Alkali-Stable Polychloro Organic Insect Toxicants ... - ACS Publications

Alkali-Stable Polychloro Organic Insect Toxicants, Aldrin and Dieldrin REX E. LIDOV, HENRY BLUESTONE, and S. BARNEY SOLOWAY, Julius Hyman & Company,

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Denver, Colo., and CLYDE W. KEARNS, University of Illinois, Urbana, III.

The chemistry and general properties of two new alkali-stable insect toxicants, aldrin and dieldrin, are discussed, and the general properties of these materials are given. Entomological data serving to illustrate the magnitude of the insect toxicity of these compounds are included. Aldrin is an alkali-stable, relatively nonresidual insect toxicant with activity equal to or greater than the activity of γ-hexachlorocyclohexane. Dieldrin is an alkali-stable in sect toxicant with high activity and high persistence. Its period of residual activity is equal to or greater than that of DDT. In general, its activity level is somewhat higher than that of aldrin.

W i t h the advent of D D T it became possible to think in terms of the eradication of insect pests instead of their control only. Although very lethal organic toxicants such as the pyrethrins and rotenone had been previously employed, their instability under normal conditions of use limited their utility. D D T is only the first of a new group of toxicants, members of which were discovered or invented independently almost simultaneously i n various parts of the world. Of these, the group of halogenated hydrocarbons, which includes D D T , toxaphene, 7-hexachlorocyclohexane, and chlordan, is the best known. Although some members of the group possess undesirable properties which severely limit their practical importance, others, like chlordan, are many times more toxic than D D T toward many insect species and possess no disadvantage not common also to D D T and other members of the group. U n t i l now, however, no compound has been available which combined high potency with the long period residual activity characteristic of D D T . One of the greatest practical disadvantages possessed b y the hitherto commonly used halogenated hydrocarbon insect toxicants has been the extreme ease with which they are dehydrohalogenated b y alkaline reagents and b y many metal halides. This of itself is serious, but even more serious is the fact that simultaneously these compounds lose all or almost all of their insecticidal activity. I n fact, so marked is this reaction pattern that some investigators have attempted to devise theories of insecticidal activity based on the ability of these compounds to lose hydrogen chloride and to correlate the degree of activ ity with the ease, under various experimental conditions, with which dehydrohalogenation could be induced.

Chemical and Physical Properties During the past 30 months two new compounds, aldrin and dieldrin, possessing great usefulness as insect toxicants, have been devised, synthesized, and studied i n the laboratories of Julius H y m a n & Company. B o t h compounds are completely impervious 175

176

ADVANCES IN CHEMISTRY SERIES


to the action of alkaline reagents, i n either aqueous or alcoholic media. Under conditions of practical use they likewise appear unaffected by acidic reagents. Despite this fact, they possess insecticidal activity equal to or greater than that of the best halogenated insect toxicants known or used. A t the time of original presentation of this paper Compounds 118 and 497 had not yet been named. Since then the Interdepartmental Committee on Pest Control of the U . S. Department of Agriculture has adopted the names aldrin and dieldrin, respectively, for (a) " a n insecticidal product having not less than 9 5 % of its principal constituent, the chemical 1,2,3,4,10,10 - hexachloro - l,4,4a,5,8,8a - hexahydro -1,4,5,8 - dimethanonaphthalene. . ." and (6) " a n insecticidal product having not less than 8 5 % of its principal constituent, the chemical 1,2,3,4,10,10-hexachloro-6,7-epoxy-l,4,4a,5,6,7,8,8a-octahydro-l,4,5,8-dimethanonaphthalene. . ." " A l d r i n (recrystailized)" and "dieldrin (recrystallized)" are defined to refer to products containing not less than 9 9 % of the above-named chemicals. Because continued use of the names 118 and 497 can only lead to confusion, the names aldrin and dieldrin have been adopted for use i n the nonentomological portions of this paper to refer to the pure chemical compounds, with the recognition that such usage does not exactly correspond with that officially adopted. Chemically, aldrin is 1,2,3,4,10,10-hexachloro-l,4,4a,5,8,8a-hexahydro-l,4,5,8-dimethanonaphthalene and possesses, in planar representation, the structure :

The planar representation shown serves, i n part, to obscure somewhat the complexity of the structural problem involved. Actually, four stereoisomers are represented by the simple planar representation shown; it is not yet known with certainty which is the one corresponding to aldrin. Physically pure aldrin is a white crystalline solid with the properties set forth in Table I. Table I.

Physical Properties of Aldrin

Melting point. 104-104.5° C. Odor. Substantially odorless at room temperature. pinelike odor when warm Solvent

Mild

Solubility of Aldrin at 30° C , Grams/100 M l .

Methanol Acetone Benzene Hexane Base oil (deobase) Water

9 159 350 98 89 Insoluble

A l d r i n exhibits i n many instances the chemical behavior expected on the basis of its structure. Thus, it is readily attacked by halogens to yield the expected halides.

Aldrin +

X

2

Cl

H

IIDOV et al.—ALDRIN AND DIELDRIN

177

Chlorine adds to form the frans-dichloride; bromine adds, i n carbon tetrachloride solution, to give a mixture of a s - and £rans-dibromides ; this addition can be directed wholly to the trans derivative b y conducting the bromination i n a mixed phase reaction i n aqueous suspension. The double bond i n the unchlorinated ring, i n the presence of acidic catalysts, adds a variety of reagents of the type H Y , illustrated i n Table I I . Table II.

Reaction of Aldrin with Reagents HY Cl

H Y


H

Aldrin + H Y

(

H

+

)

>

Product

Halide ion Ο

Halide

R—C ν\

Ester

RO—

0—

Ether

M a n y other additions, similar i n type, are possible. Although acidic reagents can bring about alterations i n aldrin, such reactions proceed only i n the presence of strong acids or strongly acidic catalysts i n the homogeneous phase and hence are without signifi cance for the conditions under which insecticides are normally utilized. Because aldrin contains the bicyclo-(2.2.1)-heptene ring structure, it reacts typically with phenyl azide to form a phenyldihydrotriazole derivative. This reaction is of impor tance i n that it provides the basis for an analytical method for determining aldrin (dis cussed more fully in 2). The double bond i n the unhalogenated ring is readily attacked b y oxidizing agents. Chromic acid i n acetic acid, and potassium permanganate i n alkaline solution, oxidize the compound to the expected dicarboxylic acid, 4,5,6,7,8,8-hexachloro-3a,4,7,7a-tetrahydro1,3-dicarboxy-4,7-methanoindane. CI

Aldrin + K M n O , CI

H

/ \ COOH

Potassium permanganate i n neutral solution and lead tetracetate give rise, respec tively, to the anticipated glycol and to its diacetate. B y far the most interesting oxidation of aldrin, at least from the present viewpoint, is the oxidation with per acids. This oxidative process, which occurs normally, produces 6,7-epoxy-6,7-dihydroaldrin, the compound now called dieldrin. Dieldrin is then 1,2,3,4,10,10-hexachloro-6,7-epoxy-l,4,4a,5,6,7,8,8a-octahydro-l,4,5,8-dimethanonaphthalene :

Dieldrin, which, when pure, is a white crystalline solid, possesses the physical prop erties shown i n Table I I I .


178

Table III.

Physical Properties of Dieldrin

Melting point.

175-176° C.

Solvent Methanol Acetone Benzene Hexane Base Oil (Std. oil 10) Water


Odor.

Odorless

Solubility of Dieldrin, Grams/100 Grams 26° C. 0° C. 4.9 54.0 75.0 7.7 4.3

3.4 35.4 36.9 2.5 1.3

Insoluble

While dieldrin will, under suitable conditions, exhibit many of the expected reactions of epoxy compounds, it is a remarkably stable oxide. Thus, in its preparation the presence in the oxidizing solution of 1% or more of sulfuric acid i n no way affects it. However, when dissolved i n b u t y l ether and refluxed with concentrated solutions of the halogen acids, dieldrin reacts typically to yield the halohydrin.

The somewhat unexpected inertness of dieldrin toward mineral acids has great practical significance; despite its structure it remains, under practical conditions of use, insecticidally active under both acidic and alkaline conditions.

Insect Toxicity The data of Table I V give a concise general summary of the relative toxicity of these two compounds to a number of common insect pests. I n each case technical chlordan is used as the standard of comparison and accordingly is assigned a base value of 10. I n some instances similar data for other of the common toxicants are included in order better to enable visualization of the relative activity levels. (In Table I V and the tables which follow 7-C H Cl6 represents the gamma isomer of hexachlorocyclohexane.) A s the data i n this table are presented the figures given represent relative a c t i v i t y ; as activity increases the relative activity figure also increases. Thus, the first line of the table indicates that a l drin is approximately four times as effective against the housefly as is chlordan and that D D T is only about one third as effective as is chlordan. 6

6

Table IV.

Relative Toxicity of Aldrin and Dieldrin to Insects Chlordan

Aldrin

Dieldrin

Housefly German roach American roach

10 10 10

40 60 60

120 300 60

Black carpet beetle Milkweed bug Squash bug

10 10 10

70 140 160

96

Confused flour beetle Differential grasshopper (adults) Fall webworm

10 10 10

68 40-50 100

Imported cabbage worm Chinch bug Plum curculio

10 10 10

40 80 60

Red spider mite Mexican bean beetle

—

_

_

-

200 70

80

+ +

DDT

Toxaphene 2

3

T-CeHeCle 40 30 40 45 30

12.5 6-7

3-4

_ -

—

—

-

+

40


LIDOV ef al.—ALDRIN AND DIELDRIN

179

Kearns, Weinman, and Decker rate the more common halogenated insect toxicants in the following order of decreasing toxicity (7) : dieldrin, aldrin, heptachlor, 7-hexachlorocyclohexane, chlordan, toxaphene, and D D T . This rating follows as the result of rather extensive tests on ten species of insects and is believed to represent, in general, the order of their relative activity. In order to evaluate the actual magnitude of the insect toxicity of aldrin and dieldrin and the utility of these new compounds, additional data must be considered. ( M a n y of the data herein presented have been obtained from letters and other unpublished communications. The details of the entomological investigations thus represented will, in most instances, be published i n appropriate journals by their authors.) Kearns, Weinman, and Decker determined the dosages of a number of the chlorinated compounds, dissolved in 9 5 % ethyl alcohol, required to produce a 5 0 % mortality of the housefly (7). The values obtained, expressed as micrograms of toxicant per gram of fly weight, are listed in Table V . Table V.

LD Values on Houseflies 50

(Based on topical application of some chlorinated compounds dissolved in 95% ethyl alcohol. Values expressed as micrograms of toxicant per gram of fly weight")

a

Compound

LDso, y

DDT Chlordan T-CeHeCU Aldrin Dieldrin

20.5 4.0 2.9 1.6 1.1

Data from results of tests made by W. N . Bruce, assistant entomologist, Illinois Natural History Survey.

The Dacus fly (Dacus oleae, olive fly), a pest producing serious damage to olives and one related to other flies that attack a variety of fruits, is also highly susceptible to aldrin (6).

Weinman and Decker list the L D o values against adult grasshoppers (M. differentialis) for a number of the more common toxicants, both as contact poisons and as stomach poisons, giving the values shown in Table V I {lJf). 5

Table VI.

LD Values for Single Compounds Tested for Contact and Stomach-Poison Effect against M. differentialis Adults 50

(Expressed as micrograms of toxicant per gram of grasshopper weight) Compound

Contact

Stomach Poisons

DDT Toxaphene Chlordan T-CeHeCle Aldrin Dieldrin

9380 61 9.8 3.4 1.8 1.4

2579 91.5 12.0 6.7 2.3 3.7

Weinman and Decker studied the toxicity of aldrin to young grasshoppers on V^th acre plots surrounded on a l l sides by untreated check plots. The small size of the test plots and the "high pressure' ' of grasshoppers from the surrounding untreated areas made it impossible to secure control under these circumstances. Nonetheless, a significant reduction i n the number of grasshoppers i n the control plots was obtained even after 5 days with application of aldrin at the very low dosage rate of 0.05 pound per acre (0.75 mg. per square foot). F o r the control of locusts, grasshoppers, and crickets, 2 to 4 ounces of aldrin per acre, applied as a spray to host crops, yield highly effective results. The 4-ounce dosage is necessary under adverse control conditions such as prevail where vegetation is dry and most of the insects are i n advanced stages of growth (9). The effectiveness of the insect toxicant aldrin to a wide variety of cotton pests has been determined through a large number of field tests. A s a result of these tests, recommendations have been published suggesting the use of a mixture of 2.5% aldrin and 5 %



180

D D T at 10 pounds per acre to control the bollworm, boll weevil, cotton fleahopper, tarnished plant bug, rapid plant bug, and some species of cutworms and thrips. (On cotton just up it was found that only 0.07 pound per acre of aldrin, applied as an emulsion, was necessary for the control of cutworms and thrips.) Significantly, no increase i n aphid population was noted following the use of the a l d r i n - D D T mixture ( 4 ) . Tests of dieldrin against cotton pests have not been as extensive, but the Mississippi 1950 Cotton Insect Control Recommendations state that " i t kills a larger proportion of immature weevils i n squares than any other insecticide tested thus far and is considered very promising for cotton insect control" ( 4 ) . A l d r i n and dieldrin have been found similarly highly effective against a wide variety of other economically important insects. In Georgia, Savage and Cowart determined the relative effectiveness of several commercial insecticides for eradication of plum curculio on peaches (10). Their data are summarized i n Table V I I . A similar order of effectiveness was found for the adult curculio. Table VII.

Plum Curculio Larvae Emergence

Toxicant

Pounds per 100 Gal.

% Infestation

Acid lead arsenate Chlordan Parathion Aldrin

2 1.5 0.45 0.75

41.59 4.08 1.87 0.30

Studies on the control of various species of ants show conclusively that aldrin consistently gives control when applied to infested turf at the rate of 1 ounce per 1000 square feet (4 ounces of 2 5 % wettable powder in 200 gallons of water). This dosage is only half of that required when chlordan is the toxicant employed (11,12). Several reports on the use of aldrin to combat other soil-infesting pests indicate its high order of effectiveness for this purpose. I n a series of field tests on Japanese beetle grubs, chinch bugs (12), white grubs (16), and tropical earthworms (15), aldrin has been found to be the most effective material tested. Against wireworms, preliminary work i n dicates aldrin to be effective when applied to the soil as a side dressing at the rate of 1.5 pounds per acre (3). One series of experiments also indicates aldrin to be at least twice as effective as chlordan in combatting the cabbage maggot (13). The foregoing comments and data, although far from complete, serve to indicate the high degree to which aldrin and dieldrin possess the property of insect toxicity. These m a terials have been tested as toxicants for more than one hundred insect genera. Although broad generalizations are unsatisfactory and inadequate, it is clear that to a large number of insect species these two compounds are the most toxic halogenated hydrocarbons yet available.

Residual Activity A l d r i n and dieldrin show high toxicity to insect life, but differ greatly with respect to the length of time during which they exhibit residual activity. A l d r i n , like chlordan, exhibits residual effectiveness under field conditions for somewhat less than 3 weeks. E v e n when aldrin is applied at the uneconomical and unnecessary rate of 5 pounds per acre, leafy material so treated exhibits only slight insect toxicity after 3 weeks. A l d r i n , therefore, falls into that class of materials which exhibit pronounced initial toxicity but relatively short residual action. The situation with respect to dieldrin is altogether different. N o insect toxicant hitherto available, with the exception of D D T , has been characterized b y the possession of insect toxicity which continued for long periods after its application. I n this respect, d i eldrin is unique i n that, i n addition to its high order of insect toxicity, it possesses a span of residual activity comparable to that of D D T . The comparative residual activity of deposits of D D T and dieldrin, using the common housefly as the test insect, is illustrated i n Table V I I I . F o r purposes of comparison, both chlordan and aldrin are included i n the tabulations. This material is taken from the p a per b y Kearns, Weinman, and Decker (7).

181

LIDOV et al.—ALDRIN AND DIELDRIN

The residual effectiveness against flies of a number of formulations of insect toxicants was studied by investigators of the U . S. Public Health Service. Over a 2-month period the formulations containing dieldrin were found to give the best results (S). Roaches have also been used i n studying the length of time for which deposits of dieldrin are active (7). Table I X gives some of the data obtained using the German roach as the test insect. I n this case, the toxicants were applied at the rate of 1 mg. per 1000 sq. cm. of surface ; the table lists the mortalities obtained when the insects were left on surfaces of various ages for periods of 24 and 48 hours. D D T is not included in this tabulation, because it is inactive at the dosage rates tested.


Table VIII.

%

Mortality of Houseflies

(24 hours after a 30-minute exposure to a deposit of 50 mg. per sq. foot of some chlorinated insecticides at various intervals after application. Each figure based on three replicates of 125 flies each. Compounds deposited on glass plates") Age of Residues, Days 21 28

35

Per Cent Mortality

Compound Chlordan Aldrin DDT Dieldrin

93.4 83.8 73.7 100.0

58.9 30.0 41.1 100.0

1.8 17.9 19.1

4.6 11.5 95.7

4.3 64.3

71.1

° Data from results of tests made by W. N . Bruce, assistant entomologist, Illinois Natural History Survey, and G . F . Ludvik, special research assistant, Illinois Natural History Survey and Illinois Agricultural Experiment Station.

Table IX.

Residual Toxicity of Chlorinated Insecticides to Adult Male German Roaches

(1 mg./1000 sq. cm. deposits at various intervals after application. Percentage dead and moribund after exposure periods of 24 and 48 hours) Age Deposit, Days 21 28 24

48

24

48

49

24

48

24

48

46

100

24

90

Per Cent Dead and Moribund

Compound Chlordan 7-CeHeCle Aldrin Dieldrin

42

Exposure Period, Hours 24 48 24 48

100 100 100 100

100 100 100 100

24 14 22 100

92 18 100 100

0 0 0 100

0 0 0 100

0 0 0 100

0 0 0 100

The formulation of aldrin and dieldrin can be readily accomplished i n normal fashion; no difficulty has been encountered i n incorporating these materials into dusts, wettable powders, or emulsifiable concentrates.

Phytotoxicity The evaluation of new materials intended for use as insect toxicants requires consider ation of the toxicity of such materials to other forms of life. The question of phytotoxicity can be disposed of very rapidly. The evidence available indicates that even when applied i n gross overdosage, neither aldrin nor dieldrin is harmful to plants. Thus, for example, the application of aldrin to the soil at the rate of 100 pounds per acre led to no apparent inhibiting effect on the germination or growth of corn or of cucumbers (16). Other more extensive investigations conducted by Bauer and D a h m , using i n some experiments soil treatment at the rate of 100 pounds per acre and in others up to seven applications of aldrin to growing plants, at the rate of 0.5 pound per acre per application, on thirteen varieties of plants showed no abnormal effects, except that lettuce seed germination was slightly reduced and bean plant emergence was delayed 2 days; tobacco plants on the treated plots developed more rapidly and bloomed earlier than did the tobacco plants grown on the untreated plots (1). Bauer and D a h m report further that the vegetables grown under these conditions possess no foreign taste or objectionable odor. These work-

182


ers further demonstrate the complete absence of aldrin i n most of the plants so raised and the presence of only trace quantities of aldrin i n soybeans and tomatoes similarly grown. Bauer and D a h m state that "the application of Compound 118 to the soil at the rate of 100 pounds per acre represents a dosage that is probably from 20 to 50 times that required for practical insect control."

Mammalian Toxicity M u c h work remains to be done before all aspects of mammalian toxicity of aldrin and dieldrin are completely known. However, the work already completed has established many important facts. When administered in edible oil to albino rats, aldrin demonstrates an acute L D ranging from 40 to 50 mg. per k g . of body weight. M u c h chronic toxicity work is i n progress. Albino rats on a daily diet containing 75 p.p.m. of aldrin incorporated in an edible oil continued normal i n all respects after 6 months. Cattle, sheep (pregnant ewes), and lactating cows with suckling calves were wintered on alfalfa hay sprayed with 0.5 pound of aldrin 8 days before harvest. The hay i n these tests was baled for storage. None of the animals fed on this hay developed abnormal symptoms, nor was evidence of damage found on autopsy of sacrificed individuals. Furthermore, aldrin could not be detected in the milk from the lactating cows (8). Dieldrin administered i n edible oil to albino rats demonstrates an acute LD50 toxicity of 50 to 55 mg. per kg. The chronic toxicity of dieldrin has not been established, a l though tests are now i n progress to determine its possible hazard to animals sprayed or dipped in formulations containing varying percentages. It has been established experimentally that rats are considerably more resistant to the action of dieldrin than rabbits. Among farm animals exposed to spray formulations containing dieldrin, swine proved to be the most resistant and very young calves proved to be the most susceptible. Preliminary results of work in this field indicate that dieldrin is less toxic to young calves than are some other comparably effective chemicals when applied i n a similar manner, although dieldrin is definitely more residual i n action against the insect parasites affecting farm animals.


5 0

Recommended Applications A l d r i n exhibits only moderate persistence and evaporates completely under field conditions in somewhat less than 3 weeks. Consequently, if the simple precaution of applying aldrin not later than 3 weeks before crop harvest is observed, the possibility of u n desired toxicant residue on harvested crops should be very slight. It is recommended that aldrin be considered, on an experimental basis, both as a crop insecticide and for the control of subterranean pests. On crops intended for human and animal food no application should be made later than 3 weeks before the harvest of these crops is planned. Although dieldrin has been found effective against all the insects susceptible to the action of aldrin, it should not at present be recommended for use against any pests in situations where its residue might constitute a hazard on edible foods or on forage crops. I t is suggested that dieldrin be employed experimentally, especially for the control of flies, mosquitoes, cotton insects, forestry pests, termites, pests i n soil, pests of lumber products, cloth-eating insects, and industrial pests not actually infesting food products. Dieldrin should be considered wherever extended residual effectiveness is advantageous.

Summary Two new insect toxicants, aldrin and dieldrin, provide new halogenated insect toxicants with an extremely high order of toxicity toward insects, combined, for the first time, w i t h complete stability to alkalies. Under all the usual conditions of use these new toxicants are also stable to acids. D a t a illustrate the order of magnitude of the insecticidal activity of these materials and their utility. A l d r i n is a relatively nonresidual material, in contrast to dieldrin which, because of its high persistence, exhibits prolonged residual activity.

LIDOV et al.—ALDRIN AND DIELDRIN

183


Literature Cited (1) Bauer, C. L . , and Dahm, P. Α., "Field Plot Studies on Compound 118 (Aldrin) in 1949," 61st Annual Meeting, Am. Assoc. Econ. Entomol., Tampa, Fla., Paper 107, Dec. 13 to 16, 1949. (2) Danish, Α. Α., and Lidov, R. E., ADVANCES IN CHEMISTRY SERIES, 1, 190 (1950). (3) Dogger, J . R., Insect Control Conference with Industry, Univ. Wisconsin, Wireworms Bull., Jan. 11, 1950. (4) Dunnam, E. W., Hamner, A . L . , Lyle, C., and Murphree, L . C., State Plant Board of Missis sippi, State College, Miss., "1950 Cotton Insect Control Recommendations," December 1949. (5) Federal Security Agency, Pub. Health Service, Atlanta, Ga., Communicable Disease Center Bull., 58 (October, November, December 1949). (6) Hadjinicolaou, J . , Reconstructionist, 7, 10 (May 15 to 31, 1949). (7) Kearns, C. W., Weinman, C. J . , and Decker, G . C., J. Econ. Entomol.,42 (1), 127-34 (February 1949); data presented at Am. Assoc. Econ. Entomol. meeting, New York, December 1948. (8) Kitselman, C. H . , Borgmann, A . R., and Dahm, P. Α., "Toxicological Studies of Compound 118 (Aldrin) on Large and Small Animals," 61st Annual Meeting, Am. Assoc. Econ. Entomol., Tampa, Fla., Paper 108, Dec. 13 to 16, 1949. (9) Medler, J . T., Insect Control Conference with Industry, Univ. Wisconsin, "Grasshopper Control in Alfalfa Seed Fields with Low Volume Sprays," Bull., Jan. 11, 1950. (10) Savage, E . F., and Cowart, F . F., Georgia Expt. Station, "Report of 1949 Spraying Experiments for Control of Plum Curculio and Other Insects on Peaches," Sept. 29, 1949. (11) Schread, J. C., Conn. Agr. Expt. Sta., Circ. 173 (1949). (12) Schread, J . C., J. Econ. Entomol., 42 (3), 499-502 (June 1949). (13) Sciaroni, R. H . , Lange, W. H . , and Carlson, E. C., Agr. Extension Service, San Mateo County, and Division of Entomology and Parasitology, Davis, Calif., "Suggestions Regarding the Control of the Cabbage Maggot in San Mateo County." (14) Weinman, C. J . , and Decker, G . C., J. Econ. Entomol., 42 (1), 135-42 (February 1949); data presented at Am. Assoc. Econ. Entomol., New York, December 1948. (15) Westchester-Connecticut Turf Improvement Assoc., Tropical Earthworm Project, Second 1949 Progress Report. (16) Wolcott, G . N . , Agr. Expt. Sta., Univ. Puerto Rico, Rio Piedras, Puerto Rico, "Effectiveness of Hyman 118 against White Grub of Puerto Rico."

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