Sirex behrensii

Taxonomy

Family: Siricidae
Subfamily: Siricinae
Genus: Sirex Linnaeus, 1760
Species: Sirex behrensii (Cresson, 1880)
Common names: none

Background

Sirex behrensii is a somewhat rare western Nearctic species. Males are easily recognized by a large brown spot behind the eye (Schiff et al. 2012).

Diagnostic characteristics

See Sirex for genus-level diagnostic characteristics.

Females:

Males:

May be confused with

Sirex behrensii females can be distinguished from the pale form of S. nigricornis by the dark bands on the wing, vein 3A, and a light-colored cornus. The males can be recognized by the brown spot on the gena, the coloring of the legs, and the antennae (Schiff et al. 2012).

Morphological and geographical variation

none recorded

Host associations

Sirex behrensii is recorded mainly on species of Pinaceae: Pinus jeffreyi (Jeffrey pine), Pinus lambertiana (sugar pine), Pinus ponderosa (ponderosa pine), Pinus radiata (Monterey pine), and Pseudotsuga menziesii (Douglas fir). Additionally there is one record from Cupressus macrocarpa (Monterey cypress) (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). It is unknown what species of fungus is harbored by the mycangia of S. behrensii individuals, though based on other Sirex species, the fungus is likely Amylostereum areolatum or A. chailletii (Hajek et al. 2013).

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. behrensii is late July to late October, with a peak in September (Schiff et al. 2012).

A parasitoid wasp species, Ibalia leucospoides, has been recorded emerging from S. behrensii (Schiff et al. 2012).

Distribution

World: North America

North America: The range of S. behrensii is restricted to the West Coast, with collections from southern British Columbia to California and Nevada. There are two collections farther east in Ohio and West Virginia, where the species is likely not established (Schiff et al. 2012).

Map data from Washington State Department of Agriculture Entomology Collection.

Details about data used for maps can be found here.

Sirex behrensii female lateral habitus; photo by Q. Baine, WSDA

Sirex behrensii female lateral habitus; photo by Q. Baine, WSDA

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

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

Sirex behrensii male lateral habitus; photo by H. Goulet, CNC

Sirex behrensii male lateral habitus; photo by H. Goulet, CNC

Sirex behrensii wing; photo by H. Goulet, CNC

Sirex behrensii wing; photo by H. Goulet, CNC

Sirex behrensii female gena; photo by H. Goulet, CNC

Sirex behrensii female gena; photo by H. Goulet, CNC

Sirex behrensii male gena; photo by H. Goulet, CNC

Sirex behrensii male gena; photo by H. Goulet, CNC

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

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

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

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