Taxonomic history

Xyleborus osumiensis Murayama, 1934: 292.

Ambrosiophilus osumiensis (Murayama): Smith et al., 2018b: 393.

Synonyms

Xyleborus metanepotulus Eggers, 1939b: 119. Smith et al., 2018b: 393.

Xyleborus nodulosus Eggers, 1941b: 233. Smith et al. 2020b: 65.

Xyleborus pernodulus Schedl, 1957: 85. Unnecessary replacement name. Browne, 1961c: 50.

Xyleborus hunanensis Browne, 1983b: 33. Beaver 2011: 283.

Ambrosiophilus peregrinus Smith and Cognato, 2015: 216. Smith et al. 2017: 552.

Diagnosis

2.3−3.2 mm long (mean = 2.6 mm; n = 7); 2.3−2.67 times as long as wide. This species can be distinguished by declivital interstriae 1 unarmed, 2 armed by 3−5 pointed tubercles along its length, major declivital tubercles on interstriae 2; weakly to moderately sulcate to striae 1, interstriae 2 convex, bearing 3−5 pointed tubercles and several small granules (near apical and basal margins) along its length; pronotum from dorsal view basic or subquadrate (type 2 or 3); and pronotum from lateral view basic (type 0).

May be confused with

Ambrosiophilus papilliferus, A. subnepotulus, and A. wantaneeae

Distribution

China (Anhui, Chongqing, Fujian, Guangxi, Guizhou, Hunan, Jiangxi*, Sichuan*, Yunnan), Japan, Taiwan, Vietnam; imported and established in USA (Smith and Cognato 2015, Schiefer 2018)

Host plants

This species is likely polyphagous and has been recorded from numerous host families including Pistacia (Anacardiaceae), Ilex (Aquifoliaceae), Quercus sp. (Fagaceae), Cinnamomum (Lauraceae), Broussonetia (Moraceace), and Ligustrum (Oleaceae) (Smith et al. 2020b).

Remarks

The morphology of A. osumiensis is highly variable in regard to numerous characteristics that are routinely used to diagnose other xyleborine species. Such variation includes: the antennal club type either 3 or 4; pronotum basic (type 2) or subquadrate (type 3) from dorsal view; elytral declivity shining or shagreened; pronotal disc shining or shagreened; number and size of tubercles on declivital interstriae 2; and a large size range with individuals differing by up to 0.9 mm in length. This variation led to A. osumiensis being described several times. Types of each species are distinct and diagnosable. Examination of the specimens listed above in ‘new records’ as well as the holotypes showed that these species formed a continuous spectrum of variation. During our fieldwork we were able to collect and sequence specimens that fell within the concept of X. metanepotulus (Vietnam), X. hunanensis (China), X. nodulosus (China), A. peregrinus (Georgia, USA), and an additional larger morphospecies from multiple localities in Vietnam. COI sequences showed that all populations differed by no more than 7.4% supporting the hypothesis of one morphologically variable species. Typical intraspecific variation in xyleborines is below 10% (Cognato et al. 2020b).

The identification of this A. nodulosus from East Malaysia by Browne (1980b) and Ohno (1990) appears to be incorrect. We have therefore omitted East Malaysia from the distribution, and also omitted the associated host records. The host records reported in Smith et al. (2017) are therefore incorrect.

DNA data

Sequences available for COI and CAD.

COI: KP236133MN619833MN619834MN619835MN619836

CAD: MN620128MN620129MN620130