Sirex varipes

• previous
 
• next

Taxonomy

Family: Siricidae
Subfamily: Siricinae
Genus: Sirex Linnaeus, 1760
Species: Sirex varipes Walker 1866
Common names: none

Background

Sirex varipes is a common western Nearctic species with black body and red legs (Schiff et al. 2012).

Diagnostic characteristics

See Sirex for genus-level diagnostic characteristics.

Females:

• hind femur light reddish-brown (Schiff et al. 2012)
• abdomen entirely black with metallic reflections (Schiff et al. 2012)
• tibia reddish-brown with black, dark brown or blue on dorsal side (Schiff et al. 2012)
• fore wing clear or with light yellow tint near stigma (Schiff et al. 2012)
• fore wing vein 3A absent (Schiff et al. 2012)
• gena pits small and scattered, about 4–10 pit diameters apart (Schiff et al. 2012)
• vertex pits dense, about 0.1–0.25 diameter of lateral ocellus (Schiff et al. 2012)
• second hind tarsomere 2–3.6 times as long as wide (Schiff et al. 2012)
• mesoscutum pit margins raised creating a net-like pattern (Schiff et al. 2012)
• second hind tarsomere with pulvillus about 0.7–0.8 times length of tarsomere (Schiff et al. 2012)

Males:

• hind femur mostly reddish-brown (Schiff et al. 2012)
• gena completely blue-black with metallic reflections (Schiff et al. 2012)
• hind tibia black, sometimes with narrow band of reddish-brown at the base (Schiff et al. 2012)
• gena pits about 1–3 diameters apart (Schiff et al. 2012)
• mesoscutum pit margins raised creating a net-like pattern (Schiff et al. 2012)
• apical abdominal segments reddish-brown (Schiff et al. 2012)
• fore wing tinted yellow or light brown (Schiff et al. 2012)
• mid tibia black on outer surface (Schiff et al. 2012)

May be confused with

Sirex varipes females can be distinguished from S. abietinus, S. cyaneus and S. nitidus by the dark band on the dorsal surface of the hind tibia. Sometimes this characteristic dark band is also present on the fore and mid tibiae (Schiff et al. 2012).

Morphological and geographical variation

Three females specimens of this species have entirely light-colored hind tibiae. This character appears to be rare (Schiff et al. 2012).

Host associations

Sirex species feed on trees of Pinaceae and Cupressaceae. Sirex varipes is recorded on species of Pinaceae: Abies amabilis (Pacific silver fir), Abies concolor (white fir), Abies grandis (grand fir), Abies magnifica (red fir), Abies lasiocarpa (subalpine fir), Picea engelmannii (Engelmann spruce), Picea sitchensis (Sitka spruce), Pinus ponderosa (ponderosa pine), Pseudotsuga menziesii (Douglas fir), and Tsuga heterophylla (western hemlock) (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).

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 flight period of S. varipes is from early July through early October, with most collections in the months of August and September (Schiff et al. 2012).

Distribution

World: North America. Interceptions have been made in England and New Zealand (Schiff et al. 2012).

North America: Sirex varipes is recorded west of the Rocky Mountains in British Columbia, Alberta, Montana, Idaho, Washington, Oregon, California, Nevada, and Arizona (Schiff et al. 2012).

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

Details about data used for maps can be found here.