X, B,3 Barber et al.: Malaria in the Philippines P41 
Not only the diminution of water but the rendering of it unfit 
for malaria-carrying mosquitoes is to be considered. Whether 
a change in water may affect the susceptibility of the mosquito 
to malaria without impairing its breeding is a question which 
cannot be solved with the data now at hand. 
Among the natural enemies of stream-breeding mosquito 
larve we have most often encountered a species of Ranatra.** 
We have observed the insects and larve of a species of the 
family Dytiscide?* feeding on mosquito larve in streams. In 
a shallow pool containing Anopheles rossii we have observed 
flies catching larve. The flies rested on twigs and on the 
surface-tension layer of the water and seized the larve from 
above when the latter came to the surface to breathe. In a 
brackish pool in Palawan Province tadpoles were observed 
catching the larve of a species of Culex. These tadpoles had 
developed legs, but were still gill-breathing. A specimen was ~ 
put into formalin and later dissected in the laboratory where 
mosquito larve were found in the upper part of its digestive 
tract. 
Where larve are protected by alge, grass roots, stones, or 
floating débris, we have observed that they breed in large num- 
bers in spite of the immediate presence of their enemies. This 
has been the observation of most workers in various countries. 
The rapid destruction of larve in breeding jars by natural ene- 
mies is not a reliable index to the behavior of these enemies in 
the natural state. It is apparent that natural enemies cannot 
alone be depended on effectively to keep down anopheles. The 
introduction of larvee-destroying fishes or other mosquito enemies 
should be practiced wherever possible. They are most effective 
in ponds, tanks, basins, or other still waters, but we would not - 
hope for much success from them in streams where larve are 
well protected. 
The destruction of adult mosquitoes in and about houses, es- 
pecially those which have taken blood, has been one of the means 
successfully used in antimalarial work in Panama. As stated 
in the description of our work in Mindoro, Doctor Daywalt, 
resident physician of the San Jose Estate, keeps a squad of 
mosquito catchers employed, and he attributes to this work no 
small part of the reduction of malaria on that estate. The suc- 
cess of this measure must depend to a great degree on assistants 
who will carry on the work persistently and throughout the year. 
* Identified by C. S. Banks. 

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