10 FISHES IN RELATION TO MOSQUITO CONTROL. 
and the other was left as a control. On October 26 no pronounced 
reduction in the number of larve in the pond which had been stocked 
was noticeable. On October 29, however, a remarkable decrease 
was evident, only a few larve being left, and these were found in 
vegetation. At the end of this time the immature mosquitoes in 
the other pond (control) were as abundant as ever. 
Many similar experiments and observations could be mentioned, 
but as the results for all were nearly identical it is not advantageous 
to do so, It then may be stated that wherever mosquitoes were 
breeding prolifically Gambusia was not present, but, if introduced, 
mosquito breeding was eliminated or at least greatly reduced. Wher- 
ever the complete elimination of mosquito larve did not result, if 
sufficient top minnows were present the immature mosquitoes were 
so protected by vegetation or débris that they could not be detected 
or reached by the fish. 
All aquatic plants, however, do not furnish protection for mosquito 
larvee and pup against fish, and some even may be repellent. The 
following-named Pea appeared to provide good protection and 
caused considerable trouble during the investigation: (a) The aquatic 
grass, Hydrochloa carolinensis; (6) ‘‘Coon-tail moss,” a species of 
Myriophyllum; and (c) Alge. The aquatic grass grows in shallow 
water and along the shores. It has many slightly submerged leaves 
over which the horizontally floating or swimming Anopheles larvee 
hover, out of sight and out of reach of fish. erever this plant 
occurs some Anopheles larve are almost sure to be present regardless 
of the abundance of Gambusia. It, therefore, is obvious that if this 
lant occurs in ponds in which mosquito control is desired, it must 
eremoved. ‘This may be done by cutting and raking, or if growing 
in soft mud it ney be pulled up by the roots. 
The plant locally known as ‘‘coon-tail moss”’ causes trouble only 
when it becomes detached and rises to the surface. This plant was 
present in only a few ponds in which an endeavor was made to 
secure mosquito control, and it caused considerable trouble in only 
one. It is ordinarily attached to the bottom, but in this instance 
some of the plants became detached from time to time and came to 
the surface. There each plant collected more or less débris, alge 
grew among its branches and thus formed a mass in which both 
types of mosquito larve found protection. This floating mass must 
be removed from time to time; this can be done best on a windy 
day when it drifts inshore. 
Algee often form mats which float at or near the surface. Mosquito 
larve, particularly Anopheles, find protection from fish over and in 
these mats. Copper sulphate was used in the proportion of 8 pounds 
to 1,000,000 gallons of water for killing the alge, but this treatment 
must usually be repeated frequently. ‘Toward the close of the season 
a light gas oil, used by fie toad! office of the United States Publie 
Health Service in antimalarial work, was sprayed on the algal pads 
wherever the use of the water did not preclude this practice. This 
oil, if used in moderate quantities, is not injurious to fish; 1t can be 
quickly and conveniently applied, and it is very effective, for the 
algal pads act like sponges, retaining the oil and making them unin- 
habitable for the mosquito. 
Water lilies do not, as a rule, appear to furnish much protection 
while growing, but some of the plants die from time to time. The 
