Tests with DDT on honey bees in small cages


Material Information

Tests with DDT on honey bees in small cages
Physical Description:
14 p. : ; 27 cm.
Woodrow, A. W
United States -- Bureau of Entomology and Plant Quarantine
U.S. Department of Agriculture, Agricultural Research Administration, Bureau of Entomology and Plant Quarantine
Place of Publication:
Washington, D.C
Publication Date:


Subjects / Keywords:
Honeybee -- Effect of insecticides on   ( lcsh )
DDT (Insecticide) -- Physiological effect   ( lcsh )
bibliography   ( marcgt )
federal government publication   ( marcgt )
non-fiction   ( marcgt )


Includes bibliographical references (p. 8).
General Note:
Caption title.
General Note:
General Note:
"December 1948."
Statement of Responsibility:
by A.W. Woodrow.

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 030294047
oclc - 780166720
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Full Text
'r .

December 1948 E-763

United States Department of Agriculture
Agricultural Research Administration
Bureau of Entomology and Plant Quarantine


|. By A. W. Woodrow, Division of Bee Culture 3/

The rapidly increasing use of DDT against insects attacking crops
visited by honey bees in their quest for pollen and nectar has caused
much concern. Some serious losses of bees following extensive field
applications of DDT have been reported, but for the most part this
material seems to cause less injury than arsenic. However, the general
effectiveness of DDT for destroying many species of insect. raises the
question whether DDT is also toxic to honey bees-

Experiments on the toxicity of DDT to caged acult bees mre reported
by Eckert. (I), Filmer (Z), and Holst (I). The experiments summarized in
this paper give additional information.

It is recognized that the behavior r1sponc of I. cc O-es
differ from those of bees in normal colonies ei--tiged in *-.eld -tlviti s.
In addition to the confinement, the lack of a queen, combs, and colony
organization, as well as changes in food, caged bees are subjected to
treatments they would not undergo in their usual enrvir--tenit. tverthe-
less, cage experiments often give fundamental information that .,rnot be
obtained otherwise,

Exp6r mental Procedure

5Aperlifents oer, :,'.nductud overg a period of 1.:.j- er -.,1: adult
bees of unknown a4es tAken from the combs of thqii: v...'.;, '*..L-
required. Variations in bees used may have affectso the unifO-r n of
rc:ilts o. th. e, aerimeats, but no differences dire:fly attrbutable Lc
this factor were observed.

The bees were placed in cages 3 1/8 inches square and 5/8 inch deen,
made of woodera f,.'mea covered or th urndh-r d rith i/8-in-scd.aA:
galvanized hArd',e wd clo ao',, on the top with 12-mesh 2iia.nm1.-; ',re f-.reen.
The wire-cloth Wo.ers and bottoms of the cages we.'e ht- I in pl,-. by saw
kerfs cut in the wooden side pieces, and they could be eoe by sliding
them horizontally. With this arrangement the bottom or floor could be
opened for filling the ca~e with bees, or a treated floor, usually a tin
or cardboard square of the same dimensions, could be substituted. The
caged bees were kept on a laboratory table ,-a i;-,6 fei a r'-percenrt sugir
Sirup except as noted. Inverted specimen vi,-.s with a l/6-in.h hole in
the cap were us-id a feeders. The temperature _'. ''. r : w
maintained within the .,:xige at *ihlcn be -!- :ve, to
90F. The relative humidity varied with dL]-y a-r; s.t.. .:.G-I fluctuations.

y/ In cooperation with the University of California.
-* 2 C '


The studies included the toxicity of DDT in the food or when brought
into external contact with the bees. The bees were fed DDT in sugar
sirup, queen-cage candy, or pollen paste; sprayed with DDT suspensions or
9'-lI:tions; dusted with DDT in talc; or brought into contact with surfaces
which had been previously sprayed or dusted with DDT preparations. Special
attention was given to external contact, since that appears to be the most
likely method of poisoning from the use of DDT on agricultural crops.

Technical DDT was used in the preparation of all materials used for
fet .... or spraying.

The following preparations were used for the feeding tests:

1. A DDT suspension was prepared by dissolving DDT in hot 95-per-
-It .thyl alcohol at the rate of 1 gram of DDT to 20 ml. of alcohol and
then pouring the solution into cold sugar sirup. In some experiments the
...h- was removed from the sirup by evaporation b.-fnre it was fed, to
av,-d alcoholic poisoning. Sirup containing DDT was fed individual bees
- a microsyringe.

2. DDT was added to queen-cage candy and to pollen paste to the
desired concentrations.

i4=-.-a.1&ls for spraying were prepared -a loilows:

1. DDT was dissolved in hot 95-percent ethyl alcohol at the rate of
1 gram to 20 ml. and then added to cold water to form a suspension.

2 ......"was dIssolved in xylene to the ,ajbijf concentrations,

3. Emulsions of DDT were prepared with Triton X-100 (an aralkyl
polyether alcohol), xylene, and water, according to common formulations.

'": api, .. -.'ith a -ra.," a'. .... ., -o. "., to use com-
*+edi air from the tank of a lmap.ack spr.ysr. This arrangement en-
t.he application of small quantities of spray and provided a con-
-I'ious flow of air for spraying.

For some of the experiments the caged bees were exposed to dried
DDT residues on tin surfaces 3 1/8 inches square, by substituting the
sprayed tin for the floor of the cage for a definite period and then re-
.- ... screen floor.

*' dusting, DDT diluted with talc was used., A 10-percent stock
dust was diluted further with talc when less concentrated dusts were
'- !,,ied. Where sulfur and DDT mixtures were used, sulfur was added to
..dust ill talc.

Zust was at first applied from a small duster with the same source
of air pressure as for spraying. In later experiments two other methods
*.- .'a,,, as follows:


1. The dust was poured into the cage onto the bees and then distrib-
uted by shaking the cage.

2. The dust was placed on a cardboard 3 1/8 inches square and dis-
tributed evenly by rubbing it with a small piece of smooth paper. The
treated cardboard was then used as the floor in the cage.

The last method was the most satisfactory one tried.

Tests in which a sprayed tin floor was placed under the bees for
definite periods showed much variability because of inadequate dosage
control and because bees often remained in other parts of the cage during
part of the exposure period. For the same reason larger dosages were
used than would be present under usual field conditions.

Response of Caged Bees to DDT

Tremors and increased activity followed by paralysis are character-
istic symptoms off DDT poisoning among caged bees. DDT in the food or in
direct external contact with the body produces partically the same

Extremely light doses of DDT may have little noticeable effect upon
the bees. When they are affected by DDT, however, symptoms usually may
be observed within a few hours after contact. Some bees completely re-
cover from the mild tremors and restlessness produced by light dosages.
Heavier dosages bring on intense tremors and frantic movements followed
by paralysis and finally death, in which the victim usually lies on its
side or back. Such violent response is often immediate, particularly
among bees sprayed or dusted directly, and frequently they sting one an-
other causing death.

The time required to kill bees treated with DDT varies according to
the dosage. With heavy dosages some may die within 1 to 4 hours, and
frequently all are dead within 18 hours. When the mortality is high, most
of the bees die the first day. Bees that survive the first 2 days in
good condition usually continue to be unaffected.

Response to the same dosage varies considerably in different lots of
bees. The factors governing this variation have not been determined,
although disturbance at the time of exposure to DDT may be an important

Bees dusted with DDT diluted with talc and those dusted with talc
alone respond at once with increased activity and frequently resort to
fighting. They immediately begin to clean the dust from their bodies and
drop it. Many of the bees hang from the cover of their cage by their
forelegs and remove the dust with their other legs. The visible dust may
be removed within an hour unless the percentage of DDT is high enough to
cause paralysis immediately. Later the bees and the cages appear to be
sorptlely free of the dust.


Effect of DDT in the F-

The results of the experiments with beoe fed a e !
summarized in table 1.

The experiments in which individual bees were fed DDT in sugar sirup
demonstrate that small quantities are poisonous when ingested with the
food. Because the suspensions settled, it is believed that the bees
actually ingested smaller quantities of DDT than are given in the table.
Minimum lethal dosages were not determined.

When the bees were fed collectively, the comparatively rapid settling
of the DDT in suspension unquestionably greatly increased this concentra-
tion at the feeding point. In other experiments 0.1 percent of DIDT killed
nearly all bees feeding on it in 24 hours, and 0.01 percent killed many

Pollen paste containing 5 percent of DDT fed to caged bees (table 2)
killed them all in 2 days, and queen-cage candy with only 0.5 percent of
DDT was equally lethal. Over 90 percent of these bees were killed in 17
hours. The greater apparent toxicity of the DDT in queen-cage candy is
due to the fact that it was eagerly consumed, whereas little of the pollen
paste was actually ingested. Most of the pollen paste was discarded and
dropped from the cage by the bees.

All bees were provided with water throughout the experiment. At the
end of the first day the remaining live bees were fed 50-percent sucrose

Effect of DDT Sprays and Spray Residues

Some results obtained with DDT sprays are given in table 3. Most of
the bees sprayed directly with xylene or water containing 1 percent of
DDT died within 6 hours. The same sprays applied to the wood of their
cages had no effect, presumably because much of it was absorbed by the
wood. Sprays containing 4 percent of DDT applied to the floors of the
cages killed nearly,all bees the first day. In later experiments (not
reported in table) 1-percent sprays were equally effective.

A sprayed tin surface was placed underneath untreated cages of bees
to determine whether the DDT had any fumigating effect on the bees. The
screen floor of the cage was about 3/32 inch above the sprayed surface.
The bees did not appear to be affected in any way. On the sixth day the
screen was removed, and the bees were allowed to come in contact with the
sprayed surface. All bees died within 48 hours.

No bees were observed attempting to remove spray residues within
their cages. There was no indication that they could even detect the
spray deposit.

The experiments summarized in table 4 show the relation of spray
dosage and the mortality of bees exposed to the residues. The 1-percent
concentration was generally very toxic with exposures of 10 minutes or


more, whereas concentrations of 0.5 percent or less were much less so.
The 0.1-percent sprays were comparatively safe for the bees. Concentration
was more important than dosage and more important, within limits, than
the exposure period. Table 5 shows the influence of the time of exposure
on mortality.

In an experiment to determine the persistence of DDT residual sprays,
several lots of bees (3 cages in each lot) were exposed consecutively to
surfaces bearing residues from single sprayings with a 1-percent DDT
suspension. The results from two dosages--0.5 gram and 0.065 gram per
cage-are ehown in table 6. Only two bees in the first five lots exposed
to the 0.5-gram dosage survived, but the 0.065-gram dosage was appreciably
effective only against the first lot. Since this experiment was carried
out over a short period, the reduction in toxicity was not due to
oxidation or evaporation.

Effect of DDT Dusts

Table 7 gives results of dusting caged bees with 10-percent DDT. The
bees reacted violently to the treatment, becoming extremely active
immediately. They cleaned the dust from their bodies. Nearly all the
bees were helpless or dead in 3 to 5 hours. Sufficient DDT remained in
the DDTY-dusted cages to kill bees placed in them later. In the DDT-dusted
cages that were restocked without further treatment all the bees were
killed in 2 days. After a second restocking, the mortality was low.

It has been reported that few bees may be found in fields of
blossoming alfalfa recently dusted with DDT where bees were plentiful
before dusting. Then after a few days bees again are numerous. Some
observers have attributed this circumstance to the death of the bees in
the field at dusting time, and others believe that the bees working in
the field are driven from it by the dust.

The tests summarized in table 8 were designed to show whether DDT ie
repellent to bees. Bees were placed in cages having only half the floor
sprayed or dusted with DDT, so that the bees were free to move away from
the treated area. Those placed in cages with half the floor sprayed with
DDT walked upon the dried-spray surface as freely as on the unsprayed.
There was no indication that they avoided the sprayed surfaces. Nearly
all were helpless in 5 hours. On the other hand, in cages with half the
floor dusted with DDT, the bees often walked into the treated area but
then immediately turned away. Dust clinging to the feet was cleaned off
and discarded. This type of repellency was more pronounced with DDT than
with talc alone. In spite of the repellency, however, sufficient DDT wis
picked up by the bees to kill them in less than 18 hours.

Relation Between Dust Concentration and Mortality

An experiment was conducted in hope of finding a concentration of
DDT dust which would not be harmful to bees but still of value in the
control of injurious insects. As shown in tables 9, 10, and 11, various
concentrations of DDT dustm were applied directly to the bees in the


cages until they were well covered with it. Dust was applied only to the
floors of the cages in the tests shown in table 12, and the bees were
exposed to the dust presumably only by walking in it. The 0.1- and 0.5-
percent concentrations failed to kill even after 5 days of exposure.
Except in the experiment summarized in table 9, where the reasons for
difference are obscure, 1-percent DDT also was practically harmless, and
it seems likely that under field conditions a somewhat more concentrated
dust, perhaps 2.5 percentwould cause little mortality among bees because
of the shorter period of exposure and the smaller quantities used. How-
ever, 5- and 10-percent or more concentrated DDT dusts are very toxic to
aes, even in small quantities, and unless care is used in their applica-
tion to avoid the contamination of blossoms visited by bees, losses may
be expected. There was no indication that sulfur in the dust mixture
(table 12) had any effect on mortality within the cages.

The lowest possible concentration of dust that will give reasonably
sar:i factory control should be used. Perhaps something less than com-
plete control of harmful insects must be accepted for the sake of pre-
serving beneficial pollinating insects. If dust of low concentration
were used, more frequent applications could be applied with less danger
to the bees. This practice would also minimize poisonous residues present
at time of harvest.

Relative Toxicity of DDT in Food, Spray, and Dust

When fed in sugar sirup, from 6 to 12 micrograms of DDT per bee
(table 1) was poisonous. Somewhat less than 12 micrograms per bee was
sufficient to kill half the bees to which it was fed.

Queen-cage candy containing 0.5 percent of DDT (table 2) killed 96
percent of the bees feeding on it within 24 hours. Each bee consumed on
an average 10.7 mg. of the candy, or 53.7 micrograms of DDT. Obviously
the median lethal dose in queen-cage candy is much below this figure. As
previously pointed out, 5 percent of DDT waa required in pollen paste to
ill; as many bees as were killed by 0.5 percent of DDT in queen-cage
cndy because the bees lid not eat the pollen paste readily.

In gen:..-al the w.-re concentrated spray residues were more toxic than
less concentrated :.)es, even though the dosage was the same. For example,
0.125 gram of 1. -rcent DDT spray killed about three times as many bees
a? did 0.25 -. of 0.5-percent spray, although each presumably supplied
1,5 mg. of DDT (table 4).

In a prisonn between sprays and dusts it is clear that sprays had
greater !.aldual action than dusts, but in initial action there seemed to
be little difference. A spray deposit of 5 mag. of DDT per cage (table 6)
sh ,1 m.d,-h -greater residual action than a dust deposit (table 7) contain-
ing 25 mg. of DDT. Both were heavy dosages. The spray adhered tenaciously
to the treated surfaces, whereas the dust was easily displaced.

In initial action 50 mg. of 2.5-percent DDT dust per cage killed
about half the bees (table 12). About the same result was obtained with
0.5 gram of a 0.5-percent spray (table 4), and 0.125 gram of a 1-percent
spray killed nearly 90 percent of the bees.

As was true of sprays, greater quantities of dust of low pDT content
did not increase the kill as much as did increases of DDT concentration.


Bees in small cages were fed, sprayed, or dusted with various prep-
arations of DDT and the resulting behavior and mortalities were observed.

Immediate tremors and greatly increased activity, followed by
paralysis and death in which the victim usually lies on its side or back,
are characteristic symptoms of DDT poisoning among caged bees. Some
affected bees recover from light dosages.
Many bees were killed by 6-micrograms of DDT in sugar sirup when fed
individually and by concentrations as low as 0.01 percent when fed
collectively. Queen-cage candy containing 0.5 percent of DDT killed all
bees to which it was fed. In pollen paste 5 percent of DDT was necessary
to kill all bees.

Bees sprayed with DDT in xylene or water were immediately affected,
and all died in less than a day. DDT had no apparent fumigating effect
on caged bees.

Residues on tin surfaces sprayed with 1 percent of DDT in water killed
most of the bees exposed to them for 10 minutes or more. With 0.5-per-
cent sprays mortality was greatly reduced, and 0.1-percent sprays were
comparatively safe for bees. Concentration apparently was of more impor-
tance than quantity of spray applied and within limits than length of the
exposure period.

DDT-water spray residues, although not repellent, were persistent in
effect, a single application killing nearly all bees in five lots consec-
utively exposed to it.

Bees dusted with 10-percent DDT or placed in dusted cages were killed,
and some cages retained sufficient DDT to kill bees placed in them later.
The dust, however, was not so persistent as spray residues.

The bees removed DDT dust and talc from their bodies and also from
their cage soon after dusting. Those dusted with 10-percent DDT died,
Bees were not observed to clean dried-spray residues from their cage.

Dusts containing 5 or 10 percent of DDT killed practically all bees
that came in contact with them, whether the bees were dusted directly or
only exposed to dusted surfaces. Dusts with 2.5 percent of DDT were less
toxic, and those of lower strength usually had little effect.


Literature Cited

(1) Eckert, J. E.
1945. The effect of DDT on honeybees. Jour. Econ. Ent. 38: 369-374.


Filmer, Robert S., and Smith, Charles L.
1944. DDT as a contact poison for honeybees. Jour. Econ. Ent.
37t 537.

(3) Hoist, E. C.
1944. DDT as a stomach and contact poison for honeybees. Jour.
Econ. Ent. 37t 159.

Table 1.-Mortality of caged bees fed DDT suspended in sugar sirup.
Quantity Mortality in --
of DDT Cages Bees __yin_-
of DDT T ....
fed ,,, 1day 2 days 5 days
Number Sumber Percent Percen Percent
Bees fed individually
6 micrograms 3 62 9.7 14.5 29.0
12 3 54 35.2 44. 55.6
30to 36 2 20 80.0 85.0 100
60 3 36 88.9 88.9 100

Bees fed collectively ad libitum
0.5 percent 1 89 93.3 98.9 100
Water only 1 102 0 45.1 100
Pure sirup 5 129 .8 .8 3.9

Table 2.-Mortality of caged bees fed pollen paste and queen-cage candy
containing DDT.

, Mortality in -
Material fed Cages Bees --,---...--
I day 2 days 5 days

Number Number Percent Percent Percent
Pollen paste:
5 percent of DDT 10 487 99.6 100 -
0.5 percent of DDT 10 503 7.2 44.3 48.1
No DDT 10 530 5.1 13.0 14.3
Queen-cage candy:
0.5 percent of DDT 10 448 96.0 100 -
No DDT 6 322 0 0 0
Water only 5 360 20.6 32.2 32.2


Table 3.-Mortality of bees sprayed with DDT or placed in sprayed cages
or close to sprayed surfaces.

STreatment Mortality in -
Object sprayed I Cages Bees I .. 2. .
#DDTI 'Diluent i day- 2 days 5 days
Percent Number Number Percent Percent Percent
Bees 1 Water 5 423 100 -
Xylene 1 53 100 -
Tin floor of
cage 4 Water 3 167 99.4 99.4 100
Xylene 4 424 100 -
Wood of cage 1 Water 1 89 1.1 1.1 1.1
Xylene 1 78 0 0 1.8
Tin under cage
with screen
floor 1 Water 2 109 0 0 0
Untreated 5 520 0 0 0

Table 4.--Mortality of bees exposed to spray residues of DDT applied at
various dosages to tin floors of cages.
._~ I I I
DDT Cages Bees I Mortality in -
Concentration v Dosage 1 1 day 1 2 days 5 days




None (untreated)





Number Percent Percent Percent













Table 5.--Mortality of bees exposed for various periods to spray residues
of DDT applied to tin floors of cages.

njw* *r. Mortality in --
DI & Exposure Cages Bees Mortality in..
concentration i day 2 days' 5 days
t t
Percent Hours Nuber Number percent Percent

1.0 0.14 3 205 2.4 7.3 15.1
.17 3 160 80,6 90.0 91.3
.25 27 1505 37.8 41.3 49.0
.5 24 13613 62.1 72.4 76.3
1 24 1411 91.0 96.0 97.0
2 28 1696 88.9 9247 94.2
3 12 637 89.5 92.9 94.7
4 13 716 95.5 99.6 99.7
6 3 114 100
8 6 362 99.7 99,7 99.7
S9 597 99.7 100m

0.5 .25 18 909 12.7 13,6 17.6
.5 21 1110 24.8 25.5 29.3
1 15 802 38.9 39.4 40.8
2 11 660 37.0 45.8 47.8
3 8 445 45.6 45.6 46.5

.1 .25 18 989 .7 1.1 3.7
.5 18 976 .6 1.1 3.9
1 18 869 3.2 3.5 6.2
2 23 1336 9.1 14.7 17.0
3 18 1092 5.4 6.1 9.9
4 17 1166 9.7 11.9 14.2
6 8 606 2.8 3.1 4.3
8 5 435 .7 .9 1.1
S4 310 1.0 1.0 1.6

None (untreated) 62 3498 .5 .9 2.3

I/ Continuous exposure.

- 10 -

- 11 -

Table 6.-Mortality of several lots of bees exposed oeaasecutively to
surfaces sprayed with 1-percent DIDT.
-I I ..i.... "--
Lot No.t Exposure Bees I Mortality in -
1 dy 2 days 5 days
Hours Number Percent Percent Percent

At dosage of 0.5 gram per cage
1 0.5 149 100 -
2 2 176 100 -
3 2 225 100 -
4 2 220 98.2 99.1 99.1
5 8 168 100 -
6 2 230 30.4 35.2 36.1
7 2 204 0 0 .5

At dosage of 0.0625 gram per cage
Series 1
1 14 154 98.1 99.4 99.4
2 8 170 1.2 1.2 3.5
3 4 255 .8 .8 2.0

Series 2
1 6 1A4 100 -
2 8 148 3.4 5.4 12.8
3 4 228 0 0 .4
Untreated checks
1 (11 cages) 604 .5 .7 .8
2 2 cages) 116 0 0 5.2
3 10 cages)- 738 .5 .7 1.4

- 12 -

Table 7.--Mortality of bees in cages dusted with 10-percent DDT and the
residual effect of the DDT when such cages were again stocked with bees.

TCages Bees Mortality in-
Treatment s 1 day 2 days 5 days

Number Number Percent Percent Percent
Bees in cages heavily
dusted with 10-
percent DDT 7 541 100 -

Cages restocked with
bees without
further treatment 4 267 52.1 100

Cages restocked with
bees second time
without further
treatment 3 173 4.6 5.2 8.7

Bees in cages heavily
dusted with talc 3 185 .5 .5 1.6

Undusted bees 3 273 .4 .4 1.1

Table 8.-Mortality of bees in cages having half the floor sprayed or
dusted with DDT or dusted with talc.

B e Mortality in -
Treatment Cages Be 1 day 2 days 5 days

Number Number Percent Percent Percent
Sprayed with 1-
percent DDT 2 136 100

Dusted with 10-
percent DEDT 2 120 100 -

DDT-dusted cages
restocked with
bees without
further treat-
ment 2 163 2.4 2.4 2.4

Heavily dusted with
talc 1 76 0 0 2.6

Untreated checks 4 233 0 0 2.1

- 13 -

Table 9.--Mortality
concentrations in

of bees dusted with 100 mg.j/ of DIT in various
cages hatv.-ig tight tin fluors.

Concentration of' Lortrality in --
DDT Cac", 1 B----. -. ...
(percent) f 1 day 2 days f 5 days

Number j'amr Ce._ Pbrceint Percent

0.1 6 452 2.2 4.9 8.6
1.0 6 434 4o.3 78.3 88.9
10.0 6 4. 100 -


Talc 3 209 1 2.4 3.9
Untreated 3 221 0 .9 3.2

1/ Equivalent to 140 lb. of dust
falls upon the floor of the cage.

per acre provided that all the dust

Table 10.-Mortality of bees dusted with 200 mag. of DDT in various
concentrations in cages having tin or screen floors. (5 cages used in
each test, 10 in the check.)

Concentration of

Iaof oger

Bees ,

~A"rtLitv in --

1 day
1 day,

2 days




SC'] l.B












Untreated checks

5 days












819 .6

14 -IMH11111 llll1 1111111 1111111
3 1262 09239 1969
Table 11.--Mortality of bees dusted with 250 mg. of DDT in various
concentrations in cages having screen floors. (10 cages used in each

Concentration of '
DDT Bees Mortality in -
(percent) 1 day 2 days 5 days

Number Percent Percent Percent
0.1 729 1.2 1.2 1.4
1.0 738 3.0 3.3 3.4
2.5 684 44.9 75.6 75.7
5.0 705 99.9 100 -
10.0 748 100 -

Untreated checks 742 .9 .9 1.1

Table 12.--Mortality of bees exposed continuously to floors dusted with 50
mg. of DDT or DDT-plus sulfur in various concentrations.
I 1 I
Concentration of ,
dust Cages Bees Mortality in -
(percent) I day I 2 das 5 days

Number Number Percent Percent Percent
DDT 0.1 10 639 0.2 0.2 0.5
1.0 10 587 2.0 2.0 2.9
2.5 10 590 42.5 58.0 58.5
5.0 10 569 99.8 100 -
10.0 10 607 99.8 100

DDT 2.5 plus sulfur
75 5 310 60.3 68.7 69.4

DDT 5.0 plus sulfur
50 5 292 99.7 100 -

Untreated checks 10 660 .2 .2 .8