December 1948 E-766 United States Department of Agriculture Agricultural Research Administration Bureau of Entomology and Plant Quarantine RESIDUAL SPRAYS FOR USE AGAINST THE CONFUSED FLOUR BEETLE R. T. Cotton, J. C. Frankenfeld, and Norman M. Dennis, Division of Cereal and Forage Insect Investigations Insects harbored in the woodwork of flour mills, warehouses, rail- way boxcars, and granaries are not readily controlled by fumigation. Until recently the only sprays available for use in such places have been of the contact type, which kill only those insects that are actually hit with the spray. These sprays consist chiefly of an odorless, stain- less, kerosene-type oil fortified with small amounts of pyrethrum, thiocyanates, rotenone- containing material, or various combinations of these toxicants. Although effective against moths and other soft- bodied flying insects, they are not highly toxic to many of the insect pests of stored grains and milled-cereal products. During the past few years a number of new and highly effective in- secticides have become .available commercially— DDT, TDE, methoxy- chlor, gamma benzene hexachloride, chlordane, chlorinated camphene, parathion, and piperonyl butoxide-pyrethrum formulations. Sprays containing them are not only effective by direct contact, but the in- secticidal residues they leave on sprayed surfaces are of great value in reducing insect populations that have become established in the wood- work of walls, floors, partitions, bins, and machinery. Some of these residues may remain effective for a year or more, and sprays contain- ing them are known as residual sprays. The toxicity of these insecticides to the confused flour beetle (Tribolium confusum Duv.) has been determined in the laboratory under various conditions. This insect was chosen for test purposes, because it is the most important insect pest of flour mills, is more resistant to insecticides than are most insects, and is unable to crawl up the smooth sides of glass vials or plastic rings used to confine it on sprayed areas. This report is not intended as a recommendation of any particular material or formulation for commercial use. -2- Technique The insecticides under discussion may be formulated in five ways — ■ as dusts, wettable powders, emulsions, solutions in oil or other solvent, and aerosols. Although all these formulations may prove useful for the control of insect pests of stored grains and milled cereals, dusts and aerosols are not discussed in this paper. In the experiments reported herein the various toxicants were applied as sprays, in carbon tetra- chloride or acetone-kerosene solutions, in xylene emulsions, and as wettable powders dispersed in water, at the rates of 50 and 10 mg. in 2 ml. of spray per 1/4 square foot. These dosages are approximately equivalent to 5- and 1 -percent sprays applied at the rate of 1 gallon per 1,000 square feet. Parathion was tested only as a wettable powder containing 15 percent of this chemical. Kerosene-oil solutions were prepared by dissolving 5 grams of the solid insecticide in 10 ml. of acetone and adding 90 ml. of oil. These stock solutions and chlordane, which was already in solution, were further diluted with oil to give the desired concentration. Stock emulsions were prepared to contain 5 grams of insecticide, 10 grams of xylene, and 5 grams of emulsifier in 80 ml of water. The stock emulsions were diluted with water to give the desired concentra- tion. Known quantities of each toxicant in dilute sprays were applied to various types of surfaces. When the spray deposits were dry, adults or immature stages, in triplicate lots of 10, were confined on each of the sprayed surfaces under glass vials 1 inch in diameter and 4 inches high. At the end of the exposure period the insects were removed to clean glass vials containing fresh flour and held for observation. Mortality counts were made every 2 days. Maximum mortality of adult beetles was usually obtained in 12 days. Larvae were consider- ably more resistant, and it was necessary to hold some of them 30 days. Comparative Effectiveness and Speed of Action The comparative effectiveness and speed of action of the various insecticide residues were determined in tests conducted with glass plates to avoid differences due to absorption. The results of tests with 50-mg. dosages are given in table 1. A dosage of 50 mg. per 1/4 square foot of gamma benzene hexa- chloride i/ in a carbon tetrachloride solution was the most rapid in its toxic action. A 30-minute exposure to the residue of this material killed all flour beetle adults within 4 days, and longer exposures did 1/ Tests with this material were restricted to the isolated gamma isomer. -3- not hasten the death of the insects. DDT and chlordane were as toxic as gamma benzene hexachloride, but slower in action at all exposures under 24 hours. TDE was slightly less toxic at a 30-minute exposure, but at all other exposures killed as rapidly as did DDT or chlordane. Methoxychlor and chlorinated camphene were much slower in action, except at the 24-hour exposure to chlorinated camphene and at the 6- and 24-hour exposures to methoxychlor. As the dosages were decreased there was a decrease in the effec- tiveness and also the speed of action of the spray deposits that was most noticeable with chlorinated camphene, methoxychlor, and gamma benzene hexachloride. At the 10-mg. dosage DDT was the most effec- tive and most rapid in action, although with exposures longer than 30 minutes chlordane equaled it in both effectiveness and speed of action. At this dosage level gamma benzene hexachloride, TDE, and methoxy- chlor were comparable in effectiveness and speed of action for nearly all exposure periods. They were slower in action than DDT and chlor- dane at exposures shorter than 6 hours. Chlorinated camphene was less effective and slower in action than the other insecticides at all expo- sures, except the 24-hour period. At a 24-hour exposure, all compounds appeared to be equally effective at all dosages tested. When the six compounds were applied in solution in refined kero- sene, in emolsions, and as wettable powders, the type of formulation used had a marked effect upon the effectiveness and the rate of kill of the spray deposit. At the 50-mg. dosage emulsions were consistently more efficient and more rapid in action than wettable-powder suspensions, or carbon tetrachloride or acetone-kerosene solutions. Furthermore, the per- formance of the six compounds was more nearly uniform in emulsions than in the other formulations. Gamma benzene hexachloride appeared to be slightly the best, but there were no really significant differences between its performance and that of DDT and chlordane. All three com- pounds were distinctly but only slightly more effective than TDE, methoxychlor, and chlorinated camphene. Dispersions of wettable powder in water were in general distinctly less effective and much slower in rate of kill than emulsions of carbon tetrachloride solutions. However, wettable-powder suspensions of DDT and gamma benzene hexachloride were only slightly slower in action than the corresponding carbon tetrachloride formulations for exposures of 30 minutes and 1 hour. The two compounds were more effective and faster in action for all exposures than the corresponding acetone-kero- sene solutions, which were in general less effective and slower in rate of kill than other formulations. However, chlordane, TDE, methoxy- chlor, and chlorinated camphene were slightly superior in acetone- kerosene solutions than as wettable powders. At lower dosages greater differences were noticeable in the effec- tiveness of the several formulations of the various compounds. With a -4- dosage of 10 mg. per 1/4 square foot DDT as a wettable powder was significantly more effective and quicker in action than all other com- pounds, except parathion, at all exposures under 6 hours. In the emul- sion DDT was almost equaled by chlordane; chlorinated camphene ranked third in effectiveness. In general the emulsions were superior in action at this dosage level. Parathion was far the most effective and most rapid in action of all the compounds tested. In tests, the results of which are not included in the data of table 1, an exposure of 30 seconds on plates sprayed with a 10-mg. dosage killed all flour beetles within 2 days after exposure. In the 24-hour exposure, all beetles were dead when removed from the plates. Duration of Effectiveness of Spray Deposits Great differences were found in the duration of effectiveness of deposits of the insecticides. The effectiveness also varied with the type of formulation and the character of the surface to which it was applied. Solutions in carbon tetrachloride or acetone-kerosene, xylene emulsions, and wettable powders were applied as sprays to glass, wood, cardboard, and cement surfaces. When the sprayed surfaces were dry, triplicate lots of adult flour beetles were exposed to them for 6 or 24 hours in the manner previously described, and the mortalities recorded every 2 days for 12 days after exposure. The sprayed surfaces were then set aside where they were exposed to ordinary indoor temperatures and daylight but not to direct sunlight. Similar exposures were made at the end of each week or month thereafter until deposits failed to show any appreciable insecticidal effect. At the 50-mg. dosage DDT residues from all formulations remained 100 percent effective on glass and wood surfaces for 1 year. Carbon tetrachloride solutions and wettable-powder suspensions remained 100 percent effective on cardboard surfaces for 1 year also, but xylene emulsions of DDT were only partially effective after 6 months. On un- finished cement surfaces the only DDT formulation remaining 100 per- cent effective after the initial exposure was the wettable powder. This formulation of DDT remained 100 percent effective for 2 months. At the same dosage rate, chlorinated camphene residues on glass from carbon tetrachloride solutions, acetone-kerosene solutions, and wettable-powder suspensions remained 100 percent effective for 1 year and xylene emulsions for 8 months. On wood surfaces carbon tetra- chloride solutions and wettable-powder suspensions were equally effec- tive for 1 year, but no formulation of chlorinated camphene was effective after the initial exposure. On cardboard surfaces carbon tetrachloride solutions remained 100 percent effective for 8 months and wettable- powder suspensions for 11 months. Xylene emulsions were ineffective after the initial exposure. On unfinished cement the residues from 5- chlorinated camphene sprays were ineffective after the initial exposure. Chlordane, gamma benzene hexachloride, TDE, and methoxychlor were effective only for much shorter periods, even on nonabsorbent surfaces (table 2). Chlordane and gamma benzene hexachloride de- posits are volatile. Of two types of chlordane tested, one remained effective much longer than the other, probably owing to its lower rate of volatilization. In general the effectiveness of residual sprays decreased with the increase in the absorptive property of the surface sprayed. However, the type of formulation also had a distinct relationship to the effec- tiveness of spray deposits on absorptive surfaces. The short duration of effectiveness of all spray deposits on unfinished cement surfaces may have been due to the highly absorptive nature of the cement, combined with the action of the free lime on the spray materials. More of the DDT was left on the surface of the cement, where it was available to kill insects coming in contact with the sprayed surface, by the water suspension than by the water solution or emulsion. On absorptive surfaces acetone-kerosene solutions and emulsions of the compounds of low volatility were much less efficient than the corresponding water suspensions of wettable powders. For immediate results the more volatile compounds, such as chlordane and gamma benzene hexachloride, were the most effective, since the fumigation effect of these spray deposits was about the same as the contact effect and persisted for about the same length of time. When wood surfaces are painted, the type of finish is likely to in- fluence the performance of the spray deposit. In studying the duration of effectiveness of DDT spray deposits recently painted wood surfaces were sprayed with xylene emulsion and wettable-powder formulations of DDT. On wood surfaces finished with cold-water paint or flat-oil paint, but not with enamel, the effectiveness of both emulsion and wet- table formulations of DDT was much less than on unpainted wooden surfaces. On an enamel finish the emulsion formulation was only slightly less effective than the wettable-powder formulation. In all tests the wettable-powder formulations were superior to the emulsion formulations. Use of Sealers on Cement Surfaces In an endeavor to improve the performance of residual spray de- posits on unfinished cement surfaces, several types of sealing mate- rials or plasticizers were used as preparatory treatments and in com- binations with DDT and chlordane sprays. Pretreatment with magnesium - zinc-silicofluoride greatly improved the performance of both sprays. Following this pretreatment excellent kills of the flour beetle were obtained, when the beetles were exposed to cement surfaces 3 months -6 after they were treated with either DDT or chlordane sprays. The addition of ammonium stearate to a DDT emulsion caused a temporary increase in toxicity, but aluminum stearate added to oil solutions of DDT did not increase its efficiency on cement surfaces. No improve- ment in the performance of chlordane sprays was obtained by the addi- tion of stearates. Effect of Mixing Residual Spray Materials Mixtures of DDT with chlordane and with gamma benzene hexa- chloride in various proportions were applied to wooden plates and tested against the confused flour beetle. The results failed to show any advantage as a result of combining the materials. Effect of Temperature and Light on Spray Deposits When residual spray deposits were being tested, it was noticed that the duration of their effectiveness was influenced by temperature. There- fore a series of experiments were set up, in which glass plates were sprayed with various materials dissolved in carbon tetrachloride. The plates were then stored in darkness at constant temperatures of 80° and 42° F. At six monthly intervals these glass plates were removed to the testing room, where adults of the confused flour beetle were con- fined on them for 1, 3, 6, and 24 hours. Storage in darkness at the higher temperature extended the period of 100 -percent effectiveness of chlordane, gamma benzene hexachloride, and TDE by 3 months, and that of methoxychlor by 5 months; at the lower temperature chlordane and gamma benzene hexachloride were still 100 percent effective after 5 months. Minimum Effective Dosages of DDT The excellent results obtained with the 10-mg. dosage of DDT led to an investigation of lower dosages of DDT in solution in acetone-kerosene and in carbon tetrachloride, and in water suspensions of a 50-percent wettable powder. Glass plates were sprayed with these formulations in dosages of 5, 2.5, and 1 mg. of DDT per 1/4 square foot. The effective- ness of the spray residues against flour beetles was determined over a period of 8 months after application. The 5-mg. dosage was 100 per- cent effective in all formulations for both 6- and 24-hour exposures, but smaller dosages did not hold up satisfactorily. A dosage of 5 mg. per 1/4 square foot is approximately equivalent to a spray containing 0.5 percent of DDT applied at the rate of 1 gallon per 1,000 square feet. - 7- Effect of Residual Sprays on Immature Stages of the Confused Flour Beetle Eggs and pupae of the confused flour beetle do not appear to be materially affected by exposure on surfaces that have been sprayed with residual sprays. Immature stages were exposed for 24 hours to deposits of DDT, chlordane, and gamma benzene hexachloride that had been applied to glass plates at the rate of 50 mg. per 1/4 square foot. Eggs hatched almost normally, the average percentage being 77 after exposure to DDT, 75 for chlordane, and 47 for gamma benzene hexa- chloride, as compared with 77 percent for the check. The fumigation effect of the gamma benzene hexachloride may have caused a slight reduction in viability of the eggs; however, no fumigation effect was noticeable with chlordane. Pupae similarly exposed on glass plates treated with DDT transformed normally. Larvae of the confused flour beetle are affected by exposure to the spray residues, although they are much more resistant than the adults. Data regarding the effectiveness of spray residues from carbon tetra- chloride solutions of DDT, chlordane, and chlorinated camphene on glass plates for 6- and 24-hour exposures are given in table 3. By comparison with table 1 it may be seen that heavier dosages were required to kill the larvae than the adults, and that a longer period was required for the residues to become effective. Effect of a Flour-Dust Coating on the Efficiency of Spray Residues The efficiency of a residual spray deposit is reduced when it be- comes coated with dust. Flour beetle adults were held for 1 week on wood surfaces that had been treated with DDT at the rate of 50 mg. per 1/4 square foot and covered with a 1/4 -inch layer of flour. At the end of that time 40 percent of the insects were still alive and active. Tests were also conducted with sprayed glass plates that were dusted lightly with flour. Confused flour beetle adults were exposed on these surfaces for 1, 6, and 24 hours. Deposits of 50-mg. dosages of DDT and chlor- dane from acetone-kerosene solutions failed to give a complete kill of the beetles at any of the three exposures. Spray deposits of DDT wet- table powder at the same rate gave a complete kill with the 24-hour exposure, but not with the 1- and 6 -hour exposures. Similar spray deposits on undusted glass plates gave complete kills with 1-hour ex- posure (table 1). The light coating of flour on the glass plates was removed by brush- ing lightly with a soft-bristle brush, and the efficiency of the spray residues against the flour beetle tested once again. The efficiency of the DDT wettable- powder deposits was apparently restored. However, some of the deposits of DDT and chlordane in acetone-kerosene solution -8- were apparently removed by the brushing, since 100 percent kill was not obtained at all exposures tried. Evidently sweeping sprayed sur- faces reduces the efficiency of the residual deposits by removing them mechanically. Influence of Emulsifiers and Wetting Agents In the tests described the various formulations were prepared in a uniform manner in order to avoid differences due to composition. A number of other tests, however, were made with formulations in which different emulsifying agents were used. In these tests the emulsions varied considerably in effectiveness. The wettable powders obtained from commercial sources differed noticeably in their physical char- acteristics. It seems likely that the effectiveness of these powders may be influenced by the diluent or the wetting agent used. The DDT wettable powder compared favorably with other formulations, whereas the wettable powders of other materials were not all so efficient as the corresponding emulsion formulations. Precautions ALL THESE RESIDUAL SPRAYS ARE POISONOUS TO WARM- BLOODED ANIMALS. Parathion is the most toxic, followed in descend- ing order by chlorinated camphene, gamma benzene hexachloride, DDT, chlordane, TDE, and methoxychlor. THE SPRAYS MUST NOT BE ALLOWED TO COME IN CONTACT WITH ANIMAL FEEDS OR HUMAN FOOD. In solution in organic sol- vents the insecticides are readily absorbed through the skin; therefore, extensive exposure of the skin to such solutions should be avoided by workmen applying them. Chlorinated camphene and gamma benzene hexachloride in powder form can also be absorbed through the skin; operators handling materials containing them should avoid continuous direct contact or wearing clothes impregnated with the dusts. Effect of Piperonyl Butoxide-Pyrethrum Formulations Interest in the possible use of spray materials less toxic to warm- blooded animals than the materials already discussed led to an investi- gation of the efficacy of pyrethrum, piperonyl butoxide, and various combinations of these materials as residual insecticides against the confused flour beetle. Piperonyl butoxide reportedly has a synergistic action on pyrethrum extract when mixed with it in insecticidal sprays. - 9- Sprays containing these materials were applied to glass, metal, and soft pine wood plates in the same manner as in the experiments with the other chemicals. The following emulsion- concentrates were formulated in refined kerosene oil to make 100 ml.: Grams 1. Pyrethrum extract containing 20 percent of pyrethrins -------------- 40 Emulsifier -------------- 12.5 2. Technical piperonyl butoxide ------ 10 Emulsifier -------------- 12.5 3. Pyrethrum extract containing 20 percent of pyrethrins -------------- 5 Technical piperonyl butoxide ------ io Emulsifier -------------- 12. 5 The emulsion concentrates were diluted with water to provide the concentration of spray residues desired. In tests with emulsions containing pyrethrins alone as the toxicant the residue from as little as 2 mg. of pyrethrins per 1/4 square foot gave a complete kill of confused flour beetle adults exposed for 24 hours on glass plates that had been allowed to dry for 24 hours before the beetles were confined on them. In similar tests with emulsions containing piperonyl butoxide alone a dosage of 200 mg. of the butoxide per 1/4 square foot of glass surface was required to give a 100 percent kill of the adults with a 24-hour exposure. When the third formula was used the addition of piperonyl butoxide to the pyrethrins in the propor- tion of 10 to 1 by weight slightly improved the residual insecticidal action of the pyrethrins The results of tests on metal surfaces were almost identical with those obtained on glass surfaces. On soft pine wood plates the residues from dosages of 40 mg. of pyrethrins alone and from 200 mg. of piperonyl butoxide alone failed to kill all the flour beetle adults that were confined on the plates for 24 hours beginning 24 hours after the sprays were applied. The addi- tion of piperonyl butoxide to the pyrethrins in the proportion of 10 to 1 by weight failed to improve the insecticidal action of the pyrethrins. - 10 Table 1.— Toxicity and speed of action of residual sprays against adult confused flour beetles. Deposits on glass plates from dosage of 50 mg. per 1/4 square foot. Percent mortality at various intervals after exposure Insecticide formulation l/2-hour exposure 1-hour exposure 2 4 6 8 10 12 2 4 6 8 10 12 days days days days days days days days days days days days Carbon tetrachloride s oluti ons: Chlordane 17 63 97 100 7 90 100 DDT 17 83 87 100 17 93 100 Gamma benzene hexachloride 20 100 13 100 TDE 0 47 67 83 83 83 0 70 100 Methoxychlor 0 0 0 0 0 7 0 17 17 23 30 30 Chlorinated camphent i 0 0 0 0 0 0 0 7 10 10 10 10 Xylene emulsions: Chlordane 0 67 100 0 90 100 DDT 0 87 100 0 100 Gamma benzene ♦ hexachloride 67 100 0 100 TDE Methoxychlor Chlorinated camphene 0 0 i o 50 53 83 93 70 97 97 70 100 97 80 100 87 0 0 0 67 60 83 90 80 100 100 90 93 100 Wettable-powder suspe nsions: Chlordane DDT Gamma benzene 0 0 0 33 3 90 3 97 3 100 3 0 0 0 40 3 97 10 100 17 17 hexachloride 0 63 90 93 100 0 60 100 TDE Methoxychlor Chlorinated camphene Parathion 0 0 j 0 100 0 0 0 0 0 3 3 27 10 3 33 10 3 33 10 0 0 0 100 0 0 0 20 50 27 27 53 37 27 67 37 33 67 37 Acetone-kerosene solutions ; Chlordane DDT Gamma benzene 0 0 0 40 10 83 27 87 40 90 53 100 0 0 0 47 17 77 20 90 30 93 40 93 hexachloride TDE Methoxychlor Chlorinated camphent 0 0 0 i 0 0 13 30 0 17 13 40 17 23 17 40 17 30 17 47 17 33 17 53 17 0 0 0 0 17 0 10 0 23 0 30 17 23 0 30 30 23 0 30 33 27 0 30 33 - 11 - Per cent mortality at various interval! 5 after exposure 3-hour exposure 6-hour exposure 24-hour exposure i/ 2 days 4 days 6 days 8 days 10 days 12 days 2 days 4 days 6 days 8 days 10 12 days days 2 days 4 days 6 days 8 days 17 37 77 100 97 100 0 100 0 47 100 0 63 67 0 7 10 0 100 0 100 70 100 0 63 100 0 77 87 0 100 0 0 57 77 0 37 100 0 100 0 0 0 0 0 33 100 33 67 73 40 77 73 40 33 97 100 93 100 13 100 3 93 100 73 77 80 0 80 100 10 10 10 10 53 63 67 73 0 100 67 100 70 100 0 87 100 63 100 60 100 93 93 100 90 90 0 20 63 80 47 100 0 100 50 53 0 50 83 83 0 10 73 73 0 0 100 57 90 63 60 93 67 93 60 93 73 53 100 77 100 80 100 90 100 70 100 73 57 100 67 100 80 100 100 80 100 100 83 100 97 7 87 93 100 47 100 90 100 60 40 100 97 7 97 97 100 87 53 97 100 100 47 73 63 27 3 0 67 100 97 100 70 40 10 33 73 40 13 40 0 67 87 100- 0 80 100 77 80 0 83 83 97 40 47 0 60 90 100 17 23 0 33 33 37 43 43 0 40 67 83 0 70 97 100 0 87 100 97 97 0 97 100 0 97 100 40 40 0 40 40 43 93 97 0 73 93 100 1/ The mortality caused by the acetone-kerosene solution of methoxychlor was 47 percent 10 days after the 24-hour exposure and 50 percent 12 days thereafter. 12- 0 T3 oJ CD •— 1 • ■<-> ■♦j 0) o CD o X «f-l £ CD u o a .—1 0 ««H tr TJ CO 0) en -\ 3 rH •s >H o CD O a +■» CO bi S SP o CD a] ■M ■— i rt O. 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Deposits of carbon tetrachloride solutions on glass plates. Period required for Insecticide and Dosage Exposure Maximum mortality maximum mortality Mg. per 1/4 sq. ft. Hours Percent Days DDT: 50 6 67 30 24 100 14 30 6 70 30 24 97 30 10 6 90 30 24 100 14 5 6 30 20 24 80 20 2.5 6 20 20 24 70 20 1 6 6 20 24 40 20 Chlordane: 50 6 90 30 24 100 18 30 6 ■ 77 30 24 100 18 10 6 57 30 24 97 30 Chlorinated camphene: 50 6 80 30 24 100 6 30 6 67 30 24 100 30 10 6 33 30 24 93 30 - 14- Summary Tests were made to determine the toxicity, speed of action, and dura- tion of effectiveness against the confused flour beetle (Tribolium confusum Duv.) of residual deposits from various formulations of DDT, chlordane, chlorinated camphene, TDE, methoxychlor, gamma benzene hexachlo- ride, parathion, piperonyl butoxide, and pyrethrum on various surfaces. Parathion was the most toxic and killed the fastest of any compound tested, although this material was tested only as a wettable -powder spray. DDT, gamma benzene hexachloride, and chlordane were next in order of toxicity when adult beetles were exposed to them for from 30 minutes to 24 hours. In general, the xylene emulsions were uniformly more efficient and more rapid in action than the corresponding sus- pensions or the carbon tetrachloride or acetone-kerosene solutions. The latter solutions were the least effective and slowest in rate of kill of all the formulations tested. DDT in all formulations and chlorinated camphene in suspensions and in carbon tetrachloride solutions remained effective on glass surfaces for more than a year. Chlordane, gamma benzene hexachloride, TDE, and methoxychlor remained effective for much shorter periods. The effectiveness of residual sprays decreased with the increase in the absorptiveness of the surface sprayed. Their effectiveness also varied with the chemical composition of the surface. On cement sur- faces the duration of effectiveness of all spray deposits was very short. Pretreatment of cement with a sealer, magnesium- zinc- silicofluoride, greatly improved the efficiency of spray deposits. On freshly painted wood surfaces the type of finish influenced the effectiveness of the spray deposit. Cold-water and flat oil paint greatly reduced the effectiveness of the spray deposits but enamel did not. Water suspensions of wettable powders were absorbed less than other formulations, so that on absorp- tive surfaces, such as cement and cardboard, and on painted wood sur- faces, they were more effective. Chlordane and gamma benzene hexachloride deposits are volatile and vapors given off killed the confused flour beetles. These fumiga- tion and contact effects were about equal and persisted for about the same length of time. Temperature and light affect the duration of effectiveness of residual spray deposits. Chlordane and gamma benzene hexachloride deposits retained their effectiveness longer when stored at low tem- peratures, and storage in darkness lengthened the period of effective- ness of chlordane, gamma benzene hexachloride, methoxychlor, and TDE. Five milligrams of DDT per 1/4 square foot was found to be the low- est effective dosage for use against confused flour beetle adults. - 15- Eggs and pupae of the confused flour beetle were not materially affected by exposure on surfaces bearing spray residues. Larvae were affected but were much more resistant than the adults. Heavier dosages were required to kill the larvae and a longer period was re- quired for the dosages to take effect. A coating of flour dust reduced the effectiveness of spray deposits and when flour was swept from surfaces a portion of the spray deposit was removed. Observations indicate that the emulsifying and wetting agents em- ployed in the manufacture of spray formulations may materially effect their efficiency. Residues from pyrethrum extracts were effective against flour beetle adults confined on glass and metal surfaces 24 hours after the sprays were applied, but were not effective on soft pine wood surfaces The efficiency of piperonyl butoxide residues against the confused flour beetle was very low, and the addition of piperonyl butoxide did not materially increase the toxicity of the pyrethrins to the beetles on glass or metal surfaces. This report is not intended as a recommendation of any particular material or formulation for commercial use. in