Sirex noctilio (Sirex woodwasp) - Fact Sheet

Identification

Adult wasps have four clear yellow membranous wings.Footnote 1 Both sexes also have a stout, cylindrical body measuring 9 to 36 mm and a pointed abdomen.Footnote 2 Footnote 1 Males have thickened, black hind legs and orange-yellow middle segments on the abdomen.Footnote 2 Footnote 1 Females have reddishbrown legs and a steel-blue body.Footnote 2 Footnote 1 Females also have a spike-like projection on their abdomen, which protects the ovipositor.Footnote 2 Footnote 1

Host Trees

Pinus (main host), Abies and Picea.Footnote 2 Footnote 1 Footnote 3

Location of Infestation within the Tree

Along the lower or middle portion of the bole, larvae feed on a symbiotic fungus within the sapwood and heartwood.Footnote 1 Footnote 4 Footnote 5 Footnote 6

Host Condition

Healthy and stressed trees (e.g. logging damage, drought, fire) or dead stems.Footnote 2 Footnote 7 Footnote 8 Footnote 9

Distribution

Europe, northern Africa, Mongolia, Siberia and Turkey. Introduced to Australia, New Zealand, South Africa, Argentina, Brazil, Uruguay and eastern North America.Footnote 2 Footnote 1 Footnote 10

Signs and Symptoms

Females use their saw-like ovipositor to cut oviposition holes 12 mm into the wood of the host tree.Footnote 1 Footnote 9 Up to 5 holes are drilled into the outer sapwood.Footnote 1 The spores of a symbiotic white rot fungus (Amylostereum areolatum), which are fed upon by the larvae, and a toxic mucus are injected into the sapwood by ovipositing females.Footnote 2 Footnote 1 Up to three eggs are laid per oviposition hole.Footnote 2 Footnote 1 The fungus and the mucus act together to kill the tree and create a suitable environment for developing larvae.Footnote 2 Footnote 1 Footnote 11 Footnote 12 When the bark is removed, a dark fungal stain can be seen extending vertically from each oviposition site.Footnote 2 Footnote 13

Larval galleries, 5 to 20 cm long, are packed with chewed wood and a fine powdery frass.Footnote 2 Footnote 1 These galleries occur at all depths in the sapwood and heartwood, even to the centre of large trees.Footnote 2 The length of the gallery and the size of the developing wasps are dependent upon the moisture content of the wood.Footnote 2 If the wood is dry, the galleries will be short, the smaller larvae will pupate earlier and become adults at a smaller size.Footnote 2 Mature larvae pupate close to the bark surface.Footnote 2 Adults emerge through circular emergence holes 3 to 8 mm in diameter.

Symptoms of attack also include beads of resin flowing from oviposition holes.Footnote 2 Footnote 4 Needles on attacked trees wilt and turn from green to yellow and finally to reddishbrown. Footnote 2 Stem growth is drastically reduced as a result of attack.Footnote 4 Mortality occurs in heavily infested trees.Footnote 2

Male Sirex noctilio. Note black hind legs and orange-yellow middle segments on abdomen.
A - Male S. noctilio. Note black hind legs and orange-yellow middle segments on abdomen.
Female Sirex noctilio. Note brown legs and steel-blue body.
B - Female S. noctilio. Note brown legs and steel-blue body.
Sirex noctilio larval gallery (5-20 centimetre long). Note chewed wood lining the gallery.
C - S. noctilio larval gallery (5-20 cm long). Note chewed wood lining the gallery.
Frass-filled Sirex noctilio larval galleries.
D - Frass-filled S. noctilio larval galleries.
Circular Sirex noctilio exit holes (3-8 millimetre wide).
E - Circular S. noctilio exit holes (3-8 mm wide).
Resin flowing from Sirex noctilio oviposition holes.
F - Resin flowing from S. noctilio oviposition holes.
Reddish-brown crowns on Sirex noctilio attacked trees.
G - Reddish-brown crowns on S. noctilio attacked trees.

Photo credits

  • A Forestry and Agricultural Biotechnology Institute, University of Pretoria, South Africa
  • B Forestry and Agricultural Biotechnology Institute, University of Pretoria, South Africa
  • C Gyorgy Csoka, Hungary Forest Research Institute, Image 1231228, www.invasive.org, Feb. 5, 2004
  • D Forests New South Wales, Department of Primary Industries, Australia
  • E Forestry and Agricultural Biotechnology Institute, University of Pretoria, South Africa
  • F Forest Research, New Zealand
  • G Forest Research, New Zealand
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