Mealybug transmission of grapevine-leafroll associated viruses

Grapevine leafroll disease is caused by grapevine leafroll associated viruses (GLRaVs). Several GLRaVs have been shown to be transmitted from vine to vine by mealybugs. Within this virus complex, GLRaV-3 is the most predominant species in the world. The invasion of the vine mealybug (Planococcus ficus) in California may result in increased disease incidence of established GLRaV-3 throughout the state. We studied characteristics of GLRaV-3 transmission [effect of acquisition and inoculation access period (AAP and IAP, respectively), latent period, virus retention, and persistence of infectivity] by the vine mealybug. Our results indicate that the vine mealybug transmits GLRaV-3 in a semi-persistent manner. First instar mealybugs were more efficient vectors than adult mealybugs. Virus transmission occurred with a 1-hour AAP and peaked with a 24-hour AAP. Vine mealybugs inoculated GLRaV-3 with a 1-hour IAP, and transmission efficiency increased with longer plant access period up to 24 hours, after which transmission rate remained constant. In addition, vine mealybugs transmitted GLRaV-3 with a short latent period. After an AAP of 48 hours, vine mealybugs lost GLRaV-3 and infectivity four days post-acquisition feeding. In summary, we systematically analyzed the transmission parameters of GLRaV-3 by the vine mealybug. This information will be valuable for the development of leafroll disease management practices.