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The use of an Immunoassay for the detection of Plasmodium falciparum and P. vivax circumsporozoite (CS) antigens in anophelines has recently incriminated other malaria vectors besides Anopheles darlingi in the Brazilian Amazon. In this study we analyzed 12,336 field-collected anophelines from endemic areas in Rondonia for plasmodial infection. Sixty-one specimens from 6 species were positive: 47 An. darlingi, 5 An. triannulatus, 4 An. albitarsis, 2 An. braziliensis, 2 An. strodei, and 1 An. oswaldoi. As concerns the species, 41 anopheles harbored P. falciparum and 20 were infected with P. vivax. An. darlingi was the most important local vector, as it was the one most frequently found infected and the only one clearly related to areas where malaria transmission was being recorded.

In view of recent studies incriminating several species of anophelines, besides Anopheles darlingi, as malaria vectors in the Brazilian Amazon, we performed an anopheline survey in four localities--Ariquemes, Cujubim, Machadinho and Itapoã do Oeste--in Rondônia, the most malarious State in the Country. Twenty species were found. An. darlingi was, by far, the dominant species and the only one whose density coincided with that of malaria. On human baits it was more numerous in the immediate vicinity of houses than indoors where, however, it was almost the only species encountered. On both situations it fed mostly at sunset and during the first half of the night. It was less numerous far from houses and scarce inside the forest. Other species (An. triannulatus, An. evansae, An. albitarsis, An. strodei) appeared in appreciable numbers only in Ariquemes, both in areas with and without malaria. The remaining species were scanty. An. darlingi was confirmed as the primary local vector.

By staining females of Anopheles cruzi with fluorescent coloured powders in a forest in the State of Santa Catarina, we showed that they move from canopy to ground and vice-versa to feed. This suggests that in areas where this mosquito is a vector of human and simian malarias sporadic infections of man with monkey plasmodia might be expected.