The Philippine journal of science. [Vol. 57, no. 1]

346 The Philippine Journal of Soience 1935
TABLE 5.-Number of collections and average numbers of the two species
of Anopheles at different salt percentages.
Number of collections containing- Average per collection.a
Salt content.
A. litoralis Both A. indefin- No larv.. itorlis. A, indefonly. species. itus only. iius larv A. toras.
Per cent.
0.0-0.9 1 10 30 4 4.9 43.3
1.0-1.9 1 22 6 6 22.5 36.8
2.0-2.9 7 5 1 1 42.9 7.9
3.0-3.9 13 2 0 1 65.5 0.7
4.0-4.9 21 0 0 -- 71.8 0.0
5.0-5.9 6 0 0 1 66.8 0.0
6.0-6.9 8 0 0 2 52.8 0.0
7.0-7.9 2 0 0 ---- 95.0 0.0
8.8 2 0 0 ------- 59.5 0.0
9.2 0 0 0 1 ---- - -------
Total or average -. 61 39 37 15 36.7 21.6
=i;....
a The averages were figured from the number of collections containing larva of either
species.
tions, which in turn vary with the seasons. This accounts for
the marked seasonal fluctuations in the abundance of the two
species.
Anopheles litoralis is predominant during the dry season,
when the salt concentration is high, and is strictly a salt-water
breeder, doing best in water containing upwards of about 3
per cent. Below this point breeding tends to diminish sharply
and, although larval development took place under certain conditions in water containing less than 2 per cent salt, the evidence points to the probability that the species would ultimately
become eliminated at low salt concentrations. During the rainy
season the larvae were gradually reduced almost to the vanishing point, and after the beginning of the dry season general
increased production was not resumed until the salt content
reached a point between 2.5 and 3.0 per cent.
The maximum salt concentration in which breeding of A.
litoralis was found was 8.8 per cent. This was recorded twice,
and on each occasion fairly large numbers of normally active
larvae and pupae were present. Larvae in the higher concentrations had a curious thickening or encrustation of the epidermis.
During the rainy season A. indefinitus becomes the predominant species, and the breeding of this mosquito is very largely
limited to brackish and fresh water. At a time when the salt
concentration was being gradually increased by evaporation, a