Semi-persistent viruses are those that can be carried by vectors from infected to healthy plants for several days at most. These viruses have less clearly defined transmission characteristics compared to non-persistent and persistent viruses. The efficiency of transmission increases as the length of acquisition and inoculation feeding times increases. There is no latent period, and the most likely time for transmission to occur is immediately after vectors leave the virus source. Pre-acquisition fasting does not affect the efficiency of transmission. These viruses are not transmitted to the vector’s progeny or present in the haemolymph, and they do not seem to pass through the moult.