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.
Sirex wasp or wood wasp
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).
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.
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.
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:
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.
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.