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Texas Invasive Species Institute

Texas Invasive Species Institute

Sirex Woodwasp

Sirex noctilio

Class: Insecta
Order: Hymenoptera
Family: Siricidae

Sirex noctilio

Photographer: Unknown Affiliation: Pest and Diseases Image Library Source: www.bugwood.org Copyright: CC BY-NC 3.0


Adult Description: Sirex noctilio is a stout and cylindrical shaped woodwasp with a pointed abdomen; somethimes they're called horn-tail wasps. The full body measures from 1-1.5 inches in length. Coloration is different between males and females. Males have thickened black hind legs and yellow-orange segments on the middle abdomen. Females have reddish legs and a steel-blue body (pictured above left) with a projection at the rear abdomen that protects the ovipositor.

Larva Description: Larvae are creamy white, legless and have a conspicuous dark spine at the rear of the abdomen.

Host Plant: This woodwasp is a pest of pine trees (Pinus spp.). In its native range, Sirex noctilio attacks Scotch, Austrian and Maritime pines. However in the United States, these woodwasps are known to attack Monterey, loblolly, slash, shortleaf, ponderosa, lodgepole and jack pine species. Sirex noctilio is also known to be a pest of spruces (Picea spp.) and fir trees (Abies spp.).

Ecological Threat

This insects is not only a pest of ecologically and economically important trees it is also able to spread quickly. In Australia, this insect has been observed to spread at a rate of up to 50 km per year. For pine plantations in Australia, South America and South Africa is has caused 80% tree mortality; so far, this has not been the case for the United States. However, this woodwasp is able to impact four native pine species and has been documented on larch trees, Douglas and other firs and spruces. If Sirex woodwasp populations were ever to become unmanageable in the United States the costs and damages would be enormous.


The one generation of Sirex noctilio takes one year to complete. Adult emergence occurs from July through September, peaking in August. Females are attracted to stressed trees and drill their ovipositors into the outer sapwood and lay 25 to 450 eggs along with a symbiotic fungus (Amylostereum areolatum) and a toxic mucus. Together the fungus and mucus kill the tree in order to create the proper environment for the eggs to grow. Unfertilized eggs become males while fertilized eggs develop into females. There are 6 to 12 larval instars and the larval stage takes about 10 to 11 months to complete. Mature larvae pupate near the bark surface and adults emerge about 3 weeks later.


A single Sirex noctilio female was first collected off of a forest survey trap in Fulton, New York in September 2004 and was identified in February 2005. From the initial sighting, positive findings occurred in 27 other New York counties. The following year Pennsylvania announced the presence of Sirex noctilio in their state.  By 2007, both Vermont and Michigan confirmed the presence of Sirex noctilio amongst their natural forests.

Native Origin

 Europe, Asia and northern Africa

Current Location

U.S. Habitat: Temperate areas where Pinus spp., Abies spp. and Picea spp. are able to grow.
                 Click here for a map of at-risk states provided by Forest Service, USDA and APHIS

U.S. Present: ME, MI, NY, PA and VT


Sirex noctilio looks like other native horntail wasps.


Studies in the United States have shown that the genotype of the fungal symbiont Amylostereum areolatum, found with invasive Sirex woodwasp; is more similar to genotypes found in Europe than in the southern hemisphere (Australasia, South America and Africa).This is encouraging because the fungal genotypes, found with S. noctilio, in the southern hemisphere have caused massive damages and costs in pine plantations while the impact in Europe is not as extreme.

Sirex woodwasp has been successfully managed using biological control agents. In the Southern hemisphere, the key agent is a parasitic nematode, Deladenus siricidicola; which infects Sirex woodwasp larvae, and ultimately sterilizes the adult females. These infected females emerge and lay infertile eggs that are filled with nematodes, which sustain and spread the nematode population. The nematodes effectively regulate the woodwasp population below damaging levels. As Sirex woodwasp establishes in new areas, this nematode can be easily mass-reared in the laboratory and introduced into infested trees. In addition to the nematode, hymenopteran parasitoids have been introduced into Sirex woodwasp populations in the Southern Hemisphere, and most of them are native to North America (e.g., Megarhyssa nortoni, Rhyssa persuasoria, Rhyssa hoferi, Schlettererius cinctipes, and Ibalia leucospoides); making the wasp parasitoids a safe/native way to control Sirex noctilio populations in North America.



Hurley BP, Slippers B, Wingfield MJ. 2007. A comparison of control results for the alien invasive woodwasp, Sirex noctilio, in the southern hemisphere. Agr For Entomol 9:159–171

Kirk AA. 1974. Siricid woodwasps and their associated parasitoids in the south eastern United States. J Ga Entomol Soc 9:139–144

Kirk AA. 1975. Siricid woodwasps and their associated parasitoids in the south western United States. Pan-Pacific Entomol 51:75–81

Nielsen, C., Williams, D. W., & Hajek, A. E. 2009. Putative source of the invasive Sirex noctilio fungal symbiont, Amylostereum areolatum, in the eastern United States and its association with native siricid woodwasps. Mycological research, 113(11), 1242-1253.

Slippers, B., Hurley, B. P., Mlonyeni, X. O., de Groot, P., & Wingfield, M. J. 2012. Factors affecting the efficacy of Deladenus siricidicola in biological control systems. In The Sirex Woodwasp and its Fungal Symbiont: (pp. 119-133). Springer Netherlands.

Williams, D. W., Zylstra, K. E., & Mastro, V. C. 2012. Ecological considerations in using Deladenus (= Beddingia) siricidicola for the biological control of Sirex noctilio in North America. In The Sirex Woodwasp and its Fungal Symbiont: (pp. 135-148). Springer Netherlands.

Internet Sources







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