Sirex noctilio (Sirex woodwasp) - Fact Sheet

Identification

Adult wasps have four clear yellow membranous wings.22 Both sexes also have a stout, cylindrical body measuring 9 to 36 mm and a pointed abdomen.4, 22 Males have thickened, black hind legs and orange-yellow middle segments on the abdomen.4, 22 Females have reddishbrown legs and a steel-blue body.4, 22 Females also have a spike-like projection on their abdomen, which protects the ovipositor.4, 22

Host Trees

Pinus (main host), Abies and Picea.4, 22, 42

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.22, 59, 107, 113

Host Condition

Healthy and stressed trees (e.g. logging damage, drought, fire) or dead stems.4, 105,116, 131

Distribution

Europe, northern Africa, Mongolia, Siberia and Turkey. Introduced to Australia, New Zealand, South Africa, Argentina, Brazil, Uruguay and eastern North America.4, 22, 125

Signs and Symptoms

Females use their saw-like ovipositor to cut oviposition holes 12 mm into the wood of the host tree.22, 131 Up to 5 holes are drilled into the outer sapwood.22 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.4, 22 Up to three eggs are laid per oviposition hole.4, 22 The fungus and the mucus act together to kill the tree and create a suitable environment for developing larvae.4, 22, 110, 118 When the bark is removed, a dark fungal stain can be seen extending vertically from each oviposition site.4, 114

Larval galleries, 5 to 20 cm long, are packed with chewed wood and a fine powdery frass.4, 22 These galleries occur at all depths in the sapwood and heartwood, even to the centre of large trees.4 The length of the gallery and the size of the developing wasps are dependent upon the moisture content of the wood.4 If the wood is dry, the galleries will be short, the smaller larvae will pupate earlier and become adults at a smaller size.4 Mature larvae pupate close to the bark surface.4 Adults emerge through circular emergence holes 3 to 8 mm in diameter.

Symptoms of attack also include beads of resin flowing from oviposition holes.4, 59 Needles on attacked trees wilt and turn from green to yellow and finally to reddishbrown. 4 Stem growth is drastically reduced as a result of attack.59 Mortality occurs in heavily infested trees.4

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