Sirex nigricornis

Taxonomy

Family: Siricidae
Subfamily: Siricinae
Genus: Sirex Linnaeus, 1760
Species: Sirex nigricornis Fabricius, 1781
Common names: none

Background

Sirex nigricornis is an eastern Nearctic species. It is generally metallic black with a partially reddish-brown abdomen, and sometimes entirely black with uniformly darkened wings (Schiff et al. 2006).

This species has two color morphs that used to be classified as two species, S. nigricornis and S. edwardsii. Morphological and genetic analysis have placed these two groups into a single species, and S. edwardsii is now a junior synonym (Schiff et al. 2012).

Diagnostic characteristics

See Sirex for genus-level diagnostic characteristics.

Females:

Males:

May be confused with

Both sexes of Sirex nigricornis can be distinguished from S. behrensii by a lack of fore wing vein 3A, lack of banded pattern on the wing, and hind leg color patterns (Schiff et al. 2012).

Morphological and geographical variation

Individuals of S. nigricornis fall into two color patterns. The pale form, with reddish-brown on the legs and abdomen, is found in higher proportions in the eastarn portion of its range, while the black form, mostly black throughout the body, is more commonly found in the west (Schiff et al. 2012).

Host associations

Sirex species feed on trees of Pinaceae and Cupressaceae. Sirex nigricornis is recorded on Pinaceae species Pinus banksiana (jack pine), P. clausa (sand pine), P. echinata (shortleaf pine), P. elliotti (slash pine), P. palustris (longleaf pine), P. resinosa (red pine), P rigida (pitch pine), P. strobus (eastern white pine), P. sylvestris (Scots pine), P. taeda (loblolly pine), P. virginiana (Virginia pine), and Picea abies (Norway spruce). The majority of specimens reared (94%) 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). The mycangia of S. nigricornis individuals harbor either Amylostereum areolatum or A. chailletii fungus (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. nigricornis is late July through early October, with most collections from mid-August through September (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

North America: The range of Sirex nigricornis is centered in the eastern Great Lakes region and New England. The range extends through southern Canada west to Alberta and south to northern Florida and Louisiana in the southern United States (Schiff et al. 2012).

No specific locality data was available for mapping the range of this species at the time of publication.

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

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

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

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

Sirex nigricornis male pale form lateral habitus; photo by H. Goulet, CNC

Sirex nigricornis male pale form lateral habitus; photo by H. Goulet, CNC

Sirex nigricornis male dark form lateral habitus; photo by H. Goulet, CNC

Sirex nigricornis male dark form lateral habitus; photo by H. Goulet, CNC

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

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

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

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

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

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

Sirex nigricornis hind tarsus; photo by H. Goulet, CNC

Sirex nigricornis hind tarsus; photo by H. Goulet, CNC

Sirex nigricornis mesoscutum; photo by H. Goulet, CNC

Sirex nigricornis mesoscutum; photo by H. Goulet, CNC

Sirex nigricornis female pale form abdomen; photo by H. Goulet, CNC

Sirex nigricornis female pale form abdomen; photo by H. Goulet, CNC