Laboratory studies with DDT against the Mexican fruitfly


Material Information

Laboratory studies with DDT against the Mexican fruitfly
Physical Description:
14, 1 p. : ill. ; 27 cm.
Plummer, C. C
United States -- Bureau of Entomology and Plant Quarantine
United States Department of Agriculture, Agricultural Research Administration, Bureau of Entomology and Plant Quarantine
Place of Publication:
Washington, D.C
Publication Date:


Subjects / Keywords:
DDT (Insecticide) -- Testing   ( lcsh )
Mexican fruit-fly -- Control   ( lcsh )
federal government publication   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )


Includes bibliographical references (p. 14).
Additional Physical Form:
Also available in electronic format.
Statement of Responsibility:
by C.C. Plummer.
General Note:
Caption title.
General Note:
General Note:
"August 1946."

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 030292303
oclc - 780063061
System ID:

Full Text

August 19h6

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


By C. C. Plummer
Division of Fruitfly Investigations

In preliminary tests DDT dissolved in acetone, when mixed with
sugar and egg albumen dissolved in water, was less toxic than tartar
eaztic to adults of the Mexican fruitfly,(Anastrepha ludens (Loew))
(2). Subsequent studies showed that the low toxicity reported was
undoubtedly due to the masking of the DDT by the sugar and albumen
upon evaporation of the acetone and water. The studies described
here show that other preparations containing DDT, especially duets,
are very toxic to adults of the Mexican fruitfly.

Toxicity of Emulsions Containing DDT in Various Solvents

Several emulsions containing DDT were prepared by dissolving
technical DDT in soybean oil, corn oil, fish oil, diethyl phthalate,
dibutyl phthalate, or acetone. These emul.sions contained either 1
or 2 pounds of DDT, 1 gallon of solvent, 20 pounds of granulated
sugar, and 1 pound of soybean flour per 100 gallons. The soybean
flour was added as an emulsifier, A mixture of tartar emetic and
sugar was included in each test for comparison. Five-milliliter
portions of each preparation were applied on 4- by 6-inch pebble-
surfaced glass plates and the water was allowed to evaporate. No
other food was furnished to the flies. One plate was used in each
cage in tests carried out at 250 C. in the manner described by
Plummer (1). The only exception to described procedures was that
the experiment was started in the morning and observations on fly
mortality were made twice dily, at about 9 a.m. and again at
about 6 p.m. The data are sunmarized in table 1.

7 These studies were conducted as part of a cooperative
project with the Secretarfa de Agricultura y Yomento, Mex.



Table l.--Toxicity of emulsions of DDT in various solvents to adults
of Anastrepha ludens at 25 C. (1 lb. of DDT per gallon of sol-
vent unless otherwise indicated, and 3 cages containing L' I; "

Time required
Kill during to attain Maj.xua
Solvent first 10 hours 50 percent length oil
..... ........mortality life
Percent Hours Hours

.- f oil (2 lb. .f DJTJ 6.1 33 96
Soybean oil 16.0 33 120
Corn oil (refined) 22.7 33 177
rh "',i1 1.5 58
Z.tAi1. phth.ial&te 7,3 48 216
r-.t 'yl phthalate 14.7 33 192
Acetcae (10 gal.) 2.0 48 168
Control (tartar emetic 2 lb.) 0.7 33 106

i/ All except 3 flies died within 192 hours, and 1 of these was
ali" shen tests were discontinued after 336 hours' exposure to pois ron

These preliminary data show considerable variation in the effec-
tivriss of DDT in different solvents. The kill during the first 1V
b.:ut .&s ,8cfinitely higher when DDT was dissolved in soybean oil,
c oil, or dibutyl phthalate than when dissolved in fish oil, di-
ethyl phthalate, or acetone. Two pounds of DDT in soybean oil was,
for some unexplained reason, less toxic than 1 pound in the same oil.
DDT dissolved in corn oil killed all but two of the flies within 96
h".' One of theie two succumbed within 130 hours and the other
after 177 hour. Fish oil appeared to be repellent to the flies.
Nen her of the phthaiates appeared to offer any particular advantage
as solvents for DDT.

Toxicity of DDT in Various Formulattions

In another experiment various formulations containing DDT were
tested. In each treatment four cages containing 50 flies each w"rt
ue&d. The flies were held at a temperature of 250 C. and a relative
humidity of 40 to 50 percent. Standard methods as described by
Plummer (1) were followed in this and subsequent experiments, the
only departures being that the experiments were started at 6 a.m.
instead of 6 p.m., and that 3 pieces of cut orange, changed frequent-
ly, and 1 cube of sugar were kept in each cagee A 4- by 6-inch


pebble-surfaced glass plate covered with a preparation containing
6 mg. of DDT was introduced into each cage. The emulsions were
pipetted on to the glass plates, and the two dusts, i.e., undiluted
technical DDT (passed No. 200 sieve) and the DDT in pyrophyllite
(passed No, 200 sieve), were spread on with a 3/8-inch flat artist's
brush with short bristles. DDT dissolved completely in the amounts
of ethyl alcohol and acetone used. A very fine precipitate of DDT
was obtained by dissolving DDT in 95 percent ethyl alcohol and then
adding water in the proportions indicated. DDT was dissolved in
soybean oil, and this in turn was dissolved in acetone to facilitate
spreading. A mixture of tartar emetic and sugar was also tested for
comparison. All preparations were allowed to dry previous to testing.
The data are summarized in table 2.

Table 2.--Mean length of life of adults of Anastrepha ludens exposed
to DDT in various formulations applied on glass plates.

Accessory material
with 6 mg. of DDT

None (undiluted tech-
nical DDT)

Pyrophyllite dust 54
rmg. (10-percent DDT)

Acetone to make 5 ml.

Ethyl alcohol (950%) to
make 5 ml.

Mean I ength
of life


Av. 1.3240

Av. 1.2273

Av. 1.8925

Av. 1.5895

Accessory material
with 6 mg. of DDT

Ethyl alcohol (95%)
0.6 ml. + water to
make 5 ml.

Soybean oil 54 mg. +
acetone to make 2.5

Control, no DDT (tar-
tar emetic 6 mg. +
sugar 54 mg. + water
to make 5 ml.)

Mean lengt)2
of life$/

Av. 1.8623

Av. 1.4617

Av. 1.4495

/ Difference required for significance at P = 0.05 is 0.2235;
at P = 0.01, 0.3042.

I . II I 111 I 12. II I III


These data show that the average mean length of life of flies
was shortest when they were exposed to DDT in pyrophyllite and Itc-
est when exposed to DDT dissolved in acetone. Flies exposed to ..< ,i-
luted DDT powder did not live so long as flies exposed to r.'.' dis-
solved in alcohol, and the differences between the two average Meame
are significant. The differences between the lowest meai; for un-
luted DDT and the highest mean for DDT in alcohol-water, as well as
that for DDT dissolved in acetone, were highly significai;t, whereas
'.n' differences between the average mean length of life of flies ex-
poued to undiluted LDT and those exposed to DDT-pyrophyllite dust,
DDT in soybean oil, or the tartar emetic ead sugar preparation were
not significant. Essentially similar res lts were obt iined whether
or not ahe" ,kata for tartsr emetic were included in the analysis of
variarne. It should be &'jphb9ized, however, that in these tests DDT
was much superior to tartar emetic because it was not mixed with
F-L i was tba tartar e.o.-tic. Previous laboratory studies (unpub-
* ( wAd) tago shew tiL,. flies die when L-bpoaed to tartar emetic
3n^i (k.,sa' in the presence of cut orange and cube sugar, whereas with
DDT, as shown in thebe experiments, many die.

th'" te .,'; 12 ,as ,..pc>d to eacl.: preparation show in table 2,
1 fly oAA,08ei to in soybean oil and 4 sp,.d to the DIDT
,:-. 're formalcition 1i-TEd more than 1,000 hours while core.tantly
-.. ','. d to th~e e pr-i:.*-t Ltoa, Similar obs;rvatious have been re-
co.:'.'i ifn ot.-r f.T.:, Its8, where an oc,9ionafl .fy .,li lived for
ex'I..,,...e,: .<,'ioda even in t. presence of 10 percent of LDT in pyro-
phylli+e. When it 1is consideredd that the plate covered with insecti-
cide has a surface equal to only about 3.6 percent of the interior
j.trface of a, it appFr8 likely that som? flick. .void contact
*s-;h the 1i-Ite.

Apilearance of DDT Deposits

The surfac.v of plates covered with preparations of DDT yhowe!j
marked differences, upon drying, wheia examined under a binocular
microscope at a mergnrification of 21x. With DDT in aceti-e 'there
were a few small agglomerations of particles, but most of the DDT
was in the form of a finely branching network, much of itinear the
edge of the plate. The deposit obtained with DDT in alcoh6i was
much the same, except that large featherlike patches of DDT appeared
at the edge of the plate. The precipitate formed when water was
added to the DDT-alcohol solution consisted'of very small particles
enmeshed within a very fine network. Evidently all the DDT remained
dissolved in the soybean oil as the mixture dried on the plates.
The tartar emetic appeared to be intimately rmixed with the sugar,
and dried as flattened, colorless to slightly whitish msses of
irregularly shaped crystals. The DDT-pyrophyllite dust and the un-
diluted technical DDT showed many reletive)y large particles on the


plates. There was a strong tendency for particles of these two
dusts to "ball up." The preparation containing DDT, xylene, end
Triton X-100 (an aralkyl polyether alcohol), which is described later,
upon-drying on a pebble-surfaced glass plate, showed smell, soft
white lumps, presumably Triton X-100, in the spaces between the ele-
vations of the glass, whereas fine needlelike lines, presumably DDT,
were visible on the sides of the elevations.

Contact Tests

The concentration of DDT at the margins of some plates upon
evaporation of organic solvents may have accounted for some of the
differences in toxicity. An experiment was devised to check this,
to eliminate possible repellency, and to obtain further data on the
effect of certain solvents on the toxicity of DDT. With both wings
held in forceps, a fly was dipped to touch the surface of a plate
covered with dried DDT at 5 different places during a period of 5
seconds. Five flies of the same sex, chosen at random from the
stock population of 400 flies, were removed 1 at a time for this
purpose, and the procedure was repeated with the opposite sex. A
total of 25 flies of each sex were handled in this way with each
treatment, and each treatment was repeated 4 times to make 4 blocks,
The ages of the flies in block 1 were 90 to 113 days; in block 2,
65 to 81 days; in block 3, 82 to 106 days) and in block 4, an un-
known number of days. The 50 flies were then held at 25 C. in
cages with food, and the dead and paralyzed flies were counted at
the end of 24 hours. Once flies are paralyzed they do not recover,
and for that reason they were counted with the dead flies. The data
are summarized in table 3.


Table 3.--Tcxicity of DDT to adults of Anastrepha ludens 24 hours
after being brought in contact with preparations of DDT on
glass plates for 5 seconds.

Accessory material
with 6 mg. of DDT

Block Flies dead or paralyzed/

Number Percent

Xylene 16.32 mg. + Triton X-100
1.68 mg. + water to make 1.20 ml.

Ethyl alcohol (95%) 0.6 ml. +
water to make 5 ml.

Soybean oil 54 mg. + acetone to
make 2.5 ml.

Ethyl alcohol (95%) to make 5 ml.

Acetone to make 5 ml.

Av. 25.63

Av. 28.50

Av. 15.65

Av. 33.13

Av. 27.03

Av. 68.83

Av. 18.23

Pyrophyllite dust 54 mag.

Control (clean plate)

is 8.24,

/ Difference required for significance at P = 0.05
at P = 0.01, 11.29.

-- 5 .. ......... '


These data clearly show the superiority of the DDT-pyrophyllite
dust over the other preparations tested. ExhandrEtion a..Jar s micro-
scope has shown that this dust adheres to the numerous short bairs
on the legs, particularly the tarsi, of the Mexican fruitfly. Most
of the dust, however, either is removed by th:e fces or falls off
within a few hours.

Analysis of variance of the angles of peicantage of the number
of dead and paralyzed flies (table 3) shows highly significant dif-
ferences between blocks and also betwe-en treatments, The t test
shows no significant difference between the average angle for the
control and the DDT in 6.oyberan oil or for TLT mixed with xylene and
Triton X-100. When comparisons are made between the averages for
DDT-xylene-Triton X-100 and for each of the other preparations, only
the average for DDT in soybean oil is significantly lower and that
for DDT in pyrophyllite h.,ily s3tiific'!rslt. higher. The DDT-soybean
oil gradually harderie, e uri;.g the time that it was held in the lab-
oratory, and this may have reduced its toxicity. The DDT-xylene-
Triton X-100 had not hardened at the time tests were made. It is
believed that preparations in which volatile solvents were used
were not altered through storage at room temperature.

Preparations on 3 of the plates mentioned in table 3--namely,
DDT in pyrophyllite, in soybean oil, and in aseicde--rere further
tested by forcing flies to walk on them for 10 seconds, 10 flies on
each plate. All the flies were dead 21 hours after exposure to
either DDT-pyrophyllite or DDT-soybean oil, whereas only 4 out
of 10 flies were dead after exposure to DDT in acetove.

gods of ActAon of DDT

The habit of rubbing the mouth parts with the legs is very
pronounced with the Wfxican fruitfly, and it is possible that DDT
may kill only through the fly's ingestion of the insecticide. An
experiment showed that DDT can ar-alyze, and thus kill the flies
by contact alone. The proboscises of several dozen flies were
sealed by touching them with a small drop of collodion prepared
commercially with ether and alcohol. Previous to incli.uion in
tests, each fly was examined under a microscope to make sure that
the mouth parts were well sealed. Each of 10 males and 10 females
was forced to walk on 10 percent DDT-pyrophyllite dust on a pebble-
surfaced glass plate for 5 seconds. Within the first hour 9 males
and 8 females and at the end of 5 hours 10 males and 9 females were
paralyzed, while all the flies in the control group remained normal.
The next day, 24 hours after the start of the test, all 20 flies in
the test cage and 7 males and 8 females in the control cage were
dead. It is presumed that the control flies died frog thirst and


Toxicity of DDT-Pyrophyllite Dusts

Toxicity tests with DDT-pyrophyllite dusts were carried on by
the method used in a previous test (p. 2). In test 1 two prepara-
tions (samples 1 and 2), each containing 10 percent of DDT in pyro-
phyllite, were used. Sample 1 was further diluted with pyrophyllite
to obtain dusts containing 2, 4, 6, and 8 percent of DDT. Sample 2
(a commercial dust) was tested only at the 10-percent strength. Ten
percent of tartar emetic in pyrophyllite was included as a control.
Fifty flies in each of four cages were exposed to each concentration.
The average mean length of life was greatest when the flies were ex-
posed to 2 percent of DDT in pyrophyllite and shortest when exposed
to 8 percent of DDT (fig. 1). when t was used to test differences
between the average mean length of life of flies exposed to sample
1 at all concentrations, it was found that only the difference be-
tween the 10-percent and the 2-percent DDT was highly significant.
The mortality of flies exposed to tartar emetic dust was very low;
only about 25 percent succumbed during the first 200 hours, and
approximately 11.5 percent remained alive 800 hours.

In test 2 a 20-percent dust, obtained by pulverizing technical
DDT in a hanmer mill with a portion of the same sample of pyrophyl-
lite used in the first test, was diluted to concentrations of 10
(sample 3), 12, 14, 16, and 18 percent, and tested at all strengths.
Sample 1 in test 1 was again included in this series. The average
mean length of life of flies exposed to these concentrations is
also shown in figure 1. According to the t test, none of the dif-
ferences between the mean for sample 1 and each of the other means
of the test are significant.

Comparison of Various Diluente for DDT Dusts

To determine whether DDT is more toxic in pyrophyllite than in
some other diluent, several dusts were prepared with 10 percent of
technical DDT in various diluents. Each diluent was first passed
through a No. 325 sieve. The methods already described were fol-
lowed, 60 mg. of dust being applied to a 4- by 6-inch glass plate
and exposed in each of 4 cages containing 50 flies. The data are
summarized in table 4. Analysis of variance shows no significant
difference in the mean length of life of flies exposed to these
various dusts.


Table 4.--Mean length of life of adults of Anastrepha ludens epcs.',
to 10 percent of DDT in various dust diluents and to undilite?
technical DDT dust.


Mean length
of life


Lo-hours I L_-houre

None (undiluted tech- 1.058
nical DDT) 1.063
Av. 1.0553

Pyrophyllite 1.091
Av. 1.1673

Talc 1.042
Av. 1.0923

Aluminum oxide 1.235
Av. 1.1205

Walnut-shell flour

Diatomaceous earth


Meof lifegt
of life

Av. 1.0833

Av. 1.1347

1. 06 S
Av. 1.0725

Most of the flies in these cages came in contact with the in-
secticide and fell to the floor in a paralyzed condition within an
hour or two. Many flies remained paralyzed for 12 hours or more
previous to death. Mortality within the first 24 hours ranged from
about 50 percent of the flies exposed to 2-percent DDT dust up to
95 percent of those exposed to 20-percent DDT dust.

Protection of Mangoes from Infestation

Laboratory studies were made to determine the possibility of
protecting mangoes from infestation by applying DDT as a dust and
also in oil emulsions. For each treatment 4 standard toxicity cages
were each stocked with 50 mature flies, 25 of each sex. At least

- 10 -

two tests were made with each treatment and the tests were run con-
currritly, as follows 1I and 2, 3 and 4, 5 and 6, and 7 and 8. The
flies were allowed constant access to water, 3 small pieces of cut
orange and 1 cube of sugar. Large green Manila mangoes were dipped
in the oil emulsions, prepared with soybean flour as an emulsifier,
and allowed to dry overnight before they were introduced into the
toxicity cages. Other maantoes were dusted lightly with a small hand
duster. Controls were not treated. With each treatment, including
the controls, there were 8 mangoes, 2 in each of 4 cages. They were
held with the flies usually for 6 days. In tests 7 and 8 dead flies
were replaced with living flies twice daily in order to maintain the
fly population at its original number, and the stock supply was ex-
hausted in 5 days. Fruit, upon removal from cages, was held over
sand in suitable boxes until all insect material had matured or had
left it. The data on infestation of treated fruit are sainarized
in table 5.

Table 5.--Laboratory infestation of Manila mangoes by Anastrepha
ludens when covered with dusts and emulsions containing DDT.



of flies-+

Infested infested

and puparia


Number Number

Emulsion, corn oil 1%:
With DDT (1 lb. per
100 gal.)

Without DDT

Control (no treatment)

Emulsion, fish oil l%6
With DDT (1 lb. per
100 gal. )

Without DDT

Pyrophyllite dust:
With 10% of DDT

Without DDT

Control (no treatment)

49 (187)

41 (192)

62 (82)

29 (188)

25 (186)


















- 11 -

Table 5.--Continued



of flieJ/

Infested infested

Livi n-
a.-id j.'uparia

recover "..i

Number Number

DDT, undiluted, tech-
nical grade
Pyrophyllite dust;
With 10% of DDT

With 5% of DDT

Without DDT

Control (no toeaitment)

DDT, undiluted, tech-
nical grade

Pyrophyllite dusts
With 10% of DDT

With 5% of DDT

Without DDT

Control (no treatment)

5 200

5 188









1/ 200 flies exposed to
otherwise in parentheses.

each preparation, except as indicated

2/ Evidently very slight infestation previous to exposure of
fruit to adults of Anastrepha ludens, since 3 adults of Mexican A.
nombinpraeoptas (auct.) were recovered.

Y Previous infestation indicated, since 2 adults of Mexican
A. mombinpraeoptans were recovered.

/ Previous infestation indicated, since 4 adults of Mexican
A. uombinpraeoptane were recovered.


NumbQ ~







- 12 -

In tests 1 and 2 the corn-oil emulsion, both with and without
DDT, markedly reduced the number of mangoes infested, as well as
the number of larvae and puparia recovered. Few flies died during
the first test; more, however, died during the second test, probably
because of the prolonged exposure to DDT of the same population of
flies, except for replacements of flies that had died. Mangoes
covered with corn-oil emulsion remained green or changed to the
typical yellow very slowly.

The fish-oil emulsion, with and without DDT, also reduced the
fly population to some extent, more in test 4 than in test 3, and
again presumably owing to the continued ex,.opure of the same popu-
lation of flies in both tests. Neither preparation with fish oil
appeared to protect the fruit so well as did the corn-oil emulsions,
when judged by the number of larvae and pupr-ria recovered from in-
fested fruit. Previous tests (table i) ni shown DDT to be more
toxic in corn oil than in Zish oil whenr 3ugar was added to the prep-
arations and when no other food was available.

When undiluted technical DDi) was used, there was a marked re-
duction in the number of mariw,3 infested, and in one test (test 8).
the fruit was completely frep of infetation. In this test an ef-
fort was made to maintain the fly population at its original level.
In the three tests with undiluted DDT (tests 5, 7, and 8) 5 of the
24 mangoes were infested as compared with 20 in the control cages.
A total of 49 larvae and puparia was re'-oiired from fruits covered
with undiluted technical DDT,while approximately 1,603 larvae and
puparia came from fruits held in untreated cages.

Ten percent of UDT in pyr.yz.>li ms. applied on a total of
40 mangoes,and not more th&e 2 mangoes were found infested. In addi-
tion to these, it appears that another mango (test 8) was infested in
the field with larvae of Mexican Anastrepha mombinpraeoptans. A total
of 27 larvae and puparia were recrverrdi, andt 7 of these were probably
Mexican A. mombinpraegptan s. Lerm-m a-,i. puperia recovered from the
40 mangoes exposed to flies in untreated cages approximated 2,354.

Of the 32 mangoes treated with 5 percent of DDT in pyrophyllite,
8 were observed to be infested. A total of 82 larvae and puparia
were recovered from this fruit, whereas 1,876 larvae and puparia
came from the untreated fruit (table 5). In 2 of the 4 tests the
dead flies were not replaced twice daily with living flies. It ap-
pears that 5 percent of DDT in pyrophyllite is not so effective as
10 percent of DDT in the same diluent.

Infestation appears to have been reduced in mangoes covered
with pyrophyllite alone. Of 48 mangoes dusted with this material,
18 were observed to be infested, as compared with 43 of the 48 fruits
held in untreated cages. A total of 481 larvae and puparia came from
dusted fruit as compared with 2,627 larvae and puparia from untreated

- 13 -

Considering the data from laboratory experiments on thb 1 ity
of several concentrations of DDT in pyrophyllite, as well a :
the protection of mangoes from infestation, it would pear t 10
percent of DDT in pyrophyllite might be a satisfactory co. to
to employ in preliminary field tests. Such a concoitration
tested in the field under conditions at Cuernavaca, M,'xico, .
Plummer and Shaw. Their preliminary data (i .bliA b) t'it that
it is not effective in controlling the Mexi'-xiy f,'u2feiy,

'unma ry

Prel ,imi-,ary tests .]... *"i', .... .' io s c L : so'.,
oil, corn oil, or dibutyl bt>.-'.'2te as solvent wtce more toxic" L,"
adults of the Mexican fr-ittf.'y (Ae" j ludiQne (Lcotw)) &t 25 0
than similar emulsions ---p: r-,d with fish oil, diethyl phthalate, or
acetone. DDT in the first .1'v&up of s aulCons was also zii t-A. :
the a &i*rtar ee ,oiu-,

In tests with driei pT .jrallois on f.l'iss plates, and in th,
presence !f gugar and *ut or-i undili.i"'-d technir. L and 10
percent r- -,ohylJ Ie d'.t wer ,'-re toxic rh&n r.'T disolved in
alcohol, acetonhe, zybean oil, or a ausp~nriion of DDT in alcohol
and water. Und"iuttl-, tuecbical DD? in t"e j-e .. *'
was rot 'i.-i fie .&.-,ly rore toxic tL't tartar t'.i mi xe wit' ai..,..

'Then id!.vi-' 1 ". were furce1 to touch depos-'tt. of DDT fro;x
d.ffsrert forwulatlons 5 tiaaa L. 5 seconrdJ and subse.uently held
for mortality r:..f, it wa, f.-, r- that 10 perent T-pyrophyllite
dust was auch mrore toxic than '- [ -'c7.vod in eithv- acetone or al-
.l, or a s.,pr)-I.L of .... i."n al'yoii.l ad water, Dirff-,ri ncca. in
tou.i'-if between VA;T in xyle- er TcK.,;.. X-a-0, DDT in -3oybar, oil,
and ar untreated check warfn not significant, howeverr in one small
tst L2T in soybean oil was show to be as toxic as i0 percent L.T--
1.yr phyllite dust when flies were forced to walk on ,..-h prepra
iicrs for 10 seconds, and DDT that hkd ben pr, with ace one
wase agair; shown to be less toxic.

When 20 flies whose probosciae hu, .-c cel ,-'>th c V..'..'. I ,',;
were exposed for 5 seconds to 10 percent DDT-pl-r'ph.yii.u d'...t, 17
of the flies were paralyzed within the first be tr and 19 i
within 5 hours.

In a series of tests with pyrophyllit9 dusts coM,-,'.:I:..' frc
2 to 10 percent of DDT, toxicity decreased at concentrations r.;low
8 percent, although only the difference between 10 pc-.- .t An` 2
percent was significant. In another series of tests no ai.7-nficant
difference was shown between the average mean length of life of
flies exposed to 10 percent DDT dust and to dusts with 12, 14, 16,
18, and 20 per.,rit.

- 14-

No significant difference in the average mean length of ifte
was shown between Mexican fruitflies exposed to widilut K o.. -'
DDT and those exposed to 10 percent of DDT in pyrophylJ-l, i.ep
aluminum oxide, walnut-shell flour, diatomaceous earth, or eo f

Mangoes were dipped in DDT emulsions : .,ut,,T.n 6r coru o d e
: i, but the results wer- "ot 'i,. 1N,, i i V
luted technical DDT and 10 ;ercant of D[r in pyrophyllite protected
other muangoee to a marked deg:re, and the 5 percent DDT-pyrophyllite
was a little less effecti,
*-.' ,,. _/..,. '_*^..,. >..i.. .,

(1) PluiMer, C. C. 1943. Tests against the Mexican fruitfly.
l2 Lr'bojto/ ,-.y .-* ,-.j ..,t'je8 of -he 1.s94aiDa. control
:j -8 ," f.I. * :..' e ".- t- . ., ;- ..|. ^ '-111,i wtori.) D. CO

(2) 1944. DDT and the aexic&a fruitfly.
(:;' '- f / ^- : &.^7 9

26 Test I

24 X A-Sample I
I a Sample 2
0 22 Test 2
4z\o r0-Sample I
2 20 + \+-Sample 3

-J 18-


12 X
+ X
i i i t I I I I I
2 4 6 8 10 12 14 16 18 20

Figure l.--Toxioity of DDT-pyrophyllite duets to adults of Anastrepha
ludens in the presence of sugar and out orange at 25 C. Data
reoorded within 2- to 10-percent range represent test 1; within
10- to 20-percent range test 2.


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