Transmission of Grapevine Ampelo- and Vitiviruses by the Bohemian Mealybug Heliococcus bohemicus Šulc (Hemiptera: Pseudococcidae)

Grapevine-infecting ampelo- and vitiviruses are transmitted by several scale insect species, including the Bohemian mealybug, Heliococcus bohemicus Šulc. Virus infectivity experiments were performed with this species to study the transmission ability of natural populations living in infected vineyards in Alsace, France. Mealybugs were sampled on vines infected by grapevine leafroll-associated viruses (GLRaV-1, -2, and -3) and by grapevine virus A (GVA), either alone or in combinations. Out of six natural populations tested, only one, located at Bennwihr, was able to transmit GLRaV-1 and -3 to healthy vines, though with low transmission rates (1.6 and 11.8%, respectively). Mealybugs from Bennwihr were also able to transmit GLRaV-3 from grapevines of another location where H. bohemicus was not a vector. Conversely, mealybugs from two other locations did not transmit any virus acquired from infected grapevines at Bennwihr. These results suggest differences in vector ability between H. bohemicus populations. Moreover, laboratory experiments were developed to estimate the minimal acquisition and inoculation access periods (AAP and IAP, respectively) for virus transmission of GLRaV-1 and -3, and GVA. First instar nymphs transmitted GLRaV-1 after 6 h AAP, GLRaV-3 and GVA together after 1 h AAP, and the three viruses after only 1 h IAP, supporting a semi-persistent mode of transmission. Second instar nymphs fed on multi-infected grapevine for 72 h then starved or fed on potatoes tested positive by RT-PCR for GLRaV-1 and -3 after up to 35 and 40 days, respectively, contrasting with the short retention times generally observed for mealybugs. These findings provide new knowledge of the vector ability of H. bohemicus.