Comparative Acquisition, Transmission, and Retention of Distinct Grapevine Red Blotch Virus Isolates in Relation to the Genotype and Sex of Spissistilus festinus, the Treehopper Vector.

Grapevine red blotch virus (GRBV), the causal agent of red blotch disease of grapevines, is transmitted by Spissistilus festinus, the threecornered alfalfa hopper. Isolates of GRBV belong to two phylogenetic clades (I and II) and S. festinus is a dimorphic insect, with two genotypes found in the western (California, CA) and the southeastern (SE) regions of the United States. The transmission of GRBV by S. festinus is circulative and nonpropagative, yet some parameters of transmission remain to be characterized. Here, we compared the acquisition, transmission, and retention of GRBV isolates from phylogenetic clades I and II by S. festinus males and females of the two genotypes. Results indicated that the SE genotype acquired GRBV more efficiently (72.5%, 29/40) than the CA genotype (22.5%, 18/80), with differences in acquisition observed between males (32.5%, 26/80) and females (52.5%, 21/40) of the two S. festinus genotypes and between GRBV isolates of phylogenetic clades I (29%, 23/80) and II (60%, 24/40). Following acquisition, both S. festinus genotypes and sexes retained GRBV isolates of phylogenetic clades I and II for at least 60 days without access to an infected plant. For transmission, the GRBV isolate of phylogenetic clade II was more efficiently transmitted by the SE genotype (54%, 13/24) than the CA genotype (17%, 4/24) and SE females (75%, 12/16) were significantly more efficient transmitters of GRBV than CA females (19%, 3/16). Together, our findings revealed that S. festinus genotype, sex, and virus isolate influence GRBV acquisition and transmission but not retention. This research addressed important knowledge gaps in S. festinus-mediated transmission of GRBV that are essential for advancing red blotch disease epidemiology and developing appropriate disease management responses.