NationalLibraryOfScotland/medical-history-of-british-india huggingface dataset:
THE CONTROL OF BLOOD-SUCKING INSECTS IN INDIA.
BY
S. K. SEN, M.Sc., F.E.S.,
Assistant Research Officer, Imperial Institute of Veterinary Research, Muktesar.
(Received for publication on 5th November 1931.)
The problem of the control of blood-sucking insects has now assumed a position
of paramount importance in Veterinary Entomology in view of the fact that several
species of these insects have, during recent years, been definitely incriminated as
the carriers of certain tropical diseases of animals. The most notable of such
diseases is surra, which has been repeatedly demonstrated by Nieschulz [1928,
1929], in Java, to be capable of being conveyed mechanically through the bite of
Tabanus rubidus, whilst Moutia [1928-29], in Mauritius, has brought forward what
would appear to be fairly convincing evidence in support of his contention that the
same disease is conveyed through the agency of Stomoxys in that country. In
India, the disease has been shewn by Cross and his collaborators [1922, 1924] to be
capable of being transmitted through the bites of several species of Tabanids,
including T. rubidus. The fact that in all cases the disease has proved to be trans-
missible mechanically makes every single biting insect a potential carrier not only
of surra, but, possibly, of several other blood-borne infections of animals.
The problem of the control of Tabanids will be discussed at length in another
article which it is proposed to submit shortly for publication in this Journal,* so
that in the present note, it is only necessary briefly to deal with this subject, but
to consider in some detail the more important measures advocated by different
workers for the control of biting flies other than the Tabanidæ. A brief mention
will also be made of some of the known methods for combating house-flies
(Muscidæ) and blow-flies (Calliphoridæ), inasmuch as these methods may prove to
be of value in devising measures for the control of blood-sucking insects.
The more important of the measures hitherto recommended for the control of
insect pests of animals may be classified under the following categories :—
I. REPELLENTS.
During recent years, a considerable number of repellents designed to repel
flies, primarily by virtue of their obnoxious smell and greasy properties, have been.
* In the series of articles entitled " A Veterinary Entomology for India," by T. Bainbrigge
Fletcher and S. K. Sen.
( 29 )
C
30 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ II, I
introduced into the field of Applied Entomology. Several of these have fish-oil as
one of their constituents, this oil having been given an extensive trial by the United
States Bureau of Entomology and found to possess sufficiently repellent properties
to keep away flies for a length of time, perhaps not exceeding 2 or 3 days. Graybill
[1914], who would appear to have carried out extensive trials with repellents,
considers fish-oil as one of the best, but he stresses the importance of application
being made lightly, as otherwise poisoning may result. Of other smelly substances
used for the same purpose, mention may be made of a recipe consisting of 5 oz.
assafœtida, 13 oz. vinegar and 20 oz. water ; it has been claimed that when
applied to the thin-skinned parts of the body, this mixture keeps away Tabanids
and Stomoxys for about a week. (Rev. App. Entom. B, 2, 202; 1914). Jensen
[1909] recommends the following repellent for dairy cows : Common laundry soap,
1 lb. ; water, 4 U. S. gallon ; crude petroleum, 1 U. S. gallon ; powdered naphtha-
line, 4 oz.; the mixture is applied once or twice with a brush.
In connection with the subject of repellents, it is of interest that Mitzmain
[1913] mentions two German chemists as having suggested that potassium tellurate
taken internally repels mosquitos, flies and ticks, but negative results were obtain-
ed by Mitzmain himself with this drug, when administered in quantities of 10
grammes per animal. Similarly, Graybill [1914] quotes Ochman as having re-
commended the same drug as an internal remedy for repelling flies and states that
in the same year, Mayer tested the drug but obtained negative results. Trials
carried out by Cross [1917] in India showed castor oil to be an effective repellent
for protecting camels from the attacks of biting flies, but, as he himself observes, it
is of little practical value inasmuch as the oil ceases to repel as soon as it gets dry.
As a matter of fact, the use of repellents is perhaps the least effective of measures
hitherto devised for the control of biting insects, and this is in a large measure to
be ascribed to the fact that, as observed by Haseman [1927], in no case are they
effective for more than a few hours, whilst most sprays are liable to cause injury to
the skin unless used sparingly.
II. ATTRACTANTS.
Attractants hold out perhaps the largest promise of success for workers in the
field of Applied Entomology in view of the highly encouraging progress already
made towards discovering substances—more precisely, stimuli—attractive for certain
species of insects, such as the oil of citronella for the peach-fly, Chælodacus zonatus.
So far as biting flies are concerned, it would appear to be generally held that their
feeding habits are largely governed by thermal stimuli, as is evidenced by the well-
known fact that heated surfaces exercise a powerful attraction for certain species of
CONTROL OF BLOOD-SUCKING INSECTS
31
mosquitos. Thus, Crumb [1922] mentions having observed that a joint of a stove
pipe placed in the woods and heated by an alcohol lamp attracted many mosquitos,
but that the crude components of blood and of perspiration apparently produced
only faint and erratic responses. Similarly, Howlett [1910], in India, showed that
certain species of mosquitos (e.g., Aëdes (Stegomyia) albopictus) could be readily
induced to bite at a tube containing water heated to the requisite degree. Accord-
ing to Metz [1920], Anophelines react sufficiently to certain stimuli to be enticed
into traps, and he recommends a study of their sensory reactions combined with
chemical analyses and experiments with a view to discovering a substance that will
prove sufficiently attractive.
III. TRAPS.
During the past two decades, a large variety of traps have been designed and
sought to be introduced into the field for the purpose of combating certain species
of insect pests of animals, notably, mosquitos, tsetse-flies (Glossina), Muscidæ and
blow-flies (Calliphoridæ), the last having received perhaps the largest share of
attention. In a short note of this kind, it is only possible to give a bare outline
of the designs of some of these traps and to indicate briefly the extent of success
obtained from their use.
(a) Traps for mosquitos.
Lefroy [1911] and Fletcher [1912], in India, have recommended the use of
simple wooden boxes with a lining of dark cloth inside. When it is kept open in
an unfrequented corner of the house, large numbers of mosquitos may be found
congregated inside the box during the day time when they can be readily
destroyed.
Recently, Bath [1931] has recorded highly satisfactory results from the use of
a trap placed on the screens of dwellings, the inmates of which served as the bait.
The trap consists of a V-shaped ridge of screening with a slit in the top, inside
which is a similar ridge with a smaller slit to prevent the exit of the trapped
mosquitos, the whole being surrounded by screening to prevent the mosquitos from
entering the house.
An efficient method of combating mosquitos is to leave, as suggested by Galli¬
valerio [1921], a few collections of stagnant water to serve as traps for the mos-
quitos to oviposit upon. The larvæ and the pupæ resulting from the eggs may be
periodically destroyed.
(b) Traps for Tabanidæ.
A perusal of the available literature shows that trapping has seldom been
resorted to as a method for combating Tabanidæ.
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32 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ II, I
Mitzmain [1913], in the Philippines, mentions trapping of Tabanids with
tanglefoot applied to the trunk and larger branches of the rain trees which form
their favourite resting places.
A measure which has been extolled by a number of workers, e.g., Portchinsky
[1915], is the pouring of some oil, such as kerosine, on the surfaces of pools usually
frequented by these flies. The Tabanidæ have the habit of skimming, while on the
wing, the surface of pools and taking up water with their proboscis, so that, if the
pools were oiled, the flies would have some of the oil clinging to the underside of
their bodies when they came in contact with the water, and this would eventually
cause their death.
In an article which has been seen only in abstract, Hewitt [1920], in Canada,
states that the results of experiments with a small wire insectary used as a trap for
Tabanidæ indicated that such a trap might be of great practical value in the
vicinity of cattle yards. In the absence of further details, it is not possible to
express an opinion upon the extent to which such traps could be used with advan-
tage for combating Tabanids in this country.
The use of dummy animals has been suggested by certain workers for attract-
ing tsetses and also certain species of Stomoxys and Tabanids, and their use is claimed
to have yielded a notable degree of success (Journ. Dept. Agric. Union S. Africa, 7,
pp. 11 and 20 ; 1923).
(c) Traps for Tsetse-flies.
Although Africa and certain parts of Arabia are the only localities where
tsetses are known to occur, a brief consideration of the traps hitherto designed to
combat these flies would be of interest for workers in India, inasmuch as both in
respect of size and feeding habits, the tsetses present some similarity to certain
species of Tabanidæ.
As early as in the year 1914, Zupitza devised the rather fantastic method
of trapping tsetses by means of a sort of armour consisting of a plaited wire-
screen of oxidized metal with a mesh of 1 cm. The trap was donned by a native
and smeared with a sticky material. As one would expect, the trap proved
thoroughly unsatisfactory, only Glossina in the immediate vicinity being caught
by this method.
What, in principle, was the same as the Zupitza trap was recommended by
Shircore [1920] in the course of a correspondence arising out of a suggestion made
by Carpenter concerning the provision of artificial shelters as breeding places for
Glossina. He suggested for this purpose the use of logs smeared with an adhesive
substance and propped up on supports 2 or 3 inches off the ground.
CONTROL OF BLOOD-SUCKING INSECTS
33
Recently, Harris [1931], working in Natal, has introduced a type of trap
which, judging from the results reported to have been obtained from its use, would
appear to represent a very notable advance towards the formulation of measures
for the control of Glossina. The construction of the trap, as described by Harris,
is as follows : "It consists of a platform, 6 feet by 3 feet, across which is an
opening 6 inches wide, extending from side to side. Attached to the ends are
folding legs which taper from 3 feet in width at the top to 6 inches at the bottom.
The whole of this table-like shape is then covered with double hessian forming
a hollow bulk. The legs are kept apart by a wooden stretcher inserted between
them. Covering the 6 inches opening in the platform is a cage fitted with a non-
return passage through which the flies go, to become entrapped in the cage. The
trap is painted white and suspended from a wire about 3 feet above the ground
surface ". The habit of the fly which it has been sought to exploit in the cons-
truction of this trap is described as follows : " When they alight on the animal,
according to Mr. Harris, tsetse-flies crawl down towards the under parts, possibly
to get out of reach of the tail or muzzle, possibly in search of softer skin"
(Times Weekly Edition, March 26, 1931). The trap, therefore, would appear to hold
out very little prospect of proving successful for the purpose of combating
Tabanids, inasmuch as these flies are seldom observed to behave in the manner of
the tsetses as described above ; on the other hand, they would appear, as a rule, to
get engorged at the very spot where they alight on their host's body.
(d) Traps for other Biting Insects.
For the control of fleas, Delanoe [1922] recommends the use of a fairly large
receptacle containing water covered with oil. In the centre of this receptacle a night
lamp is placed, and the fleas are stated to be attracted to the light and get drowned
in the oil. In one locality in Morocco, about 300 fleas are reported to have been
entrapped by this method. The same author [1922] mentions live sheep as being
quite a practicable trap, as the wool asphyxiates the fleas. Further, Delanoe
quotes Weisgerber as having stated that a sheep skin, even if washed, can be used
as a flea trap, the reason being probably that the flea is held captive by the hairs.
The control of the minute species of blood-suckers, such as sand-flies (Phleboto¬
mus) and the midges, is a matter of considerable difficulty. However, Cathcart
[1923], in Iraq, records having obtained good results in attracting and destroying
sand-flies, by the use of hurricane lamps smeared with vaseline.
(e) Traps for House-flies.
Several methods have been recommended for entrapping the larval forms of
Muscidæ, but as a consideration of these methods would have but little bearing
34 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ II, I
upon the problem of the control of blood-sucking flies, it is proposed to mention
here only the more important types of traps designed to capture the winged forms
of Muscidæ.
For the capture of adult house-flies, Burnett [1918] recommends the use of a
barrel, of which both the ends have been removed. One end of this is covered with
netting and to the other is fixed a funnel made of wire screen, the opening at the
point, ¼ to ⅜ inches, being in the centre of the barrel. The trap is placed on legs
3 inches long and is baited.
Hughens [1919] recommends a trap composed of 4 vertical sides of solid wood
with a flat top of wire-gauze and a gauze bottom raised to a ridge roof-wise. The
ridge is placed midway and is provided with ¼ inch holes along its length. The
lower edges of the box are cut away except at corners, so that the bait may be
placed under the box beneath the ridge and flies enter through the openings. The
trap stands on a wooden platform.
An ingenious method of trapping flies is that devised by Keane [1926]. The
trap, as described by him, is as follows :— " The actual trap-face is of glass, the
surface area of which measures not more than four inches by one inch in two pieces
overlapping and separated by a distance of a ¼ inch — two microscope slides may
be used. The lower and posterior glass section is flush at its lowest part with the
woodwork. The upper section allows a quarter inch space between its highest point
and the woodwork. The floor, sides and back consist of wood. A portion of the roof
consists of a glass window. The back can be opened for the purpose of cleaning
the trap." The trap may be installed in a section of a window-frame, the greater
portion of the trap projecting into the open air, and in this way illumination of its
interior is secured, for " the trap owes its success to the advantage taken of the
fly's apparent fear of darkness and its efforts, in consequence, to escape from it".
Several simple methods have been recommended for the direct destruction
of either the adult flies or their eggs. Reference need hardly be made to the
well-known bait consisting of milk and formalin, for attracting the adult
flies. Patton [1920] recommends the use of a bait whereon the flies could be
induced to oviposit; at dusk, the tray is removed and the bait containing large
numbers of eggs is placed in the incinerator. He also recommends a trap con
sisting of a large meat-safe with wire-gauze on all sides, except the top and bottom
which are made of wood. The entrance to the trap consists of 6 gauze cones,
which open almost at a level, with a door situated at the lower end of one side, the
bait being placed on the floor of the trap.
CONTROL OF BLOOD-SUCKING INSECTS
35
(f) Traps for Blow-flies.
Although blow-flies are not, as yet, known to be a serious pest in India, never-
theless it would seem desirable to give a passing consideration to some of the
methods of trapping these flies as practised in other countries, inasmuch as these
methods represent a wide range of designs in the making of traps and might be
found to furnish indications for devising measures for combating other insect pests
of animals.
A simple trap for the sheep-maggot fly (Lucilia sericata), devised by Beach
[1916], consists of a galvanized sheet-iron pan, with perforated sides and a close-
fitting weather-proof cover. The pan contains a layer of sand over which swings
another pan in which bait is placed. The perforations in the lower pan are covered
with wire-gauze large enough to allow L. sericata to enter. The flies enter the
trap, oviposit and die. The pupæ resulting from the eggs are collected from the
sand and may be fed to poultry.
Froggatt [1917] recommends a simple trap made by covering the open end of
an empty kerosene tin with a sheet of wire-gauze. Through the centre of this
gauze is let a funnel, the opening of which at the apex is inside the tin. The trap
is baited.
Adams [1918] suggests destruction of the flies by attracting them to baits
kept constantly moist by means of strips of flannel, one end of which is in contact
with the bait placed in the lower part of the trap and the other end dipped in an
arsenical solution kept in the upper part, the whole being hung by wire from
a tree.
Babcock and Bennett [1921] record having used, with much success, a trap
consisting of a cylinder of wire-gauze 24 inches high and 18 inches in diameter, with
a screened top and, at the bottom, with a cone measuring 22 inches high, with a 1½-
inch opening at the top. The trap is set in a platform and placed on a tree, about
4 or 5 feet above ground. It is baited.
Place [1922] would seem to consider any elaborate measures unnecessary for
the purpose of entrapping blow-flies, the object being achieved by means of the
simplest of traps, e.g., a kerosene tin with the top cut off and replaced by a piece
of cheese cloth, with 2 or 3 small holes along one edge. The tin is laid on its side
with a bait and is stated to be very effective.
Blow-fly traps have undergone very material modification in their design in
the hands of Edwards, and later, in the hands of Wahl and du Plessis [1923].
The Wahl and du Plessis trap has been described and figured in a number of
periodicals, and it is only necessary to indicate here the general outline of this
36 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ II, I
trap. It consists of two petrol tins placed one above the other and suitably held
in this position. The upper tin is provided with a wire-gauze pyramid and serves
as the trap proper, while the lower tin contains the bait. Entrances are provided
for the flies by making suitable slits on each of the four faces of the lower tin.
The top of the upper tin is cut out leaving a one-inch strip all round, this opening
serving as the source of light, which will attract the flies in the lower tin after
they have fed. The pyramid has a small hole at the apex pointing towards the top
of the upper tin. The trap is suitably baited and has provision for the removal of
dead flies. Details are given for the construction of the pyramid and fitting
together the various parts of the trap.
Before concluding this section, a few general remarks would seem called for
concerning the utility of traps, as also their limitation in combating insect pests
of animals. While the introduction of traps has registered a definite advance in
the field of Applied Entomology, their application is only indicated in the case of
insects whose habits preclude the adoption of the more effective method of direct
destruction. A typical example of an insect of this kind is provided by the tsetse-
fly, for, as is well known, this fly is pupiparous in its breeding habits, i.e., it
deposits full-grown larvæ which pupate shortly after extrusion, and since the
pupae usually lie secreted in the soil in the midst of bushy undergrowth, practically
the only stage of the fly that is available to deal with for control purposes is the
adult stage. On the other hand, the horse-fly (Tabanid) provides an example
where trapping would appear least likely to yield results comparable to what- would
be achieved by organized campaigns directed towards the destruction of its eggs,
for, unlike the tsetse, the horse-fly is typically oviparous, depositing its eggs in
clusters on vegetation overhanging water, and the fact that its eggs need be
looked for only in the vicinity of collections of water, very materially simplifies
the work of such campaigns. The effectiveness of this measure is strikingly
illustrated by the fact that Hine [cited by Mitzmain, 1913] reports having had
as many as 433 egg-masses collected in the short space of one hour, a simple
cluster being estimated to contain, on an average, about 250 eggs. Even in the
case of tsetses where trapping of the adult flies is reported to have yielded highly
encouraging results, some workers would appear to regard the destruction of the
pupæ as a more effective method of combating this pest. Thus, Hegh, in a
communication presented at the International Congress of Tropical Agriculture
held at Antwerp in July 1930, suggested that " experiments should be undertaken
to test the value of searching out the breeding places of tsetse flies and periodically
destroying the pupæ contained in them, as a local measure for reducing their
numbers to a negligible minimum ".