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UNITED STATES
DEPARTMENT or AGRICULTURE

DEPARTMENT CIRCULAR 367

| Washington, D. C. April, 1926

AIRPLANE DUSTING IN THE
CONTROL OF MALARIA MOSQUITOES

W. V. KING, Associate Entomologist

and

G. H. BRADLEY, Assistant Entomologist

Investigations of Insects Affecting the Health of Man and Animals
Bureau of Entomology

CONTENTS
Page Page
The insecticidal dust used_________ 2 Dusting mosquito-breeding lakes____ 5
Preliminary experiments to _ deter- Dusting -a-flooded rice field=____~__ 10
mine distribution of the dust on An additional check on the results__ iB

the ground and minimum killing SSRN ER SDI Yr ee Fe ee rote Pe A i
CLOSE, oa 8 es en 3

The use of airplanes for distributing arsenical dusts in the control
of insect pests affecting cotton has been the subject of experiment
during the last three years by the Delta Laboratory of the Bureau
of Entomology, United States Department of Agriculture, in coop-
eration with the United States Army Air Service. The headquarters
for this work was at Tallulah, La., a short distance from the bureau’s
station for malaria mosquito investigations at Mound, La., so that,
with the offer of cooperation from the Delta Laboratory and the Air
Service detachment engaged in cotton-dusting experiments, an ex-
cellent opportunity was presented for testing the possibilities of
employing airplanes? in the control of the breeding of Anopheles
mosquitoes in large swamp areas, Paris green being used as the
larvicide. It was obvious that if this insecticide should prove satis-
factory for the purpose and if its distribution by airplane should
prove successful, the extent of the area which could be treated would
be many times greater than that which could be covered by any other
treatment now in use.

1 The writers are greatly indebted to B., R. Coad, of the Bureau of Entomology ; Elmer
Johnson, of the Bureau of Public Roads; and Lieut. G. L. McNeil and Sergeants MeCon-
nell and McGinley, of the United States Army Air Service, for their cooperation and
assistance in the dusting experiments,

66832 °—26

2 Department Circular 367, U. S. Dept. of Agriculture

Considering the extent of the swamp areas in the region, the small
proportion of cultivated land, and the limited population, it did not
appear altogether likely that such a method would prove to be a
practical means of malaria control under these particular conditions.
Such swamp areas prior to drainage are, however, almost inaccessi-
ble to any other means of treatment, and it seemed entirely possible
that airplanes might be of practical use under similar or other con-
ditions where the per capita cost of the operations would not be
excessive.

In the cotton-dusting work it has been found that, under favor-
able conditions, several hundred acres an hour can be treated by
a single plane and that the dust can be thoroughly distributed over
the fields. The swamp areas, however, present much more difficult
flying conditions than the open cotton fields, and the principal pre-
liminary questions to be decided were (1) whether the planes could
be safely flown over such areas and (2) whether the dust could be
released so as to reach the water surface in effective quantities. One
factor which appeared to favor the distribution of dust in such a
manner was that the direction of the air currents is usually down-
ward over woods and bodies of water, whereas over open ground it
is upward.

The experiments were carried out during 1923 and 1924, Army
DeHaviland 4-B planes, operated by Air Service pilots, being used.
A light metal hopper designed to hold 300 pounds of calcium arsenate
was built into the rear cockpit, and the dust was released through
an opening provided in the bottom of the fuselage.

THE INSECTICIDAL DUST USED

Paris green appears to be the most promising larvicide available
for airplane dusting in control of Anopheles larve, and it was the
arsenical used in all the experiments. It has proved to be as effective
as oil in control of Anopheles larve,? is very much less costly than
oil, and can be applied in dry form suitable for distribution by air-
plane. Unfortunately it is not satisfactory as a general larvicide,
since it does not destroy the larve of other mosquitoes which do not
have the surface-feeding habits of Anopheles, and it remains effec-
tive on the water for only a very short time. On the other hand, in
the quantities used, it is not poisonous to the insects and small fishes
which prey upon mosquito larve.

Since only a very small quantity of Paris green is necessary to kill
mosquito larve, an inert dust of some sort was used as a diluent and
carrier. For the airplane mixtures a finely ground silica earth was
the diluent principally used. A “double-ground ” product was uni-
form in quality and was found to have about the same density as
Paris green, a factor thought to be of possible importance because
of the strong air blast to which the mixtures are subjected when re-
leased from the hoppers and which would tend to separate substances
of different weights and composition. A much finer “air-float”
product from the same source was also tried, as well as foundry

2A description of earlier experiments with airplanes is given in U. S. Dept. Agr. Bul.
1204, Dusting Cotton from Airplanes, by B. R. Coad, EH. Johnson, and G. L. McNeil.

8M. A. Barber and T. B. Hayne. Arsenic as a larvicide for anopheline larve. In
U. S. Pub. Health Sery., Pub. Health Rpt., vol. 36, pp. 3027-3034. 1921.

Airplane Dusting in Control of Malaria Mosquitoes 3

“parting,” but the former was found to be too light in weight and
likely to drift away without settling. The “parting” contains 2 per
cent of oils and is relatively waterproof, but unfortunately it did
not improve the floating qualities of the Paris green.

Other carriers used were ordinary road dust and a mixture of lime
and flour. In the few tests in which these were employed, no
evidence was obtained of a separation of the carrier and the arsenical;
but the tendency of the flour and lime to become packed in the
hopper, owing to the vibration of the plane, was a drawback to its
use. Although road dust is a satisfactory carrier for hand applica-
tions, it seemed desirable to obtain a substance more uniform in
quality and more certain as to source of supply for any airplane work
on a large scale.

Fic. 1.—Dusting plane flown across open field to determine the spread of the Paris
green and dust mixture under the most favorable conditions. Plane flying about
15 feet above the ground

PRELIMINARY EXPERIMENTS TO DETERMINE DISTRIBUTION OF
THE DUST ON THE GROUND AND MINIMUM KILLING DOSAGE

In preliminary ground experiments the approximate minimum
concentration of Paris green necessary to kill the larve was deter-
mined by placing side by side a series of dry glass plates 2 by 3
inches in size and open dishes containing water and Anopheles larvee
and dusting the two with varying quantities of Paris green with a
hand duster. The larve were then watched for 24 hours to deter-
mine their mortality, and the numbers of granules of the Paris green
per square inch were counted on the glass plates with a low-power
microscope.

Following this the first airplane tests were made over open ground,
glass plates being used as a means of determining the drift of the
dust and the quantity which settled to the ground. In these tests,
in which various mixtures were used, the plane was flown from 15
to 30 feet above the ground (fig. 1) and at right angles to the direc-

4. Department Circular 367, U. S. Dept. of Agriculture

tion of the wind and to two lines of glass plates placed at intervals
across an open field. In the best of the trials it was found that a
strip from 300 to 400 feet wide had been effectively treated by one
trip of the plane and that the quantity of Paris green required was
at the rate of about 1 pound to 20 acres. This represented the
minimum quantity effective on water containing almost no débris
or aquatic growth. Under such conditions the writers’ counts had
shown that 10 or more granules of Paris green per square’ inch usu-
ally gave 100 per cent mortality, whereas with a lower count some of
the larvee escaped. In these preliminary tests and in the next series
also a count of 10 granules per square inch was therefore taken as
the effective dosage, although it was found later that this quantity
was insufficient under natural breeding conditions where the larve

Fic. 2.—Dust cloud beginning to spread out among the trees following a trip of the
plane across Bunkum Woods b

are more protected by the débris and vegetation among which they
feed.

The next tests were made in two patches of woods, to deter-
mine whether the dust could be forced to the ground through a
growth of leaves and brush. In the first of these the strip of woods
was fairly narrow, with only a moderately heavy growth of timber.
Two parallel lines of glass plates were placed on the ground under
the trees and the plane was flown at right angles to these lines, mak-
ing two or three trips across the woods at about the same place each
time (fig. 2). The mixture distributed consisted usually of 100
pounds of dust containing 10 pounds of Paris green. The lines of
glass plates, with 10 in each, were distributed across a strip 750 feet
wide. In the best one of the trials all of the plates showed the pres-
ence of Paris green, and all except two in one line had 10 or more
granules per square inch.

Airplane Dusting in Control of Malaria Mosquitoes 5

In the second patch of woods the conditions for dusting were ex-
tremely difficult, as the timber was very tall and the growth was so
dense that the ground was almost completely shaded. Two lines of
glass plates were placed on the ground as before, except that they
were spaced at 100-foot instead of 75-foot intervals. Three tests
were made with the dusting plane, in none of which was there fail-
ure to find Paris green on some of the plates. In one case 8 of the
glass plates in one line and 7 in the other-were dusted. For the
three flights, the average width of the strip which received 5 or
more granules per square inch was about 300 feet, and the average
width of that receiving 10 or more grains per square inch was about
200 feet. It was thus shown that, even in dense woods, it is possible
to reach the ground through the cover of vegetation, although much
of the material is lost because it adheres to the leaves or drifts away
with the wind.

In Table 1 is given a summary of the dusting operations over the
wooded areas.

TABLE 1.—Airplane dusting over dry woods to determine distribution of the
poison on the ground underneath, Mound, La., 1923

BUNKUM WOODS

Number

| —— of glass “
Number! glass > plates wit :
: = | plates Width | 100rmore} Width
Date eee) ee dusted (2 | ofstrip | grains of | of strip
ris greer
each) per square
inch
1923 Feet | Feet
BE ee Oe ee Se 1 5-100 2 6 450 0 0
7 525 0 0
fr oe 2 ken 2s 10-100 2 : q 150
0
ly See ie GMs OES seca eens 10-100 3 a 525 4 300
3 8) 675 6 450
es 2 ee a ee 10-100 3 10 750 10 750
10 750 8 600
} ]
ASHLEY WOODS
| | Feet Feet
yemlys Se Eee 0 Eee cee) | 13-130 3 | : any : 200
: 3 200
1 jes Ate Se ASS ee BETS oy | 10-100 2 | 8 800 2 200
7 700 0 0
fe ee ee yee pone ee ' 10-100 3 4 400 2 200
5 500 3 300

i Five pounds of Paris green in 100 pounds of dust.

DUSTING MOSQUITO-BREEDING LAKES

Following these trials the dusting of mosquito-breeding lakes was
undertaken, and three locations were selected as offering suitable
conditions for the tests. These conditions were an abundance of
larvee in the water and proximity of the areas to open fields. The
latter was of importance as a possible measure of safety in the event
of a forced landing. It was desirable, moreover, that the lakes
should be as accessible as possible from solid ground, because much

6 Department Circular 367, U. S. Dept. of Agriculture

work is required in making preliminary examinations and in check-
ing the results. |

A full description of the shallow swamp lakes found in this region
has been published recently by one of the writers‘ and will not be
repeated in detail here. In general, they are the principal sources
of Anopheles mosquitoes and as a rule consist of a central treeless
area of more or less permanent water, surrounded by a dense mar-
ginal growth of trees and brush. (Fig. 3.) The central area is usu-
ally overgrown with water chinquapin and water lilies (Nelumbo
and Castalia) and other smaller aquatic vegetation. In winter the
lakes become filled and the water spreads out into the woods, often
covering large areas and producing favorable conditions for mos-
quito breeding in spring and early summer. As the excess water
drains away or evaporates, the larve are found in the more open

Hig. 3.—One of the larger swamp lakes

parts of the lakes away from the trees. The principal difficulty
anticipated in treating such areas was in reaching the larve in the
wooded marginal zones.

In the first of the three lakes selected, known as Field Lake, the
open part was something over a half mile in length and perhaps one-
fourth as wide as long. Between the lake and a cleared pasture on
one side was a narrow fringe of flooded woods varying in width
from 50 to 200 feet. Breeding was prolific in this fringe and in
places in the open lake, under the thick growth of lilies and in mats
of mud plantain and Ceratophyllum. In preparing for the dusting
flights larval examinations were made at 10 or more points in the
part of the lake to be treated, and a glass plate was left on a floating
block at each of these “ stations.” From the plates it was possible to

4G. H. Bradley. The natural breeding places of Anopheles mosquitoes in the vicinity
of Mound, La, Jn Amer. Jour. Trop Med., vol. 4, pp. 199-223, 1924.

Airplane Dusting in Control of Malaria Mosquitoes 7

determine the concentration of Paris green which had reached the
water, and on the morning following the. dusting a corroborative ex-
amination for larvee was made. The stations were usually located
in the parts of the area most difficult for treating—that is, at the ends
and in the brush at the margins.

Of the six applications given this lake the highest average mor-
tality for one set of 10 stations was 93.5 per cent. A set of sta-
tions in another portion of the lake, treated in the same operation,
showed a mortality of 87.5 per cent. In one other trial 93 per cent
was killed, but the remaining applications were variable in results
and in one instance a complete failure.

The treatment of the open part of the lake was largely a matter of
skillful flying and estimation of the wind drift. (Fig. 4.) In the
operation the planes were brought down in a dive to below the line

Fic. 4.—Dusting plane making a flight over the center of Ex Via Lake, flying below
the tops of the trees on each side

of surrounding trees, then leveled out across the lake, and “ zoomed ”
over the timber at the other end, the upward direction of the plane in
“ zooming ” serving to blow the dust with great force down into the
pockets and thick brush at the ends.

At the time at which the flights were made, usually between 8
and 11 a. m., there was always more or less of a breeze, and the
effect on the drift of the dust cloud had to be rather carefully esti-
mated to make the applications effective. This was especially im-
portant in treating the wooded areas, since the dust, when released
at the height of the tree tops, is easily carried away by the wind.
Dusting was usually discontinued when the wind velocity exceeded
from 10 to 15 miles per hour. On the other hand, when the dust
is released at the right place, a slight wind drift is of advantage in
distributing it uniformly, and especially in carrying it into the
woods at the margins. (Figs. 5 and 6.)

8 Department Circular 367, U. S. Dept. of Agriculture

Fig. 5.—Dusting the marginal zone of Field Lake. With the wind blowing toward
the lake, the plane was flown outside of the tree line and the dust drifted into the
breeding area

Fic. 6.—View of another dust cloud left in treating the marginal zone of Field Lake.
In this case the plane was flown on the lake side of the trees, since the drift was
toward the open field. The photograph also shows the heavy, growth of water
chinquapin, in a portion of the lake completely obscuring the water surface

Airplane Dusting in Control of Malaria Mosquitoes 9

In the cotton-dusting work the best time for making the appli-
cations was found to be immediately after daylight when the air is
usually still and the plants covered with dew. In the lake dusting,
however, the presence of dew was a decided disadvantage, since it
caught and held the dust particles, and this more than offset the
advantage of flying early in the morning to avoid the more irregular
air conditions encountered later.

The general results of the lake-dusting experiments in 1923 are
summarized in Table 2.

Taste 2—Results of lake-dusting experiments* for destruction of larve of
malaria mosquitoes, Mound, La., 1923

FIELD LAKE

vent | Number of | Ne
= Average | numbero Stations | Reduc-
Date | eo number of | poison with 50 tion for
siations | larvae per | granules per cent entire
| 10 dips | per square} or higher area
| inch mortality |
} | |
1923 | | Per cent
SMa Store St Se i ie 10 35.0 | 1 Ra gal _. 67.7
(Te Ut oS See) ot a be een eee 10 9.7 | r 4 See se 93. 0
= | { 10 | it @ i ame 3 34.6
ee a |e babs
| 10 } 133 1 i
ees aoe are ern ee ae { 10 { 8.6 163 | 8 87. 5
10 | 14. 24 15.
~ Sg cagen oaee Se ee elaa ae Sa { 10 { 14.4 | 38 | 7 54.9
20 { 10 { 20. 0 84 9 84.0
Sv AGT aE MOL, =i tha ) 10 | 18.0 Seen 8 88.4
j |
ALGODON LAKE
|
Sa A a See See eee 10 20. 5 | = 2 0.1
eee eee ee ee 6 14.3 | 33 3 14.4
7, (bn SEL Sb eS ee oeres 6 21.3 | 120 3 18.8
7. ee ee eee 6 22.7 | 99 4 47.1
}
TEXAS FIELD LAKE
| |
nee eee eens as ee ee 10 15.7 39 | 2 1.9
OE Scr) aa beam) Dae See emee etOe 13 | 34. 8 122 | 7 47.1
'
WALNUT BAYOU
|
Vi, Blase 2s ee ee ee eee 10 11.4 | 156 i) | 78.1

1 The mixtures used contained from 10 to 50 per cent of Paris green.

On Algodon Lake, the second area selected, conditions for dust-
ing were very difficult, in that the breeding area consisted of a long,
narrow strip of water in the midst of a particularly heavy growth
of tall willows and buttonbush trees, and without any open space to
serve as a guide mark for the pilots. The débris and aquatic growth
on the water itself were also unusually thick, and an extra quantity
of poison was required for effective results. In none of the four
trials at this place were the applications particularly successful, but
in three of the four the average quantity of arsenic found on the
plates would ordinarily have been considered sufficient. This also

10 Department Circular 567, U. S. Dept. of Agriculture

occurred in the two tests on Texas Field Lake, which was the third
lake in the series, and consisted of a central open area with a fairly
wide overflow out into the woods. The most abundant breeding
was found in the overflow water, and the dusting observations were
confined to this part of the area.

In nearly all of the lake-dusting experiments one or more places
in the lake failed to receive more than a very small quantity of —
poison; and, on one occasion, the lake under treatment was almost
completely missed because the dust drifted away before settling.
When the results of the various experiments were analyzed, how-
ever, it became apparent that in a number of cases a large quantity
of the Paris green had settled upon the water surface without de-
stroying the larve. The uniform coating of dust on the glass
plates indicated that the distribution had been thorough; and, on
one or two occasions, it was observed by the examiners that living
Anopheles larve and green arsenic pellets floating on the water were
to be picked up in the same dip. This was contrary to the writers’
experience with hand distribution, and suggested some connection
with the method of application.

For various reasons it was not possible to conduct a large series
of tests in 1924; but, from the few which were made, it was indi-
cated that the difficulty in 1923 had been due to some defect in the
Paris green itself. Two lots had been used that year, and the
trouble had arisen with the second one, although it has not as yet
been determined wherein this differed from other samples. A new
stock was obtained for 1924; and, although an excessive quantity
was put in the mixtures because of the previous experience, a num-
ber of stations gave a high larval mortality where only a small
quantity of the arsenical was found to have reached the water.

Owing to the long drought in 1924 the woods became almost com-
pletely dry, and mosquito breeding was limited to the water re-
maining in the more open parts of the swamp lakes. The experi-
ments could not therefore be repeated in timber, as had been de-
sired; but, in the two lakes where applications were made (fig. 7),
the growth of water chinquapins was extremely dense; and the
water surface was a mat of floating and partially submerged vege-
tation, so that the conditions for the tests were sufficiently difficult.

DUSTING A FLOODED RICE FIELD

Another test of special interest was made in a rice field. The plat.
selected for this was a 714-acre cut, with the rice about 20 inches
high, and the field flooded with from 4 to 6 inches of water.
Anopheles breeding was well distributed throughout. The dusting
plane was flown from Tallulah, a distance of about 25 miles, and
was landed in a near-by pasture to take on the dust load, which for
this test consisted of 5 pounds of Paris green in 100 pounds of
Tripoli earth. The actual time required for dusting the field was
a matter of only a few minutes.

During the flight the wind was rather strong, and as a result one
edge of the field was missed on account of the failure of the plane to
go far enough upwind to offset the effect of the drift. Except for
this, the distribution was rather thorough and the quantity of dust

Airplane Dusting in Control of Malaria Mosquitoes 11

used was considerably more than enough to cover the field. For the
whole cut an estimated mortality of 73 per cent resulted, but with
the exception of the one edge practically 100 per cent of the large
larvee were destroyed as well as the majority of the small ones. In
this connection it may be noted that when mortality of the larve is
not complete those from one-half to full grown are always the first
to succumb.

The level nature of the rice fields made very favorable conditions
for airplane dusting, and the only difficulties in the way of effective
treatment appeared to be in the case of fields adjoining the woods or
where the hedgerows along the ditch banks were high. Some of the

Fic. 7.—Growth of water chinquapin in Blue Front Lake at the time of the dusting
test in 1924

dust was wasted because it remained on the leaves, but when these
were dry the mixture did not adhere to them to any great extent.
It was found from other experiments that the leaves of the rice plants
are very susceptible to burning when a large quantity of Paris green
is used, but the quantity necessary to kill Anopheles larvee did not
prove destructive to the plants, and in a few small plat tests, where
excessive quantities were applied, even severe burning of the leaves
did not appear to kill the plants or to prevent normal development
of the grain.

The summaries of the dusting operations in 1924 are given in
Tables 3 and 4, which include the records for une individual stations.

12. Department Circular 367, U. S. Dept. of Agriculture

TABLE 3.—Airplane dusting* on rice field for destruction of Anopheles larve,
Mound, La., 1924

Number of
Pare of Number of | Paris green] Reduction
Station No. nelcd larve in granules | following
10 dips per saguare| dusting
inch

Per cent

ae ee eg a als ee ee 2 Ay Haste oeees 9 347 ii
QUE T DART e So eis oe A ek bes 2s Jo dogiug 4 30 236 100
Se ee ee Cee ae Oe Se |-- S00b Secs 36 84 72
PAN aS a de Me a ah es aR pee Se ee es angel eres — — COE ees 22 42 73
Fee ee Ld ee eet Ue Peete NS VER ets: ae ey eS does 26 74 Tk
GOREN re eae eee meee pet Sl dose aes 8 48 25
Tie Oe the Se Se a Se CK ah ap 4 66 50
8 ee eee ee ee > do ee 8 54 0
U1! ee eee ea, Jenene a OS Center ____ 16 68 100
I Dg at ap ee er el Ei me eS eR ee TO ed OfRS S52 10 86 90
UO ee Pees ee ae ale eee tee a en es does es 15 8 80
1420 eee ee er ee amen ae VL dose 2s 18 2 44
15 3 pea aes ee A SL EE peace So. domasne= 8 2 is
16: Be ere eens Gn anaimen en eaters Sanat ss Wiest sae 32 45 100
(ag a A SN a aN Ue mse ea wd dosee ces 18 48 100
18. se aes ee IE oem Sek au Jk) =COE= ens 11 73 82
19: Sek iS ae epee nepal eee S US 5 Tn do3e. we 25 20 80
20). JASE See ea DS ene oe ee aE Gs 4 dossna4 7 Ze 0
Average_ 16.8 72 73. 0
Average, exclusive of stations Nosi14, 15, and 20.2.2 2a ee 78.5
Per cent reduction of larve over half grown, exclusive of stations Nos. 14, 15, and 20_________ 99.0

1 Five pounds of Paris green and 100 pounds of dust were used.

TasBLe 4.—Lake dusting for destruction of Anopheles larve; Mound, La., 1924

EX VIA LAKE
Dosage: 20 pounds of Paris green to 140 pounds of Tripoliearth /

Number of : =
Number of| Paris green| Reduction eae cs
Station No. larvee in granules from tating 10
10 dips pees dusting oes Sas
: Per cent Per cent
Beg Se a PEs fe see, DU ref ES I 80 6 55 50
Din ANS coe oe UE es 2 yk ie ie eae TS, CS 36 151 94 100
Sis Sue tel ieee nL ae elie inant eer ey 44 22 93 80
Ae aes AC AND OA cee halen Aee a Meee es tt 2 24 38 100 100
5 GRE See UN ye tel SR ee eee eee e we ai: ol ea 10 232 100 100
sear I a Sa ET RS Aik A es a aah ian 16 139 100 100
SisQ elles see SS eee ae aN ew eee a 5 43 82 96 (1)
TA eee ee a Se neste ee a as ASHES Fama US SOE yn. a 2p 45 276 100 100
ZEN een ed yk fire gt Eien 2s Ree ee ees Sh 8 193 100 100
UNS =e ee aad 2 Mere ah nial eh tile aig Ree, Mavi eo See 2 a 4 146 100 (1)
hI ES Re CF IR Ses A eee Spe ale Rl a OL 20 214 100 100
1 fs is pes Mea de Ay ors ap ha eee cs wT Aa il as Ci 46 150 100 (1)
GSE Ee ak ee eR ee Ce eee 14 124 71 1
A Ui fae aS pe rt" MR sae ee ee ee 14 245 86
INGOT AGC Senarae marr aaa a mene ee. ol 28. 9 144 88. 0 91.8
1 No pan.
BLUE FRONT LAKE
Dosage: 30 pounds of Paris green to 120 pounds of Tripoli earth
el a) afin VP Ap a Op SUNT Hh ea nh OR Ne eR 20 390 100 100
yas EEA lane, wa ea Rs ees 18 662 100 100
BS peel eects, Bnei eV OEM tae Cae Sl MPR ihe; 838 100 100
ACE ap eee ee Oe eee AIR oo ee SA Sa hh 16 810 100 100
DEL ME Ie doen ee Seen ee ge. 24 420 100 100
Git Re Roker REE Sanaa eee ko eh. 14 499 100 100
{EES Se eM oy EDA ik ae ee 13 524 100 100
eee Bere Me SSR eee Se ee 25 172 100 100
OLE Le Ul Se nee See 14 419 100 100
LO a Ts Sloane eee tena EERE eas. 17 33 91 100
A Ie SS een apres ANE OR LS ready re ee ee 15 43 100 100
PA VCTAL Caen pr encnneneee elie! eee Sm. a TAD 437 99. 1 100

Airplane Dusting in Control of Malaria Mosquitoes 13
AN ADDITIONAL CHECK ON THE RESULTS

As an additional check on the results of the poisoning in the two
completed experiments porcelain pans 11 inches in diameter and
containing 10 larvee each were placed at the different stations before
the dust was applied and were examined the following day for the
percentage killed. (Fig. 8.) On Ex Via Lake all the larve were
dead in seven out of nine pans, whereas, in the other two pans, 5
larvee remained alive in one and 2 in the other. The first of these
was in a pocket along the shore, and this was the only part of the
area where any considerable number of larve were found remaining
after the treatment. A few small larve were found at several of the

Fic. 8.—One of the pans containing larvae and floating on the surface of the water
as used in the lake-dusting experinrents in 1924. The view also shows the water
conditions encountered during these tests

other stations and the total reduction for the whole area was 88 per
cent.

At the second lake the treatment was highly successful, as all of
the larve in the 11 pans were killed and none were to be found in the
lake water in any part of the area except at one place where a small
quantity of dust had fallen and where a few of the very smallest larve
had escaped. The number found remaining was less than 1 per cent
of the total counted in the examinations made previous to dusting.

SUMMARY

Dusting Paris green from airplanes to control the breeding of
Anopheles mosquitoes was tried in 1923 and 1924 on the extensive
swamp and marsh areas in the vicinity of Mound, La. Army model
DeHaviland planes were employed and were operated by United

14. Department Circular 367, U. S. Dept. of Agriculture

States Army Air Service pilots. These planes had been adapted for
cotton dusting by installing metal dust hoppers in the rear cockpits
with an arrangement provided for releasing the dust through the
bottom of the fuselage. fold

In developing the method of handling the planes so as to distribute
the dust properly and in determining the quantity of Paris green to
use, flights were made first over open fields, then over dry woods, and
finally over various types of mosquito-breeding swamp and lake
areas. As the Paris green is effective in very small quantities, it was
diluted by mixing it with an inert carrier before it was distributed.
For this purpose a fine silicious earth was used in most of the tests,
although ordinary road dust and a mixture of flour and lime were
employed on a few occasions with fairly good results.

From these tests it was found that a given area could be covered
rather thoroughly with the dust, and that by taking advantage of a
light breeze a wide strip could be treated with each trip of the plane.
A wind velocity as high as 10 to 15 miles per hour was, however, a
disadvantage in making the dust applications, and the operations
were usually discontinued when the stronger winds were blowing.

In addition to the different types of marsh and lake areas treated
in the two seasons, applications were made on a section of one of the
natural bayous and on a small field of rice. The results of the entire
series of tests in the reduction of larvee were variable, owing in part
to the failure of the dust to reach all of the area under observation
and in part to an unsatisfactory lot of Paris green which was used
in a number of the experiments and which proved to have a very
low toxicity for the larve.

With an experienced pilot, and when careful attention was given
to the spread of the dust, no special difficulty was encountered in
distributing the dust over the treeless part of the lakes. Further-
more, from the single experience in treating rice fields, this type of
breeding place appears to be particularly well adapted to control.
by airplane dusting, because of the absence of trees and other obstruc-
tions which interfere with close flying. As had been anticipated,
the most difficult conditions encountered were in the heavily wooded
areas where the water was protected by dense overhead foliage, and
where the planes had to be flown high enough from the ground to
clear the tallest trees. Even in such places, however, the dust was
found to have penetrated the thick growth and to have reached the
water in sufficient quantities to destroy the larve when enough of
the dust had been used to offset the increased wastage. Under such
conditions the loss of dust due to adherence to the leaves and to wind
drift was considerable.

The quantity of Paris green used in the experiments varied from
about one-twentieth of a pound to several pounds per acre. Ex-
clusive of the tests in which the poor sample of Paris green was used,
the writers’ experience indicates that approximately one-half pound
per acre will give a safe margin for the treatment of such places as
rice fields and the more open parts of the lakes, the quantity being
increased as necessary where the breeding area is protected by a
growth of trees and brush.

The two final tests of 1924 gave particularly clear-cut results, and
for this reason were of special interest in showing the possibilities

Airplane Dusting in Control of Malaria Mosquitoes 15

of this method of control in breeding areas of the type represented,
the lakes being overgrown with aquatic vegetation and having an
abundance of ‘Anopheles larvee well distributed throughout. In the
first of these a larval reduction of 88 per cent occurred as a result
of the treatment, and in the second over 99 per cent were killed, as
estimated by the writers’ method of examination. The only larve
remaining in the second instance were a few of the smallest size,
which were found in one small spot. In each test a series of pans
containing a counted number of larve were distributed over the
lake as a further check on the effectiveness of the poisoning. In the
first test 92 per cent of these larve were killed and in the second all
were destroyed.

ORGANIZATION OF THE
UNITED STATES DEPARTMENT OF AGRICULTURE

January 30, 1926

Secretary of Agriculture _2-). i eae W. M. JARDINE.
Assistant Secretary 22 i220 Lees R. W. DUNLAP.
Director of Scientific Work ___-.-- Sa ee
Director of Regulatory Work _-------------- WALTER G. CAMPBELL.
Director of Extension Work —~__--------__~~- C. W. WARBURTON.
Director of Inpormation —.___-- __-- - eee NELSON ANTRIM CRAWFORD.
Director of Personnel and Business Adminis- _

LEO UONW ES ee ee W. W. STOCKBERGER.
Solicitor eee a ee R. W. WILLIAMS.
WiCOLNCT BUT COAY 2 2 Pee CHARLES F. Marvin, Chief.
Bureau of Agricultural Economics___-_----—~ THOMAS P. Cooper, Chief.
Bureau of Animat Industry __.._.-_ 5.2 JOHN R. MoHLER, Chief.
Bureo. of Plant industry — :—._.: WILLIAM A. TAYLor, Chief.
TOTES CB ChINCE: Lae ae ee ee. W. B. GREELEY, Chief.
Bureau Of Chemisirijee a. re C. A. BROWNE, Chief.
BAUTEOAL Of SOUS Maen eek oA MILTON WHITNEY, Chief.
Burea Of ENtOMolwgy= oe =. eae L. O. Howarp, Chief.
Bureau of Biotegicat Survey ____- = es HK. W. NELSon, Chief.
Brea CfxePuone ROGds <<. ee Tuomas H. MacDonatp, Chief.
Bureau of Home Hoonomics______-—~_--=- = — LOUISE STANLEY, Chief.
BUGEC. Of ICI NUNG eee a Ss eee C. W. Larson, Chief.
Fixed Nitrogen Research Laboratory ___-_-__ F. G. CoTtrewyi, Director.
Ojiee of Haperwiment Stations 22... eee E. W. ALLEN, Chief.
Office of Cooperative Extension Work________ C. B. SmirH, Chief.
ROUGE) ote Maret Ee Pe alia ey BS Ve CLARIBEL R. BARNETT, Librarian.
Hederal Horticultural Board__. ... Seas C. L. MARLATT, Chairman.
Insecticide and Fungicide Board ______-—_____ J. K. HAywoop, Chairman.
Packers and Stockyards Administration__._. JOHN T. CAINE, in Charge.

Grain Futures Administration_______.___-=-___ J. W. T. DUVEL, in Charge.

This Bulletin is a contribution from

Bureaw-of Entomology. =. eee L. O. Howarp, Chief.
16

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