The VT isolate of citrus tristeza virus was transmitted efficiently by ten aphids (36%), and even with five aphids per test plant substantial transmissions (11%) were obtained. No transmission was obtained from acquisition or infection feeding periods of 5 minutes, and about 6 hours for each period was required to obtain near-maximal transmissions. Melon aphids retained inoculativity after 3.5 hours of post-acquisition fasting and when feeding for 2 or 6 hours on an intermediate cucumber plant or lime seedling, respectively. These features are characteristic of a semipersistent mode of transmission.