Robert L. Metcalf: The Mode oí Action of Organic Insecticides, National Research Council^ Washington, 1948; Studies of the Mode of Action of Parathion and Its Deriva- tives and Their Toxicity to Insects, with The Organic Ralph B. March, Journal of Economic En- tomology, volume 42, pages y21-^28, 1949. Insecticides W. E, Ripper, R. M. Greenslade, and L. A. Lickerish: Combined Chemical and Bio- logical Control of Insects by Means of a C,V,Bowen,S.A.Hall Systemic Insecticide, Nature {London), volume 16s, pages y8y-y89. 1949. Kenneth D. Roeder and Elizabeth A. The best known of the synthetic or- Weiant: The Site of Action of DDT in the ganic insecticides is DDT, but it was Cockroach, Science, volume 103, pages 304- 3oy, 1946; The Effect of DDT on Sensory not the first. Some of them have been and Motor Structures in the Cockroach Leg, in use for decades. Carbon disulfide, Journal of Cellular and Comparative Physi- /;-dichlorobcnzcnc5 and naphthalene ology, volume 32, pages iy5- 186, 1948. stand out as old-timers. Ethylene di- George D. Shafer: How Contact Insecti- chloridc, ethylene dibromidc, methyl cides Kill. I and II, Michigan Agricultural College Technical Bulletin 11, 1911 ; How bromide, and thiocyanates have been Contact Insecticides Kill. Ill, Technical used for the past quarter century. Bulletin 21, 1915. Thousands of similar compounds—r E. H. Smith and 0. W. Pearce: The Mode man-made materials whose basis is of Action of Petroleum Oils as Ovicides, carbon—have been investigated as to Journal of Economic Entomology, volume 41, pages jy3-i8o. 1948. insecticidal Value. The Department of J, M. Tobias and J. J. Kollros: Loci of Agriculture in 1922 or so began a study Action of DDT in the Cockroach (Peri- of their use as repellents and fumigants planeta americana), Biological Bulletin, and began later the synthesis of mate- volume 91, pages 24y-255. 1946. rials for testing as poisons for insects. 0. W. van Vloten, Ch. A. Kruissink, B. Strijk, and J. M. Bijvoet: Crystal Structure Phenothiazine, thiodiphenylamine, of "Gammexane," Nature (London), vol- introduced as an insecticide in 1935, urne 162, page yyi. 1948. may be considered one of the early J. Franklin Y eager and Sam C. Munson: members of the newer synthetic age. It Physiological Evidence of a Site of Action is used now to only a limited extent as of DDT in an Insect, Science, volume I02j pages 305-3oy. 1945. a codling moth insecticide, but it is used extensively for the internal medi- cation of livestock for the control and removal of injurious nematodes that infest cattle, horses, sheep, and goats. TÍ II C S C / \ / \^/ \ HC c C CH I! I c CH \ / \ / c N C H H H Phenothiazine Azobenzene, an orange crystalline material, was found in 1943 to be efiFec- tive as a fumigant for the control of mites in greenhouses. Because azoben- zene sublimes readily, a solution con- taining it may be. applied to steam Flea beetle. pipes and allowed to vaporize. The de- 209 210 Yearbook of Agriculture 1952 velopmcnt of the organic phosphorus fore the Second World War in house- compounds, however, has greatly less- hold and horticultural sprays. The so- ened its use. called lauryl thiocyanate is a mixture of compounds containing alkyl groups H H C C derived from the natural fatty acids of / \ / \ coconut oil in which the lauryl, or HC C-N=N-C CH i2-carbon, chain predominates. Other thiocyanates used as insecticides arc HC LCH HC CH the 2-(2-butoxyethoxy)ethyl ester of \/ \'' thiocyanic acid, diethylene glycol di- H H ester of thiocyanic acid, ^-thiocyano- Azobenzcne ethyl esters of aliphatic fatty acids averaging from i o to 18 carbon atoms, A group of dinitro derivatives of and isobornyl thiocyanoacctate. Be- phenol and creosol came into use before cause some of them may injure grow- the Second World War as dormant ing plants, care should be exercised in sprays in apple orchards. The simplest using them. of these, 4,6-dinitro-o-cresol, DNOC, formerly known as 3,5-dinitro-o-cresoI, IN REGENT YEARS a great deal has is a solid melting at 85.8° C. and not been said about chlorinated hydrocar- very soluble in water. The sodium de- bons as insecticides. The use of this rivative (called a salt) often is used type of compound is not new, for car- in the dormant sprays because of its bon tetrachloride and /»-dichloroben- greater solubility in water. Analogs— zene, which have been used for years, similar substances—in w^hich the are chlorinated hydrocarbons. methyl group of the cresol has been DDT is a chlorinated hydrocarbon replaced by cyclohexyl or by some other insecticide. The raw materials for its group are also used. Salts other than manufacture are chlorine, benzene, sodium, such as the dicyclohexylamine and alcohol. DDT was first described or triethanolamine salt, are also in use. in 1874 by ^ German chemist, Othmar Zeidler, but its insecticidal value was OH not discovered until about 1939 by ¿ Paul Müller, in Switzerland. It was / \ first introduced into the United States O2NC CCH3 in August 1942 when the dye firm of HC CH J. R. Geigy shipped from Switzerland \ to New York two formulations—a dust C and a wettable powder—for testing by NO2 American entomologists. Later undi- 4,6-Dinitro-o-crcsol luted DDT was imported, and in June OH 1943 the manufacture of DDT was be- I gun in the United States for use by the C Armed Forces. When the end of the / \ Second World War made DDT avail- O2NC CCeHn able for civilian use, it came into large- n¿ í„ scale use as an insecticide. The symbol DDT combines the first letters in the name dichloro-diphenyl- trichloroethane. The precise chemical 2-Gyclohexyl- name for the principal toxic ingredient 4,6-dinitrophenol of technical DDT is 1,1,1-trichloro- (DNOCHP) 2,2-bis(/7-chlorophcnyl) ethane. A dis- Aliphatic, alicyclic, and aromatic cussion of its chemistry was presented esters of thiocyanic acid w^ere used be- in Science in Farming, the Yearbook The Oruanic Insecticides 211 of Agriculture for 1943-194 7. DDT is 12.5 percent of crude benzene hexa- unstable in the presence of alkalies and chloride. Because of its odor and the consequently is not compatible with off-flavor it imparts to certain food alkaline agricultural chemicals. It is products, t(;chnical benzene hexa- also decomposed by iron and some iron chloride is limited in use. Lindane, salts. however, is practically odorless. Inves- Benzene hexachloride, or 1,2,3,4,5,6- tigations were started in 1947 to check hexachlorocyclohexane (i, e., BHC, its effect on the flavor of fruits, vegeta- HGH, or ÍÍCCH), is a chlorinated hy- bles, and meats. It is a w4iite crystalline drocarbon made by reacting chlorine solid, soluble in most of the common with benzene in the presence of ultra- orgamic solvents but insoluble in w^ater. violet light to produce a compound It has some fumigant properties and is with the molecular formula which the a contact and stomach poison. English designated as 666. The mate- In tlie early study of DDT, analyses rial was first made by Michael Faraday of the technical material revealed 4 in 1825, ^"^*t ^ts insecticida 1 action was percent of an impurity that has insecti- not known until many years later. cidal properties. The impurity was Harry Bender, an American chemist, identified as i,i-dichloro-2,2-bis(/;- in a United States patent application chlorophcnyl) ethane, a byproduct of for a method of chlorinating hydrocar- the reaction used in making DDT. The bons, mentioned in 1933 that the ben- compound has been referred to as zene hexachlorides appeared to be DI^l^ and as ll')E, from its generic good insecticides, but apparently no names dichloro - diphenyl - dichloro- use was made of the idea. A. P. W. ethane and tetrachloro - diphenyl- Dupire in France in 1941 applied for ethane. It is closely related to DDT in a French patent on the use of benzene chemical structure and properties. It hexachloride as an insecticide based on will react with alkalies and conse- entomological tests conducted in 1940. CjUi^ntly should not be formulated with In 1942 a sample of benzene hexa- alkaline materials. chloride made by F. D. Feicester in H IT H H England w^as found to be insecticidal, C--C c-c and the compound came into use in / \ TI / \ that country in place of derris in flea CIC C—C—C CCI beetle powder. \ / I \ / C —C HCCÎ2 C==C Technical benzene hexachloride is 11 II n H made up of a mixture of isomers, com- TDE pounds that are identical in chemical structure except for a difference in the Another of the analogs of DDT has orientation in space of some of the con- been given the common name meth- stituent atoms. F. J. D. Thomas in oxychlor because it has a formula in England in 1943 found that the insec- w^hich two of the chlorine atoms of ticidal principle of technical benzene DDT have been replaced by the meth- hexachloride was the gamma isomer. oxy group (CH,0-). Like DDT, tech- The isomers had bet^n named alpha, nical methoxychlor (which contains beta, gamma, and delta in the order about 80 percent of i,i,i-trichloro-2-2- in which they had been isolated, alpha bis ( /;-methoxyphenyl ) ethane ) also is a and beta by F. E. Matthews in 1891 white solid, soluble in the common and gamma and delta by T. von der organic solvents and insoluble in water. Linden, a German chemist, in 1912. It is less eíTective than DDT against In 1949, the common name lindane most insects but is less toxic to warm- was selected for the gamma isomer of blooded animals. Alkaline materials benzene hexachloride of not less than promote decomposition of methoxy- 99 percent purity after von der Linden. chlor and consequently must not be The gamma isomer comprises about used in its formulations. 212 Yearbook of Agriculture 1952 Analogs of DDT containing bromine Diels and Alder received the Nobel and fluorine have been tested for insec- prize in chemistry in 1950 for their ticidal action. s^Q-Bis (p-bromophe- work on this type of diene synthesis. nyl ) -1,151 -trichloroethane sometimes Ghlordane is a nearly odorless, viscous, has been referred to as Colorado 9. amber-colored liquid that can be dis- 1,1,1 - Trichloro - 2,2-bis(jf;-fluorophe- tilled only under high vacuum and is nyl) ethane is a constituent of an insec- soluble in the common organic sol- ticide which the Germans called Gix. vents. Ghlordane is also a good solvent Although insecticidal in action, neither for DDT. It decomposes in the pres- material has come into commercial use ence of alkalies with a resulting loss of in the United States, probably because insecticidal toxicity: consequently it their cost is greater than that of DDT. cannot be formulated with alkaline materials. H H lî H C—C XCCI2 C=C ^ \ I / \ Cl K—C C—C—C C—R II H H H H CIC CH2

R=C1 X=C1 DDT CCI2 H =CH30- =C1 Methoxychlor ,/ =Br =G1 Colorado 9 CK C C =F =G1 Gix or DFDT =C1 =H TDE or DDD C Toxaphenc, C^oHioCls, is the com- mon name for a product obtained by reacting chlorine with camphenc. It is Ghlordane more complex than benzene hexachlo- ride. Its structure is not completely Two OF THE NEWER SYNTHETIC known. The technical material consists chlorinated hydrocarbons, which were of a mixture of compounds, which con- known during their experimental test- tain 67-69 percent chlorine. It was ing period as Julius Hyman and Gom- originally known as Hercules 3956, but pany Gompounds 118 and 497, have a more descriptive name is chlorinated been given the common names, aldrin camphene. It is a cream-colored solid and dieldrin, honoring Alder and of waxy consistency. It melts over a Diels. Aldrin has been defined as con- range of 65° to 90° C. Toxaphene is taining not less than 95 percent of readily soluble in the common organic 1,2,3,4,1 o, I o-hcxachloro-1,4,4a,5,8,8a- solvents. Toxaphene will dehydro- hexahydro-1,4,5,8-dimethanonaphtha- chlorinate in the presence of alkalies. Icnc. Dieldrin (pronounced ûî^^/-drin) Like DDT, it slowly splits off hydro- has been defined as containing not less chloric acid on heating and in the pres- than 85 percent of 1,2,3,4,10,1 o-hcxa- ence of materials, such as iron com- chloro-6,7-epoxy-1,4,4a,5,6,7,8,8a - oc- pounds, that may act as catalysts. tahydro - 1,4,5^8 - dimethanonaphtha- Ghlordane, i,2,4,5,6,7,8,8-octachlo- lene. Aldrin is a white solid with a melt- ro-2,3,3a,4,7,7a-hexahydro-4,7 - meth- ing point of 104°-104.5° G. It is prac- anoindcne, iformerly known as Velsicol tically odorless at room temperature, 1068, is a chlorinated hydrocarbon ob- but it has a pinelike odor when warm. tained by subjecting two compounds Dieldrin melts at 175°-!76° G. and called hexachlorocyclopentadiene and is odorless. Aldrin is soluble in the cyclopentadiene to a reaction of a type common organic solvents. Dieldrin is developed by two German chemists. moderately soluble in the same solvents. Otto Diels and Kurt Alder, and treat- Neither is soluble in water. Aldrin ing the resulting product with chlorine. is stable in the presence of organic and The Organic Insecticides 213 inorganic alkalies and hydrated metal- ethanol and the aliphatic hydrocar- lic chlorides and therefore is compati- bons. It is insoluble in water. It belongs ble with most agricultural chemicals. to the class of compounds known as Unlike DDT, the DDT analogs, acetáis and is stable to alkalies, but on toxaphene, and chlordane^ dieldrin is boiling with dilute aqueous acids it is unaffected by alkalies. Insecticidal ef- hydrolyzed. It is used to control mites fectiveness is not lost in the presence of in fruit orchards. alkaline and acid materials that would H H H H occur in formulation; thus it is com- C=C H C-C patible with most agricultural chem- / \ I / \ CIC C-0-C-O-C CCI icals. It does react chemically with \ / I \ / strong acids. Aldrin, with a vapor pres- c—C H C=C sure approximating that of lindane, is H II H H about 20 times more volatile than Bis ( jö-chlorophcnoxy ) methane dieldrin. Because aldrin and dieldrin are One of the new insecticides that highly toxic, technical products and came out of the Second World War insecticidal formulations containing the Germans called "Lauseto neu." It them must be handled with extreme is chloromethyl p-chlorophenyl sulfone care. and is not a chlorinated hydrocarbon. Cl H It is a good insecticide but is less effec- tive than DDT against certain strains A of lice, flies, and mosquitoes. Cl / H H l CH O C—C Il / \ CCI2 CH2 ClCHs—S—C CCI Il \ / H O c—c /r / H H c/\ / H / C C Lauseto neu I I Cl H AN INTERESTING ACCOMPLISHMENT Aldrin in the preparation of synthetic organic insecticides w^as the synthesis of com- c H pounds that resemble the pyrethrins I I and cinerins, the toxic materials in c C Cl n pyrethrum flowers. In 1948, after 15 \ / \' '/ \ / years of investigation of the structure c C c of these naturally occurring insecti- 1 \ 1 CGI, CH2 cides, chemists of the Bureau of Ento- 1 / mology and Plant Quarantine pre- c C c pared pyrethrin-type esters similar to \ cinerin I. One of these synthetic esters, e/ \, /. [ \ / H theöi/-2-allyl-4-hydroxy-3-methyl-2-cy- c C I I clopenten-i-onc ester of a mixture of Cl H eis and trans ¿//-chrysanthemum car- Dieldrin boxylic acid, has been produced com- mercially and has been given the com- Bis(/?-chlorophenoxy) methane, for- mon name of alle thrin by the Inter- merly called K-1875, is a solid that departmental Committee on Pest Con- melts at eS^-eS.s"^ C. It is rather sol- trol. Allethrin is a light, yellow-colored uble in acetone, benzene, and ethyl oil and possesses solubilities similiar to ether. It is not appreciably soluble in those of the natural products so that it 214 Yearbook of Agriculture 1952 may be used in the same manner in fly British investigators have called it a sprays and aerosols. systemic insecticide because, when it is CH3 applied either to the leaf or root system CH3 H O H ¿ of a living plant, it is absorbed into the sap stream and translocated, rendering CHs—C C—C—O—C'/ ^. \:;CH2CH:CH3 the plant insecticidal to certain insect HC—CU=C (0113)2 species for several weeks. Its general H2C C=0 use on food or fodder crops is not Aliethrin recommended. Experiments have indi- cated that it may prove useful on orna- Diphcnylamine, (GoH5)2NH, is an- mental plants and cotton plants. Got- other type of organic compound that tonseed has been soaked in a very di- has been used successfully for screw- lute water solution of octamethyl pyro- worm control. I, I -Bis (/;-chlorophcn- phosphoramide and then planted. The yl ) ethanol, ( GloG^H., ) ^GOHCH,, cotton seedlings that emerged were (also called DMC from the generic found to be insecticidal to aphids and name dichlorophcnyl methylcarbinol) mites for about a month. It may also is used against mites. Pcntachlorophe- be useful on sugar beets to kill aphids nolj G0CI5OH, is used to control that carry virus yellows disease. termites. Because of their extreme toxicity to warm-blooded animals, these potent A NEW FIELD of Organic phosphorus insecticides may not be used to control insecticides was opened up during the insects affecting man and animals, such Second World War by Gerhard as household pests and cattle and sheep Schrader, a German chemist who was pests. Because they are effective at ex- engaged primarily in the search for tremely low dosages against a wide more powerful agents of chemical war- range of insect species, and when prop- fare. Schrader discovered a new series erly applied leave a negligible spray of highly toxic organic phosphorus residue on an agricultural crop, their compounds. From them, through ex- potential usefulness is great. tensive tests, came several efTectivc in- secticides. The list includes parathion, IT H tetraethyl pyrophosphate (including C2H5O S C—C \ F / \ the so-called hexaethyl tctraphos- P—O—C c—NO2 phate), and octamethyl pyrophosphor- / \ / amide. C2H5O c=c H H Parathion, a remarkably effective in- secticide, has been put to use in many Parathion countries to control many kinds of in- C2H5O 0 0 OC2H5 sects infesting various crops. \ Il II / Tetraethyl pyrophosphate and octa- P-0—P methyl pyrophosphoramide are used / \ chiefly against aphids and some mites. C2H5O OC2H5 Tetraethyl pyrophosphate kills in- Tetraethyl pyrophosphate sects rapidly, almost as soon as the ma- (CH3)2N O O N(CH3)2 terial is applied, and then, having per- \l! 11/ formed its task, the toxic insecticide p—o—P soon decomposes by hydrolysis into / \ nontoxic and water-soluble products. (CH3)2N N(C 113)2 Thus, there is no spray-residue prob- Octamethyl pyrophosphoramide lem connected with its use.

Octamethyl pyrophosphoramide has SYNTHETIC ORGANIG CHEMICALS been manufactured in the United have been used as fumigants for nearly States only on a relatively small scale. a century. They arc low-boiling com- The Organic Insecticides 215 pounds of rather simple structure. proofing materials do not have that They include hydrocarbon derivatives disadvantage. that contain sulfur, oxygen, chlorine, /?-Dichlorobenzene, GeHiGlg, a bromine, and nitrogen. Carbon disul- white, odorous solid, which melts at fide (CS2), prepared now from sulfur about 53° G., has wide use for control and coke by heating in an electric fur- of peach tree borers and clothes moths. nace, was the pioneer. Ethylene oxide, It is synthesized by reacting chlorine (CH^) jO, is a gas at ordinary temper- with benzene in the presence of the ature and was proposed as a fumigant proper catalysts. It is one of .the best in 1928. One part is used with 10 parts known fumigants because of its long of carbon dioxide to reduce the fire and wide usage. hazards. H H Among the chlorinated hydrocar- C C bons we find carbon tetrachloride, ^ \ / \ CCI4, used with ethylene dichloride, IIC C c H C2H4CI,, (1:3) since 1927; propylene I II I dichloride, C.-ÁoClg; ethylene dichlor- HC C CI! ide alone; and a mixture of 1,2-dichlor- \'' \^' opropane, C.jHoClg, and 1,3-dichloro- II H propylene, Cj^Fl^Gl,, known as D-D. Naphthalene These materials and certain bromine compounds—methyl bromide, CH^Br, Cl and ethylene dibromide, C^H4Br2— ¿ are of value against wire worms and /- \ nematodes. ne cii Hydrocyanic acid, or hydrogen cya- I li nide (HGN), is a highly poisonous gas HC CH used in fumigation of citrus trees as well as a space fumigant for ware- I houses and other enclosed places. Cl Some compounds of higher boiling /?-Dichlorobenzene point and more complex structure arc also used as fumigants because of their A desire to find materials that would high vapor pressure. Chloropicrin, increase the toxicity and thus extend Ci,CNOo, boils at 112.4° G. and is the supply of scarce insecticides, such used as a fumigant for grain and soil. as pyrethrum, has encouraged investi- It is most eíTective in a mixture of i gation in this field. Such materials are pound to I gallon of carbon tetrachlor- known as synergists. N-isobutylundecy- ide. lenamide, N-isobutylhendecenamide, Dichloroethyl ether— ( GgH^Cl ) ,0, the first Synergist developed for pyre- bis(2-chloroethyl) ether—with a boil- thrum, was introduced in 1938. It may ing point of 178.5° C. produces vapors be considered a synthetic material, al- much heavier than air and is of value though castor oil is the basic material as a soil fumigant. for its preparation. The value of sesame Naphthalene, Ci Hs, is one of the oil as a Synergist for pyrethrum was older organic insecticides not obtained discovered about the same time. Its from plants or oil. It is a hydrocarbon efl'ectiveness was shown to be due to obtained by the destructive distillation the presence of sesamin. Knowledge of of coal. This flaky white solid has been the structure of sesamin led to the syn- used for a half century to protect thesis of related compounds, including woolen cloth against clothes moths. It i^iperonyl cyclonene and piperonyl has a fumigating action, but its objec- butoxide. tionable odor is not easily removed Piperonyl butoxide, also known as from the fabric. The newer moth- (butyl carbitol) (6-propylpiperonyl) 2l6 Yearbook of Agriculture 1952 CH2—o H C ¿ \ H O / \ 0-C CH HC I II HC CCH2OC2H4OC2H4O C4H0 CH2 NCsHiT \/ HC C3H7 \ Piperonyl butoxide \ \^0 C H MGK 264 CH2 O H C ^ \ o—C CH HC C—COOR H¿ ÜH HC C—COOR c H CH R=CH3 Dimethyl phthalate CH2 CHCOOC2H5 R=C4H,» Dibutyl phthalate Alkyl—C C=0 \ / CH3 CH H H H OH CH2 H CH2 O H—C—C—C—C C C—OH C /- \ ¿ ¿ A À Á A 0-C CH Rutgers 612

O I CH H2C CH CH2 CH2 CH3 Alkyl—C C=0 \ \ / \ CH C-COOC4HÍ, Piperonyl cyclonenc ci\^ Indalone

I Í (JOOC3H7 H H i C H C / H 0-( :—COOC3H7 / HC C—COOCH3 CH2 CH3 CH. I C—COOCH3 ^ ( : ( H C H HH H i2-Pr opyl ison le Dimethyl carbate The Organic Insecticides 217 ether, is a thick, viscous liquid that con- Only a few synthetic organic com- tains as its principal active constituent pounds have been used to attract in- a-[2 - (2 - butoxyethoxy)ethoxy] - 4,5- sects. Mctaldchyde, (G2H40)4, a poly- methylenedioxy- 2-propyltoluene. Pip- mer (condensation product) of acetal- eronyi cycloncne, formerly known as dehyde, is used in baits for the control piperonyl cyclohexcnone, is the com: of garden snails and slugs. Isoamyl sali- mon name for a mixture comprised of cylate, HOGoH^GOOGr.Hn, an ester, 3-alkyl - 6 - carbcthoxy - 5 - (3,4-meth- is used to attract tobacco hornworm yienedioxyphenyl) -2-cyclohexen-1 -one moths into traps. Methyl eugenol has and 3 - alkyl - 5- ( 3,4 - methylenedioxy- proved attractive to the male oriental phenyl)-2-cyclohexen-1-one, in which fruit fly in tests in Hawaii. The paucity the "alkyl" refers to aliphatic radicals of synthetic materials used as attract- that may be varied. It is a thick, viscous ants would indicate that this might liquid. Another Synergist for pyrethrum be a good subject for more intensive is w-propyl isomc, the dipropyl ester of investigation. 1,2,3,4-tetrahydro - 3-methyl-6,7-meth- Besides the synthetic organic insecti- ylencdioxy-1,2 - naphthalenedicarbox- cides we have discussed, others of less ylic acid. Like sesamin, the three mate- importance are in use. Still others are rials all contain the methylenedioxy- in the experimental and develop- phenyl group. mental stages. The wide variety of One of the later organic insecticides, compounds that we have considered N-octylbicyclo[2.2.i]-5-heptene-2,3-di- here gives evidence that the chemistry caTboximide, MGK 264, was intro- of synthetic organic insecticides covers duced as a Synergist for pyrethrins but the entire field of organic chemistry. has also been found to be effective as an ovicidc. It is an amber-colored and G. V. BowEN, head chemist at the rather viscous liquid. It is slightly Orlando, Fla., laboratory of the divi- heavier than water. It is readily solu- sion of insects affecting man and ani- ble in the usual organic solvents and mals. Bureau of Entomology and Plant is itself a good solvent for quite a few Quarantine, entered Government em- of the other newly discovered insecti- ploy in iQ2^ in the Insecticide and cides. Fungicide Board. He taught chemistry Oil of citronella, a plant product, at Washington and I eß er son College was the standard repellent for mosqui- from ig2^ until igsJ, when he re- toes before the Second World War. turned to the division of insecticide in- During the war, however, the need for vestigations. His principal interest has repellents for chiggers, mosquitoes, and been in rese-arch on the preparation, fleas instigated the testing of many analysis, and formulation of synthetic synthetic organic compounds, Bcnzil, organic insecticides. CH^COGOCoH,, and benzyl benzo- S. A. HALL^ a chemist, began analyti- ate, GtjHsCOOCH.CfiHn, were found cal work with the Treasury Depart- to be repellent to chiggers; dimethyl ment in igs4 and in ig^g transferred phthalate to mosquitoes and mites; to the Bureau of Agricultural and In- Rutgers 612 (2-ethyl-i,3-hexanediol), dustrial Chemistry to do research on Indalone (often called n-butyl mesityl naval stores. In ig43 he joined the di- oxide oxalate but more properly the vision of insecticide investigations, Bu- butyl ester of 3,4-dihydro-2,2-dimethyl- reau of Entomology and Plant Quar- 4-0x0-2H-pyran-6-carboxylie acid) antine, at Beltsville, Md,, where he first and dimethyl carbate ( the dimethyl es- worked on DDT and the development ter of cis-hicyc\o [2.2.i]-5-heptene-2,3~ of insect repellents: dicarboxylic acid) to mosquitoes, chig- For further reading on organic insecti- gers, and fleas. A mixture of Indalone, cides the authors recommend: dimethyl phthalate, and Rutgers 612 is Bureau of Entomology and Plant (Quar- used as an all-purpose insect repellent. antine publications: E-yss, Results of Screening Tests with Materials Evaluated as Insecticides, Miticides, and Repellents at the Orlando, Fla., Laboratory, April 1942 to April 1947, 1947; E-802, A Digest of In- The Inorganic formation on Toxaphene, 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 Insect Toxicants, Aldrin and R. H. Carter Dieldrin, by R. E. Lidov, H. Bluestone, S. B. Soloway, and C. W. Kearns, pages 175-^^3- 195O' Inorganic insecticides are of mineral 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, boron, copper, fluo- 314-3^9- 1950. rine, mercury, selenium, sulfur, 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 Flower Growers Bulletin 7, is a white powder soluble in water. 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 United States 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 arsenic 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 insects. The calcium arsenate that is sold commercially as an insecticide 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