Sirex imperialis is a completely dark form species known from India (Benson 1943).
See Sirex for genus-level diagnostic characteristics.
Sirex species feed on trees of Pinaceae and Cupressaceae. Sirex imperialis is recorded feeding on Abies pindrow (west Himalayan fir), Abies spectabilis (east Himalayan fir), Cedrus deodara (Himalayan cedar), Picea smithiana (morinda spruce), and Pinus roxburghii (chir pine) (Smith 1978, Xiao and Wu 1983).
Female Sirex harbor symbiotic basidiomycete fungus in abdominal glands called mycangia. During oviposition, the site is inoculated with the fungus (Amylostereum spp.), 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). The mycangia of S. imperialis harbors Amylostereum chailletii fungus (Tabata 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).
Though S. imperialis is documented ovipositing into trees that are already dead, they are known for causing extensive damage to wood in the northwest Himalayas, making it unusable for many puposes. The flight period in high elevations is the month of July (Stebbing 1904).
World: Sirex imperialis is found in Pakistan, the Assam, Himachal Pradesh, Meghalaya, Jammu and Kashmir, and Punjab states of India, and the Guizhou, Zhejiang, and Anhui provinces of China (Kirby 1882, Benson 1943, Smith 1978, Xiao and Wu 1983, Saini et al. 2006).
North America: not recorded
No specific locality data was available for mapping the range of this species at the time of publication.