The influence of carbon tetrachloride on the toxic efficiency of certain volatile organic compounds

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The influence of carbon tetrachloride on the toxic efficiency of certain volatile organic compounds

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THE INFLUENCE OF CARBON TETRAOHLGRIBS OS THE TOXIC EFFICIENCY OF CERTAIN VOLATILE ORGANIC COMPOUNDS

by

Roland Newton Jefferson

A Thesis Submitted to the Graduate faculty for the Degree of

DOCTOR Of PHILOSOPHY

Major Subject Entomology

Approved:

Sn"'Charge " o f lla j o r ''"Sbr¥'

Bead o f Maj orf Departs^

Dean' of 'Graduate Co Iowa State College 1942

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ii TABL1 OF CONTENTS

Page UTROOTGTIGlf ........................................

1

w m i w i of L i r m a r o i i

4

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Carbon Tetrachloride as a Fumigant

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4

Jttbylene Dichloride as a Fumigant .............

5

Methyl Formate as a Fumigant

©

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Methyl Bromide as a Fumigant Gas Mixtures as Fumigants SX'FSRIMSNT

imis

7 .....

9

.......

13

........

go

Toxicity of Fumigants A l o n e ........

£0

Toxicity of Mixtures ..........

83

DISCUSSION OP W B S m S S

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29

STOttART AND OQIICKJSXOHS ............................

39

DITBflAfUHIi CITS)

42

ACKNOffXJ5DQKXRI5 TITA

.... -----

.....

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INTRODUCTION Carbon disulfide and hydrogen cyanide have been in common use for the fumigation of stored products for the last SO years.

During that period many compounds have been tested

against numerous species of insects but only a few proved to be practical fumigants.

Many gases of high'toxicity possessed

undesirable qualities such as inflammability and high boiling point, or were injurious. In recent years mixed gases have received considerable attention.

The use of mixtures holds two possibilities: first,

a reduction of the fir® hazard of many fumigants; and, second, an increase in toxicity, o r 'synergism. Bliss (1939) in a paper entitled "The Toxicity of Poisons Applied Jointly" recognizes three types of joint action: (1) Independent joint action, in which the two components act independently of each other; (2) Similar joint action, in which the two components produce similar but independent effects, and one component may be substituted for the other at a constant ratio without affecting the toxicity of the mixture; (3) Synergistic action, in which one component synergizes or antagonizes the other. The.term'synergy is defined as correlated .or cooperating action on the part of two or more organs or drugs.

Toxico-

logieally, synergism is a toxicity greater than the additive effect of the components, and antagonism is a less than additive effect.

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Synergism and antagonism in drugs have long been recog­ nized.

Bancroft and Richter (1931) point out that the older

theories of synergism and antagonism are inadequate.

These

authors state that antagonism is concerned with elimination brought about by the displacement of one drug by another from a given substrate.

This displacement of some or all of the

first drug increases its effective concentration so that it may undergo the reactions of detoxication or diffuse out more rapidly.

Thus in its simplest form antagonism occurs when one

drug is replaced by another whose physiological action is less but whose adsorption is greater. Synergism is closely related to antagonism, and Bancroft and Richter (1931) also explain it as a result of displace­ ment,

While most drugs may be preferentially adsorbed on one

tissue they may also be adsorbed to some extent on other tissues.

In low concentrations the drug will have a specific

action because the adsorption on the secondary substrate is not sufficient to exert a physiological action.

However, if

a second substance is added whose adsorption is greater on the primary substrate but is less on the secondary substrates, then the first drug is displaced from the primary substrate and its concentration is. increased on the secondary substrates. The effective concentration is thus increased the same as if a higher concentration of the drug had been used in the first place, and the concentration on the secondary substrates may now be great enough to exert a physiological action.

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file study of synergism is a promising field of investi­ gation and criteria siiould be established for separating synergistic action fro® other types of Joint action. fhe investigation herein reported was undertaken with the following objectives: (1) fo determine the dosago-nortality curves (Bliss, 1935} of methyl formate, methyl bromide, ethylene diehlorlde and carbon tetrachloride for fribolium eastaneum (Berbst) at a temperature of 30° 0. and an exposure time of two hours.

(2) fo determine the dosage-mortality

curves for f . castaneum when carbon tetrachloride is. mixed with each of the other above gases, the mixtures to b© of the following proportions on the basis of their median lethal concentrationsi'1:1, 1:3 and 3:1.

(3) fo analyze the dosage-

mortality curves of the mixtures for various types of joint action.

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j m i m oj - L v s m m m Strand 11330) reviewed the methods for 'determining the Ti lativo toxioities of insect fumigants and pointed out that the greatest errors in these petfcods was the attempt to deter­ mine minimum lethal concentrations,

1© investigated a .method

for obtaining relative toxioities by comparing concentrations which kill 50 percent in a given time, while comparing the toxieitles of fumigants at the 50 percent point was more precise than the methods previously used, it is sore-,practical to compare concentrations which give a complete or nearly complete kill,

Bliss- |193§) developed

a method for transforming the sigmoid dosage-aortality curve usually obtained to a straight line regression.

From the

equation for the regression line the theoretical dosage necessary to kill any given percentage up to 99.99 percent may be calculated.

Carbon Tetrachloride as a Fumigant The toxicity of carbon tetrachloride to insects has been investigated by numerous workers.

Among the earliest was

Britton {1908a, 1908b), who tested it against the San Jose scale on nursery stock,

Morse 11910) suggested its use as a

safe substitute'for carbon disulfide. Back and Duckett (1918) recommended carbon tetrachloride for the control of bean and pea weevils, but Blakeslee (1919),

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Brittain 11922), Reifert ©t al 11925) and urumb and Chamberlin 11936) are among those who have found it ineffective under practical conditions, the relatively low toxicity of carbon tetrachloride to a variety of insects has been demonstrated by many investiga­ tors including the following: McClintock, Hamilton and Low© 11911), Bertrand and Rosenblatt 11919), fattersfield and Roberts 11920), Meifert et al 11925), atrand 11927), Roark and cotton 11928), Shepard and Lindgren (1934), Shepard, Lindgren and Thomas (1937) and Gunderson (1940). Carbon tetrachloride is now used principally as a diluent to reduce the fire hazard of some of the more toxic gases.

Ethylene Bichloride as a Fumigant The toxicity of ethylene dichloride to stored grain insects was first investigated by Raifert et al (1925). Further tests were conducted by Roark and Cotton (1928, 1929). Shepard, Lindgren and Thomas (1937) found it to be much more toxic than carbon tetrachloride and less toxic than methyl bromide and methyl formate to T. confusum. Sitonhilua granarius and S. orvzae, Ginsburg (1933), in tests with codling moth larvae, showed ethylene dichloride to be more toxic than carbon disulfide and ethyl acetate but much less toxic than hydrogen cyanide. Sthylene dichloride was extensively tested as a soil fumigant for the peach borer by Snapp and Thomson (1934, 1936)

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and Snapp (1938). At tli© present time ethylene bichloride is seldom used alone as a fumigant for stored products because of its inflam­ mability. Methyl format® as a Fumigant The relatively high toxicity of methyl' formate to grain insects was demonstrated by Heifart et al (1925) and further Investigated by Cotton and Roark (1928) and Roark and Cotton (1929). Methyl formate is inflammable, but according to Cotton and Hoark (1928) this hazard can be eliminated by adding carbon tetrachloride until the mixture contains less than 10 percent by weight of the formate.

However, the mixture is only

slightly more toxic than carbon tetrachloride alone. Lehman (1933) determined the median lethal concentration of methyl formate to the wireworm, Llmonlus (Pheletes) californicus Mann to be 12.52 milligrams at 25° 0. and 5 hours exposure. '' Jones (1935) found that the amount of methyl formate to kill 50 percent of T. oonfusum exposed 5 hours at 30° C. was between 15 and 20 milligrams per liter.

A complete kill was

obtained with 25 milligrams per liter. Jones (1938) found methyl formate to be less toxic than ethylene oxide and methyl bromide to T. castaneum.

Shepard,

Lindgren and Thomas■(1937) reported methyl formate to be more toxic than carbon disulfide, carbon tetrachloride and ethylene

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dichlorid© to f * confusura and S. orvzae.

It was less toxic

than methyl bromide to the same insects.

Methyl Bromide as a Fumigant The first investigator to report on the' Insecticidal value of methyl- bromide was he Goupil (1932).

It has since been

extensively tested against many insects and Is now established as on® of our most important fumigants.

A detailed account of

its properties, history and uses is given by Mackie 11938). Laboratory tests against a number of insect species have shown methyl bromide to be a fumigant of high toxicity.

Fisk

and Shepard (1938) found that Its toxicity compared favorably with that of hydrogen cyanide, chloropicrin and ethylene oxide. They give its median lethal concentrations for T. confusum. S. granarlus and S. orvzae as 10.S, 5.5 and 4.0 milligrams per liter, respectively, for 5 hours exposure at 25° C. 'Jones (1938) found its median lethal concentration to T. dastaneua to be 6.13 milligrams per liter for 5 hours exposure ..at 27° C. Shepard and Buzicky I1939) determined the toxicity of methyl bromide to a considerable '.number of stored-product pests. tested.

Attagenus ulceus (Oliv.) was the most resistant species Grayson and Swank (1941), on the basis of median

lethal concentrations, found the firebrat, Thermobia domestics (Pack.),.to be less resistant to methyl bromide than any of the insect species so far investigated.

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la a trial fumigation of 80,000 bushels of wheat, Fitz­ gerald, Katcliffe and Oay 11941} found methyl bromide to be unsatisfactory." Cotton, Wagner and winburn 11941} state that methyl bromide can be used with mills of modern concrete or brick construction.

They recommend a dosage of 1 pound per

1000 cubic feet of space. Mackie 11988} listed the fruits, vegetables, stored products and living plants which have been treated with methyl bromide either experimentally or commercially.

Its us© in the

treatment- of fruits and vegetables for the control of the Japanese beetle has been described by Donohue, Johnson and Bulger (1940}.

Latta (1940) successfully used methyl bromide

.for the fumigation of green lima beans, pigeon peas and string beans for the larvae of Maruea testularis Ctoyer/'a bean pod borer.

Phillips, Monro and alien (1980) reported that the

standard methyl bromide treatment would kill insects feeding in apples but that injury to the apples resulted under certain conditions. Hamilton (1S40) showed that methyl bromide can be suc­ cessfully used as a soil fumigant to control Asiatic beetle grubs attacking azelsa plants.

On the other hand, Hchwardt

and Lincoln 11940} found it unsatisfactory as a soil fumigant for the alfalfa snout beetle, Braohyrhinus llnguatloi (L . ). Lange (1940) in tests with larvae of the artichoke plume moth, Flatyntilia oarduldaetyla (Riley), reported that at standard dosages methyl bromide gave practically a perfect kill but that

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injury to the plants occurred. Livingstone, Easter and Swank (1940) stated that an aqueous solution containing 0*3 percent, methyl bromide and 0.6 percent of denatured,ethyl alcohol was found to be of value in destroying larval in­ festations of Pantomorus jNaupactusI leucoloma and T. [J|C] peregrines in bur lapped balls o f 1ea'rtE such'as would be encountered on the roots of nursery stock. Hamilton (1941) tested the toxicity of methyl bromide to the common red spider and to greenhouse"roses*

The'data indi­

cated a definite relation between the toxic concentration of methyl bromide, the temperature of fumigation and the length of fumigation.

The kill at any temperature was essentially a

product of the length of exposure and the concentration of the methyl bromide.

Under the conditions of the experiments a

concentration of methyl bromide which gave 100 percent kill was injurious to the most susceptible of six varieties of greenhouse roses.

Gas Mixtures as Fumigants The danger of fir© or explosion with otherwise satisfac­ tory fumigants has been a factor in the development of gas mixtures in recent years.

Jones and Kennedy (1930) and Jones

(1933) have investigated the reduction of inflammability of various fumigants by the addition of carbon dioxide.

Carbon

tetrachloride has also b e e n ■extensively used for this purpose. Nelfert et al (1925), in addition to testing a large number of compounds alone, also 'tested a number of mixtures

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against grain insects,

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they found that other than carton

disulfide a mixture of ethyl acetate and carton tetrachloride was the most promising fumigant for weevils in wheat in grain ears. Back and Cotton (1925) recommended a mixture of ethyl acetate and carbon tetrachloride for the fumigation of grain in grain cars,

this mixture was non-inflammable but was later

found to leave an -objectionable odor in the grain. Hazelhoff (1928) noted that carbon dioxide has a marked effect- on the respiratory movements o f ■several insect species and suggested that carbon dioxide might be used to increase the insecticidal action of gases. Brinley and Baker 1192?) reported that a small amount of methyl acetate seemed to increase the toxicity of liquid hydrogen cyanide. Jones. {1935) found that a small quantity of methyl formate markedly increased the toxicity of a given concentration of carbon dioxide. Cotton and loung (1929), Cotton (19-30) and Back, Cotton and Ellington (1930) found that the addition of carbon dioxide increased the effectiveness of ethylene die-hlorlde, methyl ehloroaeetate, carbon disulfide, chloropicria and ethylene oxide.

Cotton (193S) found that the amount of carbon dioxide

to give the maximum increase in toxicity varied with different gases. Pratt, swain and .SMred' (1933) reported that carbon dioxide reduced the toxicity of hydrogen cyanide to ladybird

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beetles, but Guppies, Tuet and HIley (1956) found that the addition of carbon dioxide increased the toxicity of hydrogen cyanide to the red scale, Dusfcan 11938) obtained satisfactory results against mites infesting cheese by adding carbon dioxide to methyl bromide and ethylene oxide. Jones (1958) showed that carbon dioxide markedly increased the toxicitiea of methyl bromide, methyl format® and ethylene oxide to T. castaneua but that it might lower the toxicity'of the mixture when used in excess of the amounts necessary to produce the maximum increase in effectiveness. Gunderson (1940) used sublethal concentrations of ether and showed that the toxicity of carbon disulfide and carbon tetrachloride to f. confusmn increased as the concentration of ether increased but that the toxicity of ethyl acetate decreased. Cotton and Roark (192*7) and Roark end Cotton (1928) found a mixture of 3 volumes of ethylene diohloride to 1 volume of carbon tetrachloride to be the most promising fumigant for general purposes.

The 3:1 mixture of ethylene dichloride and

carbon tetrachloride has been tested against a variety of Insects by Roark and Gotton (1929), Britton (1932), Bustan and Matbowman (1932), Herrick and Griswold (1932), Hoyt (1928a, 1928b), urusb and uhamberlin (1936), Guppies, lust and Siley (1936) and uolman (1936). Shepard and JLlxtdgren (1934) obtained antagonism when ethylene dichloride or propylene diohloride was mixed with

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carbon tetrachloride..

'Che mixtures contained 25 percent

carbon tetrachloride end T» eonfusum and S. orygae were the insects used. Back and Ootton 11936) recommended the use of mixtures of carbon disulfide and of ethylene diohloride with carbon tetrachloride and of ethylene oxide with carbon dioxide for the control of pests in stored grain.

Cotton (1930) stated

that such mixtures were available commercially and recommended their use for the control of insects attacking grain in farm storage. After studying "the penetration of compact commodities by fumigants under partial vacuum", Cotton, Wagner and Young (193?) reached the conclusion "that the temperature of the ooiareodity is the most important factor governing the penetra­ tive action of gases".

This conclusion was substantiated by

the results of tests with a 20:80 carbon disulfide-carbon tetrachloride mixture against ff. ory&ae L. in wheat.

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EXPERIMENT The fumigants used in this investigation were methyl format©, methyl bromide, ethylene dichloride and carbon tetra­ chloride,

with the exception of methyl bromide they were

purified by distillation and their purities tested by deter­ mining their refractive indices.

The specifications of each

fumigant are given in table 1. The test insect used was the rust-red flour beetle, Triboliua oastaneua (Herbst).

The beetles were reared on

whole-wheat flour at a temperature of approximately 30° 0. and a relative humidity of about 73 percent,

the original

culture was obtained from shelled corn in as Agricultural Adjustment Administration bln in northern Iowa. The beetles used In the tests were selected at random. A large number were taken from each of four or five stock cultures ana placed together in a separate jar.

The beetles

In this jar were then used in the fumigation tests for a period of 3 to' 5 days.

Six fumigation flasks were available,

and before each set of tests was run all the beetles in the test culture were sifted out and a portion of them placed in a glass salve jar.

from these the number required was 'then

counted out by teas Into six salve jars.

Fifty adult beetles

from 2 to ft weeks old were used in each subsample. After fumigation the beetles were placed on whole-wheat flour in vials and kept at a temperature of 30° C. and a relative humidity of 73 percent.

Final mortality counts were

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Table 1 .— Specifications of materials. Material

Molecular weight

Boiling ' point

Refractive index

Methyl formate. (HC00 CH3 ) ■

00.03

31.0° 0, at 728.9 m u . and SB G .

Methyl bromide* {CHgBrj

94.94

4.6° 0.

sthylene diohloride (CHgCluHgCl)

98.95

82° C. at 741.7 1.4441 U 0 OG.) mm. and 25.5 0 .

Garbon tetrachloride {CCI4 }

153.83

75.1° G. at 739.5 an. and 26° C.

1.3449 (15°C.)

1.4594 (20°C.) 1.4597 i20 °O.) /I.4593 *20°G.)

* Obtained from Bow Oheaieal Company; not less than 99.4 percent 0 % B r ; inert ingredients, not more than 0.5 percent.

/ The CCI4 need in the 3:1 methyl formate-carbon tetrachloride mixture was not distilled. It was obtained from the General chemical Company, was chemically pur© and had a boiling range of 75-77° 0. Its refractive Index was determined as 1.4393.

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made on the seventh day.

Shepard, Lindgren and Thomas (1957}

and hamlim .and Meed {1927, 1928) have pointed out the diffi­ culty in determining a sharp end point.

After preliminary

tests it was decided to count as dead only those insects actually dead on the seventh day. ■It was felt that this allowed a reasonable time for revival and eliminated the neces­ sity of determining the degree of paralysis of the surviving beetles. Carbon tetrachloride* ethylene diohloride and, to a slight extent, methyl bromide, caused paralysis of the beetles.

The

number of these paralyzed beetles that were dead on the seventh day seemed to depend on the concentration of the fumigant,

.with methyl formate there was very little paralysis,

and usually the mortality counts made on the seventh day agreed with those made on the third or fourth day. The apparatus used in this investigation is in modifica­ tion of that described by Grayson and swank: 11941).

The

fumigation chamber (figure 1) consisted of a Pyrex boiling flask (A) of approximately 5.5 liters capacity, closed with a ground-glass plate (8 ). airtight seal.

Stopcock grease was used to give an

The ground-glass plat© had a hoi© in which

was inserted a one-holed rubber stopper (6).

A tub© ID) with

a ground-glass stopcock was inserted through the hole in the stopper.

The' tub© reached the bottom of the flask and was

used to break the ampul© (!) containing the fumigant.

The

cardboard paddle If) and the cage (G) containing the test insects were suspended with copper wire from the stopcock

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m

**

Figure 1.— Diagram of apparatus used in fumigation experiments.

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tube as shown la the diagram.

Both the rubber stopper and

the cardboard paddle were coated with shellac. The ampules, also known as Victor Sye-r bulbs, were blown fro® soft glass tubing.

Their weights and the lengths of

their capillary necks were recorded,

h large test tub© with

a side neck was used in filling the ampules.

The ©ads of the

capillary necks were immersed in the liquid fumigant and a partial vacuum was drawn.

Release of the vacuum forced the

liquid up into the ampules.

The ©ads of the capillary necks

were then-sealed la a flam© and the ampules were reweighed to determine the weight of liquid- in eaeh.

They were prepared in

lots of six or eight and identified by measuring the length of the capillary necks.

By packing the tube In dry ie© {solid

carbon dioxide) and placing the filled ampules, bulb downward, in a small beaker containing ships of dry ice immediately upon removal from the tube, the very volatile methyl bromide and methyl formate were easily handled. In the preparation of the mixtures a large ampule of methyl bromide or methyl formate was prepared and the weight of the liquid obtained.

The amount of carbon tetrachloride

was then calculated, weighed out and cooled with dry ice to prevent vaporization.

The ampul® of methyl bromide or methyl

formate was then immersed in the carbon tetrachloride and broken with a glass rod.

This procedure was not necessary

for the ethylene dichloride-carbon tetrachloride mixtures- as both components could b© weighed out and then mixed together.

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The mixtures were sealed in test tubes immediately after their preparation. Breaking the ampule in the flask required seme manipula­ tion of the stopcock tube.

With very volatile gases, such as

methyl bromide, it was necessary only to break the neek of the ampul©' to release the fumigant in the flask.

Less volatile

materials,;; such as carbon tetrachloride and ethylene diohloride, however, diffuse too slowly through the capillary neek and consequently it was necessary to break the bulb itself.

This

was greatly facilitated by special treatment of the rubber stopper.

A tub® of slightly less diameter than the stopcock

tube was inserted in the hole of the stopper.

The tube and

stopper were then heated to 150° 0. for 20 minutes.

This

treatment mad® the stopper pliable and molded it to the tube. Then, after the tub© was removed, the hoi® was moistened with glycerin© and the stopcock tube inserted..

An airtight fit

was thus obtained which still allowed free movement of the tube through the stopper. In making the tests the insects were placed in the cage and a partial vacuum was drawn with a filter pump.

The ampul©

was then broken by pressure from the stopcock tube and after the liquid had vaporised the flask was returned to atmospheric pressure.

There was a tendency for some of the liquid to

remain in the capillary neck but this was overcome by breaking the neck near the end.

The paddle was flipped back and forth

by shaking the flask to insure thorough mixing of the gas in the flask.

The methyl bromide and methyl format© vaporized

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instantly and the ethylene diohloride and carbon tetrachloride in 3 to 5 minutes.

The beetles war® exposed to the fumigant

. «o for 2 hours at a temperature of 30 x f 0. The check insects received exactly the same treatment as those fumigated except that no fumigant w a s .released in the flasks.

Fifty cheek insects were used to about 600-800 fumi­

gated, but when only E out of 1153 died the number of checks was reduced. ~NV.

The data obtained in these experiments were plotted and analyzed' statistically according to the method of Bliss (1935). In this method the percent mortality is converted into probits and the dosage into logarithms, the usual sigmoid dosagemortal it y curve being transformed to a straight- line regression. The chi-square test was applied to determine the homogeneity of the data, and the limits of error for each regression line wer© calculated.

The regression lines for the mixtures were

analyzed for various types of joint action*

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RESULTS

"Toxicity of fusilga&ts Alone The dtoaage^-mortality curves for methyl formate, methyl bromide, ethylsn© diehlorid© and carbon tetrachloride at 30°0. and 2 hours exposure ar® shown in figures 2 and 3.

The number

of insects used in obtaining each curve and the dosages- calcu­ lated to hill 50 percent and 99 percent of the beetles are given in table 2.

These dosages were calculated from Bliss*

formula, Y * a + biJL-x), in which Y * the mortality in probits for any given dosage X, a - y - the average probit for th® data being fitted by a straight line, x * th® average dosage in logarithms for the same data, and b is the regression coefficient.

Table S.— Toxicity of fumigants to Tribolium castaneum (Herbst); temperature, 30° 0.; exposure period, 2 hours. Concentration, ini' mg. per liter, required to killid ©ardent 9$ ner'cent

fumigant

lumber of insects tasted

.Methyl bromide

2851

14.0

■ 17.5

Methyl formate

2949

28.0

'43.4

Sthylene diohloride

2070

95.5

149.5

Qarbon tetrachloride

mm

105.8

209.1

The chi-square test, when applied to the carbon tetraohloride curve, indicated that considerably more variation was

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Reproduced with permission

C O N C E N T R A T I O N - MG. P E R 15.9 25.

8

LITER 39.8

99.8 HCOOCH 97.7

CL

84.2

5

50

>

h< Fcr o 2

prohibited without permission.

MORTALITY

Further reproduction

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PERCENT

of the copyright owner.

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h-

F- ^ 2 UJ

O cc UJ CL

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of the copyright owner.

C/) ni t '

3

2.3

2 1.6

1.8 2.0 22 2.4 LOG C O N C E N T R A T I O N - MG. PE R LITER Figure 3*— Toxicity of ethylene dichloride and carbon tetrachloride to Tribollum castaneum (Herbst).

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present than would be expected from random sampling of a homogeneous population. The dosago-raortality curve for ethylene diohloride showed a break near the lower end. break was not calculated test applied to the main

That part of the curve below the

but was

fitted by eye. The ohi-square

part of the curve indicated slight

heterogeneity. The chi-square test more variation than would

for the

methyl formatecurve indicated

b©expected in random, sampling of a

homogeneous population. The data for the methyl bromide curve, when analyzed by the chi-square test, strongly indicated that'these data are homogeneous. boa© of the probable causes of heterogeneity in these curves will be discussed in a later section*

Toxicity of Mixtures Garbon tetrachloride was mixed with each of the other gases in the ratios of 1:1, 1:3 and 3:1.

Since the mixtures

were prepared on a toxicity basis,-a 1:1 mixture contained the ingredients in the ratio of the amounts'of each required to kill 80 percent of the beetles.

Hereafter, in referring

to any mixture, the second figure in the-ratio will be the amount of carbon tetrachloride. The dosage-nortal i ty curves for methyl bromide, methyl formate and ethylene diohloride in combination with carbon

R eproduced with perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission.



-

84

~

tetrachloride at 30° 0. and Z hours exposure are shown is figures 4, 5 ash 6.

The calculated cartoon tetrachloride curve

is included for reference,

the number of insects used in

obtaining each curve and the dosages calculated to kill 50 percent and 99 .percent of the beetles are given in table 3.

Table

3.— Toxicity of fumigant mixtures to f'rltoolium oaataneua (Herbst); temperature, 30° C . ; exposure period, 2 hours. fuiber of*’ .insects 'tested

Mixture Methyl bromideCartoon tetrachloride

Methyl formateCartoon tetrachloride

Ethylene dichlorideCarbon tetrachloride

Concentration, ,in mg. per liter.required to kill50 percent 99 percent

1:1 1:3 3:1

3E95 1606 3496

49.1 79.3 41 •0

1:1 1:3 3:1

2745 £984 £488

94.7 101,3 54.0

1:1 1:3 1:3 3:1

3380 ££06 1617 5518

114.7 99.3 101.3 88.5

70.3 184.8 50.7

.

153.5 198.8 85.4 180.1 193.9 157.4

A large number of insects were used in determining the dosage-mortality curve of each mixture.

The chi-square test

was applied to the data for these curves and only in the 1:1 and 3:1 methyl bromide-carbon tetrachloride curves and 1:1 methyl formate-cartoon tetrachloride curve was heterogeneity indicated.

The latter curve is especially interesting from

this point of view and will toe discussed later.

R eproduced with perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission.

44.7

8

MG. PER

LITER

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Figure 4.— Toxicity of methyl bromide-carbon tetrachloride mixtures to Tribolium castaneum (Ilerbst).

MORTALITY

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CONCENTRATION -

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

Figure

$.— Toxicity of methyl formate-carbon Tribollum ca3taneum (Herbst).

tetrachloride

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