1.The experimental results reported in this paper incriminate four additional species of Anophelines in the Panama Canal Zone as potential malaria vectors.
2.Single specimens of A. apicimacula and A. eiseni, which were incidentally included in the experiments, were found to be infected, the former with P. falciparum and the latter with P. vivax. Additional experiments will be required to determine their relative susceptibility.
3.Thirty-one specimens of A. neomaculipalpus were examined after feeding on blood containing P. vivax. Among the mosquitoes fed when the gametocyte concentrations in the blood were 4.4 to 7.8 per 100 leukocytes, the infection rate was 14 per cent, and when the gametocytes numbered 13.4 the infection rate was 50 per cent. Further studies will be required to determine the relative importance of A. neomaculipalpus as a malaria vector.
4.A total of five hundred thirty-eight A. punctimacula were examined after feeding on blood containing malaria plasmodia, and one hundred twenty-four of these, or 22 per cent, were found to be infected. In the experiments with P. vivax the infection rate was 56 per cent in a group of mosquitoes which fed on blood containing 7 gametocytes per 100 leukocytes. In the experiments with P. falciparum, a large proportion of the mosquitoes fed at times when the blood contained relatively small numbers of gametocytes. However, in one group which took blood when the gametocyte concentration was 4 to 12 per 100 leukocytes, the infection rate was 43 per cent; and in two others fed when the gametocytes numbered 13, the infection rates were 81.8 and 90.9 per cent, respectively. The numbers of oocysts and sporozoites found in the infected mosquitoes appeared to be roughly correlated with the gametocyte content of the ingested blood. In one specimen there were more than 46 oocysts. Thus it appears that A. punctimacula possesses a high degree of susceptibility to infection with P. falciparum and with P. vivax.
5.The available information indicates that since the beginning of the Panama Canal A. punctimacula has been one of the most common anophelines in the Canal Zone, where it breeds abundantly during the entire year in shaded waters throughout the unsanitated regions. It also engages in flights, and in certain regions is commonly found in occupied dwellings, where it feeds avidly on human blood.
6.It is believed that A. punctimacula is responsible for a large part of the malaria contracted by troops in the unsanitated parts of the Canal Zone, particularly on the Fort Sherman and Corundu military reservations, and that as a malaria vector in the Canal Zone it may rank next in importance to A. albimanus.
7.As A. punctimacula usually breeds in shaded jungle waters, while A. albimanus prefers water exposed to sunlight, the methods now used for the control of the latter species are not applicable to the former. Thus the observations reported in this paper introduce another important practical problem in mosquito control for solution by those responsible for the prevention of malaria in the Panama Canal Zone.
Lieut. Colonel, Medical Corps, United States Army.
With the technical assistance of Sergeant C. G. Heilmann, and Privates First Class, W. C. Dunscombe, G. C. White, and J. D. Bartecchi, Medical Department.