a1 *Yellow Fever Research Institute, Entebbe, Uganda.
1. The work was carried out in Bwamba County, Uganda, a district where human yellow fever has recently occurred. It consisted mainly of 24-hour catches in banana plantations and rain forest combined with climate observations.
2. It was found that forest was cooler and moister by day than a banana plantation while the plantation was cooler and moister than the open air. By night, however, the climate of all three environments was strikingly similar.
3. Methods used in making 24-hour catches and large scale routine catches are described. Trials with trap nets showed these to be less efficient than hand catching.
4. Experimental catches showed that Aëdes simpsoni, the only species known to be a vector of yellow fever in Bwamba, bites mainly in coffee gardens, maize fields and the thinner parts and edges of banana plantations. It is scarce in fully exposed situations. It occurs within the edges of primeval rain forest. It prefers human blood to that of goats, fowls, and monkeys, and attacks the head and shoulders selectively.
* (This Institute is supported jointly by the Medical Department of the Uganda Protectorate and the International Health Division of The Rockefeller Foundation.).