The effectiveness and duration of treatments with technical DDT in different soils against larvae of the Japanese beetle

STATE PL-.,T BOARDD

March 1947 -71




United States Departueit of iAgriculture
Agricultural Research Adninis.tr .tlon
Bureau of T.,tomology and Plant -,;srantine



THE FFECTIV:E.z1S AMD DURATION OF TT>: :. WITh r2,lCAL DT.
IN DIFF-7 ETT SOILS t".AI: L1'1'<2 OF HE JAPAY- 2 B'.iTL.

By Walter E. FlenmLin and Iurrnr! W. Meines,
Division of Fruit Insect Investigations


When the study of DDT for control of the larvae of the Japanese
beetle (Popillia japonica ::ewm.) was begun in 1943, one problem was
to determine whether the nature of the soil was an important factor
in the initial effectiveness and the duration of the insecticidal
treatment. This phase of the investigation is still in progress,
but a report covering the results obtained by the fall of 1946 seems
desirable at this time.

THE DDT

The technical graie of DDT was used in this study. The setting
points of the various batches ranged from 91.20 to 93.9 C. It was
prepared for use by micronizing 1/ with an equal weight of pyrophyl-
lite. For application as a spray thiis 50-percent material was sus-
pended in water. For application as a dust it was diluted further
with pyrophyllite to contain 10 percent of DDT, and 3 percent of
tricalcium phosphate was added.

LAB O.ATCOR'- SST DIES3

A study of DDT in 28 soils was undertaken under controlled con-
ditions in the laboratory. The soils were obtained from the various
soil provinces of New Jersey--the Glacial, the Glacial Lake and River
Terrace, the Appalachian mountainn the Piedmont Plateau, the Limestone
Valley, and the Coastal Plain--in order to have soils from the dif-
ferent physiographic divisions. ',:ost of these soils also occur in



1/This material was micronized through the courts" of the Micro-
nizer Processing Co., Inc., "oorestown, N. J.





- 2-


-r sections of the country. Each soil was obtained from a sec-
tii -here, according to the Soil Survey maps issued by the Bureau
of plant Industry, Soils, and Agricultural Engineering, it covered
a relatively large area. Each soil was identified definitely from
the characteristics of its profile and its texture.

The soil was- taken largely from the A horizon, the one in which
-ae normally occur during the active season. For each sample
a ',it 1 cubic yard of the surface layer was removed to a depth of
3 to 6 inches, and passed through a i/4-inch mesh sieve to remove
: ones, roots, and other debris.

Experimental Procedure

The 10-percent DDT dust was thoroughly mixed with 1 cubic foot
f 3ach soil at rates equivalent to 25 and 50 pounds of DDT per acre.
CLia volume of soil in an acre to a depth of 3 inches, 10,890 cubic
it, was used as a basis for these treatments. The soil and the DDT
re mixed by passing the materials through a gyratory riddle several
*,s. Each cubic-foot unit was divided equally among three testing
,Tiys, each 18 inches square and 4 inches deep.

Groups of 150 field-collected third instars ware introduced into
.,h treated sample, and into an untreated sample, of each soil im-
lately after the application of the DDT and at various intervals
ireafter. All tests were conducted at a temperature of 80 F.

The testing with the batches of larvae introduced 14.6, 74.6,
-m 127.6 weeks after treatment was discontinued temporarily because
h,7T began to pupate during the experimental period, a condition which
....,ds to produce erratic results. During periods when suitable larvae
re not available, the soil samples were removed from the testing
-.a and transferred to earthen pots. These pots were plunged in a
bad in an open field, where they remained undisturbed and exposed to
the rain, sun, and wind for 35 weeks during the spring, summer, and
fall of 1944, for 31 weeks during these seasons in 1945, and for 30
! s in 1946. Thus, since this investigation has been in progress,
Treated soils have been exposed to weathering in the field for
than half of each year.

Results were checked at weekly intervals after the introduction
each group of larvae. The soil from each tray was passed through
a -mesh sieve, which allowed the passage of the soil but not of the
S.ae. All living larvae, including both the normal and the moribund,
Qre counted and returned with the soil to the testing tray; the dead
-_ .vae were discarded. The soil was then watered and reseeded with
1 593.










The death rate of the larvae in the untreated soils, due to
bacterial disease, nematodes, injury, and other causes, was very
low, rarely exceeding 30 percent in tests extending over several
weeks. To compensate for these losses the percentage of the larvae
killed by each treatment in the different soils was determined by
Abbott's formula.

Upon completion of observations on a group of larvae, the per-
centages of the larvae killed were plotted against the periods of
time that the insects had been in the soil. When the mortalities
were converted to probits and the intervals of time to logarithms,
a linear relationship existed between these factors which could be
expressed adequately by a straight line. Time-mortality curves were
drawn for each group of 150 larvae introduced into soil treated with
DDT. From these curves the time required for the 25- and 50-pound
treatments to kill 98 percent of the larvae was determined. The
results with the different soils are summarized in table 1.






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-8-


Variability in Susceptibility of Larvae to DDT

Every effort was made to keep the variability due to other fac-
tors than poisoning to a minimum. The tests were conducted under
carefully controlled conditions. The temperature was maintained at
80 F. with a variation of i 2. The soils were kept at their
optimum moisture content, and after each examination grass seed was
sown to assure an abundant supply of food. As no practical method
of rearing a sufficient number of larvae under controlled conditions
for tests of this nature has been developed, it was necessary to
work with field-collected third-instar larvae. The larvae were col-
lected from different localities, were of unknown age, end were
stored at a temperature between 45 and 50 F. for different periods
before being used in the tests. With stock of this nature greater
variability would be expected than with insects reared under controlled
conditions.

Table 1 shows considerable variation in the time required to kill
98 percent of the different batches of larvae. The average ti'e for
the 28 soils ranged from 2.82 to 5.63 weeks with the 25-pound treat-
ment and from 2.18 to 3.43 weeks with the 50-pound treatment. The
variations were of a rhythmic nature and, it is believed, can be at-
tributed largely to the differences in the susceptibility of the
batches of larvae. These variations are highly significant and tend
to confound the data, making it difficult for one to discern changes
in the insecticidal value of the DDT treatments.

Effect of Soil Type

As the surface of soil particles determines to some extent the
degree of absorption, a fine-grained soil may be expected to absorb
more than a coarse-grained soil. Since absorption in soils is largely
a function of the silt, clay, and humus, the type of soil might have
an important effect on the insecticidal action of DDT. Sands contain
less than 20 percent of clay and silt, gravelly and sandy loams 20 to
50 percent, the loams 50 to 70 percent, and the silt loams more than
70 percent.

The average time required to kill li percent of the larvae in all
soil types was 4 weeks with the 25-pound treatment and 2.7 weeks with
the 50-pound treatment. The average periods required in the gravelly
and shale loams, sandy loams, lo&m% and silt loams were not much dif-
ferent from'these general averas-es. It appears that there is little
difference in the rates of insecticidal action in these types of soil.
In the sands, however, the 'DT killed the larvae faster. This would










suggest that in soil containing 20 -percent or ioe o cla an
a certain portion of the DDT n-y be absorLl: d Jadse ct
inactive.

Effect of the ,igin of -i

To determine whether the source of the soil t ae
fect on the speed of the insecticidal action
grouped according to their physic. a, .;'c t .e a a
time required to obtain 98 percent mortality of t ti .s
vae was calculated for each treatment. -, data a
table 2.


The glacial soils have been derived .._ tifi
till; the Glacial Lake and River Terrace soils .
deposits; the unglaciated soils of the aea *t
weathering of gneiss rock. The iilmetone .i.-, sils ha
rived by the weathering of limestone. During ths oes
original rock has been carried away i solution ol
ties of the original rock are left to make up t]a.ia
soil. The soils of the Piedmont Plateau na been -.iT
lying crystalline and sedimentary rocks, and the soils
Plain from unconsolidated sand, clay, gravel, and -e
have been transported from the older land aeas -, pos:
under marine conditions.


3 be en e -
.most of the

fc the

L under-
che ,astal
*1rl which
". in -..'t


Although there was considerable variation in tne f in-
secticidal action within the different ,1ysiogra ".c vines t:e
was nothing to indicate that the origin of the soil asan i portat
factor. Equally good results were obtained in soils from acial
drift areas, the Appalachian mountains the Pi:,-..mt plateau, tJa
Limestone Valley, and the Coastal Plain.

Effect of Natural Draiia',

Some of the soils have been developed under condition of wood
drainage. In these well-aerated soils there is no interruption in
the oxidation processes, and leahiri., and alluviation are im rtant
factors. The minerals are in various staCes of oxidation, denitrifi-
cation is inhibited, and there is a tendency o nitrates to acculate.
Usually these soils contain little organic matter. Other soils have
been developed under conditions of inadequate or poor drain 'e, so
that they are water-logged for varying periods. In these soils the
oxidation processes are depressed, leachin, and alluviation are not
important factors, and the restricted supply of air favors the -cuu-
lation of organic matter and the loss of nitrogs-.:..


a'
I





- 10 -


Table 2.--Effeet of the original of the so.l on the insecticidal action
of DDT against third-inatar larvae of the Japanese beetle

Average tLme required
for 98 percent
Physiographic mortality at in-
provinoe Soil series Soil type dicated dosage
25 pounds 50 pounds
per acre per acre


Glacial


Glacial Lace and
River Terrace


Appalachian
Mountain


Limestone Valley

Piedmont Plateae


Coastal Plain


Gloucester
Weehington
Aethersfield


Dunellen
Merrimac


Berks
Chester


Hagerstown


Croton
Lanadale


Penn


Collington

Colts Neck

Elkton
Keyport

Lakewood


Loam
Loam
Gravelly loam
Average

Sandy loam
Sandy loam
Average

Shale loam
Loam
Average

Silt loam

Silt loam
Gravelly loam
Silt loam
Shale loam
Silt loam
Average

Sandy loam
Loam
Sandy loam
Loam
Silt loam
Sandy loam
Loam
Sand


weeks


4.07
3.05
4.52


3.56
4.49
4.03

3.54
3.98
3.76

3.5"

4.99
3.25
3.19
4.07
3.53
3.81

3.62
4.92
2.75
3.98
4.43
5.85
4.52
2.55


'.eeks

2.80
2.53
3.09
2.81

2.78
2.84
2.81

2.37
2.65
2.51

2.72

3.41
2.44
2.52
2.75
2.43
2T71

2.38
2.78
2.18
2.63
3.13
3.23
2. 86
2.18





- 11 -


Table 2.--(Continued)


Average time required
for 98 percent
Physiographic mortality at in-
province Soil series Soil type dicated dosage
25 pounds 50 pounds
___________ ___________ ______per acre per acre
Weeks Weeks

Coastal Plain Portsmouth Sandy loam 4.99 3.07
(Continued) Sassafras Sandy loam 2.61 2.12
Shrewsbury Sandy loam 6.44 3.32
Loam 2.76 2.15
St. Johns Sand 2.95 2.33
Woodstown Sandy loam 5.10 3.12
Loam 5.18 3.10
Average 4.18 2.71

General average 4.02 2.71

Differences required for significance

At 1% level --- 0.66 0.37
At 51% level ----- .50 .28






- 12 -


To determine whethere r the conditions unler which a soil had been
developed affected the insecticidal action of DDT, the soils were
grouped accordirz to their natural drainage and the ifortality results
averaged for these groups, as shown in table 3.

The results indicate that the speed of insecticidal action with
-DDT may be inhibited in the poorly drained, inadequately aerated soils,
both agricultural and nonagricultural. This retardation is probably
associated with the higher content of organic matter ir these soils,
and under natural conditions the high content of water would be a fur-
ther inhibiting factor. Some of the TDT may be absorbed by the organic
matter and made insecticidally inactive; additions of organic matter
to soil tend to retard the mortality of the larvae. The larvae also
tend to move less extensively in a medium rich in organic matter than
in one made up largely of mineral aggregates, and a longer period is
required to kill them.

Effect of I1ineral Constituents of the Soil

Although no complete chemical analysis was made of the soils
used in this study, it is known that the differeLr-t series of soils
vary considerably in their composition. Some soils, such as the Lake-
wood and Sassafras series, are thoroughly leached and alluvlated and
tend to be deficient in the fertilizing constituents and other ele-
ments. Other soils are relatively rich in one or more constituents.
Soils of the Colts :eck, Collington, "ashington, Penn, and Chester
series are rich in iron; soils of the Chester, Penn, and '".ashington
series are rich in aluminum; the Chester, Croton, Berks, Gloucester,
and Washington soils are rich in potassium; the Gloucester and
Merrimac soils tend to be high in sodium; the Berks, Chester, Gloucester,
Lansdale, Merrimac, and -ashington soils tend to be high in calcium; and
the Berks and the Lansdale soils high in magnesium. In a complex mix-
ture such as soil, it is difficult to discern the effect of a single
constituent.

The speed of insecticidal action with DDT was the most rapid in
the thoroughly leached and alluviated soils. It was somewhat retarded
in soils rich in iron, aluminum, potassium, sodium, calcium, and
magnesium, but the role of each of these minerals in inhibiting the
insecticidal action is not known.

Duration of Insecticidal Action of DDT

No correlation was found between the time required to kill the
larvae and the period the DDT was in the soil. 3o far as could be
determined from a statistical analysis of the detailed data in table 1,
the effectiveness of DDT did not chince significantly during a period
of 128 weeks in the soils used in this study.








Table 3.--Effect of natural drainage of soil on the insecticidal
action of DDT against third-instar larvae of the
Japanese beetle

Avera'C time required
for 98 percent
Soil drainage Soil series Soil type mortality at in-
dicated dosage
25 -pou-iids 50 pounds
_____p____________ ______per acre per acre


Nonagricultural soils:


Well drained
Poorly drained


Weeks

2.55
2%.


Lakewood
St. Johns


2.18
'- .3


Agricultural soils:


Well drained


Imperfectly or
poorly drained


Berks
Chester
Collington

Colts Neck

T)unellen
Gloucester
Hagerstown
Lansdale

Yerrimac
Penn

Sassafras
Washington
Wethersfield


Croton
Elkton
Keyport


Portsmouth
Shrewsbury

Woodstown


Shal
Loam

Loam
Sand
Loam
Sand
Loam
Silt
Grav
Silt
Sand
3hal
Silt
Sand
Loam
Grav

Silt
Sil]t
Sandy
Loam
6andy
Sandy
Loam
Sandy
Loam


e loam 3.5
3.98
7 loam 3.62
4.92
y loam 2.75
3.98
y loam 3.56
4.07
loam 3,57
elly loam .5.25
loam 3.19
y loam 4.49
e loam 4.07
loam 3.53
y loam 2.61
3.05
elly loam 4. 52
Average 3.69
loam 4.99
loam 4.43
rloam 5 -.
4.52
r loam 4.99
r lcs n 6.44
2.76
r loam 5.10
5.18
Average 4.92


General average


4.02


Differences required for iTi)icance


At % lev el---
At 5, leval


2.37
2.65
2.358
2.78
2.18
2.63
2.78
2,80
2.' 0
2.44
2.52
2.84
2.75
2,43
2,12

3.09
2.59
3.41
3 13
3.23
2 .co7
3.07
3.32
2.15
3.12

3 .04
2.71


0.27


0.15


- 1? -






-14-


FIELD STUDIES

In the spring of 1944 field studies were begun to determine the
possible value of DDT for controlling the larvae in established turf
and for eradicating them in the soil about the roots of nursery 2l&Lts.

Turf Treatment

Early in May 1944, four plots totaling 3.1 acres were laid out
on the turf of the Passaic County Golf Club. This turf contained on
an average 22 Japanese beetle larvae per square foot and it was rela-
tively free of bacterial diseases. The soil was of the :':errimac series
and varied in type from a sandy loam to a loam. DDT was applied to
the turf as a dust at rates ranging from 24.5 to 36.5 pounds per acre.
Then the application was completed there was some residue visible on
the blades of grass, giving the plots a grayish-white appearance until
after the first rain. After the treatment nothing was done to the
plots except to mow the grass.

These treatments were applied to control the brood which would
hatch during the summer and were not expected to have much effect on
the population then in the soil. However, when the plots were exz-iir.-n
2 weeks later, .many dead and dying larvae were found. These dying lar-
vae showed the characteristic symptoms of DDT poisoning. A survey a
month later indicated that two-thirds of the larvae in the plots re-
ceiving about 56 pounds of DDT per acre and about one-third of those
in the plots receiving 25 pounds per acre were lead.

Additional surveys were made of these plots in the fall of 19-14,
in the spring and fall of 1945, and in the fall of 1946. Fifty dig-
gings were made at random over each plot. For each digging a square
foot of sod was cut and laid back, the soil was examined to a depth
4 inches, and all the soil was shaken from the roots of the grass and
examined. The number of larvae found in each digging in the treated
plots and in an adjacent untreated plot are given in table 4.

The results obtained were very encouraging. An application of
DDT to the surface of the turf at the rate of approximately 25 pounds
per acre reduced the population of larvae to negligible proportions.
The treatment has been effective for three seasons and from the present
indications it might remain effective for several more seasons.





- 15 -


Table 4.--Effectiveness against third-instar larvae of the Japanese
beetle of DDT applied to the surface of soil of the
Merrimac series


Dosage
of DDT


Pounds
per acre


Check(no treatment)


25.4


24.5


35.6


Area of
plot


Date of
treatment
(1944)


Square
feet

40,000


40,000 May 9


36,000


30,000


30,000


Date of
survey


Larvae
found


9 ~ I .1


Apparent
reduction


Number Percent


Sept.26,1944
May 2,1945
Sept, 13,1945
Sept.19,1946
Sept.25,1944
May 2,1945
Sept.14,1945
Sept .19,1946
Sept.26,1944
May 2,1945
Sept.17,1945
Sept.20,1946
Sept.26,1944
May 2,1945
Sept.17,1945
Sept.20,1946
Sept.25,1944
May 2,1945
Sept.14,1945
Sept.19,1946


583
543
681
528
9
4
2
1
115
44
14
1
49
39
12
6
21
15
11
0


98.5
99.3
99.7
99.8
80.3
91.9
97.9
99.8
91.6
92.8
9?7.7
98.9
96.4
97.2
98.4
100.0


36.5









Nursery Treatment

Studies were begun in 1944 to determine the possibilities of
DDT for eradicating larvae in the soil about the roots of nursery
plants in beds, frames, and blocks in the field, in order to satisfy
the requirements of the quarantine. All the treatments were applied
late in the spring or early in the summer to control the summer brood.
The treatments were applied at six commercial nurseries that were
growing azaleas, blueberries, and various narrow-leaved evergreens
in localities scattered over New Jersey. The DDT was applied at rates
ranging from 10 to 55 pounds per acre.

For the treatment of beds and plots before planting, the DDT was
applied as a 10-percent dust to the surface and mixed into the upper
3 to 4 inches by cultivation. For the treatment of established
nursery stock the DDT was applied to the surface as a spray. The 50-
percent dust was suspended in water and used at the rate of 1,000
gallons per acre. This volume of water was sufficient to moisten the
surface of the ground with no hazard of a runoff. In some cases, as
with beds of azaleas and blueberries, it was not practical to attempt
to mix the material into the soil by cultivation, but wherever possible
the plots were cultivated.

In September of 1944 and 1945 surveys were made to determine the
effectiveness of the various treatments in the nurseries. In making
a survey 250 plants per acre were examined in the large plots and a
minimum of 50 plants in the small plots (1/5 acre or less). For each
examination the plant was removed and sufficient soil shaken from
the roots to determine whether larvae were present. Then the hole
from which the plant was taken was enlarged to a square foot and
examined to a depth of 3 to 4 inches. The results of these surveys
are given in table 5.

When DDT was applied as a dust or as a spray to the surface of
nursery beds and plots at the rate of approximately 25 pounds ner acre
and mixed by cultivation with the upper 3 to 4 inches of soil, com-
plete elimination of the new brood of larvae was obtained by mid-
September. When the material was applied as a spray to the surface
and not mixed into the soil, the reduction in the density of the popu-
lation was pronounced but complete elimination was not always obtained.


- 16 -





- 17 -


Table 5.--E!ffectiveness of DDT applied to soil about the roots of
plants in commercial nurseries in New Jersey against
third-instar larvae of the Japanese beetle


Dosage
of DDT


Pounds
per acre


Area Date of
Soil series of plot treatment


Date of
survey


Acres


found .1:--
Plsib: ,>r,.` ]\-o:r
c XLliJ no' 1 ",; .c,l..,

NIum ber n,;" ,-,er -"ii.,iei


Sassafras

do,


Sassafras
Seat
Sassafras

Wethersfield
P peat
Sassafras


do.


55.0 Wethersfield
i peat

DDT APPLIED AS A

24.0 Sassafras


DDT APPLIED AS A DUST

0.25 April 9,1945 Sept.10,1945

.25 May 17,1944 Sept.27,1944
Sept.10, 1945

.06 May 18,1945 Sept.10,1945

1.00 April 9,1945 Sept.10,1945

.27 May 14,1945 Sept.13,1945

.25 May 17,1944 Sept.27,1944
Sept.10,1945

.25 May 17,1944 Sept.27,1944
Sept.10,1945

.21 May 14,1945 Sept.13,1945


SPRAY

1.50


70

70




70
i00


i50



70
70
70
50
5O


4

? 2
50 0

40 1

101 0

i3 0

257 0
30 0

257 0
a 0

13 0


AND MIXED INTO SOIL ABOUT ES'L -,' :i p .

June 11,1945 Sept.12,1945 1,:


10.7

21.0


24.0

25.0

27.0

30.0


50.0





- 18 -


Table 5.--(Continued)


Larvae
found in-
Dosage Area Date of Date of Plants Check Test
of DDT oil series of plot treatment Survey examined plot plot


Pounds
per acre

DDT APPLIED AS A

10.0 Sassafras

24.6 do.

25.0 do.

25.0 Lakewood
6 peat

25.0 Lakewood
+ peat

25.0 Lakewood
4 peat

28.4 Sassafras

29.8 do.

50.0 do.


Acres

SPRAY

0.01

.10

.01

.002


TO ESTABLISHED

July 10,1944

June 13,1945

July 10,1944

June 6,1945


.002 June 6,1945


.002 June 6,1945


.15 June 13,1945

.44 June 13,1945

.01 July 10,1944


BEDS AND NOT MIX

Sept. 27,1944


Sept.

Sept.

Sept.


12,1945

27,1944

21,1945


Sept. 21,1945


Sept. 21,1945


Sept.

Sept.

Sept.


12,1945

12,1945

27,1944


Number :,umber "u.T.ber

ED INTO SOIL

70 257 12

50 45 14

70 257 1


528


238


267


60

150

70


54

135

257










The soils treated in the commercial nurseries were of the
.fra T, Ak,-wod e's-d "'ethorsfield se'tes, and in sn Rcn ser
wo-ifi'ed b, the addition of peat and '.rnare0 Thw 'T was scnie in(ippa-
tion thawwhen appliedd to the su.faco of a plot and not cutltival-'1
into the soil, the DDT was more effective in the Lakewond than n thr,
Sassafras series, but another factor, namely, the type of plant in
the plot, might have influenced the results. "'Then the DDT was mixed
with the upper 3 to 4 inches of soilthere was no diff.renrice in its
acti^ iij the 2a.isafras and in the '.;'ethersfield series.

In thu plots left intact in commercial nurseries for tyo sa ..,
a treatment applied at the rate of approximately 25 pounds per acre
eliminated two subsequent annual broods of larvae and, from present
indications, it may eliminate one or more additional broods. There
was nothing to suggest that the insecticidal value of the treatments
had deteriorated under conditions in the commercial nurseries.

SUMMARY

A study of the influence of different soils on the insecticidal
action of technical DDT against the larvae of the Japanese beetle was
begun in 1943. This investigation is still in progress, but the
results obtained by the fall of 1946 are reported.

In preliminary laboratory studies the DDT was applied as a 10-
percent dust at rates equivalent to 25 and 50 pounds per acre to 28
soils, including 21 series and 6 types, from 6 physiographic soil
divisions. The results may be summarized briefly as follows:

1. The speed of insecticidal action was faster in
the sands than in the other types of soil, but there was
no significant difference in the rates in the gravelly
loarns, shale learns, sandy loans, silt loams, and loans.

9 The origin of the soil did not seem to be an
impO tant factor. Equally as good results were obtainL.
in soils from the Glacial drift areas, the Appalachian
I:ountains, the Piedmont Plateau, the Limestone Valley,
and the Coastal Plain.

3. The speed of insecticidal action may be inhibited
in poorly drained, inadequately aerated soils. This re-
tardation is probably associated with the higher content
of organic matter in these soils.




UNIVERSITY OF FLOR A
20-11 1 1 II I11 III H111
3 1262 09239 1456


4. The insecticidal action was the most rapid in the
thoroughly leached and alluviated soils. It was somewhat
retarded in soils rich in iron, aluminum, potassium, sodium,
calcium, and magnesium, but the role each of these minerals
has in inhibiting the action is .not known.

5. No correlation was found between the effectiveness
of DDT and the period the material had been in the soil.
So far as could be determined, the effectiveness of DDT
against the third-instar larvae did not change significantly
during 128 weeks in the 28 soils used in this study.

In the field studies DDT was applied at rates ranging from 10 to
55 pounds per acre to soils of the Sassafras, Merrimac, Lakewood and
Wethersfield series. All the treatments were applied in the spring
with the object of poisoning the brood which would hatch during the
summer. The DDT was applied to established turf and in commercial
nurseries to eradicate the larvae in the soil about the roots of nur-
sery stock. The results may be summarized as follows:

1. A 10-percent DDT dust applied to the surface of
established turf at the rate of 25 pounds of DDT per acre
caused a significant reduction in the larval population
then in the soil and reduced the density of three sub-
sequent annual broods to negligible proportions.

2. When DDT was applied as a 10-percent dust or as a
spray to nursery beds and plots at the rate of 25 pounds
of DDT per acre and mixed by cultivation with the upper 3
to 4 inches of soil, two subsequent ennv1 broods were
completely eliminated by mid-Septem