Sirex and the white rot fungus, Amylostereum areolatum, have an obligate mutualistic relationship. Adult female sirex lay eggs in conifer species and simultaneously deposit a phytotoxic mucus/venom and the fungus, which weakens tree defences and eventually kills trees. The fungus derives protection, dispersal and placement into ideal conditions, while sirex is reliant on the fungus for development and nutrition of larvae.
Control of sirex wasp is achieved through an integrated combination of activities:
1. Managing pine plantations for reduced susceptibility by thinning on schedule and reducing the number of stressed trees.
2. The historical release of a number of parasitoid wasps which attack sirex larvae whilst in the tree. Of the wasps introduced into Australia, 4 have established and are active to varying degrees in areas where sirex has established in southern Australia. The most abundant is Ibalia leucospoides, which commonly reduces the sirex population by about 50% before the larvae can emerge. Other less abundant wasps include Schletererius cinctipes, Megarhyssa nortoni and Rhyssa persuasoria.
3. The most effective strategy for sirex suppression is biocontrol with the nematode Beddingia siricidicola. This nematode has a free living stage that reproduces in wood whilst feeding on A. areolatum, as well as a parasitic phase that infects sirex larvae and invades developing eggs so that adult female sirex lay packets of nematodes into trees rather than viable eggs. These nematodes move through the log and infest any healthy sirex larvae they intercept. Infested larvae continue to develop normally but will be sterile, resulting eventually in a collapse of the sirex population to low levels.
The nematode-based biocontrol program is ongoing in Tasmania, Victoria, NSW, ACT and Queensland and involves installation of trap tree plots (TTPs); groups of 10 trees treated with herbicide to create stress in the trees, thereby making them strongly attractive oviposition sites for sirex. Multiple TTPs are established every year in vulnerable forests to locally concentrate sirex. TTPs are inoculated with B. siricidicola and the emerging parasitised females disperse the biocontrol agent.
The Australian Sirex Control Strategy was developed by the NSCC in 1990 (National sirex control strategy 1990). The strategy was last updated in 2020 (Australian sirex management strategy 2021) and continues to guide current sirex control operations. It provides an outline of the sirex life cycle and the various management components.
Operations worksheets provide detailed guidance for plantation owners on the key steps to detect and monitor sirex activity, to undertake additional nematode releases in areas where sirex activity is rising or background levels of nematodes are low and to manage other biocontrol activities.
Worksheet 1: Monitoring sirex populations
Worksheet 2: Trap tree establishment
Worksheet 3: Nematode handling and inoculation
Worksheet 4: Evaluation of sirex biocontrol agents
Worksheet 5: Rearing of sirex parasitoids
Worksheet 6: Breeding nematode-free sirex
Field checklists have also been prepared to assist briefing of field crews for the major tasks.
- Trap tree plot establishment
- Monitoring trap tree plots
- Felling and inoculation of trap tree plots
- Billet collection and emergence monitoring
A comprehensive range of short-format video training resources for field crews have been prepared and are available on the NSCC Vimeo channel: https://vimeo.com/channels/1309879
As an example, one of the videos which helps crews to identify sirex struck trees is shown below:
A summary of the sirex life cycle and management options is also outlined in the following document, originally produced in 2001:Sirex noctilio, the pine-killing woodwasp.