Bulletin BULLETIN of the ILLINOIS NATURAL HISTORY SURVEY HARLOW B. MILLS, Chief Characteristics of Residual Insecticides Toxic to the House Fly WILLIS N. BRUCE ^ Printed by Authority of the STATE OF ILLINOIS ADLAI E. STEVENSON, Governor DEPARTMENT OF REGISTRATION AND EDUCATION NOBLE J, PUFFER, Director ; i STATE OF ILLINOIS Adlai E. Stevenson, Governor DEPARTMENT OF REGISTRATION AND EDUCATION Noble J. Puffer, Director NATURAL HISTORY SURVEY DIVISION Harlow B. Mills, Chief ume i:>25 BULLETIN Article 1 Characteristics of Residual Insecticides Toxic to the House Fly WILLIS N. BRUCE Prinlcd by Aulliorily of the Slate of Illinois U R B A N A , ILLINOIS July 1949 STATE OF ILLINOIS Adlai E. Stevenson, .Governor DEPARTMENT OF REGISTRATION AND EDUCATION Noble J. Puffer, Director BOARD OF NATURAL RESOURCES AND CONSERVATION Noble J. Puffer, Chairman E. Emerson, Ph.D., Biology George D. Stoddard, Ph.D., Litt.D., L.H.D., H. Tiffany, Ph.D., Forestry LL.D., President of the University of Illinois R. HowsoN, B.S.C.E., C.E., Walter H. Newhouse, Ph.D., Geology Engineering Roger Adams, Ph.D., D.Sc, Chemistry NATURAL HISTORY SURVEY DIVISION Urbana, Illinois Scientific and Technical Staff Harlow B. Mills, Ph.D., Chief Bessie B. Henderson, M.S., Assistant to the Chief Section of Economic Entomology George C. Decker, Ph.D., Entomologist and Head J. H. Bigger, M.S., Entomologist L. L. English, Ph.D., Entomologist C. J. Weinman, Ph.D., Entomologist S. C. Chandler, B.S., Associate Entomologist Willis N. Bruce, M.A., Assistant Entomologist John M. Wright, M.A., Assistant Entomologist H. B. Petty, M.A., Associate in Entomology Extension Section of Applied Botany and Plant Pa- thology Leo R. Tehon, Ph.D., Botanist and Head J. Cedric Carter, Ph.D., Plant Pathologist J. L. Forsberg, M.S., Associate Plant Patholo- gist G. H. Boewe, M.S., Assistant Plant Palhohrfisl Robert A. Evers, M.S., Assistant Botanist Section of Faunistic Surveys and Insect Identification H. H. Ross, Ph.D., Systematic Entomologist and Head Milton W. Sanderson, Ph.D., Associate Tax- onomist Lewis J. Stannard, Jr., M.S., Assistant Tax- onomist Leonora K. Gloyd, M.S., Laboratory Assistant Philip W. Smith, B.S., Laboratory Assistant Dorothy A. Moulton, Technical Assistant Section of Aquatic Biology George W. Bennett, Ph.D., Aquatic Biologist and Head William C. Starrett, Ph.D., Associate Aquat- ic Biologist D. F. Hansen, Ph.D., Assistant Aquatic Bi- ologist R. Weldon Larimore, M.S., Research Assist- ant Daniel Avery, Field Assistant Section of Forestry WiLLET N. Wandell, M.F., Forester and Head Lawson B. Culver, B.S., Associate in Forestry Extension Section of Game Research and Manage- ment Ralph E Yeatter, Ph.D., Game Specinlisi Frank C. Bellrose, B.S., Associate Game Spe- cialist Harold C. Hanson, M.S., Assistant Game Spe- cialist James S. Jordan, M.F., Assistant Game Tech- nician Section of Publications and Public Rela- tions James S. Avars, B.S., Technical Editor and Head Blanche P. Young, B..'^., Assistant Technical Editor Charles L. Scott, B.S., Assistant Technical Photographer Technical Library Marguerite Simmons, M.A., M.S., Technical Librarian Cooperative Wildlife Research (Illinois Department of Conservation and i .S. Fish and Wildlife Service^ Cooperating) Paul J. Moore, B.S., Project Leader George C. Arthur, B.S., Project Leader Lysle R. Pietsch, M.F., Project Leader John C. Calhoun, B.S., Assistant Project Leader Consultant in Herpetology: Hobart M. S.hith, Ph.D., Assistant Professor of Zoology, University oj Illinois. This paper is a contributionfrom the Section of Economic Entomology. (75462—3500—3-40) „^BgS!^2 CONTENTS NSECTICIDES UsED. . 'uRPOSE OF Study. . Acknowledgments. "esting Procedure. Experiment 1 Exposure Time for Knockdown and Mortality Experiment 2: Effect of Deposits on Mortality Experiment .! : Relationship Between Coveratie and Deposit Experiment 4: Coverage of Surface and Fly Mortality Experiment 5 : Effect of Heterogeneous Deposits Upon Flies Experiment 6: Wall Coats Containing DDT Experiment 7: Effect of Successive Exposures on Persistence of Toxic Residue Experiment 8: Fumigation Properties Experiments 9 and 10: Testing Periods Experiment 9: Field Persistence of Residues From Commercial Emulsions. .. . Experiment 10: Field Persistence of Residues From a Standardized Formula- lation of Emulsions Experiments 9 and 10 : Discussion Experiment 1 1 Experiment 12 Experiment 13 Experiment 14 Formulation Studies Laboratory Persistence of Deposits Laboratory Study of DDT Emulsion on Glass and Wood. .. . Approximate Residual Toxicity of Several New Insecticides to the House Flv. jter.\ture Cited. 1 2 2 3 6 8 9 9 10 11 11 19 20 21 22 2?, 26 28 29 29 30 31 quickly accomplished with the FxDosure of flies to surface;, Utated \vith insecticides is ... . contact with the treated panel. Characteristics of RESIDUAL INSECTICIDES Toxic to the House Fly FOR centuries the house fl\'. Miiscii (ioiitesiictt Linnaeus, has been an anno\ ing, disease-carrying menace to man and other animals. Spillman & Haushalter (1887) demonstrated the house Hy to be a possible vector of Bacillus tuberculosis. Nuttal (1899) showed that Spirillum ch'tlerae and staphylococci could be transmitted by house flies. Esten ^" Mason (1908) determined by counts that on an average a house fly carried 1,25(J,000 pathogenic organisms on its exterior sur- face. In a publication upon the typhoid or house fly, Felt (1909) estimated the indirect losses to our vital assets incurred by tvphoid at 350 million dollars annually. Also, he suggested that house flies can spread plague, trachoma, and septicemic diseases. Howard (1909) wrote that the annual cost of screening against house flies in the United States is over 10 million dollars. Later, Herms (1911) stated that the public pays over 2 million dollars for fly traps, sticky fl\ paper, poisons, and sprays each year. Pipkin (1942) pro\ed that Musca domesticti can carry Eiida- moeba histolytica on its e.xternal surface and in its digestive system long enough to effect transmission. The e\ idence pre- sented above, along with the list in Met- calf c^ Flint (1939) of 20 disease patho- gens carried by flies, is more than sufficient reason to brand the house fly as potentiall\ the animal most dangerous to human be- ings within the borders of the United States. Although the house fl>' is important as an annovance and as a vector of disease, it causes no direct injur\ to man or other animals. It is not equipped to bite or sting or in itself to cause disease by any of its life stages. WILLIS N . BRUCE Pathogenic organisms may be carried on the surface of the fl\ s hod)', adhering to the ininierous hairs, sticky puhilli, wings, and mcuthparts, or they ma\' be carried in the alimentary canal to be spread by defecation or regurgitation. The filthy feeding and breeding habits of flies make inevitable the mechanical transmission of disease by these insects. In Illinois, the house fly usuall\' winters in the pupal or larval stage ; a few adults li\e through the winter in protected places. The female fl\' deposits 2 to 21 batches of 100 to 150 eggs in manure or any other suitable decomposing organic matter. The whole life cycle through egg, larva, pupa to adult may be completed in 6 to 20 days. In Illinois there are usually 10 to 12 gener- ations of house flies each summer. These facts account for the enormous build-up of flies that usually occurs during August or September in the temperate zone. INSECTICIDES USED The five chemicals described below are the principal insecticides used in the study reported here. DDT (designation derived from the generic name dichloro-diphenyl-trichloro- ethane) was first synthesized by Zeidler (1874). Chemically this material is known as 2,2' bis (parachlorophenyl) 1,1,1-trichloroethane. The technical grade that was used in the experiments reported here consisted of a mixture of para, para'; para, ortho ; and ortho, ortho' isomers. Pure DDT may be described as an odor- less, stable, cr\stalline solid that is soluble in most organic solvents and insoluble in water. The first United States patent on it was granted to Paul Miiller in 1943 [1] Illinois Natural History Survey Eullltin Vol. 25, Art. 1 for the Geigy Company Inc., of New- York, N. Y. Although Wiesmann (1943) first described its usefulness as a residual insecticide for the control of house flies, Annand (1944) suggests that it was tested by Miiller on house flies in 1940. Rhotfiane D-3, or 2,2' bis (parachloro- phenyl) 1,1-dichloroethane, a material closely related to DDT, was found by Miiller and others to be of less promise as an insecticide than DDT. However, the Rohm & Haas Company was con- vinced it possessed some valuable insecti- cidal properties and consequently obtained a patent for its manufacture. Rhothane D-3 (also known as TDE, DDD, and D3 ) is soluble in the same solvents as DDT ; it has a higher vapor pressure and a lower melting point than DDT. Chlordan or 1,2,4,5,6,7,8,8-octachloro- 4,7-methano-3a,4,7,7 a-tetrahydroindane was first synthesized by Dr. Julius Hyman and first discussed as an insecticide by Kearns, Ingle, & Metcalf (1945), who showed that when tested in a Peet-Grady chamber chlordan was three to four times as toxic to flies as DDT. In the highly refined state chlordan is a light yellow, viscous, nearly odorless liquid that is solu- ble in aliphatic, aromatic, and chlorin- ated hydrocarbons. It is infinitely soluble in kerosene, deobase, and no. 9 oil. Such solubility is not true of DDT, Rhothane D-3, or hexachlorocyclohexane, mentioned below. Chlordan has a specific gravity of 1.61 and weighs about 13.5 pounds per gallon. The chemical 1,2,3,4,5,6-hexachlorocy- clohe.xane was described by Slade (1945) as an insecticide with outstanding proper- ties. According to Slade, Michael Faraday in 1825 first described the synthesis of hexa- chlorocyclohexane (referred to by Slade as Gammexane or 666) by the reaction of chlorine with benzene in the presence of sunlight. In 1943, Slade found the gamma isomer to be the toxic principle in the crude hexachlorocyclohexane. Usu- ally the technical material has 10 to 12 per cent by weight of the gamma isomer. Pure gamma hexachlorocyclohexane has a faint musty odor, is a colorless crystal- line material melting at 112.5 degrees C, and is soluble in most organic solvents. Toxaphene, a technical chlorinated camphene with an approximate empirical formula CmHioClg, is a soft, waxy, light yellow material that melts at 65 to 90 degrees C. and has a density of 1.6. It is readily soluble in most organic solvents and insoluble in water. Toxaphene, for- merly known as Hercules Synthetic 3956, is produced by the Hercules Powder Com- pany of Wilmington, Delaware. Stearns (1947) indicates that Toxaphene has some promise as a household insecticide. In addition to the insecticides described above are several on which preliminary studies were made. PURPOSE OF STUDY The purpose of this study was to obtain pertinent information about the residual insecticidal value of chlorinated hydrocar- bons applied to various surfaces that had been exposed to different field conditions. The investigations conducted in 1943 at Orlando, Florida, by Lindquist et al. (1944) showed DDT to possess a high degree of residual toxicity to the house fly. They also showed a difference in tox- icity of DDT when applied to painted and to unpainted wood. The need for the study reported here became apparent to the author when certain of his field applica- tions of residual toxicants failed to effect adequate insect control. The results of this study, it is hoped, may serve as a guide to persons who are seeking to control insects through applications of residual insecticides and who are concerned with residues on plants. ACKNOWLEDGMENTS The writer wishes to express his sincere appreciation to Dr. C. W. Kearns, De- partment of Entomology, University of Illinois, and to Dr. G. C. Decker, Head of the Section of Economic Entomology of the Illinois Natural History Survey, for suggestions and advice as to the course of the investigation, part of which was reported in a thesis presented in partial fulfillment of the requirements for the degree of Master of Arts in Entomology in the Graduate School of the University of Illinois, 1947. He is grateful to Dr. Kearns, Dr. William P. Hayes, Head of the Department of Entomology, Univer- sity of Illinois, and Dr. C. J. Weinman, I July, 1949 Bruce: Residlal Insecticides Toxic to the House Fly ^ Fiji. !•—Exposure cage used in the experiments. -As shown here, the cage is inverted, anil the sliding panel is partly withdrawn. Entomologist of the Illinois Natural His- tory Survey, for constructive criticism of the manuscript. TESTING PROCEDURE A versatile fiat exposure cage, hg. 1, was designed by the writer for use in the field, fig. 2, and for laboratory tests de- scribed below. The method of exposing cut film that photographers einploy sug- gested its design. Made of a three-fourths inch white pine frame 8i/j inches square by I.V4 inches deep, the cage is covered on one side by 16-mesh screen wire and fitted on the other side with a sliding panel of manila paper or sheet metal. It has an interior space of about 75 cubic inches. More than 300 cages of this design were ret]uired for the tests. All house flies used in the tests were reared according to the accepted Peet- Grady method (Anonymous 1946). About 120 pupae (2.2-2.4 grams) were placed in each exposure cage via the sliding panel, fig. 1. Flies were supplied with food, a mixture of milk and water, by means of a small shell vial fitted with a piece of cheesecloth. A shell vial was inverted up- on the screen top of each cage, permitting the adult flies to feed by contact, fig. 3. In each test of an insecticide, adult flies were exposed to a treated surface on their second day of oviposition, and on the fol- lowing da\' the mortality counts were inade. 1 he e.xposure process was simple. First the cage was placed on a clean, flat board and then the slidmg panel was removed momentarily to allow the empty pupal cases and other debris to fall out. With the panel replaced, the cage was moved and secured to the treated surface. The sliding panel was then removed to allow the flies to have direct contact with the treated surface for the desired exposure period. Obviously because of the house flies' habit of seeking the ceiling as a rest- ing place when illumination is reduced, preliminar\' tests under average laboratory lighting indicated that best replication was obtained by inverting the cages (screen side down) during the exposure, frontis- piece. However, in bright light and at temperatures between 80 and 90 degrees F. there was little difference between re- sults from the upright and the inverted position during exposure. Illinois Natural History Survey Bulletin Vol. 25, Art. The treatment of the selected surfaces was simple and >et apparently reliable. In the early tests, the quantity of prepared insecticide, containing 1 per cent of the ing spray tower, fig. 5. A Tattersfiel spray apparatus was fitted with snialh openings in order to reduce the particl size to 2—50 microns range. Even distr Fig. 2.—Practical method (not used in the experiments) of testing the toxicity of wall sui faces treated with residual insecticides. The exposure cage is hooked to the treated wall, an the metal panel is withdrawn to give flies in the cage direct contact with the wall for a give period of time. residual toxicant by weight, was measured with a pipette and spread evenly over the surface with the aid of a small brush, fig. 4. Additional water or solvent was used to wash the residue from the brush onto the surface. In later tests the deposits were obtained by means of a 6-foot stainless steel settl- bution and good replication (less than per cent variation among deposits) wei obtained with this apparatus, fig. 4. The following are some of the commo formulations of the concentrates used i making 1 per cent sprays. Formulatior other than these are indicated in the di: cussion of individual tests. 1949 Brlce: Residual Insecticides Toxic to the House Fly 5 A. Emulsions : 1. 62% chlordan + 5% Atlox UU5-A + 33% no. 9 oil by volume. 2. 25% DDT, Toxapbene, gamma isomer of hexachlorocvclohexane or Rholhane D-3 +'70% PD 544-C (solvent known also as Sovacide 544-C) + 2% emulsi- fier B-1956 and 3% Triton X-155 by weight. 15. Water-wettable powders: 50% by weight of toxicant + 2% wetting agent (Triton X-100) + 48% by weight of Cherokee clay. C. Oil solutions: 1.0% by weight of toxicant per volume of no. 9 oil. After each test the cages were decon- taminated in a mild KOH solution, washed thoroughly in soapy water, and allowed to dry in the sun for about 2 days. The manila sliding panels were discarded after being used once. With this procedure no contamination difficulties were met. Fig. 3.—Method of feeding flies in exposure cage. A shell vial filled with milk and stoppered rith one layer of cheesecloth is inverted and placed on the screen top of the exposure cage. Illinois iNatural History Survey Bulletin Vol. 25, Art. Experiment 1 : Exposure Time for Knockdown and Mortality.—In an ex- periment designed to reveal the exposure times necessary to give comparable mor- talities for the five principal materials tested, as well as to indicate the relative initial surface toxicity and speed of knock- down of Hies, lots of 100 to 120 flies each haps Monro and his co-workers used sua faces on which onh' a small amount DDT was available to the flies, and in thi first few minutes of exposure the flies rapidly eroded or removed the DDT avail- able. In speed of knockdown, gamma hexachlorocyclohexane was the material ranking first ; it was followed in order by Fig. 4.—Three glass panels similar to those used in experiment. Left, panel with insecticide applied in settling spray tower; center, panel with insecticide being applied by means of brush and pipette; right, panel with insecticide already applied by means of brush and pipette. were exposed to deposits of 50 mg. per square foot (538 mg. per square meter) of glass for each of three replicates. Table 1 clearly reveals the correlation between the length of exposure and the percentage of mortality and knockdown resulting from each of the five principal chlorinated hydrocarbons used. The sur- face toxicity as indicated by the exposure needed to effect mortality made DDT and gamma hexachlorocyclohexane appear to be the most toxic, with chlordan, Rhcthaiie D-3, and Toxaphene following in order. Monro, Beaulieu, & Delisle (1947) reported no difference in mortality among lots of flies exposed for 10, 20, 30, 40, and 50 minutes to DDT deposits. Their reported results are at variance with data obtained from the experiment described here. Table 1 exhibits clearly the relation- ship of exposure time to mortality. Per- DDT, Rhothane D-3, chlordan, and Toxaphene. Fifty per cent knockdown of house flies when exposed to Toxaphetif was reported by Block (1948i) to require in some instances only 12 minutes, a period that represents a much faster knockdown rate than the 4 to 6 hours for complete knockdown reported by Beacher & Parker (1948). Data in table 1 indicate that about 167 minutes of exposure to Toxa- phene is needed to give 50 per cent knock- down and 253 minutes for 99 per cent knockdown. It was noticed in the e.xperi- ment reported here that there was no cor- relation between time required for knock- down and time required for kill. Rho- thane D-3, which possessed much less sur- face toxicity than chlordan, actually gave quicker knockdown. Surface toxicity de- pends upon the availability of the insecti- cide as well as the actual toxicity. ly, 1949 Brl-ce: Residuai. Insecticides Toxic to the Hol'se Flv 1 Fi^. 5.—Settling spray tower. Insecticitie i* introduceil l>y a pipette into the atomizer at top ettliiig spray tower. A panel is placed on a sliding shelf in the bottom of tower. At 12.5 ids air pressure, and after 3 minutes are allowed for settling, the dosage per square foot of :1 is approximately 32.+ per cent of the quantity placed in the atomizer. Illinois Natural History Survey Bulletin Vol. 25, Art Table 1.—Effect of exposure time on mortality of house flies and time required various knockdowns of flies by five chlorinated hydrocarbons when applied as suspensions glass. Water- Wettable In.secticide Illy, 1949 Brcce: Residlal Insecticides To.mc to the House Fly 9 Table 3.—Mortality of house flies exposed to surfaces sprayed with DDT at diflerent isa^es and degrees of coverage. Ic. Of DDT Per Cent OF 10 Illinois Natural History Survey Bulletin Vol. 25, Art. 1 Table 5.—Mortality of house flies exposed to surfaces sprayed with DDT distributed heterogeneously and also homogeneously. Formulation July. 1949 Bruce: Residual Insecticides Toxic to the House Fly 11 conclusion that perfecth unitiirni deposits ma> not be necessary or e\en advantageous on surfaces on which residual toxicant de- posits are excessive. This conclusion con- firms results of experiments in which there was no apparent difference in mortality rates resulting from deposits obtained by spra\ing and those obtained b\ painting. The painted deposits were obviously not perfectl>' uniform, fig. 4. Experiment 6: Wall Coats Con- taining DDT.— \\ hen man\ so-called \\ all coats containing DDT appeared upcjii the market, laboratory tests were progress- ing upon amounts of DDT in the suspen- sion-t.\ pe wall coats needed to produce the necessary lethal action. In addition, a means was being sought whereby a good wall coat might be produced. Formula- tions containing 0.5, 2.0, 5.0, 10.0, and 25.0 per cent DDT were prepared from Rohm iSc Haas wettable DDT powder and sprayed upon glass panels at the rate of 50 mg. actual DDT per square foot. The treated panels were permitted to dry and age 4 weeks before being tested. The data in table 6 make it evident that mortality and knockdown were not changed until the concentration of DDT was reduced to 10 per cent or less. The writer is doubtful if any wall coat con- taining as little as 2 to 5 per cent DDT could compete in fly control with 50 per cent DDT water-wettable powder in field operations. In the 50 per cent water- wettable powder, approximately half of the surface particles are actual DDT, whereas in the wall coat probably 2 to 5 of 100 surface particles are actual DDT. A few experiments with laboratory wall-coat formulations, in which 25 per cent DDT emulsifiable concentrate was reduced to 5 per cent DDT by mixture with Clwrokfi- clay and used in place of the water-wettable powder, proved quite satis- factory When this formulation was spra\ed upon wood or other porous surfaces a highh' toxic bicom occurred usually with- in a week. When applied to glass, the DDT "bloomed-in" and crystallized upon the glass beneath. Used commercially, such a formulation would probably not be sprayed upon glass or (Jther highly polished surfaces and wo o r^ I r-- n -— o oo o o o do r- o — CJ o oo •J-t CN oo o o oo o o o o o o ro vo r^ r^ r^ oo t^ CS d ! oo oo Tj' cs .— oo vO •— • CN O oo CJv I O CO oo w^ On-*' In CO ooo o o o d OOOO ^'OlNOOO^O o '^ "^ iO trt Vl QQrtClJrt ra TO TO TOTOTOTO OOOOOOOO OOOO- O O " g:^000 Bruce: Residual IxsEcTicinEs Toxic to the House Fly 13 14 Illinois Natural History Survey Bulletin Vol. 25, Art. rapidl\' than the lahoratory water-wettable powder fornuilation in which Clwrokic clay is used as a diluent. The three formulations in which HB-40, xylene, and Velskol AR-60 were solvents, and Atlox 1045-/1 was used as the emulsifier, had different degrees of bloom and wear. The first test period 6 days after treatment showed considerable degradation of the well-crystallized DDT- xylene deposit; in the other two formula- tions, little loss of toxicity was noted from the first through the tenth exposure. Exam- ination under a microscope revealed no crystals present where HB-40 had been used and very few where Velskol AR-60 was employed. Five days later, when these same surfaces were again tested in like manner, the xylene treatment had eroded severely, that containing AR-60 had eroded slightly, and the HB-40 treatment showed no toxicity and no bloom. The HB-40 treatment then appeared dry, whereas in the first series of tests it had a wet appearance. A third test of only five series of exposures on the eighteenth day and examination of deposits proved the appearance of crystals upon the sur- face of the HB-40 treatment. The xylene treatment indicated a continued slow, in- conspicuous bloom, and the AR-60 treat- ment a more noticeable bloom. By the time of the last test, on the thirtieth day, of but one cage of flies, the results suggested that the rate of bloom is directly proportional to the rate of volatilization of the solvent. Thus, in 30 days HB-40 had only begun to permit the crystallization of DDT ; xylene had apparently passed its peak of crystallization by the fifth day, and Vel- skol AR-60 by the eleventh day. Probably some of the DDT remains bound in the wood as a supersaturated or saturated solution in any of these solvents for peri- ods much longer than those indicated here. Further studies with xylene as a sol- vent, as indicated in table 7, lead to the belief that, if the desirable secondary bloom is to be obtained, the flies, or what- ever device is used for seeding the surface, should be on the surface not later than the second day. Thus, the period of seeding a xylene treatment seems somewhat limited. If, however, we add to the xylene emul- sion-concentrate about 20 per cent ethylene dichloride or carbon tetrachloride we find that a deposit bearing DDT will react t the stimulus on the fourth day to produc a plainly visible heavy white crystallin mat of extremely small, fine crystals oi the wood surface. Of all tiie secde blooms, these and the ones produced by th PD 544-C treatments were the heavies and most resistant to wear at a high lev< of toxicity. Of all the formulations excep those made with water-wettable powder; the 1.62 per cent DDT solution in 95 pe cent ethyl alcohol produced the most leth; and tenacious deposits on glass surfac( when either sprayed or brushed upon th surfaces. It produced the finest crystallin deposits, and its crystallization was tli most rapid, fig. 8. Microscopic study of all solution d( posits on glass revealed that rarely wr crystallization complete. Usually a fei or many minute blobs of supersaturate solution persisted among the DDT cryi tals, fig. 12. On glass and, less noticeabl; on wood the size of the DDT crystals vvj determined by the speed of crystallizatioi which, in turn, was determined by th physical properties of the solvent, fig 6-13; rapid crystallization produced cry: tals of minute size. This phenomenon \v; especially noticeable where surface trea ments were seeded by fly activity at th proper time and crystallization was at one initiated at the innumerable sites of fl contact. Often it was noted that dus dirt, and scratches stimulated the form; tion of crystals on glass, fig. 13. Schmitz & Goette (1948) apparent! showed the degree of penetration of DD' solutions into poplar wood. The opinio of the present writer is that the degrt of penetration may be influenced by highl variable elements in the environment. Fi example, under a certain set of conditior it is possible that most of the DDT coul be crystallized on the surface of the woo if the solvent is highly supersaturate when the surface is stimulated. Withoi the stimulation, much of the DDT coul remain dissolved and held in the wood b the solvent. Certain components of woo have shown a visible influence upon th bloom ; it has been observed that f requentl bloom occurs on the soft part of the woo between the hard or resinous annual rinj before a crystalline formation occurs o the annual rings. On certain pieces ( ly, 1949 Bruce: Residual Insecticides Toxic to the House Fly 15 Fi^. 6.—DDT crystallization from PD 5-f-/-(: emulsion. X 40. Crystals of DiXV fornicil m solvents that evaporate slowly tend to be large, lie Hat on the glass, ami exhibit low icity and high resistance to erosion. Fi^. 7-—DDT crystallization from no. 9 oil on glass. X40. The large crystals are plainly ibie to the unaided eve. 16 Illinois Natural History Survey Bulletin Vol. 25, Art. 1 Fi^ 8 -DDT crystallization from ethyl alcohol solution on glass. X 40 The minute crystal not visible individually but only as dense hemispherical masses, have high toxicity and ar resistant to erosion. X 40. The very lai Fig 9.—DDT in process of crystallizing from an HB-40 solution, crystals, which lie flat upon the glass, are characteristic of very slow crystalhzation. ly, 1949 Brlce: Residual Insecticides Toxic to the House Fly 17 Fig. 10.—DDT crystallization from a I'ehicol JR-60 emulsion. X40. The crystals lying and forming a network on glass, have low toxicity and are resistant to erosion. Fig. 11.—-DDT crystallized from xylene emulsion on glass. X40. Network of crystals is lilar to that from I'elsicol AR-60, but the individual crystals are smaller. Illinois Natural History Survey Bulletin Vol. 25, Art. Fk 12—DDT in process of crystallizing from xylene solution on glass. X 40. Tl xylene droplets (center of picture) among the crystals are susceptible to seeding by dust or Hm Fig. 13.—DDT in process of crystallizing from xylene solution. X40. The solution on glass shown here was seeded by dust, and crystallization started sooner than on glass sho in fig. 12. Iv, 1949 Brlce: Residual Insecticides Toxic to the House Flv 19 )od, when a bloom occurs on the soft rt of the wood, it does not occur the annual rings. Thus, it seems that [letration or retention of DDT in the )od depends upon the physical properties the sohent and the particular piece of x)d used, in addition to en\ ironmental ments. Experiment 8: Fumigation Prop- ties-— During the course of the studies, ficult> was encountered with ct)ntamina- in of air in the room containing the fi\- (clc cage. Investigation of this situation .ealed that the only possible source of ntamination was chlordan-treated sur- :es at the opposite end of the room. Pre- linary tests indicated that Toxaphene, I'jth/iiie D-3, and DDT did not act as migants to any noticeable extent ; on the ler hand, chlordan and gamma hexa- lorocyclohexane seemed very toxic as migants. A study was made of the fumigation tion of chlordan and gamma hexachloro- :Iohexane. Caged flies were placed in a •ge battery jar (11.6 liters capacity) th 18 square inches of treated surface. The top of the jar was sealed with a glass plate smeared with a glycerine-betonite jell. Exposure times of six groups of flies to the air in the jars were, respectiveh', 15, 30, 60, 120, 240, and 480 minutes.' The results of four replicates are shown in table S. The losses of weight from the treated surfaces were used to calculate the dosage as milligrams per 1,000 cubic feet or 28.365 cubic meters. One mg. per 1,000 cubic feet is equivalent to 0.0353 mg. per cubic meter. It was diflicult to believe that the calculated dosages actually existed as a vapor, but rather existed as condensa- tions or adsorptions over the entire inside surface of each jar. It seemed conceivable that there was a transfer of the toxicant to the lipoid material in the insect's body and consequently that a lethal concentra- tion of the toxicants accumulated. These data indicate the high order of toxicity to house flies of vapors that were given off from chlordan and hexachlorocyclo- hexanc. Chlordan and hexachlorocyclo- hexane were compared with HCN, one of the most toxic fumigants, and found to be approximately 62 and 206 times as toxic, respectively. Fly fumigation data Table 8.—Mortality of house flies 24 hours after exposures of various periods to vapors chlordan and hexachlorocyclohexane residues. 20 Illinois N.atural History Survey Bulletin Vol. 25, Art. i by Eddy (1929) were used in the calcula- tions. The use of chlordan or hexachloro- cyclohexane as residual fumigants within confined spaces is suggested by results of this experiment. Experiments 9 and 10: Testini Periods.—To limit the reduction of sur face toxicity by fly erosion, the number o test periods in these experiments was heh to a minimum. Table 9.—Mortality of house flies 24 hours after exposure to various treated surface: subjected to several combinations of environmental elements. Surfaces were tested 2, 22, am 182 days after treatment with commercial emulsions of residual insecticides. Toxicant hilv, 1949 Brlce: Residlal Insecticides Toxic to the House Flv 21 Table 9 (continued) Toxicant Gamma isomer of hexachloro- cvclohexane Exposure Toxaphene Control South North North Inside South North North Inside South Inside South Inside South Inside South Inside South Inside South Inside outside . . outside sheltered - outside outside . . sheltered . outside . . outside outside . . outside outside outside South outside North outside North sheltered Inside South outside . . North outside . . North sheltered Wood Wood Wood Wood Glass Glass Glass Glass Painted wood* Painted wood* Cell'Hex Celliilex Brick Brick Concrete Concrete Whitewash. . . Whitewash . Galvanized . . Galvanized . . . Mean Per Cent Mortalitt in Three Replicates 2 Da>s After Treatment Inside Glass Wood. Wood Wood Wood. Glass . Glass. Glass. 94 23 97.17 97.53 98.33 99.13 97.00 98.66 97.87 61.70 60 37 72 63 73.77 69.03 90.67 50 03 43.97 89.00 86 90 99.80 99.47 Mean diflFerence necessary for significance, 0.05 level '. Mean difference necessary for significance, 0.01 level r 70 33 64.77 71.60 71.13 99.37 98.90 98 53 98.33 1.17 1.57 1.47 0.57 9.11 21.11 22 Davs .After 22 Illinois Natural History Survey Bulletin Vol. 25, Art. 1 to eight surfaces—planed fir, glass, painted wood (1 month old), Cellutex (similar to Celotex), brick, concrete, whitewashed wood (1 month old), and galvanized iron —at a rate of 50 mg. per square foot, table 9. Treatments on wood and glass were exposed to various elements of the weather. Three replicates of each treat- ment on glass and wood were placed in situations on the South Farm of the Uni- versity of Illinois so that one set was in- side ; another was outside on the south side of buildings e.xposed to all the ele- ments ; the third was on the north side of buildings; and the fourth was under a shelter that gave protection from sun and rain. The four positions maj' be described simply as the inside, the south exposure, the north exposure, and the sheltered. Surfaces other than glass and planed fir were placed in two positions—the south outside exposure and the inside. The ob- jective of this experiment was to obtain information on the persistence of the five toxicants on the eight surfaces under vari- ous conditions. A study of table 9 will reveal the insecticides that were found to be most persistent under various condi- tions and also the surfaces on which in- secticides were retained the greatest length of time. Experiment 10: Field Persistence of Residues From a Standardized Formulation oi Emulsions-—The plan of this experiment was essentially the same as that of experiment 9. The variable of formulation was eliminated, and better- defined positions of exposure to the cli- matic elements were set up. Treated panels were exposed by means of suitable supports, fig. 14, on top of a flat-roofed unr^r Fig. 14.—Securing treated panels to pipe rack for determining the effects of weathering upon toxicities of residues. July, 1^49 Bruce: Residual Insecticidks Toxic to the House ! i.v 23 huildiiig. Some panels were secured to a pipe rack in north and south dutside posi- tions. Otliers were phiced on racks he- neath a shelter designed to keep out rain and sunshine. Still others were kept in the laboratory. The same solvent and emulsi- fying agent were used in all formulations. The emulsiriable concentrates contained 65 per cent xylene, 10 per cent Triton X-100. and 25 per cent h\ weight of the toxicant. These were diluted with water to give an emulsion cxintaining 1 per cent of the insecticide. Incorporated with this experiment were tests with DDT water- wettable powder ; it was hoped that such a formulation would overcome some of the surface hazards encountered with emulsions. Experiments 9 and 10: Discussion. —Results of these tests are shown in tables 9 and 10. DDT was the outstand- ing residual insecticide. Rh(jlhaiif D-3 was the next most persistent material, with Toxaphene a good third choice. Gamma hexachlorocyclohexane and chlordan were the least persistent. Probabh' one of the greatest hazards was dust. Dust particles falling upon treated surfaces introduced a variant, not measureable. Nevertheless, dust presents one of the conditions fre- quently found under field conditions. Analysis of these data made it evident that differentiation among elements is difficult. Rain appeared by visual evidence and biological assa\' to be the prime ele- ment in the degradation of the residual deposits. The deposits that were expcjsed to rain were more persistent on hard im- pervious surfaces (glass and galvanized iron) than on porous surfaces (brick, fir wood, and Cellutex). On painted wood, concrete, and whitewashed wood the initial and residual toxicit)' of the insecticides to house flies was lower than on other sur- faces. I he deposit from 50 per cent DDT water-wettable powder gave promising re- sults on all surfaces. At the end of 152 da>s, the DDT suspension deposits were significantly toxic on all inside surface treatments except whitewashed wood. The emulsion containing PD 544-C and DDT that was used to obtain data in table 9 shows the typical high toxicity of the initial tests on wood ; consider- able losses were incurred as a result of erosion and degradation by the twent)- sccond day of the test. Those panels with south exposure (exposed to all the ele- ments) showed the greatest losses; those with north exposure (exposed to all ele- ments except sunshine) showed approxi- mately 20 per cent greater killing power. These losses may be accounted for by one or both of two possibilities: (1) direct sunlight or the heat produced by solar radiation; (2) rain driven onto the panels by a pre\ailing southwest wind. Wood panels sheltered from rain as well as sun exhibited about 15 per cent greater mor- tality to flies than the ones with north ex- posure. Wood panels placed within build- ings retained their toxicity beyond the 22n(l da\- and e\en to the 182nd day. The difference in toxicity between those wood panels held indoors and those in sheds where the\- were sheltered from external elements (sunshine and rain) might be assigned to one or both of two possibilities: wind erosion and dust accumulation found in the sheds. The second series of tests (experiment 10) uith uniform emulsions reveals no signilicant differences between those panels retained within the laboratory and those kept in a shelter constructed on top of a building. Both sites were relatively dust- free in contrast to the interior of the sheds used in the first test. In light of available information, it must be assumed that the real cause of degradation of the surfaces in the sheltered positions of the first series of tests (experiment 9) was dust accumula- tion and not wind erosion. The glass pa.nels treated with DDT emulsions may at first appear to oiifer somewhat contradictory evidence of tox- icity unless the difference in solvents and emulsifiers used in the first and second series of tests is kept in mind. In experiment 9, with a commercial I'D 544-C emulsion of DDT on glass, the deposits and the test clearly showed that the rain, wind, or some other element found in the outside positions caused the DDT residue, a large part of which ex- isted as a supersaturated solution in PD 544-C and emulsifier, to bloom or crystal- lize out. A microscopic comparison of the residues on the panels at the time of test- ing on the twelfth da\' revealed the pres- ence of practically no supersaturated blobs 24 Illinois Natural History Survey Bulletin Vol. 25, Art. 1 on the glass panels from the two outside positions in contrast to much supersatu- rated fluid on those inside, particularly those sheltered from all the elements, in- cluding the wind. By the 182nd day, however, the order of residual toxicity was reversed by the wear of the elements. In tests with uniform emulsions (ex- periment 10) where xylene was the solv- ent, seeded crystallization occurred on glass earlier (probably as a result of the initial fly action) than in experiment 9; that is, the xylene had probably slowly evaporated so that by the end of the first test period the blobs produced were easily crystallized when contacted by flies. There are other possible explanations for the high level of to.xicity observed in the first two test periods. One is that the Triton X-100 emulsifier containing some dissolved DDT Table 10.—Mortality of house flies 24 hours after exposure to various treated surfaces subjected to several combinations of environmental elements. Surfaces were tested 2, 12, 32, and 152 days after treatment with standard laboratory emulsions of residual insecticides. ulv, 1949 Hrlce: Residu.al Insecticides To.mc to House Fly 25 Table 10 (continued) 26 Illinois Natural History Survey Bulletin Vol. 25, Art. 1 acted as a contact poison. Another is that, previous to the first test, dust in the labo- ratory stimulated or seeded the drying de- posit. The DDT deposits on glass or gal- vanized iron in all instances were more tenacious than those on porous surfaces such as wood, brick, and Ct-llutex, where erosion was significantly high. DDT on painted wood did not appear to be toxic either initially or residually. No doubt the DDT was absorbed into the paint and retained. There was no evidence in these tests that the DDT eventually bloomed, as would be expected if the solvent capac- ity of the oil paint were exceeded. On Cellutex and brick, the DDT residues were similar in longevity and erosion to those on wood. The degradation of DDT deposits was most evident upon white- washed and concrete surfaces. In all prob- ability the alkalinity of these substrates caused a dehydrohalogenation decomposi- tion. DDT emulsions on galvanized iron exhibited high toxicity and longevity. The residual longevity of the remaining four toxicants listed in tables 9 and 10 was influenced by the same external en- vironmental degradants as was DDT, with a few exceptions that are discussed in the following paragraphs. Chlordan-treated wood panels were lit- tle influenced by any external factors since greatest loss of chlordan was through vola- tilization or absorption. In the field test, where chlordan was. formulated with no. 9 oil and emulsified with Atlox 1045-A, no erosion by rain or degradation by other elements was discernible. In experiment 10, with standardized formulations, the toxicity of chlordan on wood had declined to such a low level by tlie time of the first test after exposure to weathering that no conclusions were possible. In contrast, erosion of chlordan by rain was plainly evident on glass panels. When no. 9 oil (experiment 9) was used as the diluent, the residual toxic life of a chlordan deposit was at least twice as long as when a xylene ff)rmulation (experiment 10) was em- ployed. Similarly, when PD 544-C was used as the solvent (experiment 9), the residual toxicity of a hexachlorocyclo- hexane deposit was longer than when a xylene was employed (experiment 10). Gamma hexachlorocyclohexane also re- acted to its environment in a manner similar to the action of DDT, but hexa' chlorocyclohexane degraded rapidly ouii of doors or in strong wind currents. Mosi' of its loss was attributed to its volatility. Rlwthaiie D-3 was significantly more tenacious on glass than on wood, and re sponded to its environment in much tin same manner as did DDT. Toxaphene lost its toxicity on wooi much more rapidly than on glass panel held in the laboratory. Simple physica absorption of Toxaphene by the wood i suggested as an explanation. ] Experiment 11: Formulation Stud ies.—The data obtained in the laborator; study of the persistence of oil solutions emulsions, and suspensions are given ii table 11. Studies of duration of residu;i toxicity were conducted to see if any on formulation was more persistent on th hazardous surfaces—whitewashed wooc concrete, and painted wood—tiiat caus apparently rapid loss of toxicity. The ri suits show that water-wettable powder were generally superior to the other formw] lations on all these surfaces. ' The initial toxicity of oil solutions an emulsions of DDT, as evidenced by th data in table 11, was very low on whitt washed wood, painted wood, concrete, an unpainted wood, and very high on glas! The results here are similar to others i' this study, which indicate that oil solution/ or emulsions of DDT are low in toxicit on porous surfaces and very high on harti smooth surfaces, such as glass, if teste* before crystals have started to form. The second test period 7 days afte treatment gave high fly mortalities o wood panels and lower on glass panelii The water-wettable powders of DD'i were significantly more toxic on painte wood, whitewashed wood, and concrel than were the oil solutions or emulsionn Even with the wettable powder the alb. linity of the whitewash and concrete muii' have reached the DDT to cause a dedir' in the toxicity. This action was probabl accomplished through adsorbed wate On painted wood the toxicity decrease without any apparent reason; a possib explanation is that the oils in the under!) ing paint were capable in some manner i penetrating the wettable powder and di solving away the DDT. On glass an ilv, 1949 UrUCI:: ReSIDLAI. iNSEt'TKlDES ToXlC TO TMI- HoLSE Fl.Y 27 Table 11.—Mortality of house flies 24 hours after exposure to various surfaces treated ith oil solutions, emulsions, and water-wettable powders of UUT and chlordan. Flies were tposed to surfaces 1, 7, and 45 days after the surfaces had been treated. 28 Illinois Natural History Survey Bulletin Vol. 25, Art. 1 In addition, the emulsions had an emulsi- fier of high vapor pressure, which retards chlordan evaporation. Experiment 12: Laboratory Per- sistence of Deposits.—A plan was made to test more fully the residual properties of the three most promising toxic residual materials. At frequent intervals during a 31-day period, house flies were exposed for 15-minute periods to panels treated with DDT and gamma hexachlorocyclohexane and for 60-minute periods to panels treated with chlordan. The results are shown in table 12. The order of persistence on wood or glass was, from the most persist- ent to the least, DDT, chlordan, and gamma hexachlorocyclohexane. The sus- pension of hexachlorocyclohexane retained its toxicity at a high level for 10 days; then its toxicity declined rapidly. Chlor- dan lost its toxicity gradually through the test period, whereas DDT emulsion on wood seemed to increase in effectiveness. The lower toxicity exhibited bv the emulsion of DDT and PD 544-C on glass than on wood from the first da\' to the last is typical of DDT residues in which a slowly volatilizing solvent is used and crystallization is progressive. In other words, the frequent exposure of flies to these surfaces did not permit sufficient supersaturated fluid to accumulate, which is essential for the production of high toxicity residues composed of minute crys- tals. Again, a physical law determining crystal size was responsible for the toxicity attained. The number of crystals per unit mass is directly proportional to the rate of crystallization, which is dependent upon the degree of supersaturation. Blooming of DDT on wood occurred between the second and sixth da\s and produced a residue that remained toxic throughout this experiment. The thick white residue of the gamma hexachlorocyclohe.xane water- wettable powder was slightly more toxic and per- sistent when applied to glass than to wood. The longevity of the chlordan and hexa- Table 12.—Mortality of house flies 24 hours after exposure to wood and glass panels treated with DDT, hexachlorocyclohexane, and chlordan. Flies were exposed to treated surfaces at designated periods of time after the surfaces had been treated. Insecticide July, 194V ijRLcii: RtsiDL.M. Insectilhiks Toxic House Ki.v 29 chlorocyclohexane residues was iie:iil\ equal. Chlordan seemed slightly more last- ing on wood, and hexachlorocyclohexane lasted longer on glass. In this particular experiment, table 12. chlordan was of about equal effectiveness on wood and on glass, while in most of the previous work the chlordan emulsion resi- due on glass gave more lasting toxicity than on wood. If an explanation of these results is desired, it might be found in the difference in the composition of the wood panels or the environment in which the panels were held. The cause of the deg- radation of chlordan on glass was at- tributed to dust and debris that accumu- lated upon the oily surface. In the experi- ment described above, dust and debris left on the surface by the flies may ha\ e been more important than that floated in by air currents. Not only will dust and dirt mask the chlordan, but may assist evapo- ration by increasing the evaporation area just as with water-wettable powder (ex- periment II). It is not be\ond reason to belie\e that the chlordan-treated glass sur- face was roughened by the fly contacts of the frequent exposures, resulting in greater surface area for evaporation. Also, the higher initial toxicity of chlordan-treated panels suggests a greater loss incurred by physical contact of the flies. Experiment 13: Laboratory Study of DDT E miilsion on Glass and W nod.— I he results of experiments sum- marized in table 12 seemed to indicate some peculiar properties of the initial toxicity of DDT emulsions on glass and wood. Another experiment was undertaken to broaden the scope of the investigation. This involved a closer study of the initial toxicity periods. Consequently, data were obtained from deposits of DDT that \x ere Table 13.—Mortality of house flies exposed intervals after treatment of panels with 1 per cent loss than 1 da\ old. The results obtained, summarized in table 13, disclose the "blooming out" (crystallization of DDT on the surface) period of DDT on wood and reveal in the treatment on glass the loss of toxicity that occurred as the emul- sion dried. In this e.xperiment, as in previous tests, no toxic bloom of hne powdery crystals occurred on glass, since fly stimulation and seeding of surface were too frequent to permit the accumulation of supersaturated solvents. Consequently, there was a gradual formation of large crystals of low toxicity. The greatest fly mortality fiom exposures to glass panels occurred before any DDT crystals were found ; the opposite was true in the case of DDT emulsions on wood. Besides the seeding action by flies, many environmental com- ponents may influence the rate and kind of DDT bloom to appear on a surface. The same solvent may yield large crystals one day, and the next day, when the tempera- ture is higher and air movements greater, it may produce small crystals. Experiment 14: Approximate Residual Toxicity of Several New Insecticides to the House Fly.—Sev- eral new insecticides that have recently come under study are briefly considered here and compared with DDT and chlor- dan. Ten per cent solutions of Mailalc (4,4'-dimethox\-diphenyl trichloroethane) , J 4 (diethyl /)-nitrophenyl phosphate), PyreiKjiif (actually 10 per cent piperonyl butoxide and 0.5 per cent pvrethrins), US (I,2,3,4.I0,10-he.xachloro-l:4, 5:8- diendomethano-l,4,4a,5,8,8a-hexahydro- naphthalene), parathion (diethyl />-nitro- phenyl thiophosphate), heptaklor 1 (or 3a ) ,4,5,fa,7,8,8-heptachloro-3a,4,7,7a-tetra- hydro-4,7-methanoindene, and 497 (oxygen 15 minutes to wood and ^lass panels at stated DDT emulsion. Deposit of DDTinMg. per 30 Illinois Natural History Survey Bulletin Vol. 25, Art. 1 analogue oi 118) in Vehicol AR-60 (me- thylated naphthalenes) were sprayed in triplicate upon glass and wood panels to produce deposits of 50 mg. per square foot. Flies were exposed for 30-rninute periods to these panels each week until the to.xicants had degraded to a low level. One set of three panels of wood and glass was exposed to direct sunlight and wind but protected from rain ; a similar set was kept in the laboratory. Table 14 was designed to help evaluate the residual activities of the toxicants in periods of weeks needed to degrade a de- posit to 50 per cent of its initial toxicity. Table 14.—Approximate number of weeks required for residual insecticides to degrade to 50 per cent of their initial toxicity to house flies. Flies were exposed 30 minutes to each panel which had been treated with insecticide at the rate of 50 mg. per square foot of treated surface. Material July, 1949 Hruce: Residual Insecticides Toxic to the House Fly ene dichloride or carbon tetrachoride) as the solvents produced exceedingly heav\ mats of very fine crystals of high toxicity when seeded by fly activity. Bone glue 5 per cent, added to Deeiiale water-wet- table powder improved tenacity. DD'l , 1.26 per cent, in 95 per cent ethyl alcohol when applied to glass produced a deposit of extremely tine crystals of high toxicity and tenacity. 9. DDT-xylene emulsion deposits on glass or wood when seeded early (within 2 days after application ) produced a fairly effective secondary bloom. 10. High toxicity and tenacity of de- posits were associated with the fineness of DDT crystallization upon the surface. 11. No difference in toxicity or tenacity of deposits could be attributed to the method of application (sprajing or paint- ing)- 12. Vapors from gamma hexachloro- cyclohexane were about three times as toxic to flies as those from chlordan ; both were extremely toxic as fumigants. The fact that toxic vapors are given off from chlordan and hexachlorocyclohexane de- posits accounts for tiieir short-li\ed resi- dual action on exposed surfaces. 13. Solvents of low volatility increased the residual toxicity of the more volatile insecticides. 14. DDT was the most persistent in- secticide tested. The residual toxicity of DDT emulsions was better indoors on porous surfaces, such as wood, brick, and Cellutex, than on glass and galvanized iron. Out of doors, residues were more per- sistent on the nonporous glass and gal- \ anized iron panels. 15. The order of persistence of the resid- ual treatments was, from the most to the least. DDT, Rhnthaiie D-3, Toxapheiie, chlordan, and hexachlorocyclohexane. lb. The oil solutions and emulsions of the chlorinated hydrocarbons were rela- tively nontoxic to flies when applied to whitewash, painted wood, and concrete. \Vater-wettable powders produced effec- tive residual deposits on these same three surfaces. 1 7. Sunshine, rain, and wind were found In be significant climatic factors in the degradation of the residual surface toxic- ities of the materials tested. Wind was apparently the least significant of the three. lo. With a few exceptions, when DDT emulsions were applied to wood, the toxi- city increased as the DDT "bloomed out" ; when the emulsions were applied to glass, the toxicity decreased as the emulsions dried and crystals formed parallel to the glass surface. 19. In a study on newer insecticides, V4 and 497 on wood and glass produced residues of significant longevity with high to\icit>'. Other materials tested were less persistent. LITERATURE CITED Annand, P. N. 1944. Introductory discussion of DDT. Jour. Econ. Ent. 37( 1 ): 125-6. Anonymous 1946. Peet-Gradv Method. /;; Soap Blue Book, pp. 211-4. MacN'air-Dorland Co., New York, N. V. 263 pp. Bcacher, J. H., and W. L. Parker 1948. Residual toxicity: chorinated caraphene compared to DDT for toxic residual effects on various surfaces and in paints against the house fly. Soap and Sanit. Chem. 24(61 :139, 141, 143, 163. Block, S. S. 194S«. Insccticidal surface coatings. Soap and Sanit. Chem. 24(2) : 138-41. 171; (3):151, 153. 1948/'. Residual toxicity tests on insccticidal protective coatings. Soap and Sanit. Chem. 21(4) :155, 157, 159, 161, 207, 213. Eddy, C. O. 1929. House flv fumigation experiments with calcium cyanide. S. C. Ag. Exp. Sta. Bui. 2.S6: 1-48. Esten, U. N., and C. J. Mason 19(Ji. Sources of bacteria in milk. Conn. (Storrs) Ag. Exp. Sta. Bui. 51:65-10,j. 32 Illinois Natural History Survey Bulletin Vol. 25, Art. Felt, E. P. 1909. The typhoid or house fly and disease. N. Y. State Mus. Bui. 134. 24th Rep. State Ent.j 24-40. Herms, W. B. 1911. The house fly in its relation to public health. Calif. Ag. Exp. Sta. Bui. 215:513-44. Howard, L. O. 1909. Economic loss to the people of the U. S. through insects that carry diseases. U. S. Dept. Ag. Bur. Ent. Bui. 78:1-40. Kearns, C. W., Lester Ingle, and R. L. Metcalf 1945. A new chlorinated hydrocarbon insecticide. Jour. Econ. Ent. 38(6) :661-8. Lindquist, A. W., A. H. Madden, H. G. Wilson, and H. A. Jones 1944. The effectiveness of DDT as a residual spray against house flies. Jour. Econ. Em.- 37(1) : 132-4. Metcalf, C. L., and W. P. Flint 1939. Destructive and useful insects. McGraw-Hill Co., New York. 981 pp. Monro, H. A. U., A. A. Beaulieu, and R. Delisle 1947. DDT residues: Their toxicity to houseflies on various surfaces and materials. Soap and Sanit. Chem. 23(8) :123, 125, 127, 129, 143, 145. Nuttal, G. H. F. 1899. On the role of insects, arachnids, and myriapods as carriers in the spread of bacterial and parasitic diseases of man and animals. Johns Hopkins Hosp. Reps. 8(1 & 2) :1-155. Pipkin, A. C. 1942. Filth flies as transmitters of Endamoeba histolytica. Soc. Expt. Biol, and Med. Proc. 49:46-8. Schmitz, William R., and Mary B. Goette 1948. Penetration of DDT into wood surfaces. Soap and Sanit. Chem. 24(1) : 118-21. Slade, R. E. 1945. The gamma isomer of hexachlorocyclohexane—an insecticide with outstanding proper- ties. Chem. and Indus. 64:314. , Spillman and Haushalter 1887. Dissemination du bacille de la tuberculose par les mouches. Acad, des Sci. Colon. Paris, Compt. Rend. t. CV, 7:352-3. Stearns, L. A. 1947. A progress report on a new insecticide. Soap and Sanit. Chem. 23(1) : 119-41. Turner, Neely, and Nancy Woodruff 1948. Toxicity of DDT residues: Effect of time of exposure of insects, coverage and tenacity. Conn. Ag. Exp. Sta. Bui. 524. 36 pp. Wiesmann, R. 1943. Eine neue methode der Berkampfung der Fliegenplagen in Stallen. Anz. f. Schadlingsk. 19(1) :5-8. Zeidler, O. 1874. Verbindugen von Chloral mit Brom- und Chlorbenzol. Deut. Chem. Gesell. Ber. 7:1180-1. Recent Publications A.—ILLINOIS NATURAL HISTORY SURVEY BULLETIN. Volume 22, Article 1.—The Plant Bugs, or Miridae, of Illinois. By Harry H. Knight.; September, 1941. 234 pp., frontis. + 181 figs., bibliog., index. $1.25. Volume 22, Article 2.—Studies of North American Plecoptera, with special reference to the fauna of Illinois. By T. H. Prison. 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