Sirex Woodwasp (Sirex noctilio (F.))

Forest Health Alert - Sirex Woodwasp (Sirex noctilio (F.))


E. Czerwinski, Jason Pollard, T. Scarr

Ministry of Natural Resources, Forest Health and Silviculture Section




A native to Europe, Asia, and Northern Africa, Sirex noctilio F. has been accidentally introduced into many parts of the world, most recently North America. Sirex woodwasps, also known as horntails, attack and kill living pine trees. In its native range this insect is not considered to be a significant pest. However, in parts of its introduced range it has caused significant tree mortality.




All hard pines in Ontario are considered susceptible, these include: jack pine; Pinus banksiana Lamb; red pine; Pinus resinosa Ait; pitch pine; Pinus rigida Mill; Scots pine; Pinus sylvestris L.

Other pine species may also be susceptible.

Figure 1 Sirex noctilio F. mâle adulte
Figure 1 - Adult male Sirex woodwasp
(Photo courtesy of the USDA Forest Service)


Current Situation


This insect was first discovered in North America in a Scots pine plantation in upper New York State in 2004. In Ontario in 2005, Sirex woodwasp adults were trapped in Prince Edward County and near Prescott, Uxbridge and Cambridge. Surveys and trapping led by the Ontario Ministry of Natural Resources in partnership with the Canadian Forest Service and the Canadian Food Inspection Agency are continuing to determine its range, distribution and how this insect may be affecting Ontario’s forests.




Sirex woodwasps are large insects, 5 to 7 cm long (Figure 1).


Adults have a spear-shaped plate at the posterior end and are dark metallic blue to black. Mid-abdomen segments on males are dark orange. Antennae are entirely black. Legs are reddish-yellow, feet are black; males have black hind legs. The larvae are creamy white, legless, with a distinctive dark coloured spine at the posterior end (Figure 2).

Figure 2 Sirex woodwasp larva

Figure 2 - Sirex woodwasp larva


Life Cycle


Generally one generation per year, although this insect may take two years to fully develop in the colder parts of its range. Adult wasps emerge between July and September, with peak emergence around mid-August. Females are attracted to stressed pine trees. They drill their ovipositors into the outer sapwood and inject a fungus, toxic mucus and eggs. Females lay 25-450 eggs. The developing larvae feed on the fungus as they tunnel through the wood of the tree. The larval stage of the life cycle takes approximately 10-11 months to complete. Adults emerge three weeks later and live one to two weeks.


Signs and Symptoms


Figure 3 Resin Beading from egg laying sites

Figure 3 - Resin from egg laying sites

Attacked trees show crown symptoms within a couple of months. Crowns turn light green, needles may then wilt and turn yellow to reddish brown. Resin beading may develop on the trunk from oviposition (egg laying) wounds (Figure 3).


Fungal staining of wood from each oviposition site may be visible if bark is cut away.

Larval galleries, packed with frass, turn inward toward the heartwood and then back toward the bark (Figure 4). Emerging adults create round exit holes 3 to 8 mm in diameter (Figure 5).


Management and Control


Silvicultural treatments to maintain and enhance stand vigour are important in preventing establishment. However, thinning and pruning should be avoided during woodwasp flight season since these activities wound trees and may attract pests or leave them susceptible to infestation.


Biological controls have been successful in other jurisdictions. A parasitic nematode, Deladenus siricidicola, can penetrate larvae and render the female S. noctilio sterile. However, this nematode must be mass produced in a lab and inoculated into areas with Sirex since it does not naturally distribute well.



Figure 4 Larval gallery with frash

Figure 4 - Larval gallery with frass


Figure 5 Sirex woodwasp exit holes

Figure 5 - Sirex woodwasp exit holes

 For additional copies of this publication contact the Ontario Ministry of Natural Resources Information Centre at the number listed below.

For more information on forest health issues, contact the Ontario Ministry of Natural Resources Information Centre at 1-800-667-1940