SCIENTIFIC MEMOIRS

OFFICERS OF THE MEDICAL AND SANITARY DEPARTMENTS S nS

" OF THE y
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sa * THE IMPORTANCE OF LARVAL CHARACTERS
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‘GU LLOGSNA SONIM—'T

HO ATEVL OLLAGONAS

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aan FS est aS sath).

‘

No. 25.

(NEW SERIES.)

SCIENTIFIC MEMOIRS

BY

OFFICERS OF THE MEDICAL AND SANITARY DEPARTMENTS

OF THE

GOVERNMENT OF INDIA.

ON THE IMPORTANCE OF LARVAL CHARACTERS
IN THE CLASSIFICATION OF MOSQUITOES.

~~ » BY

CAPTAIN S*R*“CHRISTOPHERS, M.B., LMS.

ISSUED UNDER THE AUTHORITY OF THE GOVERNMENT OF INDIA
BY THE SANITARY COMMISSIONER WITH THE GOVERNMENT
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1906.

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i ay.
ks ia Say

% rn me

3 iy) aa Ms Pre nn my '0* ‘vont yy eh ae
i ana e a ara monk’ lls di Vs

A
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ON THE IMPORTANCE OF LARVAL CHARACTERS IN
THE CLASSIFICATION OF MOSQUITOES.

is collaboration with Stephens, I described, in a previous publication,’ the

ovum and larva of most of the common Anopheles mosquitoes of India.
We gave at that time a division of Anopheles into natural groups, largely based
upon variations in the immature stages. The groups noted by us, so faras
the species investigated were concerned, were practically identical with the
genera which Theobald instituted later upon variations in the scale structure of
the adult insects; but greater prominence was given to some of these genera,
by a consideration of the immature stages, than was apparent from the scale
structure of the adults alone.

Of the immature stages of mosquitoes other than Anopheles, we unfortunately
know very little. The larva of Anopheles and that of Culex were described by
Meinert in 1886." Howard’s® description of the larva of C. pungens is accurate
and detailed. James® has described and figured the larva of Stegomyia, and
was the first to draw attention to the occurrence of cannibal larve.4 The
larvee of species of Megarhinus, Toxorhynchites, Desvoidea, Theobaldia, Mela-
noconion, Grabhamia, Acartomyia, and Detnocerites have been to some extent
described by Theobald,® who also figures parts of C. fatigans, C. tigripes, and
C. mimeticus. In very few of these descriptions, unfortunately, have the points
which appear to be of most use in classification been noted. In many cases, indeed,
only characters common to nearly all mosquito larvae have been given.

Before proceeding to describe what has been determined regarding the larval
characters of a number of genera of culicidz other than anopheles, it will be
well to briefly mention features which appear to be common to all larve, and to
single out those which, in my researches, I have found to vary in the different

genera or species.
PD;

All mosquito larvz possess a head, an enlarged thorax, and nine abdominal

segments.
The Head.—The size and shape of the head vary in the different genera.

It is large in Culex and Melanoconion, smaller in Anopheles, Stegomyia, and

Tentcrhynchus.

Nore.—Mr. Theobald has kindly identified the species of mosquitoes mentioned in this paper from:

specimens of the adults which I have sent to him.
B

9
=

The upper surface is smooth and convex and carries certain hairs,
which are usually six in number. Anteriorly the head forms a rather prominent
rounded mass (the clypeus). In some cases the clypeus carries small hairs
(clypeal hairs) as in Anopheles and Stegomyia. As a rule it carries only two thorn-
like spines. When present, the clypeal hairs are of specific importance.
The clypeus, instead of projecting, may be concave and form a cup-like hollow
(cannibal larvz). In old larva of certain species a sharp beak-like process cov-
ered with hairs or spines may project from below the clypeus. At the side ofthe
head are the large compound eyes, and immediately behind these are the ocelli of
the simple eyes.

The lower surface of the head is smooth and convex and is marked by two
grooves which pass from the outer angles of the mental plate backwards. About
the middle of the lower surface of the head is a small, dark triangular plate—the
mental plate or lower lip (Meinert). The mental plate forms a hard and sharp
lower lip to the mouth. The upper lip is formed by the prominence already
mentioned (clypeus). Arising on each side of the under surface of the clypeus
are the feeding brushes. These consist, except in cannibal larvz, of numerous fine
curved hairs arranged so as to look very like a shaving brush. In cannibal species
these are much modified, each consisting of a series of stout, curved chitinous
bars, and are used as a clasfing organ for seizing their prey. The mouth is
closed in beneath by two plate-like structures,—the maxille@, which can be opened
to expose the buccal cavity, or approximated to almost meet in the middle line.
Each maxilla carries on its outer edge a stout, more or less conical, maxzllary
palp. Some variations occur in the maxilla and palps of different genera ; for
example, both are very small in A/uczdus (PI. Ill, fig. 14). Lying just behind
the maxillz are two very stout and large plates of chitin—the mandzbles. On the
inner side of each of these there is a variable number of large, strongly chitinised
teeth, which meet together, when approximated, in the neighbourhood of the
mental plate. Each mandibular plate also has, arising from its anterior edge,
a variable number of long processes which are used in combing the feeding
brushes and which vary in size and number in different genera.

On each side of the head, arising from prominences in front of the eyes, are
the antenne, These vary very considerably in different genera, and have already
been shown by us to have great significance in the classification of the anophelina.
Each antenna consists of a basal segment immoveably fixed and more or less
blended with the head mass, and a loosely jointed distal segment carrying various
spines, hairs, etc.,—the antenna proper. When fully developed, three distinct
portions, which, however, form a single unjointed piece, may be distinguished
in the distal segment, a proximal, a median, and a shorter distal portion, which
I have called the first, second, and thzrd portion respectively. At the junction

A
od

of the first and second portions a large series of long stout hairs arises which
I have termed the dasa/l tuft. At the junction of the second and _ third
portions there are generally two large and very stout hairs or spines. I have, for
descriptive purposes, termed these the medzan spines. From the end of the
third portion, one or more spines project. I have called these ¢erxminal spznes.
There is also, at the extreme end of the antenna, a papilla, which may be
large and conspicuous, possibly a sense organ. I have named it the termznal
papilla (Pl. II, fig. 16).

The antenne are often very small and poorly developed. In the case of
some species (Stegomyza) this appears due to retrograde changes, since most
of the above-mentioned structures are represented only by small hairs or spines.

The Thorax.—The thorax is more or less globular in shape, and greater in
diameter than the abdominal segments. The exact size and shape depend upon
the genus concerned. On each side, arising from papilla, are three main series
of large, stout hairs. The papilla, from which these arise, may or may not
carry a stout spine resembling a thorn, The hairs are of various lengths in
different species and may be simple, .branched, or feathered. On the whole
they do not appear to be very important from the point of view of ascertaining
the affinities of different genera. - In addition to the above there are usually a
few small hairs which arise immediately behind the head and overhang the
occiput. In certain species (open water species, e.g., Melanoconton Tenzor-
-hynchus) these are large and may form very prominent objects in the living larvz,
projecting to a great distance and appearing to act as tactile organs.

The Abdomen.—The first seven abdominal segments do not appear to be of
sufficient importance to be described in detail in the present connection, In
the Anophelzna oar-like feathered hairs arise from the first three segments.
This sub-family also differs from all other Czlzczdae in having palmate hairs
on some or all of the segments. The eighth and ninth segments require
separate mention.

The eighth abdominal segment.—This segment is profoundly modified by
the presence of the respiratory openings and their armature. In all genera but
the Anophelzna a tube carries the spiracles to a distance from the segment.
This tube has usually been called the respiratory szphon or sephon tube.

The siphon tube consists of an unbroken tubular piece of chitin of varied
shape and size in different species. It usually carries a few smali branched
hairs, and on the posterior aspect, on each side of the median line, there are
two rows of conspicuous spines, the number of which is of specific importance.
Each of these spines, is a compound one consisting of three or more long tooth-
like processes. Their actual shape seems to be much the same, even in widely

different genera, but their appearance varies considerably with the different points
B 2

4

of view. Ina few cases only (certain cannibal larve) a conspicuous series of
hairs, forming a rudder-like expansion, springs from the median line posteriorly.
On the eighth segment there are, on either side, a number of claw-like spines.
Several small branched hairs also rise near the base of the siphon tube.
Neither the spines nor the hairs appear to be of much importance in relation
to classification, since they do not vary to any extent in the genera
examined. The characters of the siphon tube are of importance, since this
organ is subject to great variations in different genera and even in different
species. The relative shortness or tenuity of the organ is an important
character. In descriptions of larva the terms employed in describing this
tube do not allow of accurate information being conveyed. I have therefore
employed what I have termed the siphonic index. This is obtained by dividing
the length by the greatest breadth of the tube. I have employed an eyepiece
micrometer for the purpose of measurement. The figures given by the
different genera have been very constant.

Stegomyia sugens : - . é a 2
; fasciata. ° 5 : p10}
5 i 5 : 3 : 5k 1s)
Desvotdea : : c : : oy
Culex fatigans . é . : 5 21033
35 ? : . . : 3 cei
i impellens c 0 5 5
sp fe C 2 . 0 &
Melanoconion c . ‘ : . 9 IRS
Tzniorhynchus tenax : : : og}
ue N. SP. 4 : A ware

In describing the siphon tube, it is desirable that a drawing accurately
measured should be given, since the siphon tube is subject to the most
extraordinary variations in size and shape. In tentorhynchus it is developed
into a long and slender tube. In certain species not yet determined, the siphon
tube is enormous.

The ninth abdominal segment.—This very much modified segment lies, during
life, so as to form an angle with the rest of the abdomen, and when the siphon
tube is large has the appearance of an appendage rather than of an abdominal
segment. It is cylindrical in shape, and covered dorsally and laterally by a
single curved piece of chitin. The ventral surface of the segment is, for the
most part, soft and membranous. Posteriorly is the opening of the anus and
around this arranged symmetrically are the four amzal papzlle. In most
larvee these papillz are of considerable size, reaching to about one-tenth of the
body length. In others they are still larger and very conspicuous (Desvoidea).
In some cases they are very small and rudimentary (cannibal larvee). The papillae

5

appear to be of the nature of gills. In the case of a species of Stegomyza, in
which these were of very great size, the larve habitually remained long periods
without rising to the surface. Dorsally, immediately above the anus, four or six
long hairs arise from one or two small chitinous plates. Ventrally, a double
row of hairs forms a large fan-like expansion. ‘The variations in the hairs of the
ninth segment are not great in the different genera and their arrangement is
very similar in Anopheles, Stegomyza, and Culex.

The Nymph.—The nymph consists of a large body formed by the conjoined
head and thorax and of a tail composed of nine segments. The general shape
and appearance of the nymph varies a little in the larger groups of mosquitoes,
and it is possible by this means to distinguish the nymphs of Anopheles, Culex,
and Mochlonyx. The most important structures showing variations are :—

The breathing trumpets.——These rise from the dorsum of the thorax and
show variations in the manner in which they project from the nymph, and in the
details of their structures. No distinct differences were found by me in species
of the same genera, but in different genera important variations were detected.
The shape of the breathing trumpets of the nymph are of important generic
significance.

The tail fins and last segment are also subject to some variations.

II,

The larval features characteristic of many of the genera can in some degree
be noted.

Stegomyza.—The ova of S. fasctata were first described by Daniels and
Ross.’ They are laid singly on the water, and form patterns as do those of
Anopheles. Each ovum is surrounded by numerous small air chambers.

The larve of Stegomyza are very characteristic and can be distinguished at
once by the naked eye. They are found especially in water of a dark brown
colour from decayed vegetable matter, but they are also found in ordinary rain or
waste water or indeed in any small collection of water and even in nearly pure
water in chatties or other receptacles. Their general appearance is more worm-like
than that of other larve. The full-grown larve are generally loaded with fat and
have a plump look. When disturbed they travel by means of a curious twisting
and lashing motion seen in some small aquatic worms. When breathing at the
sutface they adopt a nearly vertical attitude quite different from that of most
Culex \arve which rest at a distinct angle to the vertical (PI. III, figs. 22 and
20). Stegomyta larve spend much of their time at the bottom. They are vora-
‘cious feeders and can be seen nibbling at solid substances such as dead insects.

The body of the larva (PI. I, fig. 19) is cylindrical, The thorax and head

6

are small in proportion to the length of the body. The whole aspect of the
larva isin marked contrast to that of larvze to which projecting angles and hairs
give a spiny look. (JMedanoconion, Culex, etc.)

The head is smooth, and projecting hairs are inconspicuous. The clypeus
forms a prominent boss, on which are situated, in some species, hairs very closely
resembling the clypeal hairs of anopheles (PI. III, figs. 9, 10, 11), The
antennze (PI. II, figs. 4 and 5), are very distinctive. They are very small and
feeble and appear to have undergone degeneration. They are quite smooth and
free from the numerous small thorn-like spines which cover the antenna of most
other genera. The large hairs of the basal tuft are represented, as in anopheles,
by a sinall branched hair or in some species by a single short bristle only. The
median and terminal spines so conspicuous in Culex, Melanoconzon, etc., are
represented only by several extremely small spike-like processes, As a rule, the
terminal papilla (sense organ ?) is well developed and rather conspicuous. On
the whole, the antenna of S¢egomyza larva approximates most nearly to that of
anopheles, but in several points is still more rudimentary than in this sub-family
(compare figs. 1 and 5, Pl. II).

The mental plate of S. sugens is shown in PI. III, fig. 1. Those of S. fas-
ciata and S. scutellarts are very similar.

The siphon tube is very short and stout. The siphonic index is 2 or even
slightly less. The spines on the siphon vary in number according to the species.
They extend as a rule about two-thirds up the tube. There are mosquitoes,
in which the larva has tubes closely resembling those of Stegomyza, which do
not appear to belong to the genus; some of these have other features approxi-
mating to those of Stegomyza and may be really related to the genus.

The anal papillz are large and well developed.

Specific variation.—Three species were examined: S. sugens, S. fasctata,
and another species, probably S. scutellarzs. The following variations occurred :—

Clypeal hatrs.—These hairs in S. fasczata remarkably resembled those of
anopheles. The external hairs were long and simple. The two inner hairs were
shorter and branched. In this species five or six branches were present. In
S. sugens the inner hairs appeared to be absent and the clypeal hairs consisted
only of two outer simple hairs. In larve which were probably those of S.
scutellarzs the clypeal hairs were very striking. In this case each outer hair was
double and the inner hairs were conspicuously branched (PI. II], figs. 9, 10, 11).

The antenna.—The basal tuft in S. sugens was represented by a small hair
divided into three or four branches. In S. fasciata a single small hair only was
present (PI. II, fig. 5).

The anal papille—Jn S. sugens and S. fasciata these were of moderate
size, but in the larva of a third species (S. scutellarzs ?)they were extremely large,

7

‘and had obtuse ends. In this species the anal papilla appear to act as func-
tional gills, since the larva had a habit of remaining long periods at the bottom.

The siphon tube.—I\n the case of some species a variation in the number of
“spines was noted. In S. sugens and S. fasciata these spines numbered about
18. In SS. scu¢ellaris they were only nine in number. Some variations in the
exact number was, however, noted in the same species.

The nymph of Stegomyzta.—The shape of the respiratory trumpets in this
and the allied species Desvoidea are characteristic. The trumpet is short and
widens rapidly towards the free end. In mounted specimens the trumpets appear,
from flattening, to be broadly triangular. A notch, as shown in the figure, is
present (PI. I, figs. 3 and 4). In the wide trumpet opening, Stegomyza again
approaches most closely the anophelina. In anopheles, however, the trumpet is
rather flap-like and still more open than in Stegomyza (Pl. I, figs. 1 and 2).

Desvotdea.—I have not had an opportunity of seeing the larva and nymph
of this genus, but Theobald gives a drawing of the respiratory trumpet of the
nymph which is indistinguishable from that of Stegomyza (PI. I, fig. 5). The
extremely degraded antenna figured by Theobald (PI. Il, fig. 6) also closely
resembles that of Stegomyza. The siphon tube is alsoshort. Index 1°7. Inaddi-
tion James also notes that the larve adopt a vertical position when at rest. In
larval and nymphal features this genus is then almost identical with Stegomyza.

Grabhamia.—Theobald has figured the larva of G. dorsalis. The antennze
are distinctly of the Cu/ex type, but the respiratory siphon islike that of a Stego-
myia. The figure is too small to allow of a full description.

Acartomyta.—Theobald’s figure shows that the antennz closely resemble
those of Stegomyza and differ only in having small spines scattered over them.
The respiratory siphon also possesses Stegomyta characters, being extremely
short. The trumpets of the nymph, on the other hand, appear to resemble those
in Howardina and Deinocerites (both in the sub-family Adeomyina).

Culex.—The species at present forming this genus are so numerous that
generalisations cannot be made on the result of the examination of a few species.
It appears from my researches that many of the species differ more widely in
their immature than in their adult stage. Certain species now classed under
Culex are, judging by larval characters, sufficiently distinct to be placed in
new genera, but we have not at present sufficient material to discuss this group
adequately, and, indeed, a proper division of the enormous genus Culex is impos-
sible until more is known of the immature stages of the species.

Provisionally, however, we may draw attention to several groups, which
from the dissimilarity of their larval characters alone, might well form separate.
genera,

Group l. Culex (restricted sense). Culex ( fatigans).—The ova are laid

8

so as to form rafts. The length of the raft is a little greater than the breadth.
The micropilar apparatus is “ milled ” laterally.

The larve are found especially in domestic utensils, pots, barrels full of
water, etc., and are rarely found in large masses of water or in water with
much vegetation.

The head is rather large and quadrangular in shape. Some conspicuous
branched hairs arise from the dorsum. The clypeus carries two small thorn-like
spines, but no structures at all resembling clypeal hairs.

The antennz are fully developed. The basal hairs and the median and
terminal spines are long and very noticeable. The first and second portions of
the antenne form a straight line. The third portion is rather small. Small
spines are scattered over the first and the proximal part of the second portion
(Elsie ms).

The siphon tube is distinctive ; ‘21 of body length. The siphonic index is
4°3. The spines number 6 or 7 in each row and extend over the lower third
of the tube (PI. II, fig. 24).

The nymph of Culex fatigans has respiratory trumpets which project
laterally as shown in Pl. I, fig. 9. The opening calls to mind the obliquely-cut
mouthpiece of a penny whistle (Pl. I, fig. 7). This character, so far as my
researches have gone, appears to be peculiar to the restricted portion of genus
Culex we are discussing.

Specific variation.—A second species belonging to the restricted genus
Culex showed the following variation from the above.

C. ?.#—Larva found in wells and cement tanks. Antenna with the second
portion longer than in C. fatigans (PI. II, fig. 14).

Siphon tube extremely large and conspicuous; *28 of body length. Siphonic
index 411. Spines number 6 in each row and occupy the lower third of the
tube (PI. II, fig. 25). Trumpets of nymph as in C. fatigans.

C. pipiens—Theobald figures this species which clearly belongs to the
above group. The figure given is too small to allow of minute description, but
the antennze are as in C. fatigans. ‘The siphonic index 4°8. The siphon tube
similar in shape to C. fatigans,

Group II. C. ¢mpellens—A group of mosquitoes of the original
genus Culex, possessing definite larval characters.
~ Antennze asin Culex, but larger. Siphon tube more attenuated than in
C. fatigans. Siphonic index 6, Spines number 6 or more and extend over

basal one-third of tube (PI. II, fig. 23).
/ Larve found more frequently away from habitations than are those of

C. fatigans.
pinata 2 RS es Ld ee ee eee

* Norte.--Identified by Mr. Theobald as C. fatigans, but evidently a distinct species.

9

Group III. Adult mosquitoes showing scale arrangement typical of the
genus Culex, but having larval characters recalling those of Stegomyza. Four
species, all unfortunately undetermined, were noted. All the forms were found
in natural pools.

Speczes a.—Nymph trumpets, opening wide, somewhat resembling those of
Stegomyta.

Head rather broad, antennz like those of Stegomyza, but larger and having
a few small spines. Basal tufts small and composedof a few hairs. Median
and terminal spines abortive (PI. II, fig. 7). Mental plate resembles that
of S. sugens (PI. III, fig. 2). Siphon tube large (Pl. II, fig. 19), 18 of
body length. Siphonic index 1°9. Sixteen spines in each row shaped as in
Stegomyza.

Species 6,—Nymph trumpet rather broad, but narrower than above. More
truncated than in species a. Antenna resembles that of Stegomyza (PI. II,
fig. 8). Basal tuft small. Two rather large median spines present. No ter-
minal spines. The antennz are covered with a few short spines.

Siphon tube large, ‘2 of body length, Siphonic index 2°7. Eighteen spines
in each row.

Species c.—Trumpets of nymph nearly truncated, but opening slightly
obliquely (PI. I, fig. 16).

Larva long. Rests in nearly vertical position (Pl. III, fig. 26). Head
very small and like that of Stegomyza. Antenne comparatively small. Basal
tuft short, but composed of many hairs. Median and terminal spines small and
inconspicuous. Antenna covered with large and prominent spines (Pl. II,
fig. 9).

Siphon tube enormous and very massive, ‘26 of body length. Siphonic
index‘5'9. Nineteen spines in each row. Whole tube strongly chitinised and
opaque (PI. Il, fig. 21).

Spectes d.—Trumpets of nymph resembling those of species c.

Larva long’ (Pl. I, fig. 22). Rests in nearly vertical position (PI. III,
fig. 26). Head small and shaped much as in Stegomyza. Antenne long and
well developed. Basal tuft short but composed of many hairs. Median spines
fairly well developed. Third portion of antenna readily seen. Terminal portions
short and inconspicuous. The whole antenna is densely covered with long
spines (PI. II, fig. 10). Siphon tube enormous, not so massive as that of species ¢,
but very similar in its horn-like appearance, ‘28 of body of length. Siphonic
index 7°5 (Pl. II, fig. 22).

These larval characters certainly suggest that the group concerned have
little in common with the Culex fategans group.

Group IV, Culex mtmeticus.—Theobald figures the siphon tube and
Cc

10

I have been able to study the larva which occurs abundantly inthe Nilgiris. The
larval characters bave no relation to any other Culex larve. A curious point is
that the spines on the siphon tube, which is long and thin, are very large and
curved, thus differing from those of the great majority of larvae which are short,
straight spikes.

Group V. ©. concolor.—The larval characters of this species are quite
unlike those of any of the other groups. The larva of C. concolor is cannibal in
its habits and has the morphological characters of cannibal larve. (Vide
description given later of cannibal larv.)

Theobald has figured parts of the larva of C. ¢egripes. It is evident from
his drawings that the larve of this species and that of C. concolor are very
similar. These two species alone amongst mosquitoes, of which the larva has
been described, possess the peculiar rudder-like group of hairs on the siphon.
Theobald, studying the adult insects, doubted whether they should be retained
in the genus Culex. If he has not already renamed these two species, I. would
propose that they be placed in a new genus Famesta, from the name of the
first describer of a cannibal larva (see also later).

Theobaldia.—The larva of Theobaldza annulata is figured by Theobald.
The characters are almost identical with those of C. fatigans—

Ova laid in boat-shaped masses. The siphon tube as in .C. fatzgans,
Siphonie index 4. Antenna as in C. fatigans.

Metanoconion.—The cva of Melanoconion are laid in the form of rafts,
The rafts are more elongated than those of Culex. The individual ova resembie
those of Culex. .

The larvze of Melanoconion are peculiar and can be readily distinguished by
the naked eye (PI. I, fig. 20). They resemble in general aspect the larvae of
Teniorhynchus and like these are often bright green and very transparent. From
the great development of the antennz and hairs these larva have a “ spiny”
look. They occur in clear natural water where there is much vegetation.

- The head is widened transversely and is plentifully supplied with hairs.
There are two spineson the clypeus as in Cudex. The mental plate is comb-
like (PI. III, fig. 3).

The antennz are extremely large and well developed. They form antler-
like projections which are very characteristic of the genus. The three portions
of the antennz are very distinct, and the first may be curved. The hairs and
spines are all long and stout (PI. II, fig. 15).

The hairs on the thorax are numerous and long. Immediately behind the
head two large hairs arise from papilla near the middle line. These project
over the head and have already been mentioned as’ possibly being tactile in
function. |

11

The siphon tube is long and very thin ; *23 of body length. The siphonic
index is 7. ‘There are about 10 spines in each row which are rather long and
slender and extend over a little more than the basal third of the tube (PI. U,
fig. 26).

The nymph of A/elanoconion has distinctive respiratory trumpets, They are
peculiarly long and narrow and project in a more distinct curve than do those of
Culex. The end is more truncated than in Cu/ex and the opening is on this
account more circular (Pl. I, figs. 8 and 10).

Tentcrhynchus.—The ova of Tencorhynchus have been described by
Stephens and Christophers.* They are laid in the form of rafts which are
extremely long and narrow, and resemble in shape a racing skiff.

The larva is found in natural waters where much vegetation is present and
is often bright green in colour (PI. I, fig. 21).

The head is comparatively small. The clypeus is conical and so differs
from that of most larve. From the clypeus arise a few short, curved hairs. The
antennz are well developed and resemble those of Cu/ex. The basal portion
only is covered with spines (Z. tenax, Pl. II, fig. 16).

The mental plate is highly characteristic, and was similar in two species.
It is triangular in shape and the two free edges carry very fine teeth which are
at least four times smaller than those of other larve. The mental plate of
Tentorhynchus has a remarkable resemblance to a shark’s tooth (PI. III, fig. 4).

The siphon-tube is peculiar, being extraordinarily long and thin (PI. II,
fig. 27), "37 of body length. Siphonic index 12. There are about seven spines
in each row confined to the basal tenth of the tube. The hairs arising from
the tube are very short and insignificant.

The nymph has respiratory trumpets which project anteriorly and nearly
meet in the middle line (PI. I, fig. 11). The trumpets are large and pointed,
with an oblique opening (Pl. I, fig. 13). 1 have seen no other nymph in
which the trumpets project forward as they do in tentorhynchus.

Mansonia.—The nymph of Mansonia uniformis has been figured a
Theobald. The trumpets appear to project forward as in the last-mentioned
genus.

&deomyina.—Of the large number of genera in this sub- -family I am only
able to describe a very few, and those imperfectly.

Detnocerites.—Theobald has figured parts of the larva and pupa. The
siphon tube is large. The siphonic index (from Theobald’s drawing) 5°6. The
nymph has abruptly truncated trumpets.

Howardina.—The nymph has somewhat conical and abruptly truncated
trumpets (PI. i, fig. 15).

Foblotta.—Thecbald has figured the head and siphon tube of this larva. He

Cz

12

describes curious quadrangular frontal processes, but these appear to be the
widely opened maxilla. The bodies he describes as antennz are apparently
the maxillary palps. The siphon tube is very short and, from Theobald’s drawing,
appears very unlike that of other larve.

Cannibal larve.—James*‘ was the first to describe a species (C. concolor)
in which the larve possessed cannibal habits. Theobald notes that the related
species C. tigrzpes is also cannibal. The larve of Megarhinus and Toxorhyn-
chites have been described by Theobald, and from the structure of their mouth
parts, are obviously also cannibal species. Zutzia and Psorophora, according to
Lutz,? are actively cannibal. I have lately found the larva of Mucidus
scataphagoides to be cannibal and to possess the modified mouth parts which
appear to be characteristic of all these species. The following genera may be
noted as containing, and possibly consisting entirely of species having larve of
cannibal habits :—

Megarhinus.
Toxorhynchites.
Muctdus.
Psorophora.

Lutzia.
C. concolor.

Famesia C. tigripes.

(new genus).

In all cases in which the habits have been described in detail the larve are
characterised by their extreme voracity and their habit of preying solely upon
other mosquito larve. Although the species observed by us (C. concolor and
M. scataphagotdes) were seen to swallow small water-crustacea (Daphnia), yet
in the main they fed upon other larve. In both cases the larve lay horizontally,
quite motionless, with the modified brushes widely extended. When another larva
approached within a certain distance it was suddenly seized, no matter its size
or how vigorously it struggled. Small larvze were often swallowed whole. Larger
specimens were devoured except the head-case and siphon tube. When food was
abundant, these larve increased in size with remarkable rapidity and ultimately
became conspicuous as giant larve. In Mian Mir both C. concolor and M.
scataphagoides were exceedingly common and were found wherever other Culex
larvee abounded. The larve of M. scataphagoides occurred in pools with much
vegetation. C. concolor, on the other hand, was found together with C. fatigans
in pots, small dirty puddles, etc. In Mian Mir, and probably elsewhere, cannibal
species must play an important role in the reduction of the numbers of mosqui-
toes. From the examination of the two species already mentioned and from
Theobald’s drawings of Megarhinus, Toxorhynchztes, and C. tigripes, it is

13

evident that the larvae of these genera are very similar in structure and appear-
ance. They all adopt a horizontal attitude. All have specially modified mouth
parts and possess conspicuous “ clasping organs’”’ in place of the feeding
brushes. The general appearance in allis similar; the shape of the head and
clypeus is identical. The anal papillz are rudimentary or absent.

Muczdus scataphagotdes—The full grown larva is very large, and its
horizontal attitude and the curious truncated appearance of the head are
characteristic.

The head is smooth and globular. Three long, conspicuous hairs arise on
each side. These differ from hairs in other larve in not being branched. The
clypeus overhangs the mouthand forms a curious concave edge, and not, as in
non-cannibal larvee, a prominence. On each side of the clypeus a modified feed-
ing brush arises.

The feeding brushes are highly modified and form clasping organs. When
the larva is at rest, they project laterally as dark, horn-like structures. Each brush
is composed of a number of slightly curved chitinous bars, which have minute
comb-like projections on the concave side (PI. III, fig. 14). The bars lie gene-
rally closely approximated, so that the clasping organ at first sight appears to
be composed of a single dense piece of chitin. The mental plate in both Mucz-
dus and C. concolor is very similar and differs widely from that of any other larva
I have seen. In both species it carries only a few teeth, but these are of great
size (PI. III, figs.5and 6). In Muczdus the maxillary palps are very small and
do not cover in the mandibles as in non-carnivorous species. The mandibles
are conspicuous, and the mandibular plate is very solid and massive.

The antennz are small and resemble in general appearance those of
Stegomyia. The small basal tuft, however, rises very near the termination of
the antenna. The median and terminal spines are represented by a few
inconspicuous processes. There are a few small spines scattered over the
antenna (PI. II, fig, 12).

The thorax is smooth and globular. The hairs arising from it and also
the hairs arising from the abdomen are simple and spring from well-marked and
chitinised papilla. The siphon tube is long, the siphonic index being 4°6.
There are about 22 spines in each row and two conspicuous tufts of hairs above
these. There is no rudder-like fan of hairs rising from the median line as in
C. concolor and C. tzgrzpes. The ninth segment differs from that of most larve
in possessing only rudimentary anal papilla. The ventral fan of hairs has also a
more extended origin (PI. III, fig. 16).

Megarhinus and Toxorhynchites—The larva of 7. spectosus figured by
Theobald corresponds in almost every detail with the above description. The
chief differences are in the presence of short, ‘notched hairs arising from the

14

thorax of the larva of Zoxorhynchztes and the absence (?) of the spines of the
siphon tube in this species. Siphonic index is 2°5 (Pl. III, figs. 12 and 19).

C. concolor.—in general appearance the larva exactly resembles that of
Muctdus. The antennz and siphon-tube are, however, different. The antennz
are small and very unlike those of any other larva (Pl. HI, fig. 11). The siphon
tube is highly characteristic and possesses a structure not represented in any
other larva yet described (with the exception of the related species C. ¢igrtpes).
This is a large fan of hairs springing from the median posterior line of the
siphon tube (Pl. III, figs. 17 and18). The shape also of the siphon tube in
C. concolor and C. tigrzpes is quite unlike that of any other larva. The nymph
has respiratory trumpets differing from those of Cwlex. They project ina
characteristic way from the body of the nymph (PI. I, figs. 14 and 23).

Psorophora.—From Howard's description of P. cz/zata it is evident that the
larva is morphologically adapted for cannibal habits and resembles closely that
of Mucidus.

Lutzta.—The characters of this larva, so far as 1 am aware, have not been
described.

III.

From the above descriptions it will be seen that the most important varia-
tions occur on the following structures :—

. The respiratory trumpet of the nymph.

. The antenna of the larva.

. The siphon tube of the larva.

. The mental plate of the larva.

. The feeding brushes of the larva.

. The anal papille of the larva.

. The form of the ovum.

. The arrangement of ova in rafts or otherwise.
g. The form of the raft.

aA AuNbwWDND H

The shape of the nymph trumpets appears to vary little in species of the
same genus, but to be of great importance in the distinction of different genera.

By means of the variations on the trumpets the following groups may be
obtained. .

1. Trumpets expanded to form a flap (Pl. I, figs. 1 and 2). . Anophelina.
2. Trumpets expanded broadly triangular in shape (PI. I, figs. 3, 4, f Stegomyta.

and 5) Desvoidea.
3. Trumpets narrow with oblique opening (PI. I, figs. 7 and 9) - . Culex.

4. Trumpets extremely long and narrow ; opening not so oblique 1/elanoconton.
as above (PI. I, figs. 8 and 10).

5. Trumpets project forwards (Pl. I, figs. 11 and 13). : ; ee

a

Deinocerites.
6. Trumpets abruptly truncated (Pl. I, fig. 15). A .5 Howardina.

Acartomyia.
7. Trumpets contracted at opening ; opening circular : : . Mochlonyx.
8. Trumpets contracted at opening; opening slit like ¢ : . Corethra,

Two types of antennz occur in the above descriptions.

I. Stegomyia type figs. 4, 5, 6, 7, 8, 9, 10, seen in Stegomyia, Desvoidea, Acartomyta.

2. Culex type figs. 13, 14, 15, 16, seen in Culex, Melanoconion, Txentorhynchus,

Grabhamia.

The differences in the two types is so fundamental as to suggest that the
siphonate Culictde are derived from two main types, one giving rise to the
Stegomyie, the other to the Culicine (restricted sense, see later). The
antennz of C. concolor and Mucidus appear distinct from either, though that of
Mucidus approaches more closely to the Stegomyza than the Culex type.

The siphon tube is of specific value since it is subject to considerable varia-
tion in nearly related species. In many cases the characters of the siphon tube
appear also to be of generic significance, z.e., Culex, Stegomyia, Tentorhynchus,
etc.

The mental plate is a structure well worth further study. Very distinct
characters were present in S/egomyzta, Culex, Melanoconion, Teniorhynchus,
C. concolor, and Mudzcus.

It is evident that, in general, genera based upon the adult characters are
established still more firmly by a consideration of the characters of the immature
stages. But there are many points brought out very clearly by immature
characters which are not so evident on consideration of adult characters alone.
Theobald’s classification according to adult characters is briefly as follows. (The
reasons for the groups are.not given. See, however, manual of the Cudicide.)

SuB-FAMILY.

1. Sub-fam. Anophelina . : - : . Anopheles, etc., ete.

2. i Megarhinina - - 3 . Megarhinus.
Toxorhynchites.
Fanthinsoma.

3. yy Culicina 4 5 : | Psorophora.
Mucidus.
Stegomyta.
Desvotdea.

SONNE - heobaldia.

utsia.
Culex.
Gilesia.
Lastonocops.
Melanoconion,
Grabhamta.
Acartomyta.
Teniorhynchus.
Mansonia.

16

{ 4. Sub-fam. Foblotina : : : . Foblotia.
ie 35% i Heptaphlebotomyina : : . Heptaphlebotomyta.
Sec. A. 4 6. 53 Aedeomyina . : ¢ . Detnocerites.
Howardina and 18
other genera,
Secwb: 1. Sub-fam. Corethrina.

In the first place the position occupied by Stegomyia is too subordinate,
A consideration of the characters of Stegomyta show that these mosquitoes
differ much more from Cudex than do Melanoconton, Tentorhyuchus, etc.
Theobald’s classification might be modified by removing the Stegomyi@ alto-
gether from the Cuwlicina. This I propose to do and to place them in a
division Stegomyina. The groups of genera Culex, Theobaldia, Melanoconion,
Tentorhynchus, and Mansonta will then form a natural division differing widely
from the last mentioned.

Stegomytna.

Ova * laid separately upon the water. Each ovum surrounded by
small air chambers.

Larva long and worm-like. Attitude vertical. Antenne degenerate.
Basal tuft represented by small hair. Median and terminal spines
rudimentary. Siphon tube short and stout. Index=2.

Nymph trumpets expanded. Broadly triangular in shape.

Imago. Habits diurnal. Scale structure distinctive.

Culicina (restricted sense).

Ova cemented together to form rafts.

Larva more or less spiny in appearance. Antenne fully developed.
Siphon tube rather long. Index 4 to 12,

Nymph trumpets narrow. Openings oblique.

Imago. Habits nocturnal. Scale structure distinct.

In the second place it is doubtful if Megarhinus and Toxorhynchetes by
themselves should be placed in a separate sub-family—a division of equal
importance to that of Anophelina and Culccina. The character of the palps in
this case does not seem to me a sufficiently important feature upon which to found
the division, especially since in Zoxorhynchites the female palps are not much
longer than in Muccdus. The genera Megarhinus, Toxorhynchites, Mucidus, and
Psorophora appear to be a group of closely related genera showing the following
features in common :—

Larva specially modified for cannibal habits. Attitude horizontal, etc.

Imago large and conspicuous species. The palps in the female longer

than in Culex.

® I think the observation by Skuse that the ova of S. notoscrepia are laic in rafts needs confirmation
before it can be accepted,

17

To remove Mucidus and Psorophora from the Culicina and to adopt
provisionally a new division including Megarhinus, Toxorhynchites, Mucrdus,
Psorophora, and possibly Fanthznsoma and the genera Lutzza and Famesza,
would seem to be more natural.

The larval stages of the Aedeomyzna are so little known that I make no
attempt to consider the position of this group. In the few species described
there are however some features, e.g., the larval antennz, which suggest a
distant relationship to the Stegomyzna rather than to the Culzczna.

The affinities of the Cudzcide@ would then be shown as follows :—

( § Megarhinus.
Toxorhynchites.
| Mucidus.
1. Sub-fam. Megarhinina _ .4 Psorophora.
Fanthinsoma.
Lutzia. (?)
_Famesta. (?)
Stegomyia.
Desvotdea.
Hlowardina.
Detnocerites and 18 other genera (acartomyia ?).
( § Culex.
Theobaldia.
Melanoconion.
Tentorhynchus.
Mansonia.
Grabhamia. (2)

2, Sub-fam. Stegomytna

3. Sub-fam, Aedeomyina

4. Sub-fam. Culicina

I do not claim the above as, in any sense, a rigid classification, but it
appears to me that a truer proportion exists inthe groups than in the original
classification by the adult characters alone. Classification by the scale structure
has been shown even by the consideration of immature characters to be a very
natural one, but in the variations of the ovum, larva, and nymph, we have a most
important additional means of determining the natural affinities of mosquitoes.

REFERENCES.

Stephens and Christophers. Reports to the Malaria Committee of the Royal Society.
7th series. Harrison & Sons.

Also later “The Practical Study of Malaria.” Longmans, Green & Co,

James, who was associated with us, has also described the immature stages of most
of the Indian anopheles “ Malaria in India.” Scientific Memoirs by officers of
the Medical and Sanitary Departments of the Government of India. New series,
No. 2. Vide also James and Liston. Anopheles Mosquitoes of india. Thacker,
Spink, Calcutta.

2, Meinart. De Encephale Myggelarver. K. Danske veiden scabernes Selskabs
Skriften. III, Copenhagen, 1886.

on On

i8

. Howard. The Mosquitoes of the United States. Bulletin No. 5. N. S. U. S.

Department Agriculture, Division Entomology, 1896.

. James. Indian Med. Gazette. The collection of mosquitoes and their larve. ,

December 1889.

. James: Letter to Theobald. Manual of the Culicidz, Vol. II, p. 110.
. Theobald. Manual of the Culicide. Chiefly Vol. III.

. Daniels and Ross. Quoted by Theobald.

. Lutz. Communication to Theobald. Vol. I, p. 48.

a

EXPLANATION OF PLATES.

PLATE I.

. Respiratory trumpets of nymph.

. Nyssorhynchus fuligtnosus.

. Myzomyia Rossii.

. Stegomyia sugens.

. Stegomyia fasciata.

. Desvoidea fusca.

. A culex the larval characters of which differ from the type group.

Pl. Il, figs. 7 and 19, and PI. Ill, fig. 2.

. Culex fatigans.
. Melanoconion (n. sp.).
. Nymph of Cu/ex showing position of trumpets.

5 Melanoconion showing position of trumpets.
2 Tzniorhynchus ,, 93 ”
5 Culex concolor ,, » 3

. Tentorhynchus.

. Culex concolor.

. Howardina (n. sp.).

. An atypical culex. See PI. Il, figs. 9 and 21, also PI. III, fig. 7.
. The eighth and ninth abdominal segments of larva of Stegomyia sugens.
. The head of M/e/anoconton showing mental plate, structure of antenna.

. Larva of Stegomyta sugens.

3 Melanoconion, n. sp.
3 Tzntorhynchus tenax (Theo.).

See

ae A culex related to species shown in Pl. I, fig. 16. See Pl. I,

figs. 10 and 22, and PI. III, figs. 8, 23, and 24.
re Culex concolor (cannibal larva).

PLATE lI.

iy v4, we y

7

M. Rossii Stegomyia Fasciata Desvoidea Fusca
N. Fuliginosus Fig. 2. Stegomyia Sugens Fig. 4 Fig. 5.
Fig. b Fig. 3
Fig. 6.

va)
, \

~ Deh =

Melanoconion <a
Culex Fatigans Fig. 8. Y
Fig. 7 ————
—-

Melanoconion

Fig 10 Taeniorbyncus C. Concolor Taeniorbyncus

ea Fig. 12 Fig. 13
Z

a

$rd portion

Feeding Brush

of Antenna

2nd portion
of Antenna

LF. portion of Antenna.

_ Campound Eye
Cc. Concclor Bowardina
Simple Eye Fig. 14 Fig. 16.

Fig. 16

Stegomyia

fico CaMV enniag ta +i
Tht b 8) a Venined cup ent:
al re

PLATE Il.

Figs. 1--16- Antenne of larve.
1. Myzomyia Rossii,
2. Anopheles Lindesayt.
3. Mysorhynchus nigerrimus.
4. Stegomyia sugens.
5. Stegomyia fasciata.
6. Desvoidea fusca.
he
8.

9.
10.

Species of culex with antenna not of type form.

11. Culex concolor.

12. Mucidus scataphagoides.

13. Culex fatigans.

14. Culex. (?)

15. Melanoconion, n. sp.

16, Tentorhynchus tenax (Theo.).
Figs. 17—27. Siphon tubes of larva,

17. Stegomyia sugens.

18. Stegomyia fasciata.

ae } Tubes of atypical species of culex.

ak } Enormous siphon tubes (culex).

23. Culex impellens.

24. Culex fatigans.

25. Culex. (?)

26. Melanoconton, n. sp.
27. Lentorhynchus tenax.

|

ae
|

ee |
Bo |

; yzorhyncus Nigerrimus
Anopheles Lindesayt mye Mes 4 3 Stegomyia Sugens
mg.2 0 ; f Fig 4 Stegomyia Fasciata

Fig. 1

We
Culex Concolor

Fig. 11

Mucidus Scataphagoides
Fig. 12.

Culex Species ? Mclaneconion Pig 18
Fig. 13 ies Fig. 15

Culex Fatigans

g

eee,
1S
Mer aiee ae je SS i
3 eae oe!

»
»
Stegomyia Sugens ‘ ~
Sv Fig. 17 S. Fasciata N
Tan Fig. 18. Fé. 19 x 8
s
ae s :
4 | | H y
i |
2) £ f Fig. 20. |
ne q SS NaN
a cle | S
¢ Sh -S
x oe Se
/ ‘ N \
4 4 SN
4 | 4
: ‘ a N :
é i N S ~
7 : | ¢ EAS ih ess Beet 3 S NJ
| | Fig. 25, Fig. 26 | d lot 3 3
-- oh ‘i :
C Impellens ©. Fatigans Bast i
Fig. 23 Fig. 24. Melancconion 5 Sate
Taeniorhyneus Tenax Fig. 21. Fis. 20

C. Species 7

r¥

ony

Figs. 1—8.
. Stegomyta sugens.

. Culex (atypical).

. Melanoconion, n. sp.

. Tentorhynchus tenax.

. Culex concolor.

. Mucidus scataphagotdes.
. Culex (atypical).

Figs. 9—11.
Q.

10.

ae,

5 WS
aye

1 kg

elise
5. 10
Wuge
Palos
A Op
4 PAY
BO
5 BE,
bezQe
aZAk
» Be

ont antw dN

PLATE Iil.

Mental plates of larva.

Clypeal hairs.
Clypeal hairs of Stegomyta sugens.
a ss fasctata.
* op a scutellaris. |?)
Head of Toxorhynchites speciosus (after Theobald),
Head of Culex concolor.
Mouth parts of /. scataphagoides showing concave clypeus, modified
brushes, mandibles, and small maxilla.
Mouth parts of Culex concolor.

Eighth and ninth abdominal segments of W/. scataphageoides.

of Fy af 3 Culex tigripes.

35 a & * Culex concolor,

A ss 5 i Toxorhynchttes (after Theobald).
Position at rest of Culex fattgans, larva.

0 55 Teniorhynchus tenax, larva.

“3 5 Stegomyta.
Position in progression of larva with enormous siphon tube,

a at rest 5 . oF aks

) : Culex concolor, larva.

PLATE Ith.

\
. \ V

i e

; \

: ig. 9 2 S

Mola i Taeniorhyncus Tenex mee me
Stegomyia Sugens Molanoconion an: at seas ene ee Ree
ee ae a Fig. 5. Fig. 6
A

8. Fasciata S Scutellaris (?)
Fig. 10. Fig, 11.

Culex Concolor
Fig. 15.

\ i

Mucidus Seataphasgoides

Toxorhynchites ig. 16 A
Fig. 12.

i

sence lll pif

fox \

Culex Fatigans

Culex Tigripes
(after Theobaid)

(
ay

; / a (in Progression)

(at rest)

Toxorhynchites
(after Theobald)

SM

Bis

ortans

, | i nD ci |

. I No. 25.
(NEW SERIES.) ‘i
SCIENTIFIC MEMOIRS
OFFICERS OF THE MEDICAL AND SANITARY. DEPARTMENTS

OF THE

GOVERNMENT OF INDIA.

ON. THE IMPORTANCE OF LARVAL CHARACTERS
_ IN THE*CLASSIFICATION OF MOSQUITOES.

BY ;
CAPTAIN S..R. CHRISTOPHERS, M.B., I.M.S.

ISSUED UNDER THE AUTHORITY OF THE GOVERNMENT OF INDIA
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