70
164. For examining cisterns and tanks mull-mull nets on longer or shorter
handles were found effective. A net of this kind can be introduced into a
cistern and swept rapidly over the whole surface of the water and on removal
quickly inverted and washed in a white enamelled vessel of water. Larvae
if present are easily detected in this way. By the use of a net the presence of
larvæ of Neocellia stephensi was demonstrated in several hundreds of cisterns
which had previously been examined by means of dippers and declared to be
quite free of mosquito larvæ ; and it was found possible to show the presence
of larvæ in the Malabár Hill reservoir where the water is 18 feet deep and
absolutely clear, when previous examination by dippers had given uniformly
negative results.
Anopheline Larvæ.
165. During the investigation larvæ of N. stephensi were met with in
1,693 different collections of water; larvæ of 31. barbirostris in about 500
places ; larvæ of N. jamesi in nearly 100 and larvæ of M. culicifacies and
31. listoni in about 50. All these species of anopheles with the exception of
N, rossi have been found breeding most frequently in open wells.
166. The number of breeding places of Neocellia stephensi found in each
ward has been as follows :—
A.
B.
C.
D.
E.
P.
G.
Ward
..
,s
..
.. 683
. 108
472
.. 305
.. 120
.. Nil.
.. Nil.
41.1
6.3
27.8
18.0
7.8
per cent.
»
5)
i>
of total.
5>
167. The nature of the breeding places chosen by Neocellia stephensi is
shown below. Among a total of nearly 1,700 collections of water harbouring
the larvæ of this mosquito the various breeding places were approximately
as follows :—
Open wells
Open and improperly closed cisterns ..
Fountains
Masonry and other tanks
Tubs, barrels, tin-pots and minor
collections of water ..
Pools of water
65 per cent.
10
2
10
168. These breeding places may be divided into two classes :—
(1) Permanent breeding places.
(2) Temporary breeding places.
The permanent breeding places which chiefly consist of open wells, open
and improperly closed cisterns, fountains and garden and other tanks, are of the
utmost importance as they enable the mosquito to continue breeding unchecked
throughout the year and provide the source from which temporary breeding
places become infected from time to time. Besides the ordinary permanent
breeding places there are a few special ones in certain localities. The filter-beds
and reservoirs at Malabár and Bhandarwada Hills are prolific breeding grounds
and the waste water and leakage from these water works also form small
streamlets and pools in which the mosquito can breed all the year round.
Certain places on the foreshore in Colaba and Walkeshwar, where pools of
brackish water remain throughout the year, also form permanent breeding
places from which temporary pools created during the monsoon subsequently
become infected.
169. Temporary breeding places are usually only formed during the rainy
season and speedily disappear after the commencement of the dry weather.
They consist chiefly in surface pools of water which are formed after heavy rains
on the uneven surface of the ground in large compounds such as that of the
New Dock Works enclosure, the Railway Yards and many other places, earas