Sirex californicus

Taxonomy

Family: Siricidae
Subfamily: Siricinae
Genus: Sirex Linnaeus, 1760
Species: Sirex californicus (Ashmead, 1904)
Common names: none

Background

Sirex californicus is a western Nearctic species with two color forms (Schiff et al. 2012).

Diagnostic characteristics

See Sirex for genus-level diagnostic characteristics.

Females:

Males:

May be confused with

Sirex californicus females can be distinguished from most Sirex by the completely black legs and darkened fore wings, and from S. obesus and S. nigricornis by the small, scattered pits on the gena and vertex. Males are distinguished by the reddish-brown legs and the bicolored antennae (Schiff et al. 2012).

Morphological and geographical variation

There are two color morphs of S. californicus females. The dark form with entirely dark legs is common throughout the range, while the pale form, with light-colored legs, is found in the northern regions of the range (Schiff et al. 2012).

Host associations

Sirex species feed on trees of Pinaceae and Cupressaceae. Sirex californicus is recorded on Pinaceae species Larix occidentalis (western larch), Pinus albicaulis (whitebark pine), Pinus ponderosa (ponderosa pine), Pinus contorta (lodgepole pine), Pinus coulteri (Coulter pine), Pinus jeffreyi (Jeffrey pine), Pinus lambertiana (sugar pine), Pinus monticola (western white pine), and Pinus sylvestris (Scots pine). There is one record of an emergence from Cupressus macrocarpa (Monterey cypress). The majority of specimens reared (99%) have been on Pinus spp. (pine) (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. californicus, but Amylostereum areolatum and A. chailletii are associated with other Nearctic Sirex (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. californicus is late July through late September, with most collections in late August (Schiff et al. 2012). There is some evidence that trees with sustained damage, either from drought-related stress, weather, or other insect infestations, are preferred as hosts (Burnip et al. 2010).

Distribution

World: North America. At least one interception has been recorded from New Zealand (Schiff et al. 2012).

North America: Sirex californicus occurs in the Rocky Mountain region west to the Pacific Ocean, as far north as British Columbia, and south to New Mexico (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 californicus female pale form lateral habitus; photo by H. Goulet, CNC

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

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

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

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

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

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

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

Sirex californicus fore wing; photo by H. Goulet, CNC

Sirex californicus fore wing; photo by H. Goulet, CNC

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

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

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

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

Sirex californicus tarsal pulvillus; photo by H. Goulet, CNC

Sirex californicus tarsal pulvillus; photo by H. Goulet, CNC

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

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

live Sirex californicus female dark form; photo by H. Goulet, CNC

live Sirex californicus female dark form; photo by H. Goulet, CNC