Transmission of grapevine leafroll-associated virus 3 by the vine mealybug (Planococcus ficus)

Grapevine Leafroll associated-Viruses (GLRaVs) are an emerging pathogen complex which causes Grapevine Leafroll Disease, characterized by changes in leaf pigmentation, delayed fruit development, and downward rolling of leaves. Several mealybug spp. (Hemiptera) transmit GLRaVs. The invasive vine mealybug (Planococcus ficus) is found in all major grape growing regions throughout the world, and, in areas where it has been introduced, it may contribute to increased disease spread. We investigated the transmission biology of GLRaV-3, the most predominant GLRaV species, by the vine mealybug. Transmission rates between first instars and adults were compared for the vine mealybug. First instars were found to be more efficient vectors than adults. To compare transmission rates among species, we repeated this experiment with obscure (Pseudococcus viburni), longtailed (Pseudococcus longispinus), and vine mealybugs using an acquisition access period (AAP) and inoculation access period (IAP) of 48 hrs each. In additional experiments, vine mealybug transmission of GLRaV-3 occurred with a 1 hr AAP, but peaked with a 24 hr AAP. As we increased IAP to 24 hrs, transmission efficiency increased proportionally, but remained constant after 24 hrs. Further transmission studies indicated that transmission of GLRaV-3 by the vine mealybug is semi-persistent. Such information is valuable to understanding agricultural disease systems and the development of effective disease management practices.