Twenty-six cities, towns and villages located in various parts of the northern half of Venezuela were visited and inspections made to determine the extent to which the breeding of the yellow fever mosquito, Aëdes aegypti, was occurring. Observations were also made at each place on the system of water supply and on other conditions having potential influence on the breeding and distribution of this species. In practically all the places visited, the system of water supply was found to be of such a nature as to necessitate the use of numerous containers for water storage in the houses, thus providing conditions favorable for breeding of domestic mosquitoes in the habitations. Fifteen of the cities and towns had a piped water supply—at least the better class houses had this convenience—but in only one town, San Cristobal, was the supply sufficient to provide running water in the houses at all hours of the day and night. The other 11 towns and villages depended for their supply on stored rain water, wells, and nearby rivers. In 14 of the places visited, water was observed being sold in the streets by venders.
In the 26 places visited, more than 3506 houses were inspected and 10,229 water containers were examined. No Aëdes aegypti breeding was found in 3 of the towns, Calabozo, Ortiz and San Cristobal. The other 23 places were all positive. In these 23 positive towns the house visits totaled 3255 and breeding was found in 1550, giving an average house percentage of 47.61.
The water containers examined in the 23 towns numbered 9616 and consisted of the following vessels: 2725 tinajas, 2053 ollas, 1822 barrels, 1083 pilas, 824 filter stones, 288 tanks, 23 ornamental fountains, and 798 miscellaneous containers. Of these vessels, mosquito breeding was found in 2752, or 28.61 per cent. The positive containers included 1020 tinajas, 990 barrels, 278 ollas, 232 pilas, 95 filter stones, 70 tanks, 5 ornamental fountains, and 62 miscellaneous vessels.