This project built on the outcomes of FST/2011/028 “Biological control of Eucalypt pests overseas and in Australia”, which defined the need for biological control in the Mekong region, and identified Leptocybe invasa as the priority pest. The recommendation was that priority be given to establishing a regional, large-scale project in South East Asia (referred to throughout as SE Asia) focussed on biological control of the blue gum chalcid as the core activity, including strengthening the capacity to detect and monitor native and exotic forest pests in eucalypt plantations.
The core component of this project was to provide the R&D underpinnings to support the successful development of a biocontrol agent for L. invasa, with the initial task of determining the distribution of L. invasa and any existing natural enemies that could provide a local biological control option. No natural enemies were found, but the Australian parasitoid Quadrastichus mendeli was recorded and is well established in the region providing some control. Redistribution of the parasitoid into areas of high gall abundance would increase its efficacy, however, the release of an additional biocontrol agent, Selitrichodes neseri, would prove even more effective as has been shown in other countries which employ multiple control agents. It was thought that Q. mendeli may have arrived from Israel or India where it weleased as part of biocontrol programs. However, sequencing indicates a much more complex introduction history than first thought, indicating the introduction is likely from Australia. A key Australian component was to establish Australia as the putative source for L. invasa, however, surveys in Australia have failed to find L. invasa (Lineage A). Leptocybe Lineage B, previously referred to as Leptocybe sp. 9, was widespread across eastern Australia and genetic variation in these populations is wide, whilst populations in the Mekong region are very limited, suggesting a more recent introduction. Both lineages were present in the Mekong.
Prior to this project, no other biological control agent for forest pests had been developed and released in the region. Time was invested in developing the infrastructure, procedures and the technical capacity for identifying, testing, rearing and releasing a new biocontrol agent into the Mekong. Based on its efficacy and host specificity, S. neseri was selected as the most effective and safe control agent. In 2017, S. neseri was imported into the new quarantine facility where it underwent host and behavioural tests to ensure its specificity. Permission to release S. neseri was granted in 2019, with the first field release taking place in December 2019.
The project has created a collaborative multi-country network with an emphasis on developing the capacity of partners in technical and scientific aspects of biological control and forest health research and management. Plant quarantine staff were supported in developing quarantine and biosecurity policy and procedure for the import of S. neseri and pest checklists were compiled to meet phytosanitary and quarantine requirements for trade. In addition, colleagues liaised with local industry to deliver training on important Eucalyptus pests and forest health surveillance techniques to improve management strategies.
For all these successes, there have been challenges throughout. The biggest was modifying project activities to accommodate the shift away from planting susceptible varieties by industry. Leptocybe pest pressure became so intense that many producers either stopped planting eucalypts or planted non-susceptible hybrids or other tree species. This meant less emphasis on assessing the economic impact of L. invasa and more on grassroots-community and whole country assessment of the wasp’s impact. The project came to focus on working with local partners to deliver a sound control program to reduce the impact on productivity, and ultimately livelihoods. Although L. invasa is currently the key threat to eucalypt plantations in the region, it is only one of a suite of eucalypt insects spreading across the world. This project has increased the Mekong region’s capability to effectively and rapidly respond to these future threats and protect the regions planted and native forest resources.