EPG analysis of Citrophilus mealybug, Pseudococcus calceolariae (Hemiptera: Pseudococcidae), feeding behaviours on Sauvignon blanc plants

Abstract

Citrophilus mealybug, Pseudococcus calceolariae (Hemiptera: Pseudococcidae), is one of the two mealybug species mostly responsible for transmitting grapevine leafroll-associated virus 3 (GLRaV-3) in New Zealand vineyards. Electropenetrography (EPG) is used to quantify feeding behaviours of sap-sucking insects such as mealybugs. EPG involves connecting an insect to an electrical circuit using a fine wire and placing it on a plant that is also part of the circuit. When the insect inserts its mouthparts (stylet) into the plant, changes in electrical resistance are recorded, creating waveforms that can be then analysed and feeding behaviours quantified. EPG is currently the only technique available to quantify the feeding behaviours of Citrophilus mealybugs on grape plants. This study investigates the utility of using EPG to determine feeding behaviour of Citrophilus mealybugs on New Zealand’s most planted grapevine variety, Sauvignon blanc. For our experiments, second or third instar Citrophilus mealybugs were tethered to a very fine gold wire (18.5 µm diameter) using silver adhesive. Insects were then placed onto the abaxial side of the third or fourth expanded leaf of young Sauvignon blanc plants. A voltage was applied to the plant and the resulting electrical signals were recorded over a 24-hour period. Stylet penetration activities, and xylem and phloem ingestion, were quantified. Results from this study will allow future work to compare feeding behaviours of Citrophilus mealybugs on grape plants differing in their concentrations of secondary compounds and thus in the level of tolerance/resistance to mealybug attack. The results will also allow us to screen for dose-related responses by the mealybugs in relation to the levels of secondary metabolites and how breeding programmes could be tailored to maximise mealybug resistance and therefore minimise virus transmission.