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Screening Tests with Materials Evaluated as , Miticides, and Repellents at the Orlando, Fla., Laboratory, April 1942 to April 1947, 1947; E-802, A Digest of In- The Inorganic formation on , by R. C. Roark. 1950. In Advances in Chemistry, volume i: Insecticides Organic Phosphorus Insecticides, by S. A. Hall, pages 150-159; Alkali-Stable ^ Poly- chloro Organic Toxicants, and R. H. Carter , by R. E. Lidov, H. Bluestone, S. B. Soloway, and C. W. Kearns, pages 175-^^3- 195O' Inorganic insecticides are of In Chemistry and Industry: The Gamma- Isomer of Hexachlorocyclohexanc (Gam- origin, mainly compounds of antimony^ mexanc), by R. E. Slade, volume 40, pages arseniCj barium, , copper, fluo- 314-3^9- 1950. rine, mercury, selenium, , thal- In Science in Farming, Yearbook of lium, and zinc, and elemental phos- Agriculture 1943-1947: The Chemistry of phorus and sulfur. DDT, by H. L. Haller and Ruth L. Busbey, pages 616-622; Pests That Attack Man, by Antimonyl potassium tartrate, tar- E.F. Knipling, pages 632-642. 1947. tar emetic, K(SbO) G,H,Oo.i/2TLO, N. Y, State Growers Bulletin 7, is a white powder soluble in . It Revised Recommendations for Azobenzene, is sometimes used as the toxic agent in by W, E. Blauvelt, pages 15-16. 1946. ant poisons and for the control of Patents: 2,291,193, Insecti- cide, patented by Lloyd E. Smith, July 28, thrips. 1942 (U. S. Patent Office Official Gazette, Arsenical compounds are the most volume 540, page 827): 2,010,841, Chlori- widely used inorganic insecticides. nation, patented by Harry Bender, August Recommendations for their use date ^3> ^935 {volume 457, page 302). from 1681. They were probably used before that. The poisonous properties of trioxide were well known during the Middle Ages and it was a favorite instrument of murder as prac- ticed by the Borgias. This knowledge of the poisonous properties of arsenic compounds probably led to their use as insecticides. Arsenic trioxide, As^Os, also called arscnious oxide, is a wdiite crystalline material sometimes referred to as white or gray arsenic. It is the starting material in the manufacture of arseni- cal compounds used as plant insecti- cides and it is sometimes used in weed killers. It is obtained from the flue dust from copper smelters. Our supply comes from domestic and foreign sources. It is sometimes used as the toxic agent in baits to control grass- hoppers, cutworms, and other . The arsenate that is sold commercially as an is not a single chemical compound but a com- This cylindrical fungus-feeding beetle is plex mixture of several calcium arsen- admirably suited for \i\'mg in round tun- ates and an excess of calcium hydrox- nels which it bores into forest trees for the> ide. The material is made from arsenic propagation of its food. trioxide by first oxidizing it to arsenic 218 The Inorganic Insecticides 219 pentoxide with nitric and then Both forms should contain very little reacting the solution of arsenic pen- water-soluble arsenic pentoxide in toxide or arsenic acid with a slurry of order to minimize plant damage. Gen- calcium . The conditions of erally they are much less aptto burn temperature, concentration, and dura- plant fohage than is tion of reaction are important because or . The basic compound is of their influence on the physical na- safer to use on growing plants in some ture of the product. Commercial cal- localities (for example, the foggy re- cium arsenate generally is colored pink gions of California) than is the acid and is alkaline in reaction. It is a finely compound, but in general it is not so divided powder. It has been used ex- toxic to insects. tensively against certain insects affect- Acid lead arsenate is used exten- ing field , especially . It can- sively to control chewing insects on not be used safely on apples, peaches, fruits, such as apple and pear, on beans, and some other crops because , trees, and shrubs, and on vege- of its burning efí'ect on the foliage and tables, such as potato and tomato. It fruit. also has extensive use in treating Calcium arsenate-calcium arsenite to control Japanese beetle and Asiatic mixture is sold under the name london garden beetle larvae and related soil- purple. It has some use for poisoning infesting forms. insects on cotton. A number of United States patents Among the insecticidal materials cover processes for the manufacture of containing copper and arsenic, copper- magnesium arsenates for use as insec- aceto-arsenite (or paris green), 3 Cu- ticides. The magnesium arsenates (AsO,)2.Cu(C,H,0,),,'is by far the tested as insecticides consisted gener- most important. It has been used as an ally of the dimagnesium arsenate, insecticide since about 1870. For many MgHAsO^, the trimagnesium arsenate, years it was the most widely used insec- Mg3(As04)<,, or the pyroarsenate, ticide in the United States for control Mg2As^07, with varying amounts of of Colorado potato beetles. It has water of crystallization and excess mag- largely been supplanted by some of the nesium oxide or hydroxide. newer materials, but approximately 4 Magnesium arsenate has been tested million pounds are used annually by against a large number of insects af- farmers and gardeners. fecting fruits and vegetables and at one Copper arsenite, Cu-^iAsO.,) 2.XH2O; time was recommended for the control copper meta arsenite, Cu(As03)2- of the Mexican bean beetle, but its use H2O; and basic copper arsenate, Cu.r has declined. (As04)2.Cu(OH)2, have all been pro- A crude manganese arsenate once posed as insecticides but have not been was proposed as an insecticide for com- used to any extent. Compounds similar batting caterpillars on tobacco because to paris green made from organic its brown color made it less conspicu- other than acetic have also been tested ous on cured tobacco leaves than the but have not developed into commer- white lead arsenate. cial use. Sodium arsenite is formed by dis- Several chemically different com- solving arsenic trioxide in sodium pounds are known as lead arsenate. hydroxide solution. Depending on the Two of them are commonly used as in- ratios of the reacting materials, the secticides. Acid lead arsenate (dilead- products range from the monosodium ortho arsenate), PbHAsO,, is formed compound, NaAsOg, to the trisodium by the action of arsenic acid on litharge arsenite, Na;{AsO;i. A standard for- salt. It is a white powder, insoluble in mula for making so-called liquid so- water. Basic lead arsenate (lead hy- dium arsenite requires 4 pounds of droxy arsenate), Pbi(PbOK) (As04)3, white arsenic and i pound of sodium also is a white insoluble powder. hydroxide per gallon of solution. 220 Yearbook of Agriculture 1952 Sodium arsenite is not used as an and flowering plants. It is sometimes insecticide on field crops because of its used also as an cmulsifier for lubricat- corrosive action. It is used as an in- ing-oil sprays applied to fruit trees, gredient in poison baits for grasshop- such as apple, pear, quince, and peach, perSj crickets, roaches, ants, and other when they are dormant. insects, and in stock dips. It has been Several other copper compounds, used extensively as a weed killer. including the oxide, oxychloride, phos- Zinc meta arsenite, Zn(As02)25 is phate, quinolinolate, silicate, basic sul- formed when a soluble zinc salt is re- fate, and cyanide arc used as spray acted with arsenious acid or white materials. They have little insecticidal arsenic under carefully controlled con- value but are potent fungicides. ditions, as it is soluble in either acid or Hydrated lime, or calcium hydroxide alkaline solutions. Ga(OH)2, is used in the manufacture Zinc arsenite is used in wood pres- of lime-sulfur, calcium arsenate, and ervation but is not used in household bordeaux mixture. When limestone, insecticides or as a constituent of CaCOy, is heated, the carbon dioxide formulations to be used on field crops. is driven off, leaving the product Zinc arsenate, Zn3(As04) 2, has been known as quicklime, CaO. When proposed in place of lead arsenate in quicklime reacts with water, heat is codling moth control, principally be- evolved and the resulting product is cause it avoids lead residues. hydrated lime, Ca(OH)2. Hydrated Arsenates and arsenites of many of lime is not primarily an insecticide but the other elements have been investi- is used as a safener with some of the gated for insecticidal use but none has arsenical sprays. been developed into satisfactory mate- Calcium cynanide, Ga(GN) '>> reacts rials. Organic arsenicals have likewise slowly with moisture in the air to liber- failed to find a place as insecticides. ate hydrocyanic acid gas, a highly toxic Barium carbonate, BaCOj,, is a used as an insecti- white, finely divided powder which is cidal fumigant. sometimes used as the toxic agent in Compounds that contain fluorine poisons. have been in use as insecticides since , Na2B407, and , about 1890. Barium fluosilicate, H3BO3, have been used in roach pow- BaSiFß, a white, finely divided powder, ders, but more effective compounds, has been tested extensively as a substi- such as sodium fluoride, DDT, and tute for arsenicals in the control of , are available now. fruit and vegetable insects. It has Bordeaux, or bordeaux mixture, is some value in the control of flea beetles, the name applied to the compounds blister beetles, Mexican bean beetle, formed by reacting dilute solutions of and others. copper sulfate with calcium hydroxide , or sodium fluoaluminate, suspensions. If equivalent amounts of Na^AlFo, is a white crystalline material. the two materials are used, an inti- Natural cryolite (ice-stone) is mined mate mixture of the copper hydrox- in Greenland and imported into this ide, Gu(OH)2, and calcium sulfate, country. Synthetic cryolite, of similar CaS04, is formed. This suspension has composition, has been manufactured a blue color and leaves a bluish-white and sold for insecticidal use. For most deposit on sprayed surfaces. uses there is little difference in their Bordeaux mixture is primarily a effectiveness. Large quantities have fungicide but is often used in connec- been used on codling moth in the Pa- tion with insecticides such as nicotine, cific Northwest and on the tomato pin- lead arsenate, and calcium arsenate. worm, tomato fruitworm, lima-bean It is sometimes used to control the pod borer, corn earworm, Mexican potato leafhopper and as a repellent bean beetle, walnut husk , pepper for flea beetles on various vegetables weevil, cabbage caterpillars, blister The Inorganic Insecticides 221 beetles, and flea beetles. It is generally been used in the Pacific Northwest to used as a spray but may be diluted with combat on apples and grapes. talc, pyrophyllitc, or other diluents to The use of elemental sulfur and al- form a dust. kaline Sulfides as insecticides and fungi- Sodium fluoride, NaF, is a white cides on field crops and in greenhouses powder. Sometimes it is colored green dates back many years. The materials or blue so it will not be mistaken for are elemental sulfur, sulfides, polysul- baking soda. It is used extensively as a fides or salts of some of the roach powder and is effective against acids of sulfur. Elemental sulfur is used chicken and animal lice of various alone as a dust or in combination with kinds. It causes serious damage on other insecticides with many of which plants. it is compatible. The sulfur is reduced Sodium fluosilicate, Na^SiFo, is a to a very fine state of subdivision by white crystalline powder much less sol- grinding, precipitation, or sublimation. uble than sodium fluoride in water. It Dusting sulfur, or conditioned sul- has been used as a dust and spray in the fur, is finely divided elemental sulfur control of some insects on field crops, made into a free-flowing powder by the as a poison in cutworm, mole cricket, admixture of i to 5 percent of clay, and grasshopper baits and is effective talc, gypsum, tri-calcium phosphate, or as a mothproofing agent for woolen similar materials. Flotation sulfur, col- fabrics. A large number of fluorine loidal sulfur, and precipitated sulfur compounds, both inorganic and or- refer to finely divided sulfur formed ganic, have been patented for use as as a result of chemical reactions of mothproofing agents. sulfur-containing compounds with Some compounds of mercury are other compounds. Wettable sulfur is used as insecticides. Mercuric chloride finely divided sulfur that has been (corrosive sublimate), HgCL, and treated with wetting agents of various mercurous chloride (calomel), HgCl, kinds to render it wettable by water and are used against fungus gnats, earth- thus susceptible to suspension in spray worms, cabbage maggots, and onion formulations. The alkaline sulfides and maggots. Mercuric chloride is also used polysulfides, sometimes referred to as for the treatment of dormant gladiolus soluble sulfurs, are prepared by the re- corms and as a fungicide and germi- duction of the salts of some of the oxy- cide. Formulations containing mercury gen acids of sulfur or by the action of compounds are sometimes used to con- alkaline solutions on elemental sulfur. trol insects affecting man and animals. The most important compounds of this Pastes containing elemental phos- class are the polysulfides of calcium, phorus are made by grinding yellow ammonium, barium, and sodium. phosphorus in the presence of water Calcium monosulfide, GaS, has been and then mixing with flour. Glycerin used to a limited extent. It is formed is sometimes used as an ingredient. by the reduction of calcium sulfate. Such pastes are cfí*ective against the Liquid lime-sulfur or calcium poly- Am.erican . sulfide, GaSx, is formed by the reactions Selenium compounds have been between calcium hydroxide and ele- tested as insecticides, but because of mental sulfur when they are boiled to- their toxicity to man their use is not gether in water. It is assumed to con- recommended on crops intended for tain a mixture of the sulfides up to and or animal consumption. including the pentasulfide, GaSg. The Sodium selenate, Na^SeO-^, is a theoretical reaction between 3 moles water-soluble salt. Plants can take it up of hydrated lime, Ga(OH)2, and 12 from the soil in sufißcient amounts to moles of sulfur results in the formation kill feeding on the plants. A of 2 moles of calcium pentasulfide, product containing selenium and sul- GaSs, I mole of calcium thiosulfatc, fur of the formula (KNHiS)r>Se has GaSgOji, and 3 moles of water, H^O. i)70184° —52 H) 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; 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 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 . They also against . 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