2H 



the following percentages of females which took advantage of one 

 opportunity to suck blood : A. rossi, 63'6 ; A. barbirostris, 49'4 ; 

 A. minimus, 54:'8 ; A. maculatus, 50"0 and A. sinensis, 67 "8 per cent. 



The results of these investigations tend to confirm the preliminary- 

 conclusion of Walker & Barber that the chief carrier of malaria in 

 the Philippines is A. minimus. The mosquito survey has shown the 

 wide distribution of this species, the abundance of its breeding places 

 and the large number of larvae often found in them. It is a house- 

 frequenting form and readily bites human beings. Its distance of 

 flight is at least 170 paces, and the nimiber found in houses in some 

 localities w^as large in comparison with the number of larvae found 

 in the neighbouring breeding places. The distribution of malaria 

 agrees in general with the distribution of this species. In every 

 malarious town the larvae were found in or near the locality or adults 

 were caught in the houses. The high rate of malaria occurring in 

 " ditch " towns, where A. minimus breeds close to houses, tends to 

 strengthen the evidence against this species. A. rossi is responsible 

 for little, if any, transmission of malaria. There is also little correlation 

 between the breeding places of A. barbirostris and A. sinensis and the 

 presence of indigenous malaria. A. maculatus probably transmits 

 malaria in certain localities and at certain seasons. Watson believes 

 that A. 7na.culatus is the chief carrier in certain hill regions of the 

 Malay States. He records this species from an island off Singapore 

 where malaria is intense, and from Hongkong. In any case, anti- 

 malarial measures directed against A. minimus would be equally 

 efficacious against A. inaculatus, which has similar habits. 



March, April and May, in the hot season, are the months which 

 are most free from malaria. It is probable that the mortality from 

 this disease in the Philippines has been overestimated. If, as the 

 results indicate, the transmission of malaria is mainly due to a mosquito 

 of rather limited habitat, the prospect of eradicating or reducing the 

 carriers in many localities is encouraging. Antimalarial measures 

 should be based on a thorough Anojiheles and malaria survey. The 

 best single measure is the destruction of larvae of malaria] carriers, 

 and in this work the breeding places of the stream-breeders should 

 receive first attention. Permanent good may be accomplished by 

 clearing the stream bed so as to make it narrower and swifter. In 

 the Malay States a great diminution of the disease has been brought 

 about by subsoil drainage of the clear streams in which A. maculatus 

 breeds. Such a measure would be difficult to carry out in most localities 

 in the Phihppines. Larvicides are cheaper and at present offer a more 

 practical method for mosquito destruction in these islands. From 

 95 to 100 per cent, of the larvae of A. minimus may be destroyed by 

 one application of any larvicide when it is well distributed in the 

 breeding places. While drainage has imdoubtedly played a considerable 

 part in the diminution of malaria in some countries, it seems that 

 extensive cultivation of the soil might prove an important factor. 

 Not only the diminution of water, but the rendering of it unfit for 

 mosquitos is to be considered. 



Among the natural enemies of stream-breeding mosquitos, the 

 following have been encountered : — Ranatra sp., the larvae of a 

 Dytiscid beetle, flies, tadpoles and certain fish. Where larvae are 

 protected by algae, grass, stones or floating debris, they have been 



