Xyleborus atratus Eichhoff 1875

Xyleborus atratus Eichhoff, 1875

General features. Xyleborus atratus is superficially very similar to the Holarctic Anisandrus dispar (Fabricius) but may be readily distinguished from Anisandrus by the absence of a pronotal or mesonotal mycangium, as indicated by a median tuft of hairs at the base of the pronotum. In Xyleborus the mycangium usually consists of mandibular pouches, suggesting a more distant relationship (Hulcr et al. 2007). In addition to the absence of the pronotal tuft of hairs (Fig. 1 a), X. atratus can be distinguished from A. dispar by the absence of serrations on the anterior margin of the pronotum (Figs. 1 b, 1c), the more impressed, weakly bisulcate elytral declivity (Fig. 1 d), longer interstrial setae on the declivity (Fig. 1 a) and the slightly smaller size.

Diagnosis. Female. Length 3.0 mm, 2.6x longer than wide; black in maturity. Frons reticulate (Fig. 1 b), with large dense punctures, particularly on sides. Pronotum 1.1 mm long, 1.1x longer than wide (Fig. 1 a); anterior margin rounded and unarmed (Fig. 1 c); summit near middle (Fig. 1 a), sides arcuate; disc faintly reticulate, sparsely, shallowly punctured; punctures on disc moderately large, close, spaced by diameter of punctures, not deeply impressed, without setae. Elytra 1.7 mm long, 1.5x longer than wide; uniseriately punctatesetose, length of setae equal to width of interstriae, longer posteriorly (Fig. 1 a); punctures becoming granulate posteriorly and gradually increasing in size. Declivity short, steep, occupying less than posterior 20% of elytra; declivity shallowly bisulcate with interstriae 1 and 3 equal in height, interstria 2 impressed (Fig. 1 d); uniseriate granules on all interstriae abundant, small, uniform in size; strial punctures larger than pronotal ones, spaced by 0.5x their diameter; interstriae 2x wider than striae (Atkinson et al. 1990; Rabaglia et al. 2006). Male. Not found in Europe but described and illustrated by Murayama (1933).

Distribution. The species is widespread in Asia (Korea, Japan, Taiwan, Malaya, Vietnam, China, Burma). It was introduced before 1990 to North America (Atkinson et al. 1990), where it now occurs in Alabama, Delaware, Florida, Georgia, Kansas, Kentucky, Louisiana, Maryland, Mississippi, North Carolina, Ohio, South Carolina, Tennessee, Texas, Virginia and West Virginia (Wood & Bright 1992; Rabaglia et al. 2006). The species was listed also from the Philippine Islands, New Guinea and Indonesia (Borneo, Java, Sumatra) by Nobuchi (1967), and although Wood & Bright (1992) include these countries in the distribution of the species, there are no actual records of it from any of them.

Hosts. Xyleborus atratus is extremely polyphagous on broadleaved trees, although it has been occasionally reported also on pine. The main host trees, arranged in alphabetical order of family, include Acer (Aceraceae), Aralia (Araliaceae), Alnus, Betula, Carpinus (Betulaceae), Diospyros (Ebenaceae), Acacia, Albizzia, Ormosia (Fabaceae), Quercus, Fagus, Castanopsis, Lithocarpus (Fagaceae), Cinnamonum, Litsea, Machilus (Lauraceae), Morus (Moraceae), Prunus, Malus (Rosaceae), Evodia (Rutaceae), Styrax (Styracaceae), Ternstroemia (Temstroemiaceae), Camellia, Cleyera, Stewartia (Theaceae) and Ulmus (Ulmaceae) (Choo 1983).