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Laboratory of the Board of Health, Department of Sanitation






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BY 8. T. Dabling, M. D.

Page «>; 'J4th line from bottom; Delete shown in the drawings.

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hospital few days later with tertian malaria.
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Piige 38; After last line; Mr. A. H. Jennings for the indentifioatdon

of mosquitoes.

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S4HUEL T. Dabling, M. D.,
Chief, Labctatory of the Board of Health.

The following observations and experiments have developed out
of work directly or indirectly related to a study of some of the factors
concerned in the transmission and prevention of malarial fever in
the Canal Zone:

In every malarial region it is important that the varieties of mos-
quitoes common to that region should be recognized, their breeding
habits should be studied, and a determination made of the species or
anophelines hospitable to malaria, and those transmitting it. The
English observers, James, Christophers, and Stephens, noticed that
certain species of anophelines were natural transmitters of malarial
fever, while others were rarely, if ever, found infected naturally,
although it would be possible to infect them under laboratory con-
ditions. We know that the breeding habits of anophelines vary,
too, considerably, and it may be said that there is as much selection
of breeding places by anophelines as there is selection of feeding
grounds by fish. Trout, salmon, and bull-heads have their analogues
among anopheles larvae, some of the latter requiring fresh aerated
water, or water containing much green algse. Others are found in
tree holes and the recesses of epiphytic tree plants, such as bromeUas,
where they prey upon other species; while others preferring fresh
aerated water are so adaptable that they will flourish in sewage,
streams, or in brackish water containing half its volume of sea water.
Some species require an abundance of sunlight, while other sylvan
species prefer shady pools in which chlorophyll-bearing algae are
relatively absent. The anophelines insusceptible to malaria may be
more linaited in their choice of breeding places, so that in the work of
malarial-mosquito destruction the latter may be disregarded, and
attention given wholly to the breeding places of those varieties
responsible for the transmission of malarial fever.

With regard to man as a host, it is necessary to have some knowl-
edge of the limits of his infectiousness, i. e., the number of sexual
forms of the malarial parasite necessary to infect susceptible

Besides the question of hospitable species of anophelines, there are
other matters of much importance, such as latent malaria; the effect
of quinine on the parasites in man; the value of various larvacides;

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algacides; agents destructive to ditch grass, and a knowledge of the
qualit]^ of wire screening, and the size mesh necessary in keeping out


AnopheUnes of this region.

Collection of larvse.

Breeding out mosquitoes and methods of feeding.

Biting — infecting experiments.

Estimation of gametes.

Care of mosquitoes after feeding.

Method of examining for zygotes and sporozoites.

Description of the malarial parasite in the mosquito.

Table of infecting experiments.

.Notes and conclusions from table of infecting experiments.

Limit of infectiousness of man.

Notes on the bionomics of anophelines.

Effect of salt or sea water on larvse.

Experiments with larvacides.

Experiments with agents destructive to vegetation, grass, and algae.

Experiments with screening of various mesn.

Relative value of wire screening of various composition, based on
practical tests and chemical analyses.

Note on the value of the practice of kilh'ng anophelines found in
quarters and barracks.

Latent malaria.

Effect of quinine upon the parasite in mosquito and man.

The following is a fist of anophelines of the Canal Zone:

Anopheles argyritarsis, R. D.
AnoTphdes tarsimaciUatay Goeldi.
Anopheles gor^asi, D. K.
Anopheles (dh%manus. Wied.
Anopheles cruzii, D. K.
Anopheles apicmdcula, D. K.
Anopheles punctimdcuUij D. K.
Anopheles malefactor^ D. K.
Anopheles eisenij Coquill.
Anopheles franciscanus J McCrack.
Anopheles pseudopunctipennis, Theob.

The above 11 species of anophelines have been, collected in the
Canal Zone during the past five years. They are not taken, nor do
they exist in their breeding places, in anything Uke equal numbers.
For example: Only one specimen of A. gorgoM has been found. Of
the 11 species, the commonest ones are A, alhimanus, A. pseudo-
punctipennis , and A. malefactor, but this again naust be qualified by
stating that the predominance of a species varies from season to
season and from place to place. In certain villages, upon going
through the barracks only. A, alhimanus will be found, while in other
villages from 5 to 10 per cent of the mosquitoes will be A, pseudo-
punctipennis, and at Ancon during October, 1908, 27 per cent were
A. malefactor and 72 per cent A, albiman/as, Mr. A. JBusck, of the
Bureau of Entomology, United States Department of Agriculture,

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who collected and made observations on Zone mosquitoes during
1907, gave it as his opinion that A, r^seitdopunctipennis was the
commonest anopheline during the perioa of his stay.

The necessities of the canal operations in excavating and filling
change the topography of districts and locaUties so as sometimes to
convert salt marSies into fresh-water ponds, or to make tracts of land
containing few anophelines into a vast swamp in which they luxu-
riate. On the other hand, swamps and breeding places may be
drained or filled in the work of excavation. These factors, among
others, influence the number and variety of species in a locality.

The commoner anophelines of the Canal Zone may be divided into
three CToups:

(A) The white hind-footed group comprising: A. argyritarsis, A.
albimanus, A. tarsimaculata.

(B) The leg uniformly-colored group comprising: A. pseudo-
punctipennis, A. franciscanus.

(C) The spotted-leg group, comprising: A. malefactor, A. apici-

These groups present well marked differences in the markings of
adults, in the breeding habits and anatomical characters of the larvee,
and, as will be shown, they possess varying susceptibilities to malaria.

The following are descriptions of the species of anophelines of the
Canal Zone :

Anopheles argyritarsis, — Thorax with mesonotum bluish-gray, with
three more or less longitudinal lines and with pale scales over the
mesonotum, and sometimes traces of two dark lateral spots. The
abdomen dark, dusky-brown, with a few creamy scales. Legs cov-
ered with dark scales, with some of the tarsiapically white banded;
last three joints of hind legs pure white, and also apex of first; costa
dark, with two distinct and several smaller pale spots.

9 Head black, with white upright spatulate scales in front, black
behind and at the sides, a tuft of white hairs projecting forward
between the eyes. Eyes black; antennse dark, with pale silky pubes-
cence and brown hair; basal joint dark^ a few patches of white
scales on the first few basal joints; palpi covered with long black
scales, especially along toward the base; apex pure white, and there
are also two narrow white rings on the apical ends of the joints; ven-
trally, the penultimate joint has a numoer of yellowish-white scales,
which sometimes seem to form almost a ring; proboscis clothed with
short dark scales.

Thorax with a bluish-g^ray sheen, with three more or less distinct
longitudinal lines, the. middle one most distinct, and of a purplish
hue, with pale scales scattered over the mesonotum; scuteUum dark
toward the middle; mesonotum deep brown; pleura dark, with here
and there frosty tomentum (there are traces of two dark lateral
spots on the mesonotum, which are clearly seen in the St. Lucia

Abdomen dusky purplish-brown, clothed with creamy yellow
scales, especially in the middle region of the segments; the segments
have lateral tufts of gray scales on the posterior borders, projecting
from the sides; hairs long, deep bright brown; viewed with a pocket
lens the abdomen is almost black in ground color; in other specimens
dull yellowish reflections may be seen.

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Legs yellowish, covered with dark brown scales; first two tarsi
of the forelegs apically white^ last two joints dark brown, four medi-
tarsi also with small pale apical bands; mid metatarsi and first two
tarsal joints with minute apical yellow bands, last two indistinctly
banded; in the hind legs the last three joints are pure snow white, and
also the apex of the first; ungues very dark.

Wings with the costa dark, with four distinct and several smaller
white patches; there are also numerous patches of dark scales, which
vary to some extent, over the wing areas; in the 9 , from which
this description is taken, the fourth long vein is covered with pale
dusky scales, whilst in a 9 from St. Lucia it is creamy white; halteres
with pale stem and fuscous knob. Length, 4 to 6 mm.

$ Palpi dark brown, with scattered white scales, especially on the
last swollen joints; hair-tuft pale; there is a pale ring at apex of the
apical and base of the penultimate joint; antennae brown, with
brown plumes; proboscis orown and narrow. The white scales on
the head extend neariy over the neck; scales on the thorax white;
the larger ungues of the four feet biserrated. Length, 4 to 5 mm.

During the period in which these experiments were being con-
ducted I received very few specimens of this species, the sources
being Miraflores, Ancon, Culebra, Paraiso, and Corozfd. Two spec-
imens of A, argyritarsis bit a patient having one crescent to 200 leuco-
cytes and neither became infected. The patient was possibly an
unfavorable case and the experiment was not controlled by biting
susceptible A. alhimanus at the same time. On December 2 from
some anophelines collected in labor cars at Corozal, one specimen of
A, argyritarsis was found containing a malarial zygote, 29 mu. in
diameter, with fine discrete pigment.

Anopheles tarsimaculata. — ^This mosquito resembles A. albimanus
very closely, except for the different arrangement of the white bands
on the palpi shown in the drawings. This mosquito was found to
transmit malaria.

Anopheles albimanus, — This form resembles the type in all respects
except that the last tarsal joint in the hind legs has a very distinct and
persistent deep black basal band. The thorax is rather browner in
some specimens, and there are only two white bands to the 9 palpi.
The forelegs have dark scaled femora, pale beneath, with a small
white knee spot, the tibiae dusky scaled and also the metatarsus
above, pale below, apex white ; the first two tarsi have yellow apical
bands, the third dark, and the last clay colored; mid legs with a
large white spot near the apex of the femora; mid tarsi not definitely
banded, but with a faint pale band sometimes at the apex of the
metatarsus; the hind legs are dark brown, with the second, third,
and apex pf the first tarsal joints pure white, the last joint white,
with a distinct black basal band; ungues as in the type. Wings
much as in the type, but the pale scales are more yellow in color.
Length, S 3.5 to 4.5 mm.; 9 4 to 4.5 mm.

This was the commonest species of anopheline received as adults
or larvae during the period embraced by this work, and was found to
transmit both estivo-autumnal and tertian malaria.

Anopheles gorgasi. — Palpi as long as the proboscis, mostly black
scaled, the terminal and penultimate joints light scaled except at the
bases and apices; meso-thorax gray with fine brown scales, a black spot
in front of tne scutellum, a pair of sublateral black spotsmedially; wings

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with the veins scaled in black and white, two very large black patches
on the costa and a smaller one toward the base and a smaUer one
at the apex as in J.. aJbimanus Weid. The rest of the wing is
too much denuded to describe. Abdomen with groups of outstand-
ing scales laterally at the apices of the semients, the dorsum closed
with yellow scales on a dark brown, the lateral tufts black. Legs
mostly black scaled, hind legs with tne apical half of the second, the
third, and the base of the fourth joints white scaled, the remainder of
the fourth and basal half of the fifth segments black, the third joint
with a large black patch on the underside, which reaches from near
the base to beyond the middle. Length, 3.5 mm.

A single adult female of this species was collected by Mr. A. H. Jen-

Anopheles pseudopunctipennis. — Winffl much as in -4. punctipennis
Sav, but the fringe with yellow spots. Legs, long, unhanded, brown,
pale at the base. Fore ungues oi S imequal, mid and hind equal ana

9 AntennsB brown, basal joint testaceous, base of the second joint
pale, and also a small pale band at the base of all the following joints:
proboscis dark brown, labella yellowish; palpi dark brown, densely
scaled at base, ajjex yellow, and also two narrow yellow bands below,
slightly hairy, hairs black, except at the apex, where they are yellow;
clypeus dark brown. Tnorax yellowish-brown (denuded), with a
dark patch on each side of the mesonotum behind ; metanotum deep
brown; pleurse yellowish brown, with darker brown patches. Abdo-
men brown, the segment paler at the basej hairy. I^gs deep brown;
cozse. trochanters and base of femora palhd; knee spot pale; ungues
equal and simple. Halteres with pale stem and fuscous knob.

Wings with two yellowish white spots on the upper costal border,
rest of the edge black, rather denseljr scaled; first submarginal longer
and narrower than the second posterior cell, its stem nearly as long as
the cell; mid cross vein a Uttle nearer the base of the wing than the
supernumerary cross vein; posterior cross vein still nearer the base
of the wing; scales of the wmgs^disposed as follows: First long vein
with three distinct large white spots, one at the base, one underneath a
large costal spot, and one between; second long vein with a dark patch
near its base, all the lower branch of the fork cell dark, and most of the
upper ; third long vein mostly yellowish-white, with two black patches,
one toward the base and the other toward the tip; fourth long vein
mostly pale, with two small black patches, branches of the fons cell
all dark scaled; fifth long vein with a black spot near the base, rest
mostly yellow, upper branch of the fork mostly dark, a small yellow
spot at the apex and another toward its base^ lower branch mostly
yellowish, with a black apical spot; sixth vem with the basal haft
creamy, the apical half dark, except a small yellow patch where it
joins the wing border; fringe brown, with a yellow spot at the junc-
tion of each vein. Length, 5 mm.

S Last two joints of the palpi swollen and clavate, pale, basal
joints dark brown, densely scaled with deep brown scales^ with a nar-
row pale band not quite as long as the thin proboscis, which is brown.
' with yellow labellse; antennae ^ay, with narrow brown bands ana
flaxen brown hairs, the apical jomt about hatf the length of the penul-
timate joint; basal lobe of the genitalia simple, claspers long and
thin; fore ungues unequal, the larger one uniserratea, the smaller

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minute and simple; mid and hind ungues small, equal, and simple.
Wings much as m the 9 , but the fork cells shorter. Length, 5 mm.,
with proboscis 7.5 mm. Habitat: Grenada. (Doctor Hatyon, per
Doctor Daniel.) Time of capture: February.

Observations: Very like A. punctipennis Say, but can at once be
told by the wing fringe being spottea at the apex of each nerve and
by the marking of the sixth long vein. The description is drawn up
from two specimens in balsam, so that the scale structure is not evi-
dent. It is so very distinct, however, that it can easily be identified
by the characters given below. I succeeded in infectmg four speci-
mens of this species.

Mr. August 3usck found this species to be the commonest and most
widely distributed one in the zone during the season in which his col-
lections were made^ April-July, 1907.

Anopheles francucanus. — ^Male: Head dark brown, with short,
dark, erect scales toward nate, emarginate and slightly forked, vertex
and anterior part of occiput, with short, light brown scales not forked,
a tuft of light brown hsara projecting forward between the eyes, a row
of similar hairs projecting forward encircling the eyes posteriori}^;
eyes deep purplish-brown; antenn© about two-thirds length of palpi,
yellowish-brown hairs, basal joint dark brown; palpi equaling pro-
boscis in length with emarginate scales from base to tip on under and
outer surfaces, those upon outer surface dark, upon imder surface
light, long light hairs covering distal third, becoming short and stout
at the apex; an area at base of three distal segments, giving a slightly
banded appearance; two distal joints spatulate, proboscis scaled
except labella, labeUa covered with medium stout set», a few light
hairs at apex.

Thorax: Prothorax lobes dark; meto thorax dark brown at the
sides, with scattered light hairs, a broad Ught brown patch in the
middle; within this light area a median line and obscure lateral lines;
scutellum light with single horizontal row of hairs; metanotum dark
without hair; halteres dark, covered with thick pubescence and
emarginate scales; stalks light without scales.

Abdomen: Basal area of each segment light, covered sparingly
with long, Ught hairs; two stiff hairs on posterior margin of distaJ
segment, stout hairs on margin of genital lobes.

Legs: Cox8e and trochanter Ught; trochanters, femora, tibise, and
tarsi covered with short, dark, emarginate scales and set©; ungues
of front legs very unequal, the larger one with a large median tooth and
a smaller basal lobe; middle ungues covered, with blunt basal lobes;
posterior ungues equal, simple; posterior metatarsus slightly longer
than tibiae.

Wings with dark costa, with two distinct, nearly equal, yeUow
spots — one at distal end of subcostal vein, one at and involving distal
end of first long vein; fringe dark, with a yellow spot at the end of
each vein except at the end of the sixth; tne first spot carried on to
the first long vein, the apical spot carried past over long vein on to the
upper branch of the second long vein ; the second long vein dark except
for a few basal light scales ; third long vein yellow in tne middle, dark at
the base and apex ; Ught area at base of third long vein, carried over the
fourth on to the upper branch of the fifth, with a few light scales at base :
main branch of fifth long vein Ught, except at base and apex; distal
half of sixth long vein dark, except at apex, basal half Ught ; subcostal

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with a light spot carried to the first lon^ vein (in one specimen the
light spot on subcostal missing); third long vein prolor^ed slightly
into the basal cell ; first submarginal longer and slightly narrower than
second posterior cell, stem twice the length of the cell ; stem of second
posterior cell prolonged to base of wing; supernumerary cross vein
adjacent to or but very shortly removed from mid cross vein, and
equal to it in length when removed nearer to apex of wing; posterior
cross vein a Uttle longer than mid cross vein and varying in distance
from it from one half to almost twice its own length; third long vein
prolonged sUghtly into the basal cell, darkest scales on costal, sub-
costal, and first long veins.

Palpi of the female equaling proboscis in length, light area at base
of three distal segments, giving a banded appearance, clothed with
scales, short hairs and setae, as in male, distal joints not spatulate;
legs with the ungues equal ; otherwise with the male.

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