Sirex wood wasp

• Sirex adults lack the thin waist found in many wasp species.
• Females are dark, metallic blue with amber-coloured legs and wings. They have a prominent ovipositor (egg-laying apparatus, 'sting') projecting from below the abdomen.
• Males have a blue-black head and front section and an orange abdomen with a dark tip and no 'sting'.
• Females are 15–35mm long and males are 13–32mm long.
• Larvae are creamy white and have an obvious head, 3 pairs of very short legs and a segmented, cylindrical body with a typically dark spine at the rear end.
• Larvae live entirely within the host tree.

Similar species

• The exotic tremex wasp (Tremex fuscicornis) has been recorded on poplars (Populus species) and willows (Salix species) in New South Wales. Adults are very similar to S. noctilio but have shorter antennae.
• The giant woodwasp (Urocerus gigas) is a regulated quarantine pest posing a significant biosecurity threat to Australia. Males of the 2 species are very similar and require specialist identification. The U. gigas female, however, is quite distinct from S. noctilio, having a yellow (rather than black) abdomen with a broad black stripe across the middle. This wasp is not currently present in Australia.
• Other species of potential economic importance not present in Australia include:
  • horntail (Urocerus fantoma)
  • blue horntail (Sirex cyaneus)
  • steely blue wood wasp (S. juvencus)
  • Asian horntail (Eriotremex formosanus)
  • woodwasp (Xeris spectrum)
  • pigeon horntail (Tremex columbia).

• Tasmania, South Australia, Victoria and New South Wales
• Queensland's relatively temperate Stanthorpe region (in 2009), Pechey (in 2018) and Esk (in 2020)

Sirex wood wasp is not yet recorded in the main coastal plantations of Beerburrum and the Fraser Coast. However, climate-species models predict it could establish in most of Queensland's pine-growing regions.

Plantations at risk are generally 10–25 years old, although in Queensland older trees have been attacked.

Susceptible

• Radiata pine (Pinus radiata)
• Loblolly pine (P. taeda)
• Other pines grown outside Queensland such as Scots pine (P. sylvestris), Austrian pine (P. nigra), maritime pine (P. pinaster), ponderosa pine (P. ponderosa) and lodgepole pine (P. contorta)

Less susceptible

• Slash pine (P. elliottii)
• Caribbean pine (P. caribaea)
• Pine hybrids (P. elliottii var.  elliottii x P. caribaea var. hondurensis)

• Sirex females target stressed or damaged trees through early-stage attacks.
• Increasing wasp populations can attack and kill more vigorous trees.
• The Amylostereum areolatum fungus introduced by the female wasp disrupts the tree’s vascular system, causing the tree to decline.
• Larvae feed on the fungus, creating tunnels and degrading the timber.
• Damage signs include:
  • needle wilt (initially in older, then in newer foliage)
  • pale foliage, which becomes copper-coloured as it dries
  • fine pinholes (egg-laying sites) in the bark, often associated with beads and trickles of resin
  • circular adult exit holes (3–7mm in diameter) along the tree
  • brown or light yellow fungal staining of the cambium (layer just under the bark where growth occurs)
  • larval tunnels running along the grain, filled with pale, granular frass (waste).

• Female wasps use the ovipositor ('sting') to drill into the host tree, injecting spores of the disease-causing fungus Amylostereum areolatum along with a toxic mucus. When conditions are right, they also deposit 1–400 eggs in adjacent drill holes.
• The toxic mucus dries the tree tissues and the fungus begins to grow. As the fungus spreads, the tree's vascular system is disrupted, and the tree may eventually die.
• Eggs hatch when the surrounding area has been invaded by fungus.
• Larvae do not feed on the tree itself but on the fungus as it spreads through the tree.
• Mature larvae pupate close to the bark surface and adults emerge about 3 weeks later.
• Adults live for only a few days. They are present from October to April, but are most numerous from January to February.
• The life cycle is about a year or sometimes longer. The potential for warmer temperatures in subtropical regions to enable 2-yearly generations is concerning.

• Prevent attacks by thinning and maintaining a healthy stand of trees. Stressed or injured trees (such as those that have been damaged from drought, fire, wind or machinery) are very susceptible.
• Restrict log movement during the adult flight season (October–April) to help minimise the risk of spreading to new areas.
• Kiln-dry infected timber to a core temperature above 60 degrees Celsius to prevent larvae from developing.
• The most effective and widely used biological control agent is the parasitic nematode Deladenus (=Beddingia) siricidicola, which can achieve an almost 100% rate of parasitism of the sirex wasp. Inoculation is achieved by introducing laboratory-grown nematodes into infected trees using a special hammer and punch.
• D. siricidicola nematodes have 2 life forms:
  • In the free-living form, they feed on the Amylostereum areolatum fungus introduced by the wasp to feed its larvae.
  • In the parasitic form, the nematode infects sirex larvae and enters the developing eggs of sirex females. When the infected eggs are laid, instead of juvenile sirex wood wasps emerging, D. siricidicola nematodes are spread, and they go on to sterilise the next generation of females.
• Other biological controls available for Queensland are the parasitic wasps Ibalia leucospoides and Megarhyssa nortoni.

• Pests and diseases image library (PaDIL)
• Sirex wasp eradication (CSIROpedia)–the story of the wasp and the nematode
• The sirex website–Forestry, Agricultural and Biotechnology Institute, South Africa
• Australian Pesticides and Veterinary Medicines Authority (APVMA)