Friday 10 Oct 2014
   
Symbiotic fungus provides early warning of invasive and minimises forestry loses  
   

Problem statement: In 1994, while conducting research on another forestry pest, the disintegrated body parts of a metallic bluish-black wasp were found under the bark of a 40 year old Pinus radiata tree which had been felled and then rejected in a plantation outside Cape Town. Further examination revealed round exit holes similar to those described in the literature for the woodwasp Sirex noctilio, a forestry pest previously unknown in South Africa. S. noctilio originates in Eurasia and North Africa where it attacks stressed conifer species. It has since spread to plantations in other parts of the world, killing up to 70 percent of trees.

Methods: It was not possible to identify the wasp from its remains, so a sample of the wood was sent to the mycology division of the National Collection of Insects in Pretoria where it was cultured to test for the presence of a symbiotic fungus (Amylostereum areolatum). Female woodwasps inject trees with A. areolatum along with a mucus just prior to laying their eggs. Once the larvae hatch they feed on the fungus within the wood, making a U-turn when the less nutritious heart-wood is reached, and eventually pupate in the wood below the bark, before emerging as adult woodwasps after about a year. The presence of this symbiotic fungus would indirectly confirm the presence of the woodwasp.

Outcomes and impacts: Analysis confirmed the presence of A. areolatum and hence the woodwasp. The confirmation came a year before the first wasp specimen was captured. Early warning of the woodwasp’s presence allowed an immediate start to be made on the importation of biological control agents that had worked successfully in Australia and New Zealand. Within a year, the key parasitic nematode Deladenus siricidicola, had been introduced, followed a year later by other biological control agents: Hymenopterous parasitoid Ibalia leucospoides and then by Megarhyssa nortoni.

Between 1994 and 2001 the woodwasp spread 380km along the west and east coasts but successful biological control meant that at no point were more than 3 per cent of the trees lost.

Lessons: The speed with which biological control was implemented after the indirect identification of the woodwasp was directly responsible for the minimal losses experienced by the forestry industry of South Africa. Taxonomic expertise was essential for the early detection of the invasive pest and for design of the biocontrol programme that contained the threat.


References:

1. Baxter, A.P., Rong, I.H. & Schutte, et a.l. 1995. Amylostereum areolatum (Aphyllophorales: Stereaceae) in South Africa. South African Journal of Botany 61 (6): 352-354. 2. Bedding,R.A. 1993. Biological control of Sirex noctilio using the nematode Deladenus siricidicola. In: Bedding, R.A., Akhurst, R.J. & Kaya, H. (Eds) Nematodes and the Biological Control of Insect Pests. 11 – 20. CSIRO, Australia. 3. Neumann, F.G., Morey, J.L. & McKimm, R.J. 1987. The Sirex wasp in Victoria. Department of Conservation, Forests and Lands. Bulletin No. 29, 41pp. 4. Tribe, G.D. 1995. The woodwasp Sirex noctilio Fabricius (Hymenoptera: Siricidae), a pest of Pinus species, now established in South Africa. African Entomology 3: 215-217.

Contributor:

G. D. Tribe, Plant Protection Research Institute, Private Bag X5017, Stellenbosch 7599, South Africa. email: vredgt@plant3.agric.za

Regions:

Africa

Themes:

forestry

 
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