This is a final research report from Hort Innovation’s historical archives. Please note that as these reports may date back as far as the 1990s, the content and recommendations within them may be superseded by more recent research.

What was it all about?

Victoria produces more than 25 per cent of Australia’s apple production. A major economic cost to apple growers was the use of insecticides to control pests. The woolly apple aphid (WAA) was a serious pest of apples in Australia and over the previous ten years reports of its incidence had increased. It induced galls on foliage and underground parts of apple trees and also produced honeydew, which on the leaves and fruit forms a reservoir for sooty mould, reducing fruit quality and marketability and photosynthetic efficiency. Severe infestations on young trees caused stunting or even death. Woolly apple aphid was becoming a major problem for apple growers at the time, who were attempting to follow world best practice by adopting intensive production systems and reducing broad-spectrum pesticide usage. Over recent years, partly due to a reduction in use of pesticides, but also because of the use of susceptible rootstocks (including seedling stocks in ‘conventional’ plantings), WAA incidence had increased. Many growers were now routinely treating trees with chemicals to control woolly apple aphid. While this was effective on young trees, reliance on a single chemical group was unsustainable and would ultimately lead to WAA resistance to some pesticides.

The research team utilised their expertise in insect physiology, electrophysiology and applied entomology to develop a better understanding of the feeding interactions between the pest and its host-plant that and further research development this would lead to improved management of woolly apple aphid.

Developments within this project have included:

1.  Victorian grower survey highlighting woolly apple aphid distribution, infestation levels and management strategies
2. Developing a woolly apple aphid artificial diet rearing system which led to an improved understanding of the insects nutritional requirements and how this impacted on its interactions with its host-plant. Further developments in artificial diet formulation would lead to improved woolly apple aphid management.
3. An electrophysiological method called the EPG (Electrical Penetration Graph) was used to examine in fine detail the feeding behaviour of two woolly apple aphid populations on resistant and susceptible rootstocks.
4. A comparison of the feeding behaviour and survival of two geographically distinct woolly apple aphid populations, using both the artificial diet system and the EPG system, indicated that future management of WAA would be improved by considering the genetic diversity and geographical range of woolly apple aphid populations.