Sirex cyaneus

Taxonomy

Family: Siricidae
Subfamily: Siricinae
Genus: Sirex Linnaeus, 1760
Species: Sirex cyaneus Fabricius, 1781
Common names: blue horntail

Background

Sirex cyaneus is a northeastern Nearctic species with a typical metallic blue-black coloration and red legs (Schiff et al. 2012).

The European species previously identified as S. cyaneus has, through morphological and molecular analysis, been determined to be a separate species, and is now classified as S. torvus. The species previously identified as S. juvencus in North America has been re-classified as S. cyaneus (Schiff et al. 2012).

Diagnostic characteristics

See Sirex for genus-level diagnostic characteristics.

Females:

Males:

May be confused with

In its native range, Sirex cyaneus can be confused with S. nitidus and S. noctilio. The most reliable character distinguishing S. cyaneus from these species is the absence (or near absence) of pits near the base of the ovipositor. The European species S. torvus and S. juvencus can also be distinguished by this ovipositor pit character. Sirex abietinus is another similar species that occurs west of the Rocky Mountains, and it is distinguished by the cornus length (Schiff et al. 2012).

Morphological and geographical variation

none recorded

Host associations

Sirex species feed on trees of Pinaceae and Cupressaceae. Sirex cyaneus is recorded on species of Pinaceae: Abies balsamea (balsam fir), Abies fraseri (Fraser fir), Abies sp., Larix sp., Picea glauca (white spruce), Picea mariana (black spruce), Pinus strobus (eastern white pine), and Pinus elliottii (slash pine). The majority of specimens reared (99%) have been on Abies spp. (spruce) (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. cyaneus individuals harbor Amylostereum 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. cyaneus is early July through early September, with most collections in early 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).

Several parasitoid wasp species have been reared from S. cyaneus specimens: Ibalia leucospoides, Ibali rufipes, Rhyssa howdenorum, Rhyssa lineola and Rhyssa persuasoria (Schiff et al. 2012).

Distribution

World: North America. Several interceptions have been made in New Zealand (Schiff et al. 2012).

North America: The range of S. cyaneus extends from Alberta to Newfoundland in the north, south to Arizona in the west, and south to North Carolina in the east (Schiff et al. 2012).

Map data from: GBIF.org (26 June 2019) GBIF Occurrence Download Sirex cyaneus

Details about data used for maps can be found here.

Sirex cyaneus female lateral habitus; photo by H. Goulet, CNC

Sirex cyaneus female lateral habitus; photo by H. Goulet, CNC

Sirex cyaneus female lateral habitus; photo by J. Orr, WSDA

Sirex cyaneus female lateral habitus; photo by J. Orr, WSDA

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

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

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

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

Sirex cyaneus female antenna; photo by H. Goulet, CNC

Sirex cyaneus female antenna; photo by H. Goulet, CNC

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

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

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

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

Sirex cyaneus female mesoscutum; photo by H. Goulet, CNC

Sirex cyaneus female mesoscutum; photo by H. Goulet, CNC

Sirex cyaneus female cornus; photo by H. Goulet, CNC

Sirex cyaneus female cornus; photo by H. Goulet, CNC

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

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