Sirex noctilio

Taxonomy

Family: Siricidae
Subfamily: Siricinae
Genus: Sirex Linnaeus, 1760
Species: Sirex noctilio Fabricius, 1793
Common names: sirex woodwasp, European woodwasp, Eurasian woodwasp

Background

Sirex noctilio is a Palearctic species that has been introduced and become established in several regions around the world. This species is well-known as a forestry pest but is often difficult to distinguish from other Sirex species (Schiff et al. 2012).

Diagnostic characteristics

See Sirex for genus-level diagnostic characteristics.

Females:

Males:

May be confused with

Several Nearctic species have similar coloration to S. noctilio, with reddish legs and a black abdomen. The female can be distinguished in North America by the relatively short pulvilli and the larger size of the pits on the ovipositor. The male can be distinguished by the wide reddish-brown band at the base of the hind tibia (Schiff et al. 2012). Of European species, S. noctilio has similar coloration to S. juvencus and S. torvus. Sirex noctilio can be distinguished in this range by the black apical hind tarsomere and the shorter ovipositor (Benson 1943).

Morphological and geographical variation

There are two color morphs of S. noctilio. The light form found throughout its range has light-colored femora and clear wings, while the dark form, found only in Spain, Portugal, Turkey, Italy, and the Azores islands, has black femora and darkened wings (Schiff et al. 2012).

Host associations

Sirex species feed on trees of Pinaceae and Cupressaceae. Throughout the world, Sirex noctilio is mostly recorded on species of pine: Pinus contorta (lodgepole pine), Pinus resinosa (red pine), Pinus sylvestris (Scots pine), Pinus strobus (eastern white pine), Pinus caribea (Caribbean pine), Pinus echinata (shortleaf pine), Pinus elliottii (slash pine), Pinus kesiya (Khasia pine), Pinus nigra (Austrian pine), Pinus palustris (longleaf pine), Pinus patula (Mexican weeping pine), Pinus pinaster (maritime pine), Pinus pinea (stone pine), Pinus radiata (Monterey pine), and Pinus taeda (loblolly pine). Some European specimens have been reared from a single non-pine species, Pseudotsuga menziesii (Douglas fir) (Schiff et al. 2012).

Life history

Female Sirex harbor symbiotic basidiomycete fungus in abdominal glands called mycangia. During oviposition, the site is inoculated with the fungus, which begins to decompose the surrounding wood. Larvae feed on the fungus, and in the process bore galleries through the wood (Johnson 1930, Schiff et al. 2012). The mycangia of S. noctilio harbor Amylostereum areolatum fungus (Hajek et al. 2013). This species also deposits a plant toxin in the form of a mucus, that weakens plant cells to encourage the fungus’ growth (Hajek and Morris 2014).

Larvae are creamy white and grub-like in appearance with a dark head capsule. As with adults, larvae possess a short dorsal horn on the posterior end of the body. The larvae bore galleries into wood, feeding until pupation and subsequent emergence. Throughout this process, the larvae use their horn to pack the tunnel behind them with sawdust. Emergence holes are perfectly circular. The fungal symbiont is carried in specialized organs in female larvae that develop into the mycangia after metamorphosis (Schiff et al. 2012).

The documented flight period of S. noctilio is early July through early October, with most collections in late July and early August (Schiff et al. 2012).

In regions where they are native, S. notilio horntails are a secondary pest that attacks dead or damaged trees. However, in other regions, S. noctilio is documented ovipositing into otherwise healthy trees. The phytotoxic mucus in conjunction with the fungus exacerbates the damage to the tree. For these reasons, S. noctilio is considered an important forest pest (Hajek and Morris 2014).

Infestations of S. noctilio have resulted in ecological and economic loss. One incident in Australia in the 1980s saw the death of 1.8 million trees in a pine plantation (Hajek and Morris 2014). Outbreaks are correlated with drought and overcrowded stands, which may create stress and decrease resiliency in the affected tree (Madden 1988).

Several parasitoid wasp species and a species of parasitic nematodes, Deladenus siricidicola, that kill S. noctilio larvae are being considered and used for biological control of this pest (Hajek et al. 2013, Hajek and Morris 2014).

Distribution

World: The original range of S. noctilio is Europe east to Siberia. It was introduced, likely through trade of wood products, and became established in Australia, New Zealand, South Africa, Argentina, Uruguay, Brazil, Chile, and North America (Schiff et al. 2012).

North America: The first introduction of S. noctilio was recorded in northern Ontario in the early 1880s. It has since established in the Great Lakes region and occurs in Ontario, New York, and Pensylvannia (Schiff et al. 2012).

Map data from: GBIF.org (26 June 2019) GBIF Occurrence Download Sirex noctilio

Details about data used for maps can be found here.

Sirex noctilio female pale form lateral habitus; photo by H. Goulet, CNC

Sirex noctilio female pale form lateral habitus; photo by H. Goulet, CNC

Sirex noctilio female dark form lateral habitus; photo by H. Goulet, CNC

Sirex noctilio female dark form lateral habitus; photo by H. Goulet, CNC

Sirex noctilio male pale form lateral habitus; photo by H. Goulet, CNC

Sirex noctilio male pale form lateral habitus; photo by H. Goulet, CNC

Sirex noctilio male dark form lateral habitus; photo by H. Goulet, CNC

Sirex noctilio male dark form lateral habitus; photo by H. Goulet, CNC

Sirex noctilio female hind tarsomere 5; photo by H. Goulet, CNC

Sirex noctilio female hind tarsomere 5; photo by H. Goulet, CNC

Sirex noctilio female head; photo by H. Goulet, CNC

Sirex noctilio female head; photo by H. Goulet, CNC

Sirex noctilio ovipositor pits; photo by H. Goulet, CNC

Sirex noctilio ovipositor pits; photo by H. Goulet, CNC

Sirex noctilio female tarsal pulvilli; photo by H. Goulet, CNC

Sirex noctilio female tarsal pulvilli; photo by H. Goulet, CNC

Sirex noctilio mesoscutum; photo by H. Goulet, CNC

Sirex noctilio mesoscutum; photo by H. Goulet, CNC

Sirex noctilio mesoscutum texture; photo by H. Goulet, CNC

Sirex noctilio mesoscutum texture; photo by H. Goulet, CNC

live Sirex noctilio mating pair; photo by H. Goulet, CNC

live Sirex noctilio mating pair; photo by H. Goulet, CNC