Sirex juvencus

Taxonomy

Family: Siricidae
Subfamily: Siricinae
Genus: Sirex Linnaeus, 1760
Species: Sirex juvencus (Linnaeus, 1758)
Common names: steely-blue woodwasp

Background

Sirex juvencus is a Palearctic species with a typical metallic blue-black coloration and red legs (Schiff et al. 2012).

This species historically was classified into several sub-species that have since been elevated to species (S. carinthiacus, S. imperialis, S. melanopoda), and until recently was thought to be Holarctic. The Nearctic subspecies “S. juvencus californicus” has now been synonymized with S. cyaneus, and S. juvencus is restricted to Eurasia (Taeger et al. 2010, Schiff et al. 2012).

Diagnostic characteristics

See Sirex for genus-level diagnostic characteristics.

Females:

Males:

May be confused with

In its range, S. juvencus can be distinguished from S. torvus and S. noctilio by the pale base of the antennae (Benson 1943). Previously considered to be the same species, S. cyaneus is differentiated from S. juvencus by the lack of pits on the basal part of the ovipositor and the color of the antennae (Schiff et al. 2012).

Morphological and geographical variation

none recorded

Host associations

Sirex species feed on trees of Pinaceae and Cupressaceae. Sirex juvencus is recorded on Pinus sylvestris (Scots pine), Pinus strobus (eastern white pine), Pinus rigida (pitch pine), Pinus banksiana (jack pine), Pinus sibirica (Siberian stone pine), Picea jezoensis (yeddo spruce), Picea sitchensis (Sitka spruce), Picea omorika (Serbian spruce), Picea abies (Norway spruce), Picea spp., Abies alba (silver fir), Abies sibirica (Siberian fir), Abies spp., Pseudotsuga menziesii (Douglas fir), Chamaecyparis lawsoniana (Port Orford cedar), and Larix spp. (larch) (Smith 1978, Schiff et al. 2012). Because of historic taxonomical confusion with S. juvencus, some of these records may be inaccurate.

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 (Schiff et al. 2012).

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).

Sirex juvencus in England have been observed flying in July through September (Curtis 1829).

Distribution

World: Sirex juvencus occurs widely in Europe, from the British Isles east into Russia (Smith 1978). It has been intercepted in North America, New Zealand, Australia, and the Philippines, but there is no evidence that it has become established (Schiff et al. 2012).

North America: This species has been intercepted at ports on the East Coast of the United States and Canada (Schiff et al. 2012).

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

Details about data used for maps can be found here.

Sirex juvencus female lateral habitus; photo by J. Orr, WSDA

Sirex juvencus female lateral habitus; photo by J. Orr, WSDA

Sirex juvencus female dorsal habitus; photo by J. Orr, WSDA

Sirex juvencus female dorsal habitus; photo by J. Orr, WSDA

Sirex juvencus male lateral habitus; photo by J. Orr, WSDA

Sirex juvencus male lateral habitus; photo by J. Orr, WSDA

Sirex juvencus male dorsal habitus; photo by J. Orr, WSDA

Sirex juvencus male dorsal habitus; photo by J. Orr, WSDA