Diversity of ampeloviruses in mealybug and soft scale vectors and in grapevine hosts from leafroll-affected vineyards

The occurrence and diversity of Grapevine leafroll-associated virus 1 (GLRaV-1) and Grapevine leafroll-associated virus 3 (GLRaV-3) in the soft scales Parthenolecanium corni and Pulvinaria innumerabilis and in the mealybug Pseudococcus maritimus was determined in leafroll-affected vineyards in the Finger Lakes region of New York. Groups of 1 to 4 specimens were collected under loose grapevine bark and tested by reverse-transcription polymerase chain reaction (RT-PCR) for segments of the second diverged copy of the GLRaV-1 coat protein gene or GLRaV-3 heat-shock protein 70-homologue gene. Virus-specific RT-PCR products were amplified from immature insect vectors and adult mealybugs. Single viral amplicons were obtained mostly from immature vectors (35%, 30 of 85) and dual viral amplicons from immature (16%, 10 of 61) and adult (100%, 14 of 14) mealybugs, including individuals. These observations suggested a simultaneous uptake of GLRaV-1 and GLRaV-3 by individual mealybugs. Furthermore, a comparative nucleotide sequence analysis of viral amplicons from soft scales, mealybugs, and grapevines from which vectors were collected showed identical or highly similar haplotypes, indicating that uptake of GLRaV-1 and GLRaV-3 likely occurred by direct feeding of vectors on their host plants.