NationalLibraryOfScotland/medical-history-of-british-india huggingface dataset:
( 34 )
The distinctions between the different species in the above genera are
based upon the markings on the wings, legs, and palpi, these markings being
caused by patches of light and dark scales. The species" named above can
be distinguished by the use of the following tables :—
1. GENUS Anopheles.
A.—WINGS
SPOTTED.
A. gigas (Giles)
A. lindesayii (Giles)
The wing has two large black spots
along the costa. The logs are band-
ed with pale white bands at the
joints. The palpi are unhanded.
The wing has one large white spot
near the apex. The femora of the
hind legs have a broad pure white
band. The palpi are unbanded.
B.—WINGS UNSPOTTED.
A aji]kenii (James)
A. immaculatus (James and Theobald).
The first submargmal cell of the wing
is much longer and narrower than
the second posterior cell. Palpi
with no trace of banding. Legs with
no trace of banding.
Palpi with a broad white band includ-
ing the tips and two narrow ones.
Tarsal segments of the legs have
pale bands apically.
2. GENUS Myzomyia.
M. listoni (Listen)
....
M. culicifacies (Giles)
M. turkhudi (Listen)
.
.
.
Wings spotted. The third longitudinal
vein is white scaled in almost its
whole length. Legs black with no
trace of banding. Palpi with three
white bands, the outermost of which
includes the tips.
Wings spotted. The third longitudinal
vein is black scaled in its whole
length. Legs black with a few light
scales at the tibio-rnetatarsal joints.
Palpi with three yellow bands.
A large brown mosquito quite different
in appearance from the above. The
palpi have three white bands, but
the tips of the palpi are black.
There are light scales at the distal
extremities of the femora and tibiae
in ail the legs, and the hind femora
have a broad pale area in the middle
third of their length.
( 35 )
3. GENUS Stethomyia.
S. culiciformis (James and Liston)
Wings unspotted. Palpi with no trace
of banding. Legs brown, without
banding.
4. GENUS Myzorhynchits.
M. barbirostris (Van der wulp)
M. nigerrimus (Giles)
Palpi
unbanded and covered with
broad black scales. The costa of
the wing is black scaled except for
one white spot at its distal extremity.
The legs have white scales at the
joints.
Palpi with four white bands, the outer-
most of which includes the tip-
Costa with two large white spots.
The legs have white scales at the
joints.
5. GENUS Pyretophorus.
P. nigrifasciatus (Theobald)
P. jeyporicnsis (James) .
P. elegans (James)
....
Palpi with three white bands, but tips
of palpi black. Legs unbanded.
Palpi with three white bands. Tips
white. Legs black with minute
bands at the tarsal joints. It is a
small dark mosquito like listoni and
culicifacies.
Palpi with four white bands. Tips white
Legs speckled and banded. A broad
white band at the tibio-metatarsal
joint of the hind leg.
D 2
( 36 )
6. GENUS Nyssorhynchus.
A.—PALPI WITH THREE WHITE BANDS.
One of more of the hind tarasal segments
are pure white.
N. maculatus (Theobald)
N. willmori (James)
N. fuliginosus (Giles) .
N. jamesii (Theobald)
N. maculipalpis (Giles)
N. tlieobaldi (Giles) .
N. stephensi (James and Listen)
. Only the 5th hind tarsal segment is
white.
. Only the 5th hind tarsal segment ]
white, but differs from maculatus in
having the abdomen thickly scaled
. The 3rd, 4th and 5th hind tarsal seg
ments are white. Legs not speckled
. Like fuliginosus, but the legs are
speckled.
. Like fuliginosus, but the legs and pal
are speckled.
. Only the 4th and 5th hind tarsal seg
ments are white. Legs speckled.
. The legs are speckled. Tarsal join
banded, but none of the hind
tarsal segments pure white.
B.—PALPI WITH FOUR WHITE BANDS.
N. karwari (James)
. The 5th hind tarsal segment is white.
Legs not speckled.
7. GENUS Cellia.
C. pulcherrima (Theobald)
C. punclulata (Dönitz)
Palpi with four white bands. The last
three hind tarsal segments pure
white.
Palpi with four white bands. Hone of
the hind tarsal segments pure white.
8. GENUS Neocellia.
Ne. indica (Theobald)
Ne. dudgeonii (Theobald)
Ne. intermedia (Roth well)
Palpi with three white bands. The
tips of the palpi black. Only the
terminal tarsal segment of the hind
leg is white.
Palpi with three white bands. The
tips of the palpi white. Only the
terminal tarsal segment of the hind
leg is white.
Palpi
with four white bands. None of
the hind tarsal segments is white.
( 37 )
It has been mentioned already that there are some who maintain that a
generic grouping based on scale structure is not satisfactory, and it is admitted
by all who have studied the subject that the distinctions between some of the
genera are very slight and therefore that it is difficult to decide whether a
specimen shall be classified for example as an Anopheles or as a, Myzomyia
or as a Pyretophorus. Not everyone, also, has sufficient perseverance, or
sufficient leisure, to study the subject carefully, and for this reason it is
fortunate that the number of different species of Anopheline mosquitoes in any
particular area, or indeed in any particular country, is not so great that it is
difficult, even without the aid of generic grouping, to determine the correct
specific name of any specimen ; and this, of course, is the main object which
the student of tropical medicine has in view.
The attempt to ascertain the correct genus of an Anopheline is therefore
a task which the student of tropical medicine need not necessarily undertake,
and those who decide to neglect the generic grouping of the Anophelince will
be able to ascertain the correct specific name of any species which they may
find in India by the use of the following table.
TABLE OF THE INDIAN SPECIES OF ANOPHELINCE.
I.—WINGS UNSPOTTED.
A.—PALPI UNBANDED.
A. aitkenii (James)
....
S. culiciformis (James and Listen) .
A small dark mosquito. No flat scales
on head. Transverse veins of wings
not in one line.
A rather large brown mosquito. A few
flat scales on the median Ai-ea of the
head. Transverse wing veins in one
line.
B.—PALPI WITH WHITE BANDS.
A- immaculatus (Theobald).
( 38 )
II.-WINGS SPOTTED,
A.—PALPI UNBANDED.
A. lindesayii (Giles).
M. barbirostris (Van der wulp) .
M. gigas (Giles)
The wing has one large white spot
near the apex. Femora of hind legs
with a broad white band. Palpi not
densely scaled.
A very large species with black
densely scaled palpi.
One white
spot at distal end of wing.
A very large hill species. Costa of
wing has two black spots.
B.—PALPI WITH FOUR WHITE BANDS.
M. nigerrimus (Giles)
G. pulcherrima (Theobald)
C. punctulata (Dönita)
Ne. intermedia (Kothwell).
P. elegans (James)
N. 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 segments pure
white. Abdomen with white scales
which form tufts at the sides.
Like punctulata, but the abdominal
scales are less dense and do not form
tufts at the sides.
Like punctulata, but no scales on
abdomen.
Legs not speckled, but with bands
at the joints. The 5th tarsal
segment of hind legs pure white.
C.—PALPI WITH THREE WHITE BANDS.
I.—Tips of palpi black,
M. turkhudi (Listen)
P. nigrifaciatus (Theobald)
Ne. indica (Theobald)
None of the hind tarsal segments
white. Thorax with hair-like scales.
Liketurkhudi, but the thorax has
narrow curved scales.
Only the 5th hind tarsal segment is
pure white. Abdomen with flat
scales.
( 39 )
C.—PALPI WITH THREE WHITE BANDS—continued.
II.—Tips of palpi white.
One or more of the
hind tarsal seg-
ments are
pur
white.
Tarsal
joints
banded, but none
of the hind tarsal
segments pure
white.
Legs
uniformly
coloured with-
out bands or
white segments.
N. fuliginosus (Giles)
N. jamesii (Theobald)
N. maculipalpis (Giles)
N. theobaldi (Giles) .
N. maculatus (Theobald) .
N. willmori (James)
N. dudgeonii (Theobald). .
Ps. rossii (Giles)
N. Stephens!, (Lisbon and
James).
M . listoni (Liston) .
M. jeyporiensis (James) .
M. culicifacies (Giles)
Tarsal joints banded ; 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 5th hind tarsal
segments are pure white.
Only the. 5th hind tarsal segment is
pure white.
Differs from maculatus in having
many scales on the abdomen.
Very like willmori.
The legs are not speckled.
The legs are speckled. Abdomen
covered with scales.
The third longitudinal vein of wing
white scaled. Six white patches on
wing fringe.
Seven white patches on wing fringe.
Faint 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 illustrata the method of using this table.
Example I.—A female mosquito with palpi as long as the proboscis, i.e.,
it belongs to the sub-family Anophelince.
Wings. —Spotted.
Palpi.—With three white bands or rings, one broad ring including the
tips (which are therefore white), and two narrower ones.
( 40 )
It therefore comes among the spotted winged Anophelines under the
group C, sub-group II.
Legs.—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 legs in
addition to the bands.
Diagnosis.—rossii.
Confirm by careful examination of the wing markings. (See Plate IV, i.)
Example 2.—A female Anopheline.
Wings.—Spotted.
Palpi.—With three white rings, the outermost of which 'ncludes the tips.
In addition to the three complete rings there are one or two small patches of
\ill\ scales, which do not amount to a complete ring or band, on the upper
surrace 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.—maculipalpis.
Example 3.—A female Anopheline.
Wings.—Spotted.
Palpi.—With three white rings and the tips white.
Legs.— Uniformly coloured without definite bands at the tarsal joints.
Diagnosis.—listoni.
jeyporiensis or
culicifacies.
Separate by careful examination of the wing markings.
This completes our study of the adult insects, and we must now learn
about the eggs, larvæ and pupæ.
The eggs of
Anopheline
mosquitoes.
(1) The eggs of Anopheline mosquitoes are laid separately, and when
deposited on water they quickly separate from one another and float as
isolated eggs scattered irregularly on the surface of the water. They are tiny
rod-shaped bodies which cannot be seen plainly except with the aid of a
magnifying glass. If one of them is taken up in a spoon or on the edge of
a piece of blotting paper and transferred to a drop of water on a glass slide
(
41
)
it can be examined with a low power of the microscope ( rds inch
objective). It will then be seen that along the middle portion of each
side of the egg is attached an oval "ribbed" air-containing float, which
is a very characteristic structure not present in the eggs of any other kind
of mosquito as yet described. (Plate IV, a.) Thus it is easy to distinguish
the eggs of an Anopheline from those of any other kind of mosquito.
The eggs of
oilier mos-
quitoes.
The eggs of most mosquitoes in other sub-families are collected together
before being deposited by the mosquito, into an elongated boat-shaped mass
consisting of several hundred eggs joined to one another by their edges.
When this egg-boat or egg-raft has been constructed the insect allows it to
drop into the water, where it floats as a small boat-shaped body looking
very like a small lump of soot.
Mosquito
larvæ.
(2) If any one who has not seen a mosquito larva will look in the
tins or tubs of water that have remained in his garden unemptied
for some days he will very probably find a number of small, very active
creatures about - 1 / 16 th to ¼th of an inch long, wriggling about in the water and
alternately struggling to the bottom and floating up to the surface to breathe,
which they do by means of an air tube (or siphon-tube as it is called)
attached near the tail. If some of these little animals are collected in a glass
bottle and watched from the side it will be seen that when they come to the
surface to breathe they hang obliquely with their heads downwards and with
only the tips of their air-tubes at the surface of the water. (Plate IV, b.)
How to recog-
nise Anophe-
line larvæ.
These are the larvæ of the commoner kinds of mosquitoes often referred to
collectively as the group of " culex mosquitoes." On closer examination it
will be seen that each larva is divided into three regions, the head, the thorax
and the abdomen ; also that the abdomen is divided into nine segments and that
the long air-tube, by the tip of which the larva seems to hang suspended from
the surface of the water, projects upwards from the 8th segment. The
attitude adopted by the larvæ of Anopheline mosquitoes when resting at the
surface of the water is quite different from that of the larvæ of other mos-
quitoes and affords an easy way of recognising these larvæ. An Anopheline
larva instead of lying with its head and body sloping downwards beneath the
surface in an oblique direction, lies flat at the surface, nearly the whole of its
body lying parallel to and touching the surface film (Plate IV, c}. There are two
( 42 )
reasons for this attitude, namely, (1) Anopheline larvae do not possess the
characteristic external air-tube already mentioned, and (2) on the upper surface
of the abdominal segments of Anopheline larvæ there are little cup-shaped
structures called palmate hairs which open at the surface of the water and.
acting like floats, keep the body of the larva in contact with the surface.
These palmate hairs can be easily seen by examining an Anopheline larvæ in a
drop of water under a low power of the microscope ; they are not present in
the larvæ of any other kind of mosquito and together with the absence of the
external air-tube render it easy to recognise such larvæ. (Plate IV, d.)
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 Anopheline larvæ are often difficult to see, we should not leave
any pool or stream because we cannot see larvæ in it, but 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 bottles, keeping the larvæ from different pools in
different bottles.
The mouths of the bottles should be covered with a
piece of coarse muslin, and after a few days the larvæ will develop into
pupae 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 mosquitoes are found in the different
breeding places.
The pupæ of
mosquitoes.
(3) 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. It is not always easy to distinguish the pupæ of
Anopheline from those of other kinds of mosquitoes, but as the matter is not
of much importance we need not consider it here. A drawing of an
Anopheline pupa is given in Plate IV. e.
( 43 }
The breeding places of Anopheline mosquitoes.
In localities where mosquitoes are abundant, larvæ can usually be found in
collections of water of every kind. Thus they may be found in the few drops of
water which collect at the base of a leaf of a tree, or in broken earthenware pots,
or in bottles or tins; in fire buckets, rain-water tubs or iron tanks ; in clean
and dirty puddles by the roadside or in large ponds and irrigated rice fields;
in the foul water of a cesspool ; in the eddies and backwaters of a mountain
stream. In particular instances this statement will be found to be true as
regards the larvæ of Anopheline as well as of other kinds of mosquitoes, and it
teaches us that when searching for Anopheline larvæ we must not neglect to
examine every collection of water. A very interesting and important
observation has been made, however, regarding Anopheline mosquitoes,
namely that under favourable conditions they select, to a great extent, the
kind of collection of water in which to deposit their eggs. Thus in a place
surrounded by many different kinds of collections of water the larvæ of one
species of Anopheline will be found in shallow muddy pools only, the larvæ of
another species in deep ponds only, and the larvæ of a third species in irrig-
ation watercourses or running streams only. It is possible to arrange the
species of Anopheline mosquitoes met with in India in groups, each group
containing the species which are alike in their choice of breeding places.
Different
species are
found in
different
kinds of
collections
of water.
The chief and most distinct of these groups are as follow:—
Group I.— Species breeding in open water with much aquatic vegetation,
at some distance from houses, such as deep ponds, swamps, marshes and deep
pools under trees or in a wood.
barbirostris.
nigerrimus.
The adult insects of this group are very rarely found in houses ; they are
essentially " wild " mosquitoes.
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 (culicifacies).
listoni.
jeyporiensis.
culicifacies.
( 44 )
In places where such breeding places are common the adult insects of this
group are abundant in the houses.
Group III,—Pool breeding species. The most important of these species is
rossii, which is almost always found breeding in shallow muddy pools in the vici-
nity of houses. As would be expected from the nature of its breeding grounds,
this species is the most widely distributed in India and after the rains may be
found in enormous numbers in houses. It is essentially a " domestic " species.
With these remarks as a guide it should not be difficult for anyone
to find out the favourite breeding places of the different species of Anopheline
mosquitoes in his district.
Other habits of Anopheline mosquitoes.
We know very
little about
the habits of
mosquitoes.
Although many observers have studied Anopheline mosquitoes we know
comparatively little about their habits, and we know almost nothing about
the habits of individual species. The subject is not difficult, and it would be
of great service if students and others would observe throughout the year the
habits of each species of Anopheline present in their districts. In addition to
breeding grounds we require observations on seasonal prevalence, on the
relative abundance of different species, on distance of flight, on the food
supply of different species, on methods by which different species tide over
the winter and on many other problems. At present our knowledge regarding
habits has to be summed up in a general way somewhat as follows. (1)
Anopheline mosquitoes are essentially nocturnal in habit; during the daytime
they rest in dark corners of rooms, outhouses and sheds. (2) The food of
female Anophelines is the blood of man or of animals. Information is much
needed regarding the habitual food of different species. Do the females of all
species feed always on the blood of man only or do they sometimes or
always feed on that of animals ? If it were proved that rossii, for example,
feeds habitually on the blood of animals instead of on that of
man* it would explain why this species has not been found to be a malaria-
carrier in nature. (3) The seasonal prevalence of different species differs consi-
derably. Upon what factors does this depend ? In one place in the Punjab
it has been found, for example, that the malaria-carrying species culicifacies
* This would be a profitable line of investigation for those interested in the biologi-
cal tests for the blood of different mammals.
( 45 )
becomes prevalent before the rains begin because its eggs are laid in the
irrigation canals and not in rain-formed pools. Rossii, on the other hand,
does not become prevalent until after the rains because its eggs are laid
chiefly in such pools, not in the canals. (4) Anopheline mosquitoes do not
habitually fly very far. This is a general statement to which many exceptions
may be found, and it is very important to ascertain the usual limit of flight
of Anophelines in one's district. (5) Some species tide over the winter
by the hybernation of adults, others by the hybernation of larvæ, others
perhaps migrate to warmer places at the onset of the cold weather. How is
it that in very cold places where it is probable that all adult Anophelines and
larvæ are killed by the cold of winter they appear again abundantly in the
spring ? The cold of winter is probably a more efficient method of killing off
all Anophelines in a place than any which man can devise yet in India, even
in places where the winter is as cold as it is in Simla, Anophelines become
plentiful every summer. (6) The length of life of Anophelines is not known
with certainty, but it is known that some species can live for many months.
We may conclude this account of the practical work with which a student
of the malarial fevers should be acquainted, with a summary of the method
of finding out whether a place is malarious or not, the degree to which it is
so, and the factors on which it depends.
6.—How to determine whether a place is malarious.
.here are three ways of ascertaining the prevalence of malaria in a place
or district:—
(1) By examining the statistics in hospitals and dispensaries.
(2) By ascertaining the proportion of people suffering from enlargement
of the spleen.
(3) By examining the blood of a number of people to ascertain how
many are infected with malaria parasites.
The splenic
index.
The first of these methods is of very little value. The second method
is useful in places where kala azar and other diseases which, in addition to
malaria, cause enlargement of the spleen do not occur. In making the count
only those people should be examined who are between two years and ten
years of age (Stephens and Christophers). The percentage of people between
these ages who have enlarged spleens is called " the splenic index of malaria."