Efforts to combat giant pine scale gather pace in Australia

Giant pine scale, which is native to pine forests in the Eastern Mediterranean region, has become established in Melbourne on Pinus radiata. It is also known to infest other softwood conifers such as spruce, cedar and fir. If not addressed, it has the potential to cause extensive damage to the Australian pine resource.

As part of a collaborative project between LaTrobe University and Western Sydney University, a team of researchers is working to discover more about the little understood pest, to develop insights that will help guide future interventions.

“The biology and ecology of the insect in Australia and Europe is poorly understood, which limits our capacity to predict its pest potential and the likely efficacy of management using a classical biological control approach,” said Associate Professor Martin Steinbauer from La Trobe University.

The team is therefore using a range of methods, including regular field surveys of scale abundances and lifecycle stages, studies of the growth of infested pine trees, and measurements of tree vigor and its impact on infestation success. 

The giant pine scale excretes excess sap as honeydew, a food source that attracts other invasive insects including exotic species of ant, European wasps and feral honeybees. The team is therefore also observing communities of such insects, to help address a range of fundamental questions.

The research will provide important insights into giant pine scale in Australia, specifically around the damage it has the potential to cause, when and where this damage is likely to occur, and the extent to which other species might facilitate invasion beyond current infestations.

Could chemicals have the answer?

A team from HVP Plantations has recently completed a research study into potential chemical treatments for giant pine scale. The goal was to explore which insecticides and application methods showed the most promise for the reduction of scale populations.

Field trials were conducted across numerous sites, with numerous treatments applied to trees of various sizes. These treatments consisted of six insecticides applied at a variety of rates and using numerous application techniques, ranging from foliar spray to stem injection, bark spray and soil drench.

Following treatment, branches were removed from the trees at three and nine months, with the number and life stage of giant pine scale present being assessed.

During the early phases of testing, two insecticides were found to significantly reduce giant pine scale abundance, namely dimethoate and clothianadin. Stem injections were found to be the most promising application technique for larger trees, while foliar treatments were shown to have more potential in very small trees. However, during subsequent phases retreatment with higher rates did not reduce giant pine scale levels to zero.

While this project did not identify a ‘silver bullet’ for the chemical treatment of giant pine scale, the work has demonstrated the best approach we currently have for controlling infestations is to remove the impacted trees and help slow the spread.

To this end, growers from across Australia have allocated funds to support landowners to remove infested trees, while research around other possible interventions continues.

An international effort

A team of Agriculture Victoria research scientists at the AgriBio Centre for AgriBioscience is undertaking research that will assess the risks associated with the introduction of one potential biological control agent for giant pine scale, and determine its suitability for long-term, sustainable management in Australia.

“Many people are unaware of the years of research, detailed risk analysis and stakeholder and public consultation that is required before any new biocontrol agent can be released,” said Greg Lefoe of Agriculture Victoria.

If results are promising, the team will prepare an application to introduce the agent locally, to complement other management practices aimed at preventing or slowing the spread of giant pine scale into softwood plantations.

The work comes after a previously completed feasibility study conducted by Agriculture Victoria, which involved field surveys in Greece and Italy, and identified the fly species Neoleucopis as having considerable potential for use as a biological control agent.  

This project is building on the outcomes of this study by conducting additional work in Greece, applying morphological and molecular techniques to confirm which species of Neoleucopis will be most effective, as well as studying reproductive behaviour to inform the development of rearing techniques.

“We’re particularly interested in discovering more about the extent to which Neoleucopis preys on giant pine scale, and whether it attacks other insect species that may be present,” said Lefoe.

“The results of this aspect of our work have so far been very positive. Neoleucopis has proven its potential as an important predator of giant pine scale, and our team has found no evidence of off-target attack.”

The team in Greece is also working to understand the most appropriate rearing methods for the development of colonies in a laboratory setting, including optimal conditions and requirements for mating, egg-laying and growth. 

“While lab rearing is not always straightforward, the team in Greece has recently successfully reared its first colony, which represents quite a milestone,” said Lefoe. 

“They’ll now focus on refining their methods to produce more agents, more reliably, and then ship them for quarantine in Australia.”

Back in Australia, the team has been working to demonstrate that the proposed biocontrol agent will not represent a threat to Australian agriculture or biodiversity. Most at risk from its introduction would be Australian native scale insects, meaning a large segment of the work will be focused on exposing Neoleucopis to a range of native scale insects during lab experiments.

“Because very little is known about Australian scale insects, much of our early work has focused on identifying them with morphological and molecular techniques, and gathering data on their distribution across the country and what they use for food,” said Lefoe.

“Thanks to the work of the Agriculture Victoria team and our native scale specialist - Penny Mills of the University of Queensland - we are now at the stage where we can commence the laboratory rearing process here in Australia, and are awaiting a shipment of the biocontrol agent from Greece.”