Xyleborinus octiesdentatus (Murayama, 1931: 46)

J. Rabaglia, Robert, Knizek, Milos & Johnson, Wood, 2010, First records of Xyleborinus octiesdentatus (Murayama) (Coleoptera, Curculionidae, Scolytinae) from North America, ZooKeys 56, pp. 219-226 : 221-223

Xyleborinus octiesdentatus (Murayama, 1931: 46) Figs 123

Diagnosis.

Specimens of Xyleborinus octiesdentatus can be easily distinguished from other members of Xyleborinus occurring in North America by the sulcate shape of the elytral declivity, and the elevated lateral declivital margins which bear four pairs of long, narrow, sharply pointed spines, increasing in length approaching the posterior margin.

Revised Key to Xyleborinus in America north of Mexico.

The following key, modified from the key to Xyleborinus in Rabaglia et al. (2006), will enable the identification of the five species of Xyleborinus known from America north of Mexico. It includes the recently established Xyleborinus andrewsi in Florida ( Okins and Thomas 2010).

Description.

The species was redescribed by Nunberg (1982)

Female. Length 2.1-2.4 mm (from anterior margin of pronotum to posterior margin of elytra, excluding spines), 2.5 × as long as wide; color brown to dark brown, matt. Frons convex, strongly reticulate, with large, shallow, rather dense punctures. Antennal club round with two round sutures on its anterior side and one strongly apically displaced suture on posterior side. Pronotum cylindrical, 1.2 × as long as wide, frontal edge broadly rounded bearing small tubercles as continuation of very fine asperities on anterior half, posterior half finely shagreened, with minute, shallow punctures. Scutellum typical for the genus, conical, visible between the emarginated bases of the elytra. Elytra cylindrical 1.5 × as long as wide, 1.3 × as long as pronotum, side straight on anterior half, narrowed on posterior half; striae on the disk very shallowly impressed, regularly and rather densely punctured; interstriae flat, finely and regularly punctured; interstriae 1, 2 and 3 with small tubercles just before the upper margin of the declivity. Elytral declivity long, nearly from the middle of elytra, sulcate, sutural interstriae weakly elevated on upper part, not elevated below, without granules; lateral edges formed by strongly elevated continuation of 3rd interstriae, which bears four pairs of long, narrow, posteriorly directed sharply pointed spines, which increase in length approaching posterior margin, the last two pair exceeding outline of the elytral edge; several small, fine spines on the lateral raised margin of declivity. Vestiture consisting of moderately long, fine setae in uniseriate rows on interstriae, longer on declivity. Legs yellowish, brown.

Male. Not examined.

Distribution.

China, Japan, South Korea ( Wood and Bright 1992). United States (all records new to North America, numbers of specimens collected at each location shown in parentheses.): ALABAMA, Tuscaloosa County: Vance, 14 August 2008, ethanol-baited funnel trap (1);LOUISIANA, Winn Parish: Kisatchie National Forest, 6 miles w. of Winnfield, 24 April 2008, α-β-pinene (70:30) and ethanol-baited funnel trap (1); 23 March 2009, α-β-pinene (70:30) and ethanol-baited funnel trap (3), ethanol-baited funnel trap (3), phoebe oil-baited funnel trap (2); 9 April 2009, α-β-pinene (70:30) and ethanol-baited funnel trap (1),: ethanol-baited funnel trap (2); 21 April 2009, α-β-pinene (70:30) and ethanol-baited funnel trap (7), ethanol-baited funnel trap (4); 29 April 2009, α-β-pinene (70:30) and ethanol-baited funnel trap (3), ethanol-baited funnel trap (6),: phoebe oil-baited funnel trap (2); 21 May 2009,: α-β-pinene (70:30) and ethanol-baited funnel trap (1); 3 June 2009, trap on girdled yaupon (14); 9 June 2009,: trap on girdled yaupon (3); 15 June 2009, trap on girdled yaupon (3); 14 July 2009, trap on girdled yaupon (2); 4 August 2009,: trap on girdled yaupon (2). All specimens collected in North America are females.

Biology, habits, and host.

In its native Asian range, the known hosts for Xyleborinus octiesdentatus are Carpinus laxiflora (Siebold and Zuccarini) Blume ( Corylaceae ), Cleyera sp., Eurya japonica Thunberg ( Theaceae ) and Illicium religiosum Siebold ( Illiaceae ) ( Wood and Bright 1992), and Illex rotunda Thunberg ( Aquifoliaceae ) ( Murayama 1934).

Although this species is certainly established in the Winnfield area of Louisiana (Winn Parish) and probably in Alabama (Tuscaloosa Co.), it has not been collected from any host trees. In May, 2009, on the Kisatchie National Forest, Ilex vomitoria Aiton (yaupon), Ilex opaca Aiton (American holly) ( Aquifoliaceae ) and Carpinus caroliniana Walter (ironwood) ( Corylaceae ) were girdled and a sticky band placed on the trees to act as attractant/trap trees for the beetle. These species were selected because known hosts of the beetles belonging to these genera occur in Asia. During the month following this treatment 27 specimens were collected on the sticky band on the girdled yaupon whereas no specimens were collected from the other species. No specimens of Xyleborinus octiesdentatus were found boring into the yaupon tree.

The impact Xyleborinus octiesdentatus will have in North America is still uncertain. All species of xyleborines carry symbiotic ambrosia fungi that are usually benign to hosts in their native range. However, as recently discovered with Xyleborus glabratus Eichhoff, 1877, another ambrosia beetle introduced from Asia, certain ambrosial fungi may prove to be very pathogenic on new, novel hosts in North America ( Fraedrich et al. 2008). Future studies with Xyleborinus octiesdentatus will attempt to identify fungal associates, and test their pathogenicity against North American host trees.