Haemagogus spegazzinii falco Kumm et al. (1946) is the proved vector of jungle yellow fever in the endemic region around Villavicencio, in the Intendencia of Meta, Colombia. This species has been found naturally infected with yellow fever virus on many occasions. Bates (1949) states that this species and the closely related H. spegazzinii Brethes have been found infected at least 17 different times in Colombia and Brazil.
Several observers have noted the difficulty in finding the larval breeding places of this and closely related species in numbers sufficient to account for the swarms of adults which can be captured on elevated platforms in the forest. Causey and Dos Santos (1949) mention the scarcity of larvae of H. spegazzinii in the region around Passos, in Minas Geraes, Brazil. Bugher et al. (1944) state: “larvae (of H. falco) in nature are found almost entirely in tree-holes, but this finding is irregular and the number found does not always seem commensurate with the population of adult mosquitoes.”