Xyleborus bispinatus Eichhoff

Faccoli, Massimo, Campo, Giuseppe, Perrotta, Giancarlo & Rassati, Davide, 2016, Two newly introduced tropical bark and ambrosia beetles (Coleoptera: Curculionidae, Scolytinae) damaging figs (Ficus carica) in southern Italy, Zootaxa 4138 (1), pp. 189-194 : 191-192

Xyleborus bispinatus Eichhoff

Description. Accurate description and detailed photos of X. bispinatus are reported by Kirkendall and Jordal (2006) and Atkinson et al. (2013). As in many Xyleborus species, a strong sexual dimorphism occurs with females (2.8–3.2 mm) ( Fig. 2 ) sensibly larger than males (1.6–1.9 mm). Females of X. bispinatus are characterized by the moderately steep, flattened and shining elytral declivity armed on interstriae 3 by one pair of rather prominent tubercles located closer to the base of declivity than apex, and sometimes showing 1 to 3 smaller additional tubercles ( Fig. 3 ). Declivital interstriae 1 and 2 are each usually armed with a small tubercle at their extreme base ( Fig. 3 A and 3B).

According to the size and declivital characteristics, X. bispinatus could be confused with the European Xyleborus eurygraphus (Ratzburg) and Xyleborus monographus (Fabricius) ( Faccoli et al. 2009) . However, X. eurygraphus is sensibly larger (3.4–4.0 mm) than X. bispinatus , with the anterior margin of pronotum distinctly subtruncate (rounded in X. bispinatus ), and with a pair of major tubercles on the interstria 1 in the middle of the declivity. Furthermore, X. eurygraphus infests only pines. Xyleborus monographus is a little bit larger (3.0– 3.5 mm) than X. bispinatus , and the interstria 3 is always armed with two stout, conical tubercles forming the corners of a square occurring in the middle of the declivity. Other interstriae on declivity are flat, dull, impunctate, with no or very few small granules. Finally, X. monographus lives mainly on oaks. The other European species belonging to the genus Xyleborus have declivity armed only with uniform small granules, and devoid of large prominent tubercles ( Faccoli 2008).

Distribution. X. bispinatus is a species native to Neotropical and sub-tropical regions which has been introduced into new territories with international trade of tropical timber. X. bispinatus is broadly spread in lowland Neotropical areas—mainly of Central and northern South America—although in the last years it has been found also in many US states of the eastern coast (introduced). In detail, in North America X. bispinatus was found in México and the USA (Florida, Georgia, Indiana, Louisiana, Maryland, North Carolina, New York, and Texas); in Central America in Belize, Costa Rica (including Cocos Island), Guatemala, Honduras, and Panamá; in South America in Bolivia, Brazil, Ecuador, Perú, and Venezuela. This is the first record of breeding populations of X. bispinatus to Italy and Europe.

Host plants. Because of the long synonymy of X. bispinatus with Xyleborus ferrugineus (F.) (see Taxonomic notes), specific data concerning the host trees of X. bispinatus are few. Xyleborus ferrugineus is reported to be highly polyphagous, with about 200 unrelated broadleaf tree host species ( Schedl 1962; Wood 1982, 2007), In Florida, X. bispinatus was associated with wilted trees of avocado Persea americana (Mill.) , swampbay Persea palustris (Raf.) (Fam. Lauraceae ), and foxtail palm Wodyetia bifurcata Irvine (Fam. Arecaceae ) ( Atkinson et al. 2013). Some findings are known also from Quercus spp. (Fam. Fagaceae ) and Swietenia macrophylla (Fam. Meliaceae ). In Sicily X. bispinatus has been found only on wild and cultivated varieties of the common fig, Ficus carica (Fam. Moraceae ).

Taxonomic notes. For long time X. bispinatus and X. impressus Eichhoff were considered as synonyms of X. ferrugineus , an invasive species currently found in all tropical and warm temperate areas of the world ( Bright 1968; Wood 1982; Wood & Bright 1992). X. bispinatus and X. ferrugineus are broadly sympatric in Central and northern South America, and were clearly distinguished by Blandford (1905) for Central America, although then placed in synonymy by Schedl (1960). A closer examination of the variability of characters within regions has shown that these synonymies were unjustified, and both X. impressus and X. bispinatus were recently resurrected from X.

ferrugineus ( Rabaglia 2005 and Kirkendall & Jordal 2006, respectively). Later, Atkinson et al. (2013) discussed new characters allowing the definitive separation of these three species after a comparison of a large series of specimens. The validity of these two species was finally confirmed by Gohli et al. (2016).

Position of the major spines along the declivity and body size are the most consistent and useful characters for distinguishing X. bispinatus and X. ferrugineus ( Kirkendall and Jordal 2006; Atkinson et al. 2013). Major spines along the declivital interstria 3 are usually closer to the base of the declivity than apex in X. bispinatus , while they are in the middle of the declivity in X. ferrugineus ( Kirkendall & Jordal 2006) . Xyleborus bispinatus is, moreover, slightly darker and larger (2.8–3.2 mm) than X. ferrugineus (2.4–2.9 mm), with non-overlapping size ranges in Florida ( Atkinson et al. 2013) though not in all regions (Kirkendall, pers. comm.). In addition, large interstrial setae are clearly visible on the declivity and elytral disc of X. bispinatus but they are sparse on the declivity, and generally absent from the disc, in X. ferrugineus ( Kirkendall & Jordal 2006; Atkinson et al. 2013).

Figures

FIGURE 2. Female of Xyleborus bispinatus, dorsal view

FIGURE 3. Xyleborus bispinatus: A) female lateral view; B) declivity.