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 and 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

• Sirex noctilio is the only Siricid wasp established in Queensland.
• Local outbreaks of the related tremex wasp (Tremex fuscicornis) on poplars (Populus spp.) and willow (Salix spp.) 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. The U. gigas female is quite distinct from S. noctilio, having a yellow, rather than black, abdomen with a broad black stripe across the middle. Males of the 2 species are very similar and require accurate identification.
• 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).

• Recorded in Queensland's Stanthorpe relatively temperate region in 2009.
• Not yet recorded in the main coastal plantations of Beerburrum and the Fraser Coast.
• Climate-species models predict it could establish in most of Queensland's pine-growing regions.
• Recorded in Tasmania in 1952 and Victoria in 1961 and spread through Victorian pine plantations.
• Recorded in South Australia and New South Wales by 1980 and spread gradually.

Susceptible:

• Pinus radiata
• P. taeda
• other Pinus species grown in Australian plantations.

More resistant:

• Pinus elliottii

Unknown susceptibility of the main subtropical pines:

• Pinus caribaea
• 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.
• Damage signs include:
  • needle wilt (initially in older, then in newer foliage)
  • pale foliage, which becomes coppered-coloured as it dries
  • fine pin-holes (egg-laying sites) in the bark, often associated with beads and trickles of resin
  • circular adult exit holes (3–7mm diameter) along the tree
  • brown fungal staining of the cambium (layer just under the bark where growth occurs)
  • plantations at risk are generally 10–25 years old, although in Queensland, older trees have been attacked.

• Female wasps use the ovipositor ('sting') to drill into the host tree, injecting spores of tree disease-causing fungus Amylostereum areolatum along with a phytotoxic (plant-poisioning) mucus. When conditions are right, they also deposit at least 1 egg in adjacent drill holes.
• Mucus dries tree tissues, so fungus can grow. Trees die as fungus spreads, disrupting the tree's vascular system.
• Larvae do not feed on the tree itself but on the fungus as it spreads through the tree.
• Larval tunnels run along the grain and are filled with pale, granular frass (waste) and may be stained light yellow by the fungus.
• Mature larvae pupate close to the bark surface and adults emerge about 3 weeks later.
• Adults live for only a few days. Present from late November to April, they are most numerous in January to February. Life cycle is about a year or sometimes longer. The potential for warmer temperatures in subtropical regions to produce 2 yearly generations is concerning.

• Prevent by thinning and maintaining a healthy stand of trees because unthinned stands and stressed or injured trees (e.g. following damage from drought, fire, wind or logging) are very susceptible.
• Nematode inoculations occur in Queensland. The nematode, Deladenus (Beddingia) siricidicola, is the most widely used for biological control and can achieve almost 100% rate of parasitism of the wasp. Nematodes have a fungal feeding stage, free-living within pine trees and a parasitic stage within wasp larvae. Spreading occurs naturally when infected wasps lay packets of nematodes instead of fertile eggs into trees or operationally by inoculating laboratory-cultured nematodes into trees.
• Other biological controls available for Queensland are the parasitic wasps Ibalia leucospoides and Megarhyssa nortoni.
• Restrict log movement during the adult flight season (October–April) to help minimise the risk of spreading to new areas within Queensland.
• Kiln dry timber to a core temperature above 60°C will prevent larvae from developing.

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