Stylet penetration behaviour of Pseudococcus longispinus in relation to acquisition of grapevine leafroll virus 3

Abstract

Grapevine leafroll–associated virus-3 (GLRaV-3) is transmitted from infected grapevines to healthy vines by mealybugs. The stylet penetration behaviour of Pseudococcus longispinus (Hemiptera: Pseudococcidae) was electronically monitored on leaves of grape plants to quantify the time taken to access the phloem and the duration of phloem ingestion. More of the first instar nymphs than of the adults showed sustained (>10 min) phloem ingestion; however, nymphs were affected adversely by longer monitoring periods. The probing and phloem ingestion periods of adults on GLRaV-3-infected Red Globe and uninfected Pinot noir were not significantly different from each other. Most adults showed the first phloem ingestion and the first sustained phloem ingestion after 12 h and after 24 h of their first probe, respectively. Free (unwired) and electrical penetration graph (EPG)-monitored (wired) P. longispinus adults were tested for acquisition of virus after different acquisition access periods (AAP). Acquired GLRaV-3 RNA in extracts of whole insects was detected by reverse transcription and polymerase chain reaction amplification. For the unwired adult mealybugs, 30 % that had an AAP of 48 h and 90 % that had an AAP of 72 or 96 h were positive for GLRaV-3. Five out of 24 (21 %) of the wired mealybugs allowed at least 24 h APP (1.8–44.4 h of phloem ingestion) were positive for GLRaV-3. None of the adult mealybugs acquired virus during the first 24 h of AAP. We conclude that GLRaV-3 acquisition by P. longispinus generally occurs within 24–72 h AAP with as little as 1.8 h of phloem ingestion.