KING INSTITUTE, GUINDY, FOR 1927-28
33
situated in street corners and many are disused. There are many more private
ones, and some are now only very sparingly used because of the introduction of a
piped water public supply. Only a few of the wells in private houses could be
examined because entry to many houses was not allowed. Larvæ of A. stephensi
were found not only in the large disused wells but also in some of the smaller ones
in use.
Table II shows the result of examination of the wells in the different areas
together with the observations on the p.H. of the water, and of its electrical
conductivity, in order to give information on its salinity.
It will be seen that out of the 40 wells examined in the fort, Temple
and Chengalraopeta wards, A. stephensi has been found in 20, giving a larval
index of 50 per cent. Conditions are different in the other wards where, with the
exception of Chakkalipeta, wells are rare. Careful search failed to discover
A. stephensi larvæ in these. .
( b ) The Vottu Gedda near scandal point. —This is a slender seepage
stream and the only one of the several geddas which contained any water at
all. All the varieties of anophelines noted in the present survey were being
bred in it, including three worst carriers, A. stephensi, A. culicifacies and
A. listoni.
A. stephensi.— A. stephensi is ordinarily a well-breeder and its presence
in a stream is unusual, but it has been the most numerous species found in the
Vottu Gedda Daily collections of larvæ were made in order to note the relative
prevalence of the different species. It was found that after the first few days in.
March, when A. rossi (subpictus) was the most numerous, A. stephensi became
the most predominant species and on several occasions was the only species
present. Curiously enough, A. stephensi has been absent from the three wells
situated in the bed of the stream.
A. culicifacies.— A . culicifacies was also found in the small pools by the
side of the main stream, but there was not the same amount of breeding noted by
Mr. Senior White in April 1926.
A. listoni,.— Only half a dozen specimens were obtained in April, but
Col,. Frazer, I.M.S., has found them in the same locality in much greater number s
at other times.
Only a few specimens of A. minimus (var-varuna) and A. vagus were
obtained.
(c) Yerri gedda.—A channel running along the northern outskirts of
the Allipur ward by the side of Dondaparty. This was also almost dry except for
the presence of a few shallow pools on its bed where the upwelling seepage water
had collected. Larvæ of A. culicifacies and A. minimus (var-varuna) have been
repeatedly obtained from these source. Observations on the surface temperature
of the water were made here to determine, if possible, the temperatures that these
larvae tolerate under natural conditions. In one of the pools which is not shaded
by any trees on the bank, larvæ of A. culicifacies (but no pupæ) were readily
obtained even after the maximum temperature (taken about 2 p.m. daily) of
104°F. had been reached for several days. At another spot about a mile away in
the same stream bed near Gnanapuram, A. culicifacies were also found.
( d) Vupputeru swamp.— An extensive swampy area of nearly 60 acres
lying east of the railway line between Vizagapatam and Waltair stations; the
greater part of it was dry, but even so, it was the largest anopheline breeding
ground in the town. Larvæ were so numerous in places as to form a continuo-us
sheet, in the clearances amidst the coarse grass. Larva were obtained from
every one of over 100 spots where a search was made, they were all A. rossi
(subpictus) and no malaria, carrying mosquito larvæ was encountered. Thus,
though a source of general mosquito nuisance, its importance from a malaria point
of view so far does not appear to be very great. The reason for this is that the
water is salty, its salinity is about 70 per cent of that of sea water. It will be
interesting to watch if this is altered during the rains sufficiently to allow of other
species of anophelines breeding.
5