Understanding the fundamental interactions between grapevine Phylloxera and Vitis species

Abstract

A PhD student project examined fundamentals of grapevine phylloxera feeding behaviour. Developed an in vitro feeding bioassay to determine phylloxera nutritional requirements which would allow rapid screening of novel antimetabolites. Modified and electrophysiological monitoring system to characterise phylloxera feeding behaviour on susceptible grapevines. Conducted detailed study on morphology of phylloxera digestive system.

Summary

Clarification of fundamental interactions between grapevine phylloxera and Vitis species was seen as a major deficiency in knowledge. Previous research, for example, had left some things unclear about how this insect feeds (although described as “aphid like” it differs in feeding behavior and digestive characteristics). To address this, a major study with several sub programs was instigated. A key component was a GWRDC-funded PhD scholarship awarded to Kim Kingston. Several techniques which had been applied for understanding other sap-sucking insects and their interactions with their host plants were tested and modified. These included: molecular techniques to identify bacterial endosymbionts (concerning micro-organisms living within insects); electrophysical ways of characterising feeding behavior (using wires attached to the insect while it feeds, with behavior changes identified by electrical waves); microscopy for detailing internal and external morphological features; and use of artificial diets to assess essential nutritional requirements. The overall result has been a significant contribution to knowledge of phylloxera and the insect’s requirements of its host. Electrophysical techniques, for example, were able to expand on the understanding of root feeding and reactions to resistant and susceptible rootstocks. A major outcome was development of the first artificial diet feeding system after experimenting with two feeding chambers and 20 diet formulations – this enabled identification of nutritional factors influencing feeding behavior. Importantly, the artificial diet work means there is now an ideal method for maintaining insect colonies for laboratory studies. Among other things, researchers were able to characterise the structure and biochemistry of grapevine phylloxera’s digestive and salivary system. Using light and electron microscopy techniques it was revealed that the insect has a modified gut structure and capacity to generate high egg production with minimal waste excretion. This project will be of great benefit to further research into grapevine phylloxera, expanding on knowledge of the insect and providing improved techniques for use in studies. For grape growers, who to date have really only had resistant rootstocks in their armoury, there is the prospect of other avenues of management arising from expanded knowledge of the pest’s behavior.