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E-548 STTATE PLANT ^^^^ ^.^^^^^^^ September 1941 
 
 < U.S. ^ 
 
 or 
 AGRICULTURE 
 
 BUREAU OF 
 ENTOMOLOGY AHO 
 PLANT QUARANTINE 
 
 PHTHALONITRILE AS AN INSECTICIDE 
 
 By M C. Swingle. J. B. Gahan , and A. M. Phillips 
 Division of Control Investigations 
 
 For several years the Division of Control Investigations of the 
 Bureau of Entomology and Plant Quarantine has maintained a laboratory at 
 Sanford, Fla. . for studying the insecticidal action of synthetic organic 
 compounds and other samples supplied chiefly by the Division of Insecticide 
 Investigations of this Bureau. The purpose of these investigations is the 
 development of new insecticidal materials which may be either more economical 
 or more effective than present commercial insecticides which are limited in 
 number and effectiveness. Although the results of laboratory tests should 
 not be used as a basis of practical control recommendations until tests have 
 been made in the field, they give some indication of the results that may 
 be expected in the field. The results obtained on promising compounds 
 will be published from time to time to invite further testing by those 
 engaged in specific field problems. 
 
 One of the most promising of the organic compounds tested was phthalo- 
 nitrile, and it was later patented by M. S. Schechter and H. L.J. Haller, of 
 the Division of Insecticide Investigations (3) . Phthalonitrile, or ortho- 
 dicyanobenzene {CeH4(CN)2), is an organic compound used commercially in the 
 preparation of a new class of blue and green pigments, the phthalocyanines 
 (1). It is a colorless, crystalline solid, insoluble in water but soluble 
 in most organic solvents. 
 
 Testing of the compound followed a definite system recently described 
 by the authors (5) . These tests were designed to give preliminary evidence 
 of toxicity, and then to show in more detail the mode of toxic action, the 
 amount of dust or concentration of spray required for satisfactory control 
 of various insects, and the utility of the compound as a spray on tender 
 foliage. 
 
2 - 
 
 Insects Tested 
 
 Nearly full grown larvae were generally used in the tests, because 
 they are more resistant to insecticides and therefore gave a better index 
 to the toxic value. All larvae were reared in the laboratory by methods 
 previously described (4) . The various species used and the plants on which 
 they were tested are as follows: 
 
 Insect Foliage 
 
 Colorado potato beetle (L eptinotars a decemlineata (Say)) Potato 
 
 Diamondback moth ( Plutell a maculipennis (Curt.)) Collards 
 
 Greenhouse leaf tier ( Phlycta e nia rubigalis (Guen.)) Do. 
 
 Hawaiian beet webworm (Hymenia fascialis (Cram.)) Swiss chard and beet 
 
 Imported cabbage worm (Pieris rapae L. ) Collards 
 
 Kelonworm (Diaphania hyalinata (L.)) Pumpkin and squash 
 
 Southern armyworra (Prode nia eridania (Cram.)) Collards 
 
 Southern beet webworm (Pachy zancla biounctalis (F.)) Swiss chard and beet 
 
 Yellow woolly bear ( Diacrisia virginica (F.)) Collards 
 
 Preliminary Petri-Dish Tests 
 
 The preliminary tests were made by feeding insects foliage that had 
 been rather heavily dusted with the pure compound. The dust was applied in 
 the dusting chamber previously described (5). The insects were confined with 
 the dusted foliage in Petri dishes, which were held at room temperature for 
 48 hours and then examined for insect mortality and quantity of foliage con- 
 sumed. From 25 to 30 insects were used in each test. Because the Petri 
 dishes were closed and the larvae were able to crawl over the dusted leaves 
 mortality might result from fumigation, contact, or feeding. 
 
 Paralleling these tests were tests of the standard insecticide used for 
 controlling each species. 
 
 Phthalonitrile was found to be very tcxic to all nine species of insects 
 (table 1), in this respect being equal to or better than the standard insecti- 
 cides. The results indicate that a deposit of 40 micrograms per square centi- 
 meter would probably give satisfactory control of most species under the condi- 
 tions of these tests. The data presented for the Colorado potato beetle the 
 diamondback moth, the greenhouse leaf tier, and the yellow woolly bear are 
 fragmentary, because these insects were not reared over a period sufficient for 
 completion of the tests. Very light deposits were effective on the Hawaiian 
 beet webworm, the melonworm, the southern beet webworm. and the southern army- 
 worm. The imported cabbage worm appeared to be the most resistant, but even 
 here the lightest deposit gave 40 percent mortality. 
 
E-548 x^,-i:i^^^^^i==if^ • September 1941 
 
 PHTHALONITRILE AS AN INSECTICIDE 
 
 By M C. Swingle. J. B. Gahan, and A. M. Phillips. 
 Division of Control Investigations 
 
 For several years the Division of Control Investigations of the 
 Bureau of Entomology and Plant Quarantine has maintained a laboratory at 
 Sanfnrd, Fla . , for studying the insecticidal action of synthetic organic 
 compounds and other samples supplied chiefly by the Division of Insecticide 
 Investigations of this Bureau. The purpose of these investigations is the 
 development of new insecticidal materials which may be either more economical 
 or more effective than present commercial insecticides which are limited in 
 number and effectiveness. Although the results of laboratory tests should 
 not be used as a basis of practical control recommendations until tests have 
 been made in the field, they give some indication of the results that may 
 be expected in the field. The results obtained on promising compounds 
 will be published from time to time to invite further testing by those 
 engaged in specific field problems. 
 
 One of the most promising of the organic compounds tested was phthalo- 
 nitrile, and it was later patented by M. S. Schechter and H. L. J. Haller, of 
 the Division of Insecticide Investigations (3). Phthalonitrile, or ortho- 
 dicyanobenzene (C6H4(CN)2), is an organic compound used commercially in the 
 preparation of a new class of blue and green pigments, the phthalocyanines 
 (1). It is a colorless, crystalline solid, insoluble in water but soluble 
 in most organic solvents. 
 
 Testing of the compound followed a definite system recently described 
 by the authors (5). These tests were designed to give preliminary evidence 
 of toxicity, and then to show in more detail the mode of toxic action, the 
 amount of dust or concentration of spray required for satisfactory control 
 of various insects, and the utility of the compound as a spray on tender 
 foliage. 
 
- 2 
 
 Insects Tested 
 
 Nearly full grown larvae were generally used in the tests, because 
 they are more resistant to insecticides and therefore gave a better index 
 to the toxic value. All larvae were reared in the laboratory by methods 
 previously described (4) . The various species used and the plants on which 
 they were tested are as follows* 
 
 Insect 
 
 Foliage 
 
 Colorado potato beetle (L eptinotars a d ecemlineata (Say)) Potato 
 
 Diaraondback moth ( Plute lla maculip ennis (Curt.)) 
 Greenhouse leaf tier (P hlycta enia rub.i galis (Guen.)) 
 Hawaiian beet webworm (Hy menia fascialis (Cram.)) 
 Imported cabbage worm (Pie ris rapae L.) 
 Melonworm ( Diaphania hy alina ta (L.)) 
 Southern armyworm (Prode nia er idania (Cram.)) 
 Southern beet webworm (Pachyzanola b ipunctalis (F.)) 
 Yellow woolly bear ( Diacrisia v irginica (F.)) 
 
 Collards 
 
 Do. 
 Swiss chard and beet 
 Collards 
 
 Pumpkin and squash 
 Collards 
 
 Swiss chard and beet 
 Collards 
 
 Preliminary Petri-Dish Tests 
 
 The preliminary tests were made by feeding insects foliage that had 
 been rather heavily dusted with the pure compound. The dust was applied in 
 the dusting chamber previously described (5) . The insects were confined with 
 the dusted foliage in Petri dishes, which were held at room temperature for 
 48 hours and then examined for insect mortality and quantity of foliage con- 
 sumed. From 25 to 30 insects were used in each test. Because the Petri 
 dishes were closed and the larvae were able to crawl over the dusted leaves, 
 mortality might result from fumigation, contact, or feeding. 
 
 Paralleling these tests were tests of the standard insecticide used for 
 controlling each species. 
 
 Phthalonitrile was found to be very toxic to all nine species of insects 
 (table 1), in this respect being equal to or better than the standard insecti- 
 cides. The results indicate that a deposit of 40 micrograms per square centi- 
 meter would probably give satisfactory control of most species under the condi- 
 tions of these tests. The data presented for the Colorado potato beetle, the 
 diaraondback moth, the greenhouse leaf tier, and the yellow woolly bear are 
 fragmentary, because these insects were not reared over a period sufficient for 
 completion of the tests. Very light deposits were effective on the Hawaiian 
 beet webworm, the melonworm, the southern beet webworm, and the southern army- 
 worm. The imported cabbage worm appeared to be the most resistant, but even 
 here the lightest deposit gave 40 percent mortality. 
 
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 Fumigation Tests in Petri Dishes 
 
 Although no odor could be detected from the compound, fumigation 
 tests were made to check the possibility of fumigation having occurred in 
 the Petri-dish tests. Unmeasured quantities of the dust were placed in the 
 lids of Petri dishes in such a way that only the vapor could permeate the 
 dish and come in contact with the larvae, which were confined with untreated 
 foliage. The dishes were held for 48 hours at room temperature as in the 
 previous tests. As no significant mortality occurred in tests with larvae 
 of the melonworm, the southern beet webworra, and the Hawaiian beet webworm, 
 it was concluded that no fumigating action occurred in the tests reported 
 in table 1. but that the mortality was due to contact or stcmach-poison 
 action. 
 
 Screen-Cage Tests 
 
 With the toxicity of phthalonitrile established by the preliminary 
 tests, a study was made of the effectiveness of spray deposits on potted 
 plants in cylindrical screen cages. For this purpose the compound was made 
 up as a spray at concentrations of 8, 4, 2, and 1 pound per 100 gallons 
 of water and each spray applied to two plants with a compressed-air spray 
 gun. When the plants were dry, 15 larvae were confined on each plant by a 
 cylindrical screen cage. The cages were examined at 2-day intervals for 
 larval mortality and the feeding on the plants. 
 
 The method by which a spray suspension is made may determine its ef- 
 fectiveness as an insecticide. A spray suspension that can be applied with 
 little run-off is essential for comparing various concentrations of spray. 
 Obviously, if run-off is not prevented, an 8-100 spray may be no more effec- 
 tive than a 2-100 spray properly made and applied. Suitable methods of 
 preparation will vary with the insecticidal compound, the water used, and 
 the foliage on which the spray is to be applied. Since some of the first 
 sprays made up gave low toxicity as compared with the preliminary tests, 
 several dispersing and wetting agents were tried to increase the effec- 
 tiveness of the phthalonitrile. 
 
 Of the various wetting agents tried, t.he most satisfactory was 
 found to be saponin. The weighed portion of phthalonitrile was dissolved 
 in 5 cc. of acetone and slowly poured, with agitation, into 95 cc. of water 
 containing 0.12 percent (by weight) of saponin (equivalent to 1/8 pound of 
 saponin per 100 gallons of water) . The phthalonitrile was recrystallized 
 in the form of fine white needles, which remained well in suspension. 
 This spray could be applied heavily to collards without run-off, but it was 
 not ideal for pumpkin and squash, which wet more readily. 
 
 A satisfactory spray was also made with bentonite, although with 
 more difficulty owing to its sticky nature when wet. Best results were 
 obtained by first wetting the bentonite with alcohol or acetone and then 
 diluting gradually with the full amount of water. With the bentonite in 
 suspension, an acetone solution of phthalonitrile was added with constant 
 
 UBRARY 
 STATE PLANT BOARD 
 
- 6 - 
 
 agitation. The bentonite was always used at a 1-percent concentration in 
 water. This spray was not always satisfactory on collards, but it worked 
 well on pumpkin foliage. 
 
 Fairly good results were also obtained with calcium caseinate, 
 sodium monosulfonate of monobutyldiphenyl, and saponin alone without ace- 
 tone. Each was ground to a thin paste with the insecticide and a little 
 water and then gradually diluted with water to the desired concentration. 
 Fish-oil soap and sodium oleyl sulfate made inferior suspensions, and some 
 other wetting agents were entirely unsatisfactory. 
 
 Spray suspensions were tested against five species of insects (table 
 2) . Phthalonitrile was effective on all species at a concentration as low 
 as 4 pounds per 100 gallons. The melonworm was most susceptible, ccmplete 
 control resulting from a 2-100 spraj''. Fair results were obtained v/ith this 
 spray on the southern and Hawaiian beet webworms, but not on the imported 
 cabbage worm or the southern armyworm. 
 
 In general, phthalonitrile does not appear to be so effective as 
 the standard insecticides when tested as a spray deposit. Actually the 
 material is as effective at the higher concentrations, but it appears to 
 become less effective with dilution. Since the compound is slowly volatile, 
 it apparently cannot long maintain a lethal deposit when applied in such 
 low concentrations. 
 
 Plant-Tolerance Tests 
 
 Early in this work an experiment was conducted to determine the 
 tolerance of tender truck-crop plants to spray deposits of phthalonitrile. 
 The spray was made at a concentration of 8 pounds of phthalonitrile and 
 8 pounds of bentonite per 100 gallons of water, as described under the 
 cage tests. Small field plots containing from 4 to 20 plants each were 
 sprayed with a hand sprayer and examined at intervals for symptoms of 
 injury. The plants included bean, collards, squash, potato, tomato, beet, 
 and Swiss chard. Weather conditions during the period were fair with no 
 rainfall. 
 
 For 12 days after the spray was applied the treated plants appeared 
 to be unaffected. A second application was then made, and the plots were 
 observed over an additional 12-day period. Since no visible differences 
 could be found between the sprayed and unsprayed check plots, it was con- 
 cluded that, under certain conditions at least, phthalonitrile may be 
 safely applied to foliage. 
 
 Field-Laboratory Tests 
 
 The effect of exposure or weathering on spray deposits of phthalo- 
 nitr.i.le was then studied by means of tests combining field and laboratory 
 technique. An 8-8-100 spray with bentonite was applied with a knapsack 
 sprayer to a field plot containing 10 to 12 plants. Collard plants were 
 
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 used in tests against the southern armyworm and pumpkin plants against the 
 melonworm. Other plots were sprayed with lead arsenate or derris, plus 
 bentonite, and others with bentonite alone. V^hen thoroughly dry, 3 plants 
 in each plot were infested with nearly full grown larvae (10 per plant), 
 which were confined by screen cages. At the same time samples of 6 leaves 
 were taken at random from the remaining plants in each plot to be fed to 
 larvae (5 per leaf) in Petri dishes in the laboratory. Similar samples 
 of leaves were taken from the plants at 2-day intervals thereafter for 10 
 days and fed to larvae in the laboratory. Observations for insect mortality 
 were made 2 and 4 days after the leaf samples were infested, and the amount 
 of feeding was observed after 4 days (table 3). 
 
 In the field-cage tests against the melonworm phthalonitrile was 
 more effective than derris, the results being almost identical with those 
 for the same spray in table 2, except that the derris was slightly less 
 effective. Against the southern armyworm phthalonitrile was only slightly 
 less effective than lead arsenate, the mortality being in general slightly 
 lower than in table 2. Although these tests are similar to the laboratory 
 screen-cage tests, the plants were more exposed to heavy dew and sunshine, 
 two important factors in weathering. 
 
 The field-laboratory tests of leaf samples revealed a character- 
 istic of phthalonitrile that was not apparent in any of the other tests. 
 In the tests on the southern armyworm 48 hours of weathering greatly reduced 
 the toxicity of the deposit, and after 96 hours it was practically non- 
 toxic. Against the melonworm the deposit was effective about 48 hours 
 longer than against the southern armyworm. The results indicate that 
 deposits of phthalonitrile may remain toxic only 3 to 5 days after applica- 
 tion. Derris and lead arsenate deposits remained effective for 10 days. 
 The increased mortality with lead arsenate after 8 and 10 days is not con- 
 sidered significant. A greater number of samples might show less variation. 
 
 Volatility appeared to be a likely cause of the loss in effectiveness 
 of the phthalonitrile, because no extreme change in temperature or rainfall 
 had occurred during the test period. To check on this possibility, glass 
 slides were coated with the spray and exposed to the air in the laboratory. 
 Examination under the microscope at daily intervals showed that the deposit 
 gradually decreased, until on the fourth or fifth day it had disappeared. 
 The period of volatilization would undoubtedly vary with the weight of the 
 deposit and possibly with the wetting and emulsifying agents used. 
 
 Tests on Termites 
 
 Phthalonitrile was also tested as a soil treatment for the control 
 of termites (Re ticuli te rme s sp.). The method described by Hockenyos (2) 
 was used. A weighed quantity of the insecticide, according to the concen- 
 tration desired, and 40 grams of sanc'y soil were ground in a mortar until 
 thoroughly mixed and then poured into a 150-cc. beaker containing about 
 12 CO. of water and a little tissue paper. After the dry soil had absorbed 
 the water, 30 adults or large nymphs of the worker caste were placed in the 
 beaker, which was held for 3 days in a cabinet at approximately 80° F. 
 
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11 
 
 All concentrations down to 1 part in 3,000 parts "of soil by v/eight 
 killed all the termites within 24 to 48 hours. They were not repelled by 
 the insecticide, for they penetrated the soil to the usual depth. At con- 
 centrations of 1-4,000 and 1-5,000 approximately 93 percent of the termites 
 were killed in 3 days; at 1-10,000 only 12 percent were killed in 5 days. 
 Orthodichlorobenzene, a material often used in the control of termites, at 
 a concentration of 1-1,000 repelled them, preventing penetration of the 
 soil, but caused no mortality within 4 days. 
 
 Summary 
 
 Phthalonitrile, or orthodicyanobenzene, was tested on nine species 
 of leaf-eating insects in comparison with standard insecticides against 
 the respective species. When used in preliminary tests as a dust on foliage, 
 this material was in general superior to the standard insecticide with which 
 it was compared. Fumigation tests with phthalonitrile in closed Petri 
 dishes gave no mortality, showing the compound to be either a stomach or a 
 contact poison. 
 
 Sprays made up with various wetting and dispersing agents showed 
 considerable variation in effectiveness. The most satisfactory spray used on 
 cruciferous plants was made by dissolving the phthalonitrile in acetone and 
 adding the solution to water containing saponin. 
 
 In cage tests with various concentrations of spray, phthalonitrile 
 was effective when used at 2 pounds per 100 gallons. At very dilute con- 
 centrations phthalonitrile was not so effective as the standard insec- 
 ticides . 
 
 Small field plots of collard and pumpkin plants were sprayed with an 
 8-8-100 concentration of phthalonitrile with bentonite, and leaf samples 
 taken from the plots every 2 days were fed to insects in the laboratory. 
 The leaves were toxic to larvae for the first 96 hours after spraying, but 
 were almost nontoxic thereafter. 
 
 An 8-100 concentration of spray applied to several varieties of 
 truck-crop plants caused no injury within a 24-day period of observation. 
 
 Phthalonitrile was effective against termites when applied as a soil 
 treatment at a concentration of 1-3,000. 
 
 Literature Cited 
 
 (1) Dahlen, Miles A. 
 
 1939. The phthalocyanines . A new class of synthetic pigments 
 and dyes. Indus, and Engin. Chem. 31: 839-847, illus. 
 
 (2) Hockenyos, 0. L. 
 
 1939. Laboratory evaluation of soil poisons used in termite 
 control. Jour. Econ. Ent. 32: 147-149. 
 
12 
 
 3 1262 69230 4020 
 
 (3) Schechter, M. S., and Haller, H. L. J 
 
 1940. Phthalonitrile a new insecticide. U.S. Patent 2,200,564, 
 
 issued May 14. 
 
 (4) Swingle, M. C, Gahan, J. B., and Phillips, A. M. 
 
 1941. Laboratory rearing of certain leaf-eating insects. Jour. 
 
 Econ. Ent. 34: 90-95, illus. 
 
 (5) . Phillips, A. M., and Gahan, J. B. 
 
 1941. Laboratory testing of natural and synthetic organic 
 
 substances as insecticides. Jour. Econ. Ent. 34: 
 95-99, illus.