Family: Siricidae
Subfamily: Siricinae
Genus: Sirex Linnaeus, 1760
Species: Sirex obesus Bradley, 1913
Common names: none
Sirex obesus is a somewhat rare species from the southwestern United States with a stout, dark body (Schiff et al. 2012).
See Sirex for genus-level diagnostic characteristics.
Females:
Males:
Sirex obesus females can be distinguished from S. areolatus and the dark form of S. californicus by the length of the second hind tarsomere and by the dense gena pits. The males can be recognized by the black antennae and the yellow-tinted fore wing (Schiff et al. 2012).
none recorded
One specimen of S. obesus was collected from Pinus ponderosa (ponderosa pine) (Schiff et al. 2012).
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. obesus is from late July through late September (Schiff et al. 2012).
World: North America
North America: Sirex obesus is only known from Arizona and New Mexico in the southwestern United States (Schiff et al. 2012).
No specific locality data was available for mapping the range of this species at the time of publication.
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