Transmission of Grapevine leafroll-associated virus-1 (Ampelovirus) and Grapevine virus A (Vitivirus) by the Cottony Grape Scale, Pulvinaria vitis (Hemiptera: Coccidae)

Abstract

The cottony grape scale Pulvinaria vitis is a scale insect colonizing grapevine; however, its capacity as a vector of grapevine viruses is poorly known in comparison to other scale species that are vectors of viral species in the genera Ampelovirus and Vitivirus. The ability of P. vitis to transmit the ampeloviruses Grapevine leafroll-associated viruses [GLRaV]-1, -3, and -4, and the vitivirus Grapevine virus A (GVA), to healthy vine cuttings was assessed. The scale insects used originated from commercial vine plots located in Alsace, Eastern France. When nymphs sampled from leafroll-infected vineyard plants were transferred onto healthy cuttings, only one event of transmission was obtained. However, when laboratory-reared, non-viruliferous nymphs were allowed to acquire viruses under controlled conditions, both first and second instar nymphs derived from two vineyards were able to transmit GLRaV-1 and GVA. This is the first report of GLRaV-1 and GVA transmission from grapevine to grapevine by this species.

Keywords: Betaflexiviridae; Closteroviridae; Coccidae; Vitis vinifera; soft scale.

Figure 1

(a) Pulvinaria vitis specimens on a grapevine. Left: female with ovisac. Red arrow: three empty plate-like tests or “puparia” of males. (b) Second instar nymphs (L2) of P. vitis on a grapevine leaf, with honeydew drops. (c) Crawlers of P. vitis fed across a Parafilm^TM membrane stretched over a drop of purified virions added with methylene blue. Blue stain is visible in the gut of the nymph.

Figure 2

Agarose gel electrophoretic analysis of DNA fragments amplified from Pulvinaria vitis crawlers fed with purified GVA virions by reverse transcription-polymerase chain reaction (RT-PCR). L: 100-bp DNA ladder; lanes a to c: batches of P. crawlers fed on purified GVA virions collected on Parafilm^TM membrane; lane a: batch of 10 crawlers; lane b: batch of 20 crawlers; lane c: batch of 30 crawlers; lane d: batch of 30 crawlers non feeding on purified GVA virions and collected from the box wall; lane e: purified GVA virions; lane f: healthy control = water with primers; lane g: leaf extract of the accession Y258 used as positive control for GLRaV−1, GLRaV−3 and GVA; 1 = GVA band (524 bp), 2 = GLRaV−1 band (382 bp), 3 = GLRaV−3 band (282 bp).