows from Ontario to Florida and as far west as central Texas. It grows luxuriantly on waste or submarginal land that will support scarcely any other plant life. Until a few years ago no use was made of this plant, except as a fish poison in certain parts of Texas. Studies carried on by the Division of Insecticide Investigations of the Bureau of Entomology and Plant Quarantine disclosed that the roots of this plant contain rotenone, the chief insecticidal principle of derris and cube. Some specimens of devil’s shoestring from eastern Texas have been found t o contain as much as 4 per cent of rotenone. Cooperative work between the Texas Agricultural College and the United States Department of Agriculture is now under way to develop a strain of this plant high in rotenone. This undertaking may lead to making the United States independent of foreign countries for its rotenone supply. The following plants are selected from many that have been tested in a preliminary way and are known to have insecticidal value: Haplophyton cimicidum (family Apocynaceae) has long been used in Mexico for combating flies, fleas, and other household insect pests, It is known as the cucaracha (cockroach) plant. It grows in the southwestern states and is especially abundant
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INDUSTRIAL AND ENGINEERING CHEMISTRY
in Arizona. Very little ir knovn concerning the active principles of this-piant, hut they are different from those of any other in-
secticide.
Phelbdodend?on amwense (family Rutaceae), the Amur cork tree of Japan. Fruit from this tree growing on the grounds of the Library of Congress was recently found to have distinct insecticidal value. This tree could he grown in the latitude of Wash-
ington, D. C .
N i o l i a m g l o w (family Solanaceae), the tree tobacco of the Southwest, contains anabasine, an alkaloid similar to nicotine hut even more potent as an aphicide. There is evidence that anabasine may prove &s valuable an insecticide as nicotine. NiGotiana sybestris (family Solanaceae) is ,a weed that contains nornicotine, an alkaloid of proved insecticidal value and of greater potency than nicotine for the control of certain insects. Anabasis aphylla (family Chenopodiaeeae) also contains anabasine and is the sole commercial souree of this alkaloid, at present monopolized by the U. S. S. R. This plant should grow readily in the semiarid regions of the linited States.
S y n t h e t i c Insecticides from Agricultural Products Certain synt.hetic organic compounds derived from agricultural products appear very promising as insecticides. Lauryl thiocyanate, a derivative of lauric acid from the coconut, is a potent contact insecticide. From castor oil by destructive distillation and combination with isobutylamine, a compound called isobutyl undecyleneamide is formed. This product has just been put on the market and is reported to be effective as a By spray when dissolved in kerosene together with pyrethrum extract. Its value appears to be that i t can replace in part the pyrethrum flowers which this country must, now impoit Oat hulls and corncobs yield furfural, and derivatives of this remarkable compound have given promising results when test,ed against. flies and other insects, Sulfur may be chemically introduced int,o the
Corn, rice, wheat, and other agricultural surpluses may be fermented to produce alcohols, which are converted by the action of carbon disulfide and alkali into xanthates. These xanthates have both insecticidal and fungicidal value, and their copper and zinc salts are especially potent pest-control products. Odorous compounds which may be derived from essential oils but which to an increasing extent are of synthetie origin are useful for luring insects into traps. A prominent example is geraniol, which is widely used as an attractant for the Japanese beetle. Terpinyl acetate and methyl cinnamate, both synthetic products, are effective attractants for trapping bhe Oriental fruit moth. The field of synthetic aromatics is large, and many of them will undoubtedly find use in baiting insect traps. At present synthetic organic insecticides are made chiefly from constituents of natural gas, coal tar, or petroleum, rather than from agricultural products. Rut there is a trend towards the use of oils, alcohols, and other y r d u c t s of plant origin as stariing materials for the synthesis, not only of insecticides, hut also of wetters, spreaders, stickers, etc., used with them. For example, sillfated oils such as sulfated castor oil and sulfated alcohols such as oleyl sulfate and decyl sulfate, in the form of their sodiiim salts. find extensive use as netting agents in sprays. Summary To combat pests causing an annual loss of 3 billiondollars in the United States, farmers employ about 100million dollars’ worth of insecticides and fungjcides. Although the materials now largely used for this purpose (compounds of arsenic, fluorine, lead, copper, and sulfur) are from the mineral kingdom, products derived from the vegetable kingdom are being used to an increasing extent. This is because many organic compounds are more toxic to insects but less toxic to man than are lead arsenate and other inorganic poisons. Organic insecticides may exist naturally in plants; nicotine, anabasine, the pyrethrins, rotenone, peanut oil, and other plant oils are examples. Products derived from coniferous trees, such as pinetar oil, are also valuable insecticides. Synthetics derived from oils, alcohols, furfural, and other plant products appear especially promising as insecticides and are now coming into cominercial use. Insecticides of the futurewiil he mostly organic cornpounds obtained frum plants now regarded as worthless weeds or synthesized from products of plant origin. The possibilities of constructive chemical research in this field arelimitless and should result in numeruus products of great economic value.
CHARACTERISTIC FEEDING OF LARVAE AND ADULTS OF MEXICANBEANBEETLESON A BEANLEAF
molecule of unsaturated acids and their glycerides found in various plant oils, and these sulfuriz& products have enhanced value both as such and also when converted to soaus. A fruitful field of research awaits the investigator of these sulfurized products.
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Literature Cited
(1) Crcssman and Duwsey, unpubiislied dsta. ( 2 ) Guppies, H. L., J . Ecm. Fntaol.. 31, 68-70 (1838). (3) Fulton, R. A., and Howard, N. I?.,Jbid., 31,405-10 (1938). (4) Goodhue, L. D., and Fiemiw, W. E.. Ibid.. 29, 580-3 (1036). (5) Steiner, L. F.. and Sazarna. R. F., Ibid.. 31, 366-74 (1938). R ~ c s r v s oSeptember 12, 1938.
