NationalLibraryOfScotland/medical-history-of-british-india huggingface dataset:
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larvæ of anophelet es, on the other hand, have no external air-tube and
the result of this is that they lie flat at the surface of the water.
They move along at the surface; when disturbed, in a backward
direction, by a series of darting, jerky movements. They are
thus easily distinguished from culex larvæ ; an anopheles larva
lies flat at the surface, and a culex larva lies with its head and
body sloping downwards beneath the surface in an oblique direction.
(3) The pupœ of culex and anopheles.—The pupæ are small
comma-shaped creatures bearing no resemblance to the larvæ, and
they breathe by means of two trumpet-shaped projections attached
to the head, so that they lie with their heads at the surface and
their tails downwards.
The trumpet-shaped breathing tubes of the pupæ of culex mos-
quitoes are longer and more slender than those of the anopheles genus.
(4) The adult insects.—Before we can distinguish between the
adult insects of these two genera, it is necessary to know the differ-
ences between a male and female adult mosquito. The chief
difference is that in male mosquitoes the antennæ or feelers are
covered with long hairs, so that each antenna forms a feather-like
tuft in front of the head. In female mosquitoes the antennæ have
no long hairs and are nearly bare. (See Plate III, Figs. II, III,
IV.) In females too it may often be seen that the abdomen is
distended with eggs, or the stomach may be full of blood, and as
only female mosquitoes suck blood, we know at once that mosquitoes
containing blood must be females.
The following are the ways by which adult culex and anopheles
mosquitoes may be distinguished from each other :—
(1) The correct way is to make a careful examination of the
palpi and proboscis of the mosquito with a lens. In anopheles
mosquitoes the palpi are the same length as the proboscis in both
sexes, so that female anopheletes have long palpi. In culex mos-
quitoes the palpi of the male are long but those of the female
are very short; female culices have short palpi. (See Plate III,
Figs. III, IV.)
(2) The attitude of the majority of anopheletes when resting on
a wall or roof is very characteristic and quite different from the atti-
tude of culex mosquitoes. When an anopheles is resting on a
wall it keeps its proboscis, head, thorax and abdomen in one line,
and the hinder part of its body projects outwards from the wall so
that the insect frequently appears to be standing on the tip of its
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proboscis. With culex mosquitoes the body is either kept parallel
to the wall, or the tail end is even nearer to the wall than the front
part of the body, so that a culex appears " hunch-backed." We
must remember, however, that this attitude of anopheletes does not
apply to the whole genus. There is one very important anopheles (A.
culicifacies) which when sitting on a wall looks exactly like a small
brown culex and keeps its body parallel to the wall as a culex does.*
(3) As a general rule it may be said that most anopheletes have
spotted wings while in most culices the wings are quite plain and
uniformly coloured. We must be careful, however, to avoid using
this character as a test without subsequent careful examination of
the palpi, for in India there is at least one species of culex
(C. mimeticus) with well marked spots on the wings, and at least
two species of anopheletes (A. immaculatus and A. Aitkeni) with
quite unspotted wings.
We should, however, aim at something more than a knowledge
of the distinctions between the two genera culex and anopheles : we
should try, if possible, to ascertain what species of anopheles we are
dealing with. The importance of this has already been indicated
in the remarks on the conditions which determine differences in the
prevalence of malaria at different places. It was noted in those
remarks that some species of anopheletes are better malaria carriers
in nature than others, and it is especially important therefore to be
able to recognise the species which have been proved to have most
influence on the spread of malaria in India. Owing, however, to
the comparatively large number of species of anopheletes that exist
in India, and to the fact that many of these species resemble one
another very closely, it is a matter of some difficulty to correctly
identify any particular specimen of anopheles. The subject is
however a very important one, which will well repay the expendi-
ture of much time and trouble. One of the most important things
in a study of malaria in any place is to collect and identify the
various species of anopheletes prevalent in the district, and to find
out as far as possible by a study of the habits, relative abundance,
seasonal prevalence, and other particulars of the life history of each
species, what connection it has with the prevalence of malaria. To
do this it is necessary to know how to collect anopheletes, how to
mount and preserve them, and how to examine and identify them.
* At least one of the unspotted winged species of anopheles referred to
later also adopts the attitude of culex mosquitoas when resting on a wall.
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How to collect adult anopheletes.
One of the habits of anopheles mosquitoes is that they only
fly about after dusk and during the night; in the daytime they
seek some dark shed, outhouse, or stable, where they rest on the
walls and roof, until evening. In these places they can be easily
caught, the necessary implements being a few dry test tubes and a
large dry bottle. When a mosquito is seen sitting on the wall or
roof, the mouth of a test tube is placed very gently over it. It will
fly into the tube, the mouth of which can then be closed with a plug
of cotton wool. As each mosquito is caught it may be transferred
to the large glass bottle by placing the mouth of the tube over that
of the bottle and removing the cotton wool plug. The mosquito
will fly into the large bottle and the tube can be used again. If
anopheletes are at all abundant twenty or thirty can be caught in
this way in a very short time. . The best places in which to search
for them are outhouses, cowsheds, woodsheds, and thatched un-
occupied rooms with dirty smoke-blackened walls and many cob-
webs. It is almost useless to search in a new whitewashed house.
Even in places which appear favourable, mosquitoes are often difficult
to detect, and some species hide among the straw of a thatched roof
or in holes and corners of the wall with great success. For search-
ing the roof a ladder should be used, so that the eye is not more
than a foot or so off the roof, and every part of the thatch should
be carefully examined. The commoner anopheletes are light coloured
and stand out against the black background of dirt and soot like
little white thorns hanging from the roof, but even an experienced
observer may sometimes miss the small brown species which, as we
shall see, are so important from the point of view of malaria.
How to mount and examine anopheletes.
The mosquitoes that have been caught should be killed by placing
a drop or two of chloroform on the muslin cover of the bottle. The
dead mosquitoes are then turned out on to a clean white sheet of
paper and mounted as quickly as possible.
The following articles are necessary for mounting a mosquito :
(1) A supply of fine silver pins, No. 20 size,
(2) A pair of forceps for holding the pins.
(8) Small discs of thin cardboard.
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(4) Ordinary pins.
(5) A box in the bottom of which a layer of cork
or pith is fixed.
Mosquitoes which are required for identification should never be
touched with the fingers. A pin or needle should be used for
moving them when this is necessary. A card-disc should be taken
and one of the No. 20 silver pins thrust through its centre, so that
about half the pin projects each side. The mosquito to be mounted
is turned over on to its back, and the point of the pin carrying
the disc is entered into its thorax at the point of origin of the legs,
and made to emerge through the dorsum of the thorax. On turn-
ing the disc over, the mosquito will be found to be mounted in its
natural position, right side uppermost, and its legs and wings can
be gently arranged on the card-disc with the aid of a pin. An
ordinary pin is now thrust through the edge of the card disc to
attach it to the cork in the bottom of the box. (See figure 1.)
FIGURE 1.
(After Theobald.)
METHOD OP MOUNTING A MOSQUITO.
a. pin through card disc, (b); c. label for date, locality, etc.; d. No. 20 pin
through card disc (b) and mosquito (f); e, point of d through thorax of
mosquito.
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For the proper examination and identification of adult mosquitoes
a low power microscope is almost a necessity, but in the absence of
this it will be found that most of the marking's and characters, ex-
cept those relating to the shape of the scales, can be made out,
though less easily, with a hand-lens.
For the examination under a microscope, the mosquito, which
has already been mounted on a card-disc in the manner above
described, is fixed by a pin thrust through the edge of the disc
to a flat piece of cork about an inch square. This cork carrying the
mosquito is placed on the microscope stage and can be moved about
at will, so as to bring all parts of the mosquito under the lens.
It is best to begin with an examination of the palpi and to
work backwards, noting every marking and character that presents
itself. The palpi, proboscis, and antennae will be first examined, and
from the length of the palpi we shall be able to see whether the
mosquito belongs to the culex or anopheles genus, and from the cha-
racter of the antennæ whether it is a male or female. At the same
time we shall note whether the palpi have any white bands, and if
so their number and relative width, and also whether the tips of the
palpi are white or black. On the head we shall note the upright
forked scales which are so characteristic of the anopheles genus, and
on the dorsum of the thorax there will probably be a number of
small white spindle-shaped scales, and some white or brown hairs.
Passing on to the abdomen we shall find that in most species it is
thickly covered with long brownish hairs, but that very few if any
scales are present. In one or two species, however, we shall find
that the abdomen is very thickly covered with broad silvery scales,
and we shall recognise that this is a very important aid in the identi-
fication of these species. In the examination of the legs we shall
note that each consists of a femur, tibia, and five tarsal segments,
the terminal of which is very short and carries the ungues,—very
sharp-pointed horny structures which enable the mosquito to rest in
any position on a wall or roof without falling. In some species we
shall see that the legs are of a uniform brown or black colour without
any white bands at the joints, in others there will be a more or less
broad white band at each joint, and in some the whole of the last
one, two, or three, tarsal segments of the hind legs will be pure white.
In addition to the bands at the joints, the femora and tibiæ may
*
*
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in some species, be brilliantly speckled with white scales. In the
examination of the wings we shall note that some of the scales are
white and others dark coloured, forming alternate black and white
scaled areas ("spots"), and taking each vein separately the
number of dark and light scaled areas will be noted.
Having in this way noted the markings and characters of each
structure, we shall, in the majority of instances, be able to correctly
identify the species by means of the following table,
TABLE OF THE INDIAN SPECIES OF
ANOPHELETES.
I.—WINGS UNSPOTTED.
A.—PALPI UNBANDED.
A. Aitkeni (James).
B.-PALPI WITH WHITE BANDS.
A. immaculatus (Theobald).
II.—WINGS SPOTTED.
A.-PALPI UNBANDED.
A. Lindesayi (Giles)
A. barbirostris (Van der
wulp).
A. gig as (Giles)
The wing has one large white
spot near the apex. Femora
of hind legs with a broad
white band.
A very large species with black
densely scaled palpi.
A very large hill species.
B.-PALPI WITH FOUR WHITE BANDS.
A. sinensis (Wiedmann)
and its allied species
A. nigerrimus (Giles).
A. pulcherrimus (Theo-
bald).
A. leuccsphyrus (Dönitz)
A. karwari
(James)
Tarsal joints banded but none of
the hind tarsal segments pure
white.
Abdomen covered with broad
white scales. Legs speckled.
The 3rd, 4th and 5th hind
tarsal segments pure white.
Legs banded and speckled, but
none of the hind tarsal seg-
ments pure white.
Legs not speckled, but with
bands at the joints. The 5th
tarsal segment of hind legs
pure white.
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C.—PALPI WITH THREE WHITE BANDS.
I.—Tips of palpi black,
One or more of
the hind tarsa
segments are
pure white.
Tarsal
joints
banded
but
none of the
hind
tarsal
segments pure
white.
Legs uniformly
coloured with-
out bands or
white
seg-
ments.
A. Turlchudi (Liston)
A. nagpori (James)
None of the hind tarsal seg-
ments white.
The 4th and 5th hind tarsal seg-
ments pure white.
II.— Tips of palpi white.
A. fuliginosus (Giles)
A. Jamesi (Theobald)
A. maculipal pis (Giles) .
A. Theobaldi (Giles)
A. maculatus (Theobald)
A. Willmori (James)
A. Rossi
(Giles)*
A. Stephensi (Liston and
James).
A. fluviatilis (Liston and
James).
( A. jeyporiensis (James)
A. culicifacies (Giles)
Tarsal joints banded but legs
not speckled. The 3rd, 4th
and 5th hind tarsal segments
pure white.
As above, but with speckled legs.
As above, but with legs and
palpi speckled.
Only the 4th and 6th hind tarsal
segments are pure white.
Only the 5th hind tarsal seg-
ment is pure white.
Differs from A. maculalus in
having many scales on the
abdomen.
The legs are not speckled.
The legs are speckled. Abdomen
covered with scales.
Third longitudinal vein of
wing white scaled. Six white
patches on wing fringe.
Seven white patches on wing
fringe. Paint white spots at
some of the joints of the legs.
Third longitudinal vein of wing
black scaled. Faint white
spots at some of the joints of
the legs.
A few examples will serve to illustrate the method of using-
this table.
Example 1.—A. female mosquito with palpi as long as the
proboscis, i.e., it belongs to the anopheles genus.
* When a mosquito is named after any person the accepted rule for forming
its specific name is to add one i. to the person's name. This well known mos-
quito for example is named after Major Ross, I.M.S., and not after an Italian
named Rossi. Its specific name should therefore be Rossi and not Rossii as
usually written. (Dönitz. Zeitschrift fur Hygiene, XLIII, 1, page 238.)
C 2
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Wings,— Spotted.
Palpi,—With three white bands or rings, one broad ring in-
cluding the tips (which are therefore white), and two narrower
ones.
It therefore comes under the group C, sub-group II.
Leys.—There are white bands at the tarsal joints but none of
the hind tarsal segments are pure white, and there is no speckling
of the leers in addition to the bands.
Diagnosis.—A. Rossi.
Confirm by careful examination of the wing markings.
Example 2.—A female anopheles.
Wings. — Spotted,
Palpi.—With three white rings, the outermost of which includes
the tips. In addition to the three complete rings there are one
or two small patches of white scales, which do not amount to
a complete ring or band, on the upper surface of each palp; i.e.,
the palpi are marked with three bands and are speckled in
addition.
Legs.—The 3rd, 4th, 5th, and the apex of the 2nd tarsal
segments of the hind legs are pure white. There are white bands
at the other tarsal joints and the femora and tibiæ are brilliantly
speckled with white scales.
Diagnosis.—-A. maculipalpis.
Example 3.—A female anopheles.
Wings.—Spotted.
Palpi.—With three white rings and the tips white.
Legs.—Uniformly coloured without bands at the tarsal joints.
Diagnosis—A. fluviatilis.,
A. jeyporiensis or
A. culicifacies.
Separate by careful examination of the wing markings.
The breeding places of CULEX and ANOPHELES mosquitoes,
Having learnt how to find and distinguish the different kinds of
adult mosquitoes, we shall next desire to know something of the
places where they breed. This is very important because in the
first place it is much easier to kill mosquitoes in their larval condi-
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tion in water than it is to kill the adults, and in the second if we
can do away with all breeding places, it is evident that no adult
insects can be produced.
We have seen that culex mosquitoes have no connection with
the transmission of human malaria, but as it has been proved that
they are the agents by which another very important disease of
India, viz., elephantiasis, is transmitted, it is well to destroy their
breeding places wherever we can do so. Oar great object should
be, however, to find and destroy the breeding places of anopheletes.
If we can find mosquito larvæ in any collection of water we
know that such a collection is a breeding place of the particular
kind of mosquito whose larvæ we have found, and it is therefore
necessary to know how to collect larvæ and how to breed them out
into adult mosquitoes, before we can tell what are the breeding
places of any particular kind of mosquito.
How to collect larvæ and breed them out.—When going out to
collect larvæ it is best to take a large tin mug with a handle
and some wide-mouthed bottles. As anopheles larvæ are often
difficult to see, we should not leave any pool or stream because we
cannot see larvæ in it, hut should stoop down at the edge of the
water and scoop the tin quickly through it under the grass at the
edge, bringing it out full of water. Then, if the tin is allowed
to stand on the ground for a few moments, any larvæ that have
been dipped up in it will rise to the surface and be easily recognised.
By fishing in this way at the edges of several parts of a pool or
stream we shall either catch a good many larvæ or make certain
that the pool or stream is free from them.
If any are caught they should be transferred with some of the
water into one of the wide-mouthed hottles, keeping the larvæ
from different pools in different bottles. The mouths of the
bottles should afterwards be covered with a piece of coarse muslin,
and after a few days the larvæ will develop into pupæ and
then into adult mosquitoes, which can be transferred to another
bottle, killed, and mounted for examination. In this way we
shall learn after a time exactly what species of anopheletes are found
in the different breeding places.
Culex larvæ may be found in abundance in almost any collection
of water that has remained on the ground, or in a tin tub, gumlah
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or tank for some days. From the few drops of water which collect
at the base of the leaves of trees in a wood to the largest tank or
irrigated rice field ; in the smallest and dirtiest puddles by the road
side, or in the eddies and back-waters of a mountain stream ; in the
foul water of a cesspool or in the clear rain or well water kept, in an
ron tank or fire bucket ; in broken chatties, old bottles, in any thing
in fact where a few ounces of water can lodge, culex larvæ
may be found.
Anopheles larvæ may also be found in any or all of the above
situations. This is a very important fact because it shows that
when searching for anopheles larvæ we must not neglect to
examine every collection of water of whatever kind it may be.
Although in referring to the whole genus anopheles we may say
that their larvæ are found in any collection of water, still when we
come to examine the subject more closely we shall note that all
the different species of the genus are not equally common in all
breeding places. A breeding place which is suitable for one
species is not so for another, so that while we find one species
always breeding in shallow muddy pools near houses, the larvæ
of another species are always found in more or less swiftly running
streams, and of another in the clean stagnant water of wells,
gumlahs, etc.
We have already seen that the prevalence of anophelete; in a
village depends on the number of breeding places near, and we may
now add that the prevalence of any particular species will depend
on the number of suitable breeding places for that species. Thus
in a place surrounded only by shallow muddy pools we shall find
only that species to be prevalent which breeds successfully in such
collections of water ; in a place near which there are many small
streams we shall find a stream-breeding species, and so on.
It is important therefore to know the favourite breeding places
of the more important species of Indian anopheletes, and this subject
has been rendered easier by the fact that, as regards habits
and breeding places, the different species may be divided into
certain natural groups, the members of which are alike in these
respects.
The chief and most distinct of these groups are as follow :—
Group I.—Species breeding in open water with much aquatic
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vegetation, at some distance from houses, such as deep ponds,
swamps, marshes and deep pools under trees or in a wood.
A. barbirostris.
A.
sinensis.
A. nigerrimus.
The adult insects of this group are very rarely found in houses ;
they are essentially " wild " mosquitoes.
Their relation to the prevalence of malaria.—Although the
species in this group feed on the blood of man and are capable of
transmitting malarial fevers, yet from the fact that they are rarely
met with in houses it is probable that they exert very little, if any,
influence on the prevalence of malaria.
Group II.—Stream breeding species. The larvæ of these
species are almost always found in more or less swiftly running
streams. Irrigation watercourses form the chief breeding places in
the Punjab for one of the members of this group (A. culicifacies).
A. fluviatilis.
A. jeyporiensis.
A. culicifacies.
In places where such breeding places are common the adult
insects of this group are abundant in the houses.
Their relation to the prevalence of malaria.—The members of this
group form the chief malaria-carrying species in India and Africa.
Wherever malarial fevers are very prevalent one or other of these
species will be found, and although other species may be present as
well, observations have shown that the prevalence of malaria is to
be ascribed chiefly, if not entirely, to the presence of a member of
this group.
Group III.—Pool breeding species. The most important of these
species is A. Rossi, which is almost always found breeding in
shallow muddy pools in the vicinity of houses. As would be expected
from the nature of its breeding grounds, this species is the most
widely distributed in India, and may be found in enormous numbers
in the houses after the rains. It is essentially a " domestic " species.
Its relation to the prevalence of malaria.—Although this species
is so abundant and so widely distributed, it a pears to have little if
any influence on the prevalence of malaria in nature. Like all other
anopheletes with which experiments have -been made, it has been
proved to be capable of transmitting malarial fevers under