E-700 Auf.ust 1%6 United States Department of Agriculture Agricultural Research Administration Bureau of £ntoiaology and Plamt Quarantine LABORATORY STUDIES WITH DDT AGAINST THE MEXICAN FRUITFLvi/ By C. C. PlunBJser Diyiaion of Fruitfly Investigations In preliminary tests DDT dissolTad in acetone, vhen mixed with sugar and egg albumen disBolved in water, was less toxic than tartar eiaetic to adults of the Mexican f mi t fl y > ( Ana s t re pha ludene (Loew)) (2). Subsequent studies showed that the low toxicity reported was undoubtedly due to the masking of the DDT by the sugar and albmaen upon evaporation of the acetone and water. The studies described here show that other preparations containing DDT| especially dusts, are vexT^ toxic to adults of the Mexican fruitfly. Toxicity of Emulsions Containing DDT in Various Solvents Several emulsions containing DDT were prepared by dissolving tachnical DDT in soybean oil, com oil, fish oil, diethyl phthalate, dibutyl phthalate, or acetone. T^ese emaljsJLons contained either 1 or 2 pounds of DDT, 1 gallon of solvent, 20 pounds of granulated sugar, and 1 pound of soybean flour per 100 gallons. Itie soybean floxir was added as an emulBifler, A mixture of tartar emetic and sugar was included in each test for comparison. Five -mill 11 iter portions of each preparation were applied on 4-- by 6-inch pebble- surfaced glass plates and the water was allowed to evaporate. No other food was furnished to the flies. One plate was used in each cage in tests carried out at 25^ C, in the manner described by Flummer (1). The only e; ;eption to described procedures was that the experiment was started in the morning and observations on fly mortsLlity were made twice d*iily, at about 9 &.m. and again at about 6 p.m. The data are sumaariEed in table 1. TJ These studies were conducted as part of a cooperative project with the Secretarfa de Agricultura y Fomento, Uex. - 2 - Table 1,— Toxicity of •mulaiona of DDT in various solvente to adults of Anastrepha ludens at 25** C. (l lb, of DDT per gallon of sol- rent unless otherwise indicated, and 3 cages containing 50 flies each) • Tiae required SolTent Kill during first 10 hours to attain 50 percent mortality Maximun length of life Percent Hours Hours Soybean oil (2 lb. of DDT) 6.1 33 Soybeajt oil 16.0 33 120 Corn oil (refined) 22.7 33 177 Fish oil 1.5 58 i{ Diethyl phthalate 7.3 48 Dibutyl phthalate 14.7 33 192 Acetone (10 gal.) 2.0 48 168 Control (tartar eawtie 2 lb.) 0.7 33 106 1/ All except 3 flies died vithin 192 hours, and 1 of these vae allTs when tests were discontinued eUTter 336 hours' exposure to poison. These preliminary data show considerable rariation in the effec- tiveness of DDT in different solvents. The kill during the first 10 hours was definitely higher when DDT was dissolved in soybesun oil, com oily or dibutyl phthalate than when dissolved in fish oil, di- ethyl phthalate, or acetone. Two pounds of DDT in soybean oil was, for some unexplained x^ason, less toxic than 1 pound in the same oil. DDT dissolved in com oil killed all but two of the flies within 96 hours. One of these two succumbed within I30 hours and the other after 177 hours. Fish oil appeared to be repellent to the flies. Neither of the phthalates appeared to offer any particular advantage as solvents for DDT. Toxicity of DDT in Various Formulations In another experiment various formulations containing DDT were tested. In each treatment four cages containing 50 flies each were used. The flies were held at a temperature of 25** C. and a relative humidity of 40 to 50 percent. Standard methods as described by FluoHDer (l) were followed in this and subsequ^t experiments, the only departures being that the experiments were started at 6 a.m. instead of 6 p.m., and that 3 pieces of cut orange, changed frequent- ly, and 1 cube of sugar were kept in each cage^ A 4- by 6-inch - 3 - pebble-surfaced glass plate covered with a preparation containing 6 mg. of DDT was introduced into each cage. The emulsions were pipetted on to the glass plates, and the two dusts, i«e,, undiluted technical DDT (passed No, 200 sieve) and the DDT in pyrophyllite (passed No, 200 sieve), were spread on with a ^Q'inch flat artist's brush with shoz*t bristles. DDT dissolved completely in the amounts of ethyl alcohol ajid acetone used. A very fine precipitate of DDT was obtained by dissolving DDT in 95 percent ethyl alcohol and then adding water in the proportions indicated. DDT was dissolved in soybean oil, and this in turn was dissolved in acetone to facilitate spreading. A mixture of tartar emetic and sugar was also tested for comparison. All preparations were allowed to dry previous to testing. The data are summarized in table 2, Table 2«—-Uean length of life of adults of Anastrepha ludens exposed to DDT in various formulations applied on glass plates. Accessory material with 6 mg, of DDT Mean length of life!/ None (undiluted tech- nical DDT) Pyrophyllite dust 54- mg, (lO-percent DDT) Acetone to make 5 ml. Ethyl alcohol (95^) to make $ ml. Log-hours 1.499 1.405 1.233 1.159 Av. 1.3240 1.335 1.327 1,141 1,106 Av. 1.2273 1.805 1.959 1.930 1.876 Av. 1.8925 1.745 1.668 1.550 1.395 Av. 1.5895 Accessory material with 6 mg, of DDT Ifean length of life!/ Ethyl alcohol (95^) 0,6 ml. * water to aaike $ ml. Soybean oil 54 mg, acetone io make 2,5 ml. Lo£-hour8 2,0U 1.885 1.906 1.647 Av. 1.8623 1.505 1.741 1.238 1.363 Av, 1,4617 Control, no DDT (tar- 1.340 tar emetic 6 mg, 1,650 sugar 54 mg, + water 1,308 to make 5 ml.) 1,500 Av, 1,4495 1/ Difference required for significance at P. = 0,05 is 0,2235} at P'a 0.01, 0.3042. - 4 - These data show that the average mean length of life of flies Tiaa shortest when they were exposed to DDT in pyrophyllite and long- est when exposed to DDT dissolved in acetone. Flies exposed to undi- luted DDT powder did not live so long as flies exposed to DDT dis- solved in alcohol, and the differences between the two average means are significant. The differences between the lowest mean for undi- luted DDT and the highest mean for DDT in alcohol -water, as well as that for DDT dissolved in acetone, were highly significant, whereas the differences between the average meeui length of life of flies ex- posed to undiluted DDT and those exposed to DDT-pyrophyllite dust, DDT in soybean oil, or the tartar emetic and sugar preparation were not significant. Essentially similar results were obtained iriiether or not the data for tartar emetic were included in the analysis of variance. It should be emphasized, however, that in these tests DDT was much superior to tartar emetic because it was not mixed with sugar as was the tartar emetic. Previous laboratory studies (unpub- lished) have shown that fer flies die when exposed to tartar emetic and sugar in the presence of cut orange and cube sugar, whereas with DDT, as shown in these experiments, many die. Of the 200 flies exposed to each preparation shown in table 2, 1 fly exposed to DDT in soybecin oil and 4 flies exposed to the DD1V acetone formulation lived more than 1,000 hours while constantly exposed to these preparations. Similar observations have been re- corded in other experiments, where an occasioned fly has lived for extended periods even in the presence of 10 percent of DDT in pyro- phyllite. When it is considered that the plate covered with insecti- cide has a surface equal to only about 3«6 percent of the interior surface of a cage, it appears likely that some flies avoid contact with the plate. Appearance of DDT Deposits The surfaces of plates covered with preparations of DDT showed msirked differences, upon drying, i^en examined under a binocular microscope at a magnification of 21x. With DDT in acetone there were a few small agglomerations of particles, but most of the DDT was in the form of a finely breuiching network, much of it » near the edge of the plate. The deposit obtained with DDT in alcohol was much the same, except that large featherlike patches of DDT appeared at the edge of the plate. The precipitate formed when water was added to the DDT-alcohol solution consisted 'of very small particles enmeshed within a very fine network. Evidently all the DDT remained dissolved in the soybean oil as the mixture dried 9n- the plates. The tartar emetic appeared to be intimately K±>:ed with the sugar, and dried as flattened, colorless to slightly whitish iresses of irregularly shaped cryetale. The DDT-pyrophyllite dust and the un- diluted technical DDT showed inany relatively large particles on the plates. There vae a strong tendency for particles of these two dusts to "ball up.** The preparation containing DDT, xylene, and Triton X-100 (an aralkyl polyetber alcohol), irtiich is described later, upon 'drying on a pebble-surfaced glass plate, showed small, soft white lumps, presumably Triton X-100, in the spaces between the ele- vations of the glee 8, whereas fine needlelike lines, presumably DDT, were visible on the sides of the elevations. Contact Tests The concentration of DDT at the margine of some plates upon evaporatioti of organic solvents may have accounted for some of the differences in toxicity. An experiment was devised to check this, to eliminate possible repellency, and to obtain further data on the effect of certain solvents on the toxicity of DDT, With both wings held in forceps, a fly was dipped to touch the surface of a plate covered with dried DDT at 5 different places during a period of 5 seconds. Five flies of the same sex, chosen at random from the stock popiilation of 400 flies, were removed 1 at a time for this purpose, and the procedure was repeated with the opposite sex, A total of 25 flies of each sex were handled in this way with each treatment, and each treatment was repeated 4 times to make 4 blocks. The ages of the flies in block 1 were 90 to 113 days; in block 2, 65 to 81 daysj in block 3» ^2 to 106 daysj and in block 4, an un- known number of days. The $0 flies were then held at 25* C. in cages with food, end the dead and paralyzed flies were counted at the end of 24 hours. Once flies are paralyzed they do not recover, and for that reason they were counted with the dead flies. The data az*e summariEed in table 3. ^ 6 - Table 3« "-Toxicity of DDT to adults of Anastrepha ludens 24 hours after being brought in contact with preparations of DDT on glass plates for 5 seconds. Accessory material . with 6 mg, of DDT Block Flies dead or paralyzedi/ Ntunber Percent Angle Xylene 16.32 mg. + Triton X-100 1 20 40 39.2 1.68 mg. + water to make 1,20 ml, 2 3 6 14.2 I 13 26 30.7 4 5 10 ie.4 Av. 25.63 Ethyl alcohol (95^) 0.6 ml, + water to make 5 ml. Soybean oil 54 mg, + acetone to make 2,5 ml. Ethyl alcohol (95^) "to make 5 ml. Acetone to make 5 ml. Pyrophyllite dust 54 mg. Control (clean plate) 1 27 54 47.3 2 11 22 28,0 3 6 12 20.3 4 5 10 18,4 Av. 28. 5C 1 10 20 26.6 2 1 2 8.1 3 4 8 16,4 4 2 4 11.5 Av. 15.65 1 18 36 36.9 2 11 22 28,0 3 18 36 36.9 4 13 26 30.7 Av. 33.13 1 15 30 33.2 2 6 12 20.3 3 10 20 26o6 4 11 22 28.0 Av. 27.03 1 44 88 69.7 2 42 84 66.4 3 47 94 75.8 4 40 80 63.4 Av. 68,83 1 7 14 22.0 2 4 8 16,4 3 6 12 20,3 4 3 6 14.2 Av. 18.23 i/ Difference required for significance at P « 0.05 is 8.24, at P a 0.01, 11.29. These data clearly show the superiority of the DDT-pyrophyllite dust over the other preparations tested. Examination under a micro- scope has shown that this dust adheres to the numerouB short hairii on the legs, particularly the tarsi, of the Mexican fruitfly. Most of the dust, hovever, either is removed by the flies or falls off within a few hours. Analysis of variance of the angles of percentage of the number of dead and paralyzed flies (table 3) shows highly significant dif- ferences between blocks and also between treatments, Kie t test shows no significant difference between the average angle for the control and the DDT in soybean oil or for DDT aiixed with xylene and Triton X-100, When comxjarisons are made between the averages for DDT-xylene -Triton X-100 and for each of the other preparations, only the average for DDT in soybean oil is significantly lower and that for DDT in pyrophyllite hij^hly significantly higher. Hhe DDT-soybean oil gredually hardened durii:.g the time that it was held in the lab- oratory, and this laay have reduced its toxicity. The DDT-xylene- Triton X-100 had not hardened at the time tests were made. It is believed that preparations in which volatile solvents were used were not altered through storage at room temperature. Preparations on 3 of "^^^ plates mentioned in table 3— namely, DDT in pyrophyllite, in soybean oil, and in acetone — were further tested by forcing flies to walk on them for 10 seconds, 10 flies on each plate. All the flies were dead 21 hours after exposure to either DDT-pyrophyllite or DDT-soybean oil, whereas only 4 out of 10 flies were dead after exposure to DDT in acetone. Mode of Action of DDT The habit of rubbing the mouth parts with the legs is very pronounced with the Mexican fruitfly, and it is possible that DDT may kill only through the fly's ingestion of the insecticide. An experiment showed tiiat DDT can paralyze, and thus kill the flies by contact alone. The proboscises of several dozen flies were sealed by touching them with a small drop of collodion prepared commercially with ether and alcohol. Previous to inclusion in tests, each fly was examined \mder a microscope to make sure that the mouth parte were well sealed. Each of 10 males and 10 females was forced to walk on 10 percent DDT-pyrophyllite dust on a pebble- surfaced glass plate for 5 seconds. Within the first hour 9 males and 8 females and at the end of 5 hours 10 males and 9 femsJ.es were paralyzed, while all the flies in the control group remained normal. The next day, 24 hours after the start of the test, all 20 flies in the test cage and 7 males and 8 females in the control cage were dead. It is presiuned that the control flies died from thirst and starvation. - 8 - Toxicity of DDT-Pyrcphyllite Dusts Toxicity tests with DDT-pyrophyllite dusts were carried on by the method used in a previous test (p. 2). In test 1 two prepara- tions (samples 1 and 2), each containing 10 percent of DDT in pyro- phyllite, were used. Sample 1 was further diluted with pyropbyllite to obtain dusts containing 2, 4, 6, and 8 percent of DDT, Sample 2 (a coianercial dust) was tested only at the lOpercent strength. Ten percent of tarter emetic in pyrophyllite was included as a control. Fifty flies in each of four cages were exposed to each concentration. The average mean length of life was greatest when the flies were ex- posed to 2 percent of DDT in pyrophyllite and shori^est ^en exposed to 8 percent of DDT (fig. l). When t was used to test differences between the average mean length of life of flies exposed to sample 1 at all concentrations, it was found that only the difference be- tween the 10-percent and the 2-percent DDT was highly significant. The mortality of flies exposed to tartar emetic dust was very low} only about 25 percent succumbed during the first 200 hours, and approximately 11,5 percent remained alive 800 hours. In test 2 a 20-percent dust, obtained by pulverizing technical DDT in a hammer mill with a portion of the same sample of pyrophyl- lite used in the first test, was diluted to concentrations of 10 (sample 3)> 12, 14, l6, and 16 percent, and tested at all strengths. Sample 1 in test 1 was again included in this series. The average mean length of life of flies exposed to these concentrations is also shown in figure 1. According to the t test, none of the dif- ferences between the mean for sample 1 and each of the other means of the test are significant. Comparison of Various Diluents for DDT Dusts To determine whether DDT is more toxic in pyrophyllite than in some other diluent, several dusts were prepared with 10 percent of technical DDT in various diluents. Each diluent was first passed through a No. 325 sieve. The methods already described were fol- lowed, 60 mg. of duet being applied to a 4- by 6-inch glass plate and exposed in each of 4 cages containing 50 flies. The data are sunmarized in table 4. Analysis of variance shows no significant difference in the mean length of life of flies exposed to these V8.rioue dusts. - 9 - Table 4,— Mean length of life of adults of Anastrepha ludeps exposed to 10 percent of DDT in various dust diluent e and to undiluted technical DDT dust. Diluent Mean length of lift Diluent Mean length of life LoK-hours Log-hours None (undiluted tech- nical DDT) ' Av, 1.058 1.063 1.046 1.054 1.0553 Walnut-shell flour Av. 1.044 1.069 1.091 1.109 1.0833 Pyrophyllite Av. 1.091 1.300 1.178 1.100 1.1673 Diatoisaceous earth Av. 1.145 1.208 1.078 1.108 1.1347 Talc Av. 1.042 1.145 1.072 1.110 1.0923 Sulfur Av. 1.068 1.068 1.052 1.102 1.0725 Aluminum oxide Av. 1.235 1.232 1.058 0.957 1.1205 Most of the flies in these cages c&sae in contact with the in- eecticide and fell to the floor in a paralyzed condition withijt an hour or two. Many flies remained paralyzed for 12 hours or more previous to death. Mortality within the first 24 hours ranged froai about 50 percent of the flies exposed to 2-percent DDT dust up to 95 percent of those exposed to 20-percent DDT dust. Protection of Mangoes from Infestation Laboratory studies were made to determine the possibility of protecting mangoes froDi infestation by applying DDT as a duet and also in oil emulsions. For each treatment 4 standard toxicity cages were each stocked with 50 mature flies, 25 of each sex. At least - 10 two teats were made with efich tr'SHtment and the tests were run con- curr^jfitly, as follows: 1 and 2, 3 4, 5 and 6, and 7 and 8, The flies were allowed constant access to water, 3 small pieces of cut orangti, and 1 cube of sugar. Large green Manila mangoes were dipped in the oil emulsions, prepared with soybean flour as an eraulsifier, and allowed to dry overnight before they were introduced into the toxicity cages. Other mangoes were dusted lightly with a small hand duster. Controls were not treated. With each treatment, including the controls, there were 8 mangoes, 2 in each of 4- cages. They were held with the flies usually for 6 days. In tests 7 and 8 dead flies were replaced with living flies twice daily in order to maintain the fly population at its original number, and the stock supply was ex- hausted in 5 days. Fruit, upon removal from cages, was held over sand in suitable boxes until all insect material had matured or had left it. The data on infestation of treated fruit are saumarized in table 5» Table 5»"""I^tor^tory infestation of Manila mangoes by Anastrepha ludens when covered with dusts and emulsions containing DDT, Mangoes Preparation Test No. Mortality, t^^^^^+^a ^^'^ x«rva« of fliae±/ infested and puparia recovered Living larva© Emulsion, corn oil l%t With DDT (1 lb. per 100 gal.) Without DDT Control (no treatment) Emulsion, fish oil X%t With DDT (1 lb, per 100 gal. ) Without DDT Pyrophyllite dust* With 10^ of DDT Without DDT 1 2 1 2 1 2 3 4 3 4 3 4 3 4 Number 10 44 11 7 10 8 Number Number Control (no treatment) 3 4 13 49 (187) 8 41 (192) 118 62 (82) 12 29 (188) 14 25 (186) 2 , 2 2 3 8 8 6 3 5 2 1 2 2 5 3 6 Number 35 129 2/938 ^136 222 7 15 751 - 11 - Table $^-"^ontin\xei Mangoes Preparation Test Mortality i^feeted No, of fliesi/ Living larvae Not infested and puparia recovered Number Number Number Number DDT, undiluted, tech- nical grade 5 200 2 6 14 Pyrophyllit© duets With 10% of DDT 5 ✓ 188 8 With of DDT 5 6 159 154 1 2 7 ) 6 ) ^20 Without DDT 5 V 29 1 7 7 ) 1 ) 239 Control (no treatment) 5 6 24 32 8 8 ) ) ^546 DDTy undiluted, tech- nical grade n I 8 646 702 3 5 8 35 Pyrojhyllite duett With 10% of DDT 7 8 286 351 1 7 8 With 5% of DDT 7 8 126 199 4 1 4 7 53 9 Without DDT 7 8 7 10 7 1 1 7 221 6 Control (no treatment) 7 8 10 12 6 6 2 2 773 557 ^ 200 flies exposed to each preparation, except as indicated ethervise in parentheses. 2/ Evidently very slight infestation previoue to exposure of fniit to adults of Anaetrepha ludens, since 3 adults of Mexican A. aombinpraeo ptans (auct.) vere recovered. ~ ^ Previous infestation indicated, since 2 adults of Mexican A. Mombinpraeo ptans were recovered. ^ Previous infestation indicated, since 4 adults of Mexican A. Mombinpraeo ptans were recovered. - 12 - In tests 1 and 2 the cona-oil emulsion, both with and without DDT, markedly reduced the number of mangoes infested, as well as the number of larvae and puparia recovered. Few flies died during the first testj more, however, died during the second test, probably because of the prolonged exposure to DDT of the same population of flies, except for replaceiaents of flies that had died. Mangoes covered with corn'-oil emulsion remained green or changed to the typical yellow very slowly. The fish-oil emulsion, with and without DDT, also reduced the fly population to some extent, more in test 4 than in test 3, and again presumably owing to the continued exposure of the same popu- lation of flies in both tests. Neither preparation with fish oil appeared to protect the fruit so well as did the corn-oil emulsions , idien Judged by the number of laz*vae and puparia recovered from in- fested fruit. Previous tests (table l) had shown DDT to be more toxic in com oil than in fish oil when sugar was added to the prep- arations and lAien no other food was available, Ihen undiluted technical DDT was used, there was a marked re- duction in the number of mangoes infested, and in one test (test 8). the fruit was completely fi^ee of infestation. In this test an ef- fort was made to maintain the fly population at its original level. In the three tests with undiluted DDT (tests 5» 7i 8) 5 of the 24 mangoes were infested as compared with 20 in the control cages. A total of 49 larvae and puparia was recovered from fruits covered with undiluted technical DDT, while approximately 1,603 larvae and puparia came from fruits held in untreated cages. Ten percent of DDT in pyrophyllite was applied on a total of 40 B6uigoe8,and not more than 2 mangoes were found infested. In addi- tion to these, it appears that another mango (test 8) was infested in the field with larvae of Mexican Anastrepha mombinpraeoptans , A total of 27 larvae and puparia were recovered, and 7 of these were probably Mexican A. mombinpraeoptans . Larvae and puparia recovered from the 40 mangoes exposed to flies in untreated cages approximated 2,35^* Of the 32 mangoes treated with $ percent of DDT in pyrophyllite, 8 were observed to be infested, A total of 82 larvae and puparia were recovered from this fruit, whereas 1,876 larvae and puparia came from the untreated fruit (table 5). In 2 of the 4 tests the dead flies were not replaced twice daily with living flies. It ap- pears that 5 percent of DDT in pyrophyllite is not so effective as 10 percent of DDT in the same diluent. Infestation appears to have been reduced in mangoes covered with pyrophyllite alone. Of 48 mangoes dusted with this material, 18 were observed to be infested, as compared with 43 of the 48 fnxits held in untreated cages, A total of 48l larvae and puparia came from dusted fruit as compared with 2,627 larvae and puparia from untreated fruit. - 13 - Considering the data from laboratory ©xperimenta on the toxicity of gevoral concentrations of DDT in pyrophyllite, as well as data on the protection of mangoes from infestation, it would appear that 10 percent of DDT in pyrophyllite might be a satisfactory concentration to employ in preliminary field tests. Such a concentration was tested in the field under conditions at Cuemavacaj, Mexico, by ELunaner and Shaw, Their preliminary data (unpublished) show that it is not effectiTe in controlling the Mexican fruitfly, SuDBoary Preliminary tests showed that DDT omulsions containing soybean oil, com oil, or dibutyl phthalate as solvent were more toxic to adults of the Mexican fruitfly ( Anastrepha ludene (Loew)) at 25° 0, than similar emulsions prepared with fish oil, diethyl phthalate, or acetone. DDT in the first group of emulsions was also more toxic that), a tartar emetic-sugar solution. In testa with dried preparations on glass plates, and in the presence of sugar cmd cut orange, undiluted technical DDT and 10 percent DDT-pyrophyl} Ite dust were more toxic than DDT dissolved in alcohol f acetone, soybean oil, or a suspension of DDT in alcohol and w&ter>. Undiluted technical DDT in the presence of cut orange was yot jlgnif icantly more toxic than tartar emetic mixed with sugar, iShen indiyidual flies were forced to touch deposits of DDT from different feraruiations 5 tioaes h. 5 seconds and subsequently held for mortality records, it was found that 10 percent DDT-pyrophyllite dust was much more toxic than DDT dissolved in either acetone or al- cohol, or a suspension of DDT in alcohol and water. Differences in toxicity between DDT in xylene and Triton X-100, DDT in soybean oil, and an untreated check were not significant. However, in one small test DDT in soybean oil was shown to be as toxic as 10 percent DDT- pyrophyllite dust irtien flies were forced to walk on such prepara- tions for 10 seconds, and DDT that had been prepared with acetone was again shown to be less toxic. When 20 flies whose proboscises had been closed with collodion were exposed for 5 seconds to 10 percent DDT-pyrophyllite dust, 17 of the flies were paralyzed within the first hour and 19 flies within 5 hours. In a series of tests with pyrophyllite dusts containing from 2 to 10 percent of DDT, toxicity decreased at concentrations below 8 percent, although only the difference between 10 percent and 2 percent was significant. In another series of tests no significant difference was shown between the average mean length of life of flies exposed to 10 percent DDT dust and to dusts with 12, 14, l6, l8, and 20 percent. No signifloant difftrence in the arerage mean length of life was shown betveen Uaxican froitfllee exposed to undiluted technical DDT and those exposed to 10 percent of DDT in pyrophyllite , tale, alufflinuffl oxide, iralnut -shell flour, diatomaceous earth, or sulfur. Mangoes were dipped in DDT emulsions containing com oil and fish oil, hut the results vers not promising. Dusting vith undi" luted technical DDT and 10 percent of DDT in pyrophyllite protected other mangoes to a marked degree, and the 5 percent DDT-pyrophyllite was a little less ef fee tiro . LIT2SRATURB CITSD (1) Fluansr, C. C. 1943* Tests against the Mexican fruitfly. In Laboratory procedures in studies of the chemical control of insects, edited by 7* L. Campbell and 7* R, Moulton, Aner* Assoc, Adv. Sci*, Pub, 20( 107-111, Washington, D. C, (2) 1944. DDT and the Mexican fruitfly. (Scientific Note) Jour. Scon, Snt. 371 158. q: 26 24 O 22 * UJ a: UJ o 20 (8 16 u 14 12 Test I A- Sample 1 □ - Sample 2 Test 2 o -Sample I + -Sample 3 ± 2 4 6 8 10 12 14 16 IB 20 PERCENTAGE OF DDT IN PYROPHYLLITE Figure 1,— Toxicity of DDT-pyrophyllite dusts to adults of Anastropha Ittdona in the presence of sugar and cut orange at 25« C. Data recorded within 2- to 10-percent range represent test Ij within 10- to 20-percent range test 2.