An In vitro feeding technique was developed to detect arbovirus transmission by mosquitoes. The technique was demonstrated to be as sensitive as engorgement upon suckling mice for the detection of yellow fever virus transmission by Aedes aegypti mosquitoes. In studies to determine the ability of geographic strains of Ae. aegypti to transmit yellow fever virus, the Caribbean strain was the most efficient transmitter; the African strain was intermediate: and the Asian strain was the least efficient.