1.In a malaria survey of Costa Rica 9,126 children in 168 different localities were palpated for splenomegaly, and 3,981 blood films were examined for malaria parasites.
2.The places with a high degree of endemic malaria were generally situated at elevations of less than 1,000 feet.
3.Plasmodium vivax and P. falciparum were found throughout the malarious regions of this Republic, whereas P. malariae was distinctly more common on the Pacific Littoral.
4.Fifteen species of Anopheles were obtained in the 175 localities studied for their anopheline fauna.
5.Anopheles albimanus was present in abundance in practically all of the endemic malarious regions, whereas A. argyritorsis attained its maximum prevalence where malaria did not occur.
6.The only anopheline to be found naturally infected with malaria parasites was A. albimanus.
7.Anopheles albimanus was the species most commonly taken inside houses and traps, whereas A. argyritarsis and A. pseudopunctipennis, though frequently found as larvae, were only rarely captured as adults.
8.We have no evidence as yet that any anopheline except A. albimanus acts as a natural vector of malaria in Costa Rica.