Sirex woodwasp

  • Adult female Sirex wood wasp showing characteristic, blue-black colour
    Adult female Sirex wood wasp showing characteristic, blue-black colour
  • Adult male Sirex wood wasp showing characteristic, orange body colour.
    Male sirex wood wasp
  • A pine stem showing emergence holes left by adult sirex wood wasps that have completed their feeding cycle in the sapwood
    A pine stem showing emergence holes left by adult sirex wood wasps that have completed their feeding cycle in the sapwood
  • section through pine showing tunnels and a Sirex wood wasp larva and a pupa.
    section through pine showing tunnels and a Sirex wood wasp larva and a pupa.

General information

Sirex wood wasp, Sirex noctilio, is the most damaging invasive pest in pine plantations in the Southern Hemisphere, killing millions of trees within its exotic range. The pest has been present in Tasmania since 1952 and mainland Australia since 1961, but has only recently arrived in Queensland. It has not yet spread to the main, coastal plantation regions of Beerburrum and the Fraser Coast. However, climate-species modelling predicts most of Queensland´s pine growing regions are suitable for its establishment.

Scientific name

Sirex noctilio

Other names

Sirex wasp or wood wasp

Description
  • Sirex adults lack the thin waist characteristic of 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 half of the body, and an orange abdomen with a dark tip, and no 'sting'
  • females are 15-35 mm long and males are 13-32 mm long
  • larvae are creamy white and have an obvious head, three pairs of very short legs and a segmented, cylindrical body with a characteristic 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. There have been local outbreaks of the related tremex wasp (Tremex fuscicornis) on poplars, Populus species and willow, Salix species in New South Wales. Adults are very similar to S. noctilio but have shorter antennae.

The giant woodwasp, Urocerus gigas, is listed as an exotic, 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 two 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) and Pigeon horntail (Tremex columbia).

Distribution

Sirex is native to Eurasia and Morocco but, during the last century, it was accidentally introduced to the Southern Hemisphere, including Australia, New Zealand, South Africa and South America. It recently arrived also in North America.

First detected in Tasmania in 1952 and Victoria in 1961, it spread through Victrian pine plantations, reaching South Australia and New South Wales by 1980. It spread gradually through New South Wales until, in 2009, it was detected in the relatively temperate pine plantations in Queensland's Stanthorpe region.

It has not yet spread to the main, coastal plantation regions of Beerburrum and the Fraser Coast. However, climate-species modelling predicts most of Queensland´s pine growing regions are suitable for it to become established.

Hosts
  • Susceptible tree species include; Pinus radiata, P. taeda and some other Pinus species grown in Australian plantations.
  • More resistant tree species include; P. elliotii.
  • The susceptibility of the main subtropical pines, including Pinus caribaea and the hybrid P. elliottii var. elliottii x P. caribaea var. hondurensis, is not known.
Biology
  • Female wasps use the ovipositor to drill into the host tree, injecting spores of the tree pathogenic fungus Amylostereum areolatum along with a phytotoxic mucus. When conditions are right, they also deposit at least one egg in adjacent drill holes.
  • The mucus dries the tree tissues, providing the right conditions for the fungus to grow. The tree dies as the fungus spreads - primarily by disrupting the tree´s vascular system.
  • Developing Sirex 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 three weeks later.
  • Adults live for only a few days. They are present from late November to April and most numerous in January to February

The life cycle of the Sirex woodwasp takes about a year but can be longer. There are concerns that the warmer temperatures in subtropical regions may result in a second annual generation.

Tree symptoms

In the early stages of infestation, Sirex females are attracted to stressed or damaged trees. As the wasp population builds, more vigorous trees can also be attacked and killed. Damage symptoms include:

  • needle wilt, initially in older, then in newer foliage
  • foliage becomes pale then coppered-coloured as it dries
  • fine pin-holes (egg-laying sites) in the bark, often associated with beads and trickles of resin
  • circular adult emergence holes (3-7 mm diameter) located along the length of the tree
  • brown fungal staining of the cambium
  • susceptible plantations are generally 10-25 years old, although older trees have been attacked in Queensland
Management

Unthinned stands and stressed or injured trees (e.g. following damage from drought, fire, wind or logging) are particularly susceptible, so the primary preventative measures are thinning and maintaining a healthy stand.

The nematode, Deladenus (Beddingia) siricidicola is the most widely used biological control agent and can achieve almost 100% parasitism rates. Its complex lifecycle has a free-living fungal feeding stage within pine trees, and a parasitic stage within wasp larvae. Nematodes are spread naturally when infected wasps lay packets of nematodes in place of fertile eggs into trees, and operationally by inoculating laboratory-cultured nematodes into trees. Nematode inoculations have commenced in Queensland.

Other biological control agents available for Queensland are the parasitic wasps, Ibalia leucospoides and Megarhyssa nortoni.

Restricting log movement during the adult flight season (October to April) would help minimise the risk of spread to new areas within Queensland.

Kiln drying timber to a core temperature above 60°C will prevent larval development.

Comments

Through much of its introduced range, Sirex woodwasp is under effective biological control from the nematode species, D. siricidicola. As it spreads into the subtropical plantations in southeast Queensland, however, it will encounter substantially different climatic conditions and new, native and exotic hosts with unknown susceptibility.

We don't yet know what impacts this will have on the wasp's population dynamics, or how effective the biological control will be. Some nematode biological control has failed in regions like South Africa and South America, which is of great concern for Australia. Research by the Department of Agriculture and Fisheries, Queensland and HQ Plantations Pty Ltd is underway to predict how well existing control options will perform on the new pine taxa and under subtropical conditions.

Additional information

Last updated 30 June 2016