. (From Bull.
47, U.S. Fish Com.)]

[Illustration: FIG. 95--An old watering trough, an excellent
breeding-place for mosquitoes.]

FIGHTING THE LARVAE

All of the efforts directed against the adult mosquitoes are usually of
little avail in decreasing the number in any region. It is comparatively
easy, however, to fight them successfully in the larval stage. We have
seen that standing water is absolutely necessary for mosquitoes to breed
in. This makes the problem much simpler than if they could breed in any
moist places such as well-sprinkled lawns, a shady part of the garden,
etc. The whole problem of successful campaigns against the mosquitoes
resolves itself into the problem of finding and destroying or properly
treating their breeding-places. We have seen how certain kinds, such as
the yellow fever mosquito, are "domestic" species. They never go far
from their breeding-places. If a house is infected by one of these
species the immediate premises should be searched for the source.
Cisterns, rain-barrels, sewer-traps, cesspools, tubs or buckets of water
or old tin cans in out-of-the-way corners, are all suitable places for
them to breed in. Cisterns and rain-barrels should be thoroughly
screened so that no mosquitoes can get in or out, or the surface should
be covered with a film of kerosene which will kill all the larvae in the
water when they come to the surface to breathe, and will also kill the
females when they come to deposit their eggs. The vent to open cesspools
should be thoroughly screened or the surface of the water kept well
covered with oil. Water standing in any vessels in the yards should be
emptied every week or ten days and the old tin cans destroyed or hauled
away. In fighting these domestic species you need be concerned only with
your own yard and that of your near-by neighbors. Other species, while
also rather local in their distribution, fly much farther than the
really domestic ones. In fighting these the region for a considerable
distance around must be taken into consideration. Watering-troughs (Fig.
95) that are left filled from week to week, the overflow from such
places, and the tracks made in the mud round about them (Fig. 96), small
sluggish streams, irrigating ditches, and small ponds or lakes not
supplied with fish are excellent breeding-places for several species of
mosquitoes including _Anopheles_ and others. The remedy at once suggests
itself. The watering-trough can be emptied an