'(13' .

L .

..
1
H” “I... M‘IU (1‘ |

H: use

L
l h

‘
u

M.” s. M ..
fit I). U. A ..:W «V ‘

‘3
1
C!
l-‘fifi'
h
obi,“
i-
u
:“
1.3.

..,.
'v

1(
E: ,.

m3 5 :-

O
.1 v.
..., in L

i 0
V.
125t-
gt

:51
2: ‘

‘3‘?
L..~ N CC “hf CENTMTION
RA
.33.:

“I". .J. \ d. r . 3 ..4 .‘lWL\¢
.uli ‘ ”wk .u .

Q . fl 2 u. A a ‘.

us: . . ‘1 4 St,

in. an.“ a? I... Mr... :.

t“ do JV ‘3 m.

U .5» ‘0‘ A
D a. m. 1. - a P. J M».
”U NU. a n0 n3.
4 .V I: :4. In... .x}. 3.4
*1 . ‘ I. v ‘4. 1' ‘ H's
5 V 3. in. .3 J 8
I I) 1 Out!“ t‘ .10.“ i

Am 9% my. 8 3mm «g

n U.‘ .

V3 .40.“ 1n. v. JV‘ .5.

4“ Nb... h. .i

- .u .
WRAU ELI
\ .

_: 2% 2:32:31, 2:;

 

 

 

'.":1: l. I
. Emir , _ '
n, ... . _ ( ‘
I'M l :
‘1 .\.\ i.
I
I l
\ r
I
.l
‘ l
' l
i l
\ , l
n I . ’ p
. - _. I ’ J l - v
i '1 - I
l I
'I
l
n" '
I. '\

 

This is to certify that the

thesis entitled }

A STUDY OF THE EFFECT ' .
0F HYDROGEN-ION CONCENTRATION .- 3
ON THE TQXICITI OF ' é

“-50-? O ‘l I F I-‘Iw,(?
-‘
I

 

CERTAIN INSECTICIDAL SPRAYS - '
presented by I ‘_ ’ l
Geary Masami 80116 i . 1 - ‘ ;
.5)
i" has been accepted towards fulfillment r)’ ‘

J.

of the requirements for
K Lame mm b
I

 

 

 

 

,. ‘2'
l ' IL»
:2: 7-, )I.
.l ', .
if I ‘
' I
§ *1 .
,6, ajor professor l l ‘
g I i
I. I
I I. .
.', Date November 9, 195]. f . , f ’ g. I
I“ t 4 '
r‘ .‘ ;
| ju l ‘
fl . , .. _ - l
L5 0159 L-" ' ' ' .
., I f ‘ .
f f f "TV ' r I . g
l ,"
. 9' 1
I. . i
l l ' 0‘
‘ t
‘ l
I . if
. .I1
I' ' 1
. \ ‘
1
r}
. 4

O
‘

I —.

 

S
n l

.ll

.v

. I!“
1 1 .1...“ ‘HJ

\l.

i‘.

‘1‘
.l. l‘. ‘1’}

fi

.1},

.i. a. filifislhaa 3W2“

I
HMHNIIHCU v.

A STUDY OF THE EFFECT OF HYDROGEN-ION CONCENTRATION
ON THE TOXICITY OF CERTAIN INSECTICIDAL SPRAYS

BI

GEEBIHMLSKMI-QQHE_

A THESIS

Submitted to the School of Graduate Studies of Michigan
State College or.Lgriculture and Applied Science
in.partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Entomology

.1951

lbw"

ACUOWIEDCMENTS

the writer wishes to express his thanks to Professor
Ray Hutson and Associate Professor Herman 1... King of the
Michigan State college Entomology Department for their
suggestions and guidance in the preparation of this
thesis, and to his wife, Monica Bone, for the preliminary
typing of the manuscript.

268380

TABLE OF CONTENTS

I. INTRODUCTION . . . . . . .
II. REVIEW OF LITERATURE . . .
III.‘METHODS AND PROCEDURES . .
IV. DISCUSSION . . . . . . . .
V} SUMMARY . . . . . . . . .
VI. EXPERIMENTAL DATA . . . .
VII. LITERATURE CITED . . . . .

Page

11
15
20
25
34

I. INTRODUCTION

The fact that various diluents of an insecticidal
composition have an effect upon insect toxicity has long
been known to chemists and entomologists.

In general, the components of a composition may affect
each other physically or chemically. There are many fac-
tors which govern the physical and chemical preperties of
an insecticidal composition. Physical properties may be
altered.by wetting ability, emulsifying characteristics,
penetration power, sticking prOperties, dispersing char-
acteristics, specific gravity, electrical charge and vola-
tility.

Examples of chemical preperties altered by the compo-
nents of the composition are factors such as pH (a measure
of the acidity or alkalinity of a dispersion or a compo-
sition), ability to combine or polymerize with one or more
components, oxidizing and reducing characteristics, and
buffering ability.

Chemical and physical changes in the composition are
brought about by additional factors such.as temperature,
humidity, presence or absence of water, nature of container
(iron, paper, glass), character of the surface upon which
the composition is applied (whether treated with other non-
compatible pesticides), pH of leaf surface, and.pH of water

2.

used for spray.

It is known that many insecticides are less effective
under certain alkaline conditions than neutral or slightly
acidic condition. The spray water in.Michigan is Obtained
from such sources as ponds, rivers, reservoirs, lakes and,
to a limited extent, from municipal water supplies. The
waters from these sources have varying pH ranges.

Records1 show the pH of the surface water in this state
to be alkaline in reaction. The Institute for Fisheries
Research of the Michigan Department of Conservation gave
records on the alkalinity of 111 lakes in 24 counties. Of
these, only six gave an acid reaction, ranging from pH 5.9
to 6.8. The remaining 105 lakes ranged from pH 7.2 to 9.2.

Few data were available for the streams of Michigan,
but they too indicate that waters are predominantly alkaline.
One study on.Michigan streams, that of Creaser and Brown2
(1927) on the streams in the upper portion of the Lower Penin-
sula, reported a range of pH 7.1 to 8.2, all alkaline.

The pH of the municipal water supplies ranges from 7.1
to 7.7. This range of pH fluctuates daily depending upon the

condition of the raw water.

1Institute for Fisheries Research, Michigan Department of
Conservation.

2Hydrogen-ion Concentration of Brook Trout water of Northern
Lower Michigan, Ecology 8:98-105.

3.

The writer took ten samples from spray water sources
in various parts of the agricultural area of this State.
The pH ranged from 7.8 to 8.1, all alkaline.

With alkalinity of’Michigan surface water as high as
pH.9.2, it seemed possible that water used for spraying
purposes might have detrimental effects on the toxicity of
insecticides. This possibility led to an inquiry into the
effects of pH on the toxicity of insecticides.

II. REVIEW OF LITERATURE

Richardson and Shepard (1950) studied the toxicity of
nicotine to the house mosquito M pipiens L. in aqueous
solutions at various pH values. A few similar experiments
were also made with pyridine and m’ethylpyrrolidine. Solu-
tions of 0.05 M concentration, adjusted to pH values of 2.4,
3.6, 5.0, and 7.0 with sulphuric acid, and at pH 9.7 (the
free base) showed a toxic action that increased with increas-
ing pH value. Solutions adjusted to pH 3.6 and 5.0 with
hydrochloric acid gave similar results to those adjusted with
sulphuric acid. Solutions of 0.1 M, 0.03 M, 0.01 M and
0.001 M concentrations were adjusted to pH 5.0 with sulphuric
acid and compared in toxicity with solutions of the base of
the same molar concentrations. it each nicotine concentra-
tion, the free base was about 5 to 7 times more toxic than
was the nicotine sulphate solution at pH 5.0. The addition
of an inorganic hydroxide (0.05 to 0.001 N) to an aqueous
solution in nicotine had no apparent effect on the toxicity
of that solution. Pyridine solutions (0.03 M and 0.12 M)
were about twice as toxic as solutions of the same molar con-
centration titrated to pH 5.0 to 4.9 respectively, with sul-
phuric acid. Methylpyrrolidine solution (0.05 M) was about
19 times more toxic than methylpyrrolidine hydrochloride
solution of pH 5.0. It was discovered that the speed of toxic

5.

action to the larva of 933.35 pipiens of nicotine, pyridine,
and methylpyrrolidine in aqueous solution was directly re-
lated to the concentration of the undissociated molecules.
It was believed that the toxicity resulted largely from the
penetration of the molecules into the body through the wall
of the alimentary tract. Nicotine ions were somewhat toxic
but much less so than nicotine molecules. It was believed
that the change in toxicity of a nicotine solution with
change in pH resulted largely from the dissociation of pyrro-
lidine nitrogen. In this study it was also shown that the
free base in solution was much.more toxic than nicotine sul-
phate.

Brown and Hoskins (1959) found that pH not only affected
the toxicity of insecticides but that it had an important
relation to the amount of oil deposited by petroleum oil
emulsions emulsified with sodium oleate triethanolamine and
hemoglobin. 011 deposit-increased when the pH was increased
from 2.5 to 10.0.

Carter (1940) demonstrated the relationship of pH values
of cryolite to its phytotoxicity. He took eight samples of
natural cryolite and reported that pH values ranged from 8.00
to 7.10. The pH value of the domestic synthetic cryolite
ranged from 7.45 to 8.10. He found that the foreign synthetic
cryolite varied considerably in.pR. Carter believed the titra-
table acidity and low pH values of some of the samples might
have been partially responsible for the burning that sometimes

6.

followed the applications of cryolite insecticides. Two
samples of cryolite were reported to have caused excessive
burning when used on vegetations such as beans, peas, corn,
cotton and peanuts. However, other samples having a greater
titratable acidity have not been reported as causing burning.

Baker and Questal (1959) reported that corn appeared to
be susceptible to injury when treated with domestic synthetic
cryolite. In an effort to reduce this injury, colloidal ben-
tonite clay was added to these nicotines to act as a possible
buffer.

Hoskins (1940) stated that stomach poisons are nearly
always swallowed along with the food to which.they have been
added and hence are subjected to the conditions prevailing
during the digestive process. It is to be expected then that
the manner and severity of the toxic action will be dependent
upon the chemical substances which occur in the fluids of the
digestive tract. Hoskins observed definitely that the pH of
the digestive tract affected the toxicity of certain types of
insecticides.

Wigglesworth (1935) demonstrated that the digestive-
juices of most insects were weakly acid or weakly alkaline.
The pH of the mid-gut contents in the cockroach averaged 6.2,
in Disippus 7.0-7.5, in Chironomus larvae 7.2-7.8, in Glossina
6.5-6.6, in Apia 5.6-6.5, and in 5113 larva 6.8. Wigglesworth

7.

observed that more acid conditions sometimes resulted in
bacterial fermentation notably in the crop of Orthoptera, in
which the pH commonly ranged from 5.0 to 5.9. This effect
naturally varied with the diet. In the cockroach.Blatella
the pH in the crap fell to 4.4 after feeding with glucose
which is readily broken down to lactic acid, 4.8 after lac-
tose and 6.5 after protein. Wigglesworth demonstrated that it
was characteristic of larvae of TrichOptera and.Lepidoptera
that mid-gut contents were always strongly alkaline (pH 9.0—
9.4). Similar conditions were met with in some herbiverous
Coleeptera, but in the case of LepidOptera, alkalinity was not
confined to phytophagous species. Wigglesworth also observed
that in a few insects, there were localized differences within
the mid-gut. In genebrio larvae the anterior two-thirds of
the mid-gut turns litmus red while the posterior third turns
it blue. In Lucilia larvae the short middle segment of the
mid-gut was strongly acid, with.a.pH of 5.0 to 5.5, while the
segments anterior and posterior to it were about pH 7.5, exr
cept toward the hind end, where the contents were strongly
alkaline as the result of ammonia production. ‘A similar re-
gion, with a pH of 5.0, occurred near the junction of mid-gut
and hind gut in the wood-feeding termite. The nature of the
acid in these cases was not known with certainty, but it was
thought to be phosphoric acid.

H. S. Swingle (1958) made a study on the pH of insect

8.

digestive tracts and the effect on various arsenicals. He
found phosphate as a component of the digestive secretions
from nine species of insects. He found that the formation of
soluble arsenic from acid lead arsenate, calcium arsenate and
magnesium arsenate was largely dependent on the hydrogen-ion
concentration of the solution. It was influenced to a lesser
extent by the concentration of acids, bases, and salts in the
solution. The presence of phosphates greatly increased the
amount of soluble arsenic formed from acid lead arsenate in
alkaline solutions. This was apparently due to precipitation
of part of the lead as lead.phosphate, as this compound.was
found to be very insoluble in alkaline solutions. Phosphates
influenced the solubility of the arsenic in calcium and.magb
nesium arsenates to only a slight extent. It was discovered
that the relative toxicity of acid lead arsenate, calcium ar-
senate and magnesium arsenate to nine species of phytophagous
insects was correlated with the relative amounts of soluble
arsenic formed from the arsenates in phosphate solutions having
the same pH was was found in the mid-guts of these insects.
For insects having alkaline reaction in their mid-gut, acid
lead arsenate was least toxic; for insects having an acid re-
action of pH 6.0 in their mid-gut, magnesium arsenate was most
toxic and acid lead arsenate least toxic. It appeared possible
to predict the relative order of toxicity of acid lead arsen-

ate, calcium lead arsenate and magnesium arsenate to chewing

insects, if the hydrogen-ion concentrations in the insects'
mid-guts were known.

Kenaga (1950) studied the effects of pH on several or-
ganic toxicants. He showed that certain alkaline conditions
were detrimental to the insecticidal properties of lindane,
parathion, and the dicyclohexylamine salt of 2-cyclo-hexyl-4,
6 dinitrophenol. In tests with lindane at pH 10.25, 80% mor-
tality was observed on southern army worm. With the same to-
xicant, but with pH 6.5, mortality dropped to 70%. He also
found that the alkaline dispersions of dicyclohexylamine salts
of 2-cyclohexyl-4, 6 dinitrophenol were inferior to neutral
dispersions in contact action against the two-spotted mite
adults. With a pH of 10.25, only 15% mortality was attained.
However, with a pH of 6.7, 100% mortality was observed. It
was also found that alkaline compositions of parathion were
significantly less effective than neutral dispersions in re-
sidual action. .Against the two-spotted spider mite 100% mor-
tality was attained with.a pH of 10.2, but the residual
action drOpped markedly. With a pH of 7.0, a mortality of
100% was observed, but there was no marked drOp in the resi-
dual action. '

Ginsburg (1957) studied the relationship of 002 to the
solubility of arsenates. He discovered that 002 did not in-
crease the solubility of lead arsenate. However, 002 did in-
crease the solubility of calcium arsenate. Since calcium ar-

senate contains 002, this was considered one of the factors

in considering the solubility of arsenic.

10.

III. METHODS AND PROCEDURES

The experiment was carried out under laboratory con—
ditions. Mexican bean beetle larvaegpilachna varivestus
Mule. were used in testing the effects of pH levels on the
toxicity of four groups of insecticides. Only the third
instar larvae were used for this purpose. This insect was
chosen since it is relatively easy to rear under greenhouse
conditions and is a pest of economic importance. The in-
sects were reared in the greenhouse on cranberry beans. Be-
fore each test, the required number of third instar larvae
were collected in a glass container with cranberry leaves

Cranberry bean plants were used as host plants for
spraying. This variety was very appropriate since the plant
maintained its rigidity throughout its growth. In addition
to the above quality, this variety of beans was readily at-
tacked by the insects. The test plants were grown individu-
ally in 4—inch flower pots. These plants developed mature
primary leaves only and attained the height of six inches
when used. In order to encourage large primary leaves,
potassium nitrate fertilizer was used.

.Alkaline and acid conditions of the spray water were
obtained by adding magnesium carbonate and glacial acetic
acid, respectively, to distilled.water with a pH level of

12.

7.0. The acid water was buffered.with magnesium carbonate

to stabilize the hydrogen—ion concentration. .Alkalinity was
maintained at a pH level of 8. ,Acidity was stabilized at
the pH level of 6. Since the distilled water indicated pH
7.0, it was used without any chemical alteration. The pH
levels were measured by a Hellige pH colorimeter and were
corrected with a Beckman glass electrode pH meter. There was
a difference of .4 in the pH reading between two types of pH
indicators. Each solution was checked with both pH meters
before being used as a spray diluent.

The pH levels of 6, 7, and 8 were chosen since the sur-
face and the ground.waters of the state vary in pH levels from
6 to 8.1. The writer also took ten samples from various parts
of the agricultural area of the state. These samples showed a
range in pH from 7.8 to 8.1.

In order to study the effects of pH on sprays, four in-
secticides were used. These represented such groups as bota-
nical, chlorinated hydrocarbon, inorganic, and organic phos-
phate insecticides. Retenone was used as a botanical insecti-
cide, DDT for a chlorinated hydrocarbon, lead arsenate for an
inorganic material and parathion for the organic phosphate
group. All formulations used in this study were wettable pow-
ders containing 4%, 15% or 50% toxicant, an inert diluent and
small amounts of surface active ingredients (See Table V).

Two different methods of applying toxicants to the host

plants were attempted before a suitable method was chosen. At

15.

first, cranberry bean plants containing mature primary leaves
were dipped in each insecticidal diapersion of various concen-
trations. This method was abandoned since there was an ex-
cessive amount of spray run-off and there were no possible
means of controlling the amount of spray deposits on the
plants. Furthermore, this method of dipping did not simulate
the natural spraying conditions. These factors necessitated
the use of another method.

The second method was the Spraying of the insecticide
with a De Vilbiss atomizer sprayer, type LXG, No. 5021. This
proved to be an excellent choise. All sprays were applied
under a pressure of ten pounds. The turntable in the spray
chamber rotated at the speed of fourteen revolutions per min—
ute. Each.plant was placed on the turntable until nine revo-

lutions were completed. At this time there was an indication
(of run-off and the spraying was considered complete.

Preliminary spray tests were made before the actual exp
periment was started to determine the range of concentrations
in which the dosage mortality curve occurred. Rotenone, para-
thion, lead arsenate, and DDT were used. Individual insecti-
cides were tested at five different concentrations. All four
insecticides were dispersed in distilled water at pH 7.0.

For the final test each material was tested at three pH
levels, using five concentrations of insecticides and a blank
at each pH level. The test was replicated five times. Each
replicate plant was infested with five third-instar larvae

14.

immediately after the spray application. The plants were
covered with screen cylinders after the infestation.

The mortality counts were made at varying lengths of time
since the insecticides used varied in toxicity. All comparable
replicates were checked at identical length of time.

IV. DISCUSSION

Whether an arsenical is quickly toxic to either animal
or plant life depends largely upon the solubility of the com-
pound. Particle size, the minerals which occur in water
supplies, the other insecticides, fungicides and additives
which are mixed with arsenical suSpensions, the carbon dio-
xide present in the air or produced by plant respiration, the
hydrogen-ion concentration of the liquid medium, whether it
be in the spray tank or in the digestive tract of the insect,
all have decided relation to solubility and ultimate effect-
iveness. This experiment has been limited to the effect of
hydrogen-ion concentration on the toxicity of the insecticide.

Volck (1911) pointed out that acid lead arsenate is
stable under acid condition, but is changed to basic lead ar-
senate under neutral or alkaline conditions with liberation
of excess arsenic oxide. This liberation of arsenic oxide is
necessary in the change from acid to basic arsenates, for
acid lead arsenate contains 55%.A82)5 and basic lead arsenate
only 25%.

Results obtained in the study of the effect of hydrogen-
ion concentration on lead arsenate are given in Table I, in
which the data are given, and in Fig. l, which presents the
data graphically. At pH 8, the toxicity of lead arsenate
was less than at pH levels of 6 and 7. This difference in
toxicity was greatest at the median lethal concentration,

16.

which is considered to be a critical point. At this point
the sensitivity of such tests is the greatest. Since lead
arsenate is stable under acid condition and unstable under
alkaline conditions, there is contradiction in the experi-
mental data. Since the solubility of acid lead arsenate is
enhanced by the alkalinity of the water, it is possible that
some soluble arsenic, which is the toxic component, was lost
by run-off from the test plant, leaving the insoluble residue
reduced in Quantity of total arsenic. At pH 6 and pH 7, the
loss of soluble arsenic through.run-off was slight since at
these pH levels, lead arsenate is stable and only a small
amount of soluble arsenic is produced. Therefore, the stable
form adhered to the plant without reduction of total arsenic.
At a high concentration of lead arsenate, the hydrogen-ion
concentration had no significant effect on toxicity. High
concentration probably compensated for the loss of toxicity
through hydrolysis.

Parathion (0,O-diethyl-O-p-nitrOphenyl thiOphosphate,
010H14N05PS) is an organic phosphate preduced by German re-
search laboratories. It was made available in the United
States in 1946. It is only slightly soluble in water,
Islightly soluble or insoluble in petroleum ether, kerosene,
or refined spray oil, and completely miscible in acetone,
ethyl ether, cyclohexanone, alcohols, esters, and animal or
vegetable oils. It is hydrolyzed in the presence of alkaline

material such as lime, lime-sulfur, and bordeaux mixture.

17.

The effects of hydrogen-ion concentration upon a para-
thion spray solution are shown in Fig. 2 and Table II. There
appeared to be no significant difference in toxicity of the
parathion at pH 6 and pH 7. Slight acidity of the spray di-
luent did not cause any.appreciab1e change in toxicity in
comparison to neutral water. There was a significant differ-
ence in the toxicity at pH 8 up to the median lethal concenp
tration. The experiment indicated that slight alkalinity
hydrolyzed parathion to the point which.reduced the kill of
third instar larvae approximately 12%. This reduction of
kill was consistent at varying concentrations up to the median
lethal concentration. The median lethal dosage was i lbs. per
100 gallons of water. Above this critical area of the toxicity
curve, the curve approached closer to the toxicity curve of
pH 6 and pH 7. This was probably due to increased concentrae
tion of toxicant which overcame the reduction in toxicity from
hydrolysis of parathion. There is also some possibility of
fumigant effect with an increase in concentration of parathion.
However, it is believed that the Mexican bean beetles are not
affected by fumigants as much as small organisms such as mites
and aphids.

In studying the effects of hydrogen-ion concentration on
various insecticides, rotenone was used as a representative of
the group of botanical insecticides. Plants belonging to the

genera Derris, Lonchocarpus, Tephrosia, and.Milletia are re-

18.

presented by the largest number of species known to contain
rotenone and rotenoids. Rotenone is not a stable insecticide.
It decomposes in various organic solvents. The rate of this
decomposition depends on the solvent, temperature, access of
air and other factors.

Experimental data shown in Fig. 5 and Table III indicate
that there are no significant changes in the toxicity of rote-
none at the pH level of 6 in comparison to neutral water. The
toxicity of rotenone at the pH level of 8 was consistently
lower than at pH 6 and 7.

‘ Rotenone is unstable in alkaline media. This experiment
has shown that alkalinity can reduce toxicity significantly.
The greatest reduction in toxicity appeared at median lethal
concentration. .At low and high concentrations of rotenone,
the toxicity was almost uniformly reduced. At a pH level of
8, the hydrogen-ion concentration reduced the toxicity of ro—
tenone even at high concentration. It is believed that alka-
linity splits the molecule at the central pyrone ring or, when
dilute, racemizes the compound and promotes oxidation. The
first stage in decomposition results in the formation of a
hydroxyl group, the second, in the production of dehydrorote-
none, and the third, in a split molecule.

Dichlorodi phenyltrichloroethane, c1439015 (commonly
known as DDT) was tested at three hydrogen-ion levels, pH 6,
pH 7 and pH 8. It is commonly understood that DDT should not

19.

be compounded with strong alkalies. This experiment showed
no significant reduction in toxicity by using water at pH 8

as indicated in Fig. 4 and Table IV. At the concentration

of 1% lbs. of DDT per 100 gallons of water, there was some
difference in mortality at the three pH levels. However, it
was concluded that the difference was not significant. The
conclusion was derived by using Wilcoxon's rapid approximate
statistical procedures. It was evident that the hydrogen-ion
concentration must be higher than pH 8 to have any significant
reduction in the toxicity of DDT.

V. SUMMARY

One of the factors which may alter the effectiveness of
insecticidal sprays is the pH, which is a measure of the
acidity or alkalinity of the mixture. It is known that many
insecticides are less effective under alkaline conditions
than under neutral or slightly acidic condition.

It has been found that the formation of soluble arsenic
from acid lead arsenate, calcium arsenate and magnesium ar-
senate is largely dependent on the hydrogen-ion concentra-
tion of the solution. It is influenced to a lesser extent by
the acids, bases, or salt in the sclution. It has been shown
that certain alkaline conditions are detrimental to the in-
secticidal properties of lindane, parathion, and DDT.

The writer undertook a study of the effect of hydrogen-
ion concentration on the toxicity of certain insecticidal
sprays in relation to the pH of spray water in the state of
Michigan.

Ten samples of spray water were collected from various
parts of the agricultural area of the state. The pH ranged
from 7.8 to 8.1, all alkaline. With ten samples of spray
‘water having pH values as high as 8.1, it seemed probable that
water used for spraying purposes might have detrimental effects
on the toxicity of the insecticides.

21.

The effects of pH levels on the toxicity of four insecti-
cides were tested under laboratory conditions, using third
instar Mexican bean beetle larvae Epilachna varivestis Mule.
as a test insect. The insects were reared in the greenhouse
on cranberry beans.

Alkaline and acid conditions of Spray water were obtained
by adding magnesium carbonate and glacial acetic acid, res-
pectively, to distilled water. The acid water was buffered
with magnesium carbonate to stabilize the hydrogen-ion con-
centration. The three pH levels used for spray formulation
were 6, 7, and 8. These levels were chosen since the samples
collected at various water sources fell approximately in this
range. The pH levels were measured by a Hellige pH calorimeter
and were checked with.a Beckman glass electrode pH meter.

Four insecticides were used in this experiment, namely,
rotenone, DDT, lead arsenate, and.parathion.(See Table V for
insecticide formulations).

Two different methods of spray applications were used.
First, plants were dipped in various insecticidal disperions.
Later this method was abandoned since there was an excessive
amount of spray runroff and there were no possible means of
controlling the amount of spray deposit. This method did not
simulate the natural spraying conditions. The second.method
of spray application was with the De Vilbiss atomizer sprayer.
All plants were sprayed to the point when there was indication
of run-off. At this point the spraying was considered complete.

22.

Preliminary tests were made to determine the range of
concentrations in which dosage mortality curve would occur.

For the final test each material was tested at three pH levels
using five concentrations of each insecticides and a blank at

each pH level. The test was replicated five times. Each re-

plicate (one plant) was infested with five third-instar larvae
immediately after the spray application.

For each type of spray, different time intervals were used
in making mortality counts since the insecticides used varied
in toxicity. All comparable replicates were checked at iden-
tical lengths of time.

The results of the experiment have shown that at pH 8, the
relative toxicity of lead arsenate was less than at pH levels
of 6 and 7. The difference in toxicity was greatest at the
median lethal concentration which was considered to be a cri-
tical point. It was concluded that since the solubility of
acid lead arsenate is enhanced by the alkalinity of the water,
it was possible that soluble arsenic was lost by run-off which
caused the reduction in toxicity of lead arsenate.

There was no significant change in the toxicity of the
parathion at pH 6 or pH 7. Slight acidity of the spray diluent
did not cause appreciable change in toxicity. There was sig-
nificant difference in toxicity at pH 8 up to_the median/lethal
concentration. The experiment indicated that slight alkali-
nity hydrolyzed parathion at the lower concentration to the
point which reduced the kill approximately twelve percent.

23.

The amount of parathion above the median lethal concentration
was not affected significantly by the variation in hydrogen-
‘ion concentration.

Experimental data indicated that there was no significant
differences in the toxicity of rotenone at the pH levels of 6
and 7. The toxicity of this insecticide at the pH level of 8
was consistently lower. The experiment showed that weak alkali
can significantly lower the toxicity of rotenone. The greatest
reduction in toxicity appeared at the median lethal concentra-
tion.

It is generally understood that DDT should not be com-
pounded with strongly alkaline media. However, this experiment
indicated that there were no significant differences in toxicity
caused by using water at pH 8. It was evident that hydrogen-
ion cencentration must be higher than pH 8 to have any reduction.
in the toxicity of DDT. 4

The final conclusion derived from this study of the hydro-
gen-ion concentration on the toxicity of lead arsenate, para-
thion, rotenone, and DDT is that these insecticides were affected
only slightly by using water in which the pH ranged from 6 to
8.1. These were the pH levels found in the ten samples of water
collected from the agricultural area. The greatest reduction
in toxicity at pH 8 was found at the median lethal concentra-
tion and there were no significant changes above this concen-

tration. Since the grower strives for a kill of 95 percent or

24.

more and at that level the experiments indicated that there
were no appreciable reductions in toxicity at pH 8, it could
be concluded that alkalinity at pH level of 8 has little or
no detrimental effect at concentrations where most of the in-
sects are killed. .
The entire experiment was limited to the study of the
effects of hydrogen-ion concentration on the toxicity of lead
arsenate, parathion, rotenone, and DDT. No discussion was
made of possible reactions of magnesium salts. However, it
should be recognized that magnesium carbonate, or other salts,

might cause variation in toxicity.

Percentage

Mortality

100

60

20

 

25.

 

use

'6

/ //fl7

/
/
/
/
/
. / /
/+/
/
/
/
{/
/
/
/
/
//
/
)
/

1 a 5 A I

Concentration of lead arsenate (acid)
(1b. ./100 “10)

fig. 1. Mortality of lexicon Bean Beetles following treat-at
Iith load arsenate. Mortality observed 60 hours
after treatment.

Psrosntsp

Mortal “V

100

20

26.

 

 

PH 6
P3 7
/ pa 6
/
/
/
//
)g I
/
/
/
! V
/ / ’
/
/ .
/ /
/
/
a A/
.g /
l // /
/
/

0 1/52 1/16 1/5 1A 5/5 I

Oomsntrstion of firsthion (lbs./lOO pl.)

fig. 2. Mortality of Mexican Bean Beetles following treatment
with parathion. lbrtslity observed 6 hours after
treatment.

Percentage
Mortality

100

A0

20

 

 

 

o i} 5 A} 6
Concentration of Rotsnons (lbs./100 gel. )

Mg. 5. Mortality of Mexican lean Isstlos following treatment
with rotenone. Mortality observed 60 hours after
treatment.

 

 

Pbrcontsgsll
Mortality
100
vs 6
8° /: m 7
,/ /
53/ ’
/ ,-.-» 96 ”pa 8
/ " f
. /
60 /
4 /
/
/
I /
no /2(
/ /
/
20
/
/
0 1/4 1/2’ 5/5 1 ii “"

Concentration of DDT (lbs./100 gal.)

71;. A. Mortslity of Mexican Bssn Isstlss following treatment

with DDT. Mortality observed 60 hours after
treatment.

29.

TABLE I

MORTALITY OF MEXICAN BEAN BEETLES
FOLLOWING TRMTMENT WITH LEAD ARSENATE AT THREE pH LEVELS

(Each replicate consisted of five 5rd instar larvae.
Counts were made 60 hours after treatment).

 

 

 

 

 

 

 

 

 

 

 

ApH6
AI HPFBplicates AI
Cone. I II III IV V Avgs.
Ulbs. 0 0 0 (T 0 TI
1 . 1 1 l g 2 o 1.0 fi‘
2 " l 2 2 5 l 1.8 g
_5 " 2 2 5 4 5 2.8
4 ' 2 5 4 4 5 5.2
5 ' 5 5 5 4 4 5.4
_ pH? 1
Replicates

I III

 

 

 

 

 

 

 

 

 

 

 

 

 

Replicates

Cone. I II III IV V Avgs.
WA—
% l 1 1 O 91 0.6
WA” g 1 Al 1 2 l 1.2 L
5 " 4 1 2 5 g l 2.0

4 ' g 4 4 114 ~41 A l 2.8

5 ' 5 5 5 5 5 5.4

50.

TABLE II

MORTALITY OF MEXICAN BEAN BEETLES
FOILOWING TREATMENT WITH PARATHION AT THREE pH LEVELS

(Each replicate consisted of five 5rd instar larvae.
Counts were made 6 hours after treatment).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

_ pH6
Replicates T
Cons. I II III IV_ V _ Avgs.
0 lbs. 0 0 0 0 0 __ 0
52 ' O l l O O 0.4
1 l6 ' 2 l 2 l 5 1.8
4 5 2 5 I . ___
1/4 " 4 5 4 _ g 0_ 5.0
5/16 " 5 5 5 5 4 4.4
H7
Replicates
Cone. I II III IV V % Avgs.
0 lbs. 0 0 0 0 0 0
_l/52 " g 1 l 2 0 l 1.1
__1/ls ' 2 g 2 1 2 l A 1.8
1/8 " 5 5 2 A g 2% 2.4 _
1/4 " 4 2 0 4 4 2.8
5116 ' 4 A 4 4 4 5 4.2
.1 H pH8 fig
Replicates
Cons. I ‘ II III IV V Avgs.
0 lbs. 0 0 0 0 0 0
1/52 " 0 0 l 0 0 _ 0.2
1/16 ' 2 1 2 0 l l.2__
_1/8 I 3 2 1 2 2 2.0
*1/4 " 4 4 5 2 2 5.0_
5/16 ' 5 4 4 4 5 4.0

51.

TABLE III

MORTALITY OF MEXICAN BEAN BEETLES
FOLLOWING TREATMENT WITH ROTENONE AT THREE pH' LEVELS

(Each replicate consisted of five 5rd instar larvae.
Counts were made 60 hours after treatment).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

PBS _1
Replicates
Cons. I II III IV V .Avgg.
0 lbs. 0, 0 0 _ 0 0 g
__1_g ' 1 l 1 o o 0.6
5 ' 0 0 2 2 4 1.6
4% ' 2 2 5 l 5 2.2
“,6 ' 4 5 4 4 5 400,11
7% ' 4 4 5 5 5 4.6
ngV
‘ Replicates
Conc. I II III IV V Avgs.
__ 0 lbs. 0 0 0 0 0 0
1% ' 0 1 l A 0 110 g 1 0.4 _
_g5 ' 2 l 2 l 1 1.4
4% ' 5 2 2 l 4 2.4
6 ' 4' 5 6 4 5 5.8
7% ' 4 5 5 5 5 4.4

EH8

 

 

 

 

 

 

Replicates

Cons. I II III IV V Avgs.

0 lbs. 0 O O O O O
l} ' l 0 0 0 0 0.2
5 ' __2 9 2 l 0 1.0
3% ' 2 l 2 2 2 1.8
_16 ' 5 5 4g, 5 4 5 5.2
7% ' 4 5 4 5 4 4.0

 

52.

TABLEIV

MORTALITY OF MEXICAN BEAN BEETLES
FOLLOWING TREATMENT WITH DDT AT THREE pH LEVELS

(Each replicate consisted of five 5rd instar larvae.
Counts were made 60 hours after treatment).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

   

 

 

 

 

 

 

1 JHS :_
Replicates
Gone. I II III IV V Avgs.
0 lbs. 0 0 0 0 0 0
1/4 " l 0 0 l 0 0.4
1/2 " j l 4 2 2 2.4 4
5/4 " 5 2A 4 5 4 5.2 A
_ 1 . 5 4 A 4 s 5 5.8 ._
1% ' 4 4 4 4 5 4.2
1 1 an! _ 1 _
Replicates
_ anc. I II III IV V Avgs. _
0 lbs. 0 0 0 0 0 0 M
1/4 " 0 _ 2 l g l l 1.0
1/2 . s 2 2 s 1 3.2 w
5/4 " 2 2 4 4 4 5.2 g
l " 5 _ 5 2 5 4 5.4 __A
1% " 4 5 4 4 5 4.0
-_”-:§§111_1-
Replicates
Cons. I II III IV V Avgs.A
‘ 0 lbs. 0 O _ O O O 0
M1/4 " 1 1 l .1 2 0g 1.0
ml/g 'L # g 5 A 5“ 5 A 2 2.6
_ 5/4 " 2 5 4 5 M4 5.2
.1 l " _ 5 4 4 5 5 g 5.4
' 4 4 4 .5 5 5.6

It

55.

TABLEV

CONCENTRATION AND KIND OF INSECTICIDE APPLIED
STUDY OF THE EFFECT OF HYDROGEN-ION CONCENTRATION
ON ITS TOXICITY

 

it

Pounds per
Insecticides 100 Gallons
of Water

____.._ __; ‘

Arsenate of leads

Parathion (15%)4 1/32

Rotenone (4%)5 1%

DDT (50%)5 1/4

 

SDrtho Arsenate of Lead, California Spray and Chemical
Company, Richmond, California.

4Dow Chemical Company, Midland, Michigan.

5E-Z-Flo Rotenone Spray Dust No. 44, Michigan Fertilizer
Company, Lansing, Michigan.

6Deenate, E. I. DuPont de Nemour and Company, In.,
Wilmington, Delaware.

54.

LITERATURE CITED

Baker, W. A. and D. D. Questal
1959' Investigations of Insecticides for Control of
European Corn Borer at Toledo, Ohio, 1957-58.
Journ. Econ. Ento., 52:526-550.

Carter, Re R.
1940 The Titratable Acidities and pH Values of Cryo-
lite Insecticides. Jour. Econ. Ent., 55:699.

Fleck, Es Be, and. Haj-191', He Ls .
1946 Stability of DDT and Related Compounds.
Jo Arno Chemo 8000, 68:142-145.

 

Frear, D. E. H. .
1948 Chemistry of Insecticides, Fungicides, and Herbi-
cides. D. Van Nostrand Company, Inc., 2:11-59.

Hoskins, W} M.
1959 Recent Contribution of Insect Physiology to In-
sect Toxicology and Control. Hilgardia 15, No. 6,
558-555. ‘

Kenaga, Eugene E.

1949 Insecticidal Activity of Various Formulations of
Several Organic Toxicants with Special Reference to
pH. Proceedings of the Fifth Annual Meeting of the
North Central State Branch of the American.Asso-
ciation of Economic Entomologist, 8-10.

Jones, H. A., and.Haller, H. L.
1951 The I'Yellow Compounds' Resulting from the Decom-

position of Rotenone in Solution. J. Am. Chem. Soc.,

55:2520-2524.

 

1951 Agricultural Entomologist, Dow Chemical Company,
AMidland, Michigan. (oral communication).

Richardson, C. H.
1942 Inorganic Stomach Poisons. Chem. and Chemical Ens
AgineeringANews., 20:241.

 

Richardson, C. H. and H. H. Shepard
1950 Hydrogenvion Effect on Nicotine. Aggur. Agri. Res.,
41:557-548.

 

55.

Shepard, H. H.
1959 The Chemistry and Toxicology of Insecticides.

Burgess Publishing Co.,'Minneapolis, Minnesota.
79-900

Shepard, H. H.
1951 The Chemistry and Action of Insecticides.

Burgess Publishing 60., Minneapolis, Minnesota.
526-527.

ASWIHgle, Ho So

1958 Relative Toxicities to Insects of Acid Lead Arsen-
ate, Calcium Arsenate and.Magnesium Arsenate.
Jour. Econ. Ent., 51:450-441.A

Volck, W. H.

1911 The Significance of Lead.Arsenate Composition.
Science., 866-870.

Wigglesworth, V. B. .
1957. The Principles of Insect Physiology. E. P.

Dutton & Company, Inc., New York, New Yerk.
272-277.

Wilcoxon, F.
1949 Some Rapid Approximate Statistical Procedures.

American Cyanamid Co., New York, New York.
4-5.

ROOM US? Nil ‘1!

 

MICHI IGAN STATE UNIVERSITY LIBRARIE

lWIIIIL IL LIIIILIIIIL LLIH