Transmission of filaree red-leaf virus (FRLV) byAcyrthosiphon pelargonii zerozalphum(Knowlton) was further characterized. Acquisition and inoculation efficiencies were similar at 20 and 25°C, but young larvae were more efficient than apterae. The proportion of aphids transmitting virus/hour of inoculation access time tended to decrease exponentially with time.The median latent period in larvae that were born on and that acquired virus from FRLV-infected white-stem filaree,Erodium moschatumL'Her., was ca. 48 h at both 20° and 25°C. The average retention period was 9.5 days at 20° and 7 days at 25°C. Infective aphids lived as long and produced as many larvae as did noninfective ones.Twelve-day old aphids that had acquired virus as 1st instar jarvae, and whose rate of transmission had declined increased their rate of transmission after being fed on a virus source. Another latent period followed the 2nd acquisition access period. The maximum rate of transmission following reacquisition of virus was less than that attained after the initial larvae acquisition feeding, but it was comparable to that found with aphids that first acquired virus when they were 12 days old.