Acanthotomicus suncei Cognato, 2018

Gao, Lei & Cognato, Anthony I., 2018, Acanthotomicus suncei, a new sweetgum tree pest in China (Coleoptera: Curculionidae: Scolytinae: Ipini), Zootaxa 4471 (3), pp. 595-599 : 596-598

Acanthotomicus suncei Cognato , sp. n.

( Figs. 1–6 )

Diagnosis. The placement of elytral declivital spines on interstriae 2, 4, 6, and 8 and the connection of spines 1 and 2 by a tumescence distinguish A. suncei n. sp. from all other Oriental Acanthotomicus species. The elytral declivital spines occur on interstriae 1, 2, and 4 for A. perexiguus (Blandford, 1896) and on interstriae 2–9 for A. spinosus (Blandford, 1894) . Acanthtomicus suncei , A. spinosus and A. perexiguus are the only species reported from China.

Description. Holotype, male, total length 2.4 mm (2.3–2.5 mm, n = 12), 3.43 times as long as wide, antennae, head, legs, thorax, and elytra reddish-brown ( Fig. 1 ).

Head. Epistomal setae present. Frons slightly convex, granulate, punctures in concentric rows; scattered frontal tubercles approximately mid-frons; ( Figs. 2 & 3 ). Scape longer than funicle; five funicular segments, including pedicel; antennal club flattened, with sensillae on anterior face, partitioned by two procurved sutures ( Fig. 4 ).

Pronotum. 0.8 mm wide (0.7–1.0 mm, n = 12), 1.14 times as long as wide; summit approximately on anterior third, scalpriform rugosities with interspersed setae on anterior half; posterior half disc shining, shallowly, minutely punctate, with scattered erect hair-like setae; base transverse, curved laterally ( Figs. 1 & 2 ).

Scutellum. Triangular, flush with elytra ( Fig. 1 ).

Elytra. 2.0 times as long as wide, 1.12 times longer than pronotum. Elytral base transverse. Discal strial punctures uniseriate, nearly contiguous, shallowly impressed, with erect hair-like setae, setae longer near declivital base; interstrial punctures uniseriate, shallow, one quarter diameter of strial punctures, with hair-like setae approximately 0.5–0.75 shorter than strial setae ( Fig. 1 ). Declivital margin of each elytron with four sub-equal acute spines, each approximately as long as two strial punctures; first spine arising from interstria 2; second spine arising from interstria 4 connected to the first spine by a low tumescence; third spine arising from interstria 6; fourth spine arising from interstria 8 connected by a tumescence reaching the apex of the declivity; apical third of fifth–ninth interstriae granulate/tuberculate, interstria 7 with a larger tubercle near edge of declivital margin ( Figs. 1, 2 , & 5). Declivital face with striae 1 and 2 curving laterally, declivital suture setose.

Terminalia. Aedeagus without seminal trough, internal sac “tuning-fork” shaped subequal in length to median tube; median struts one-third longer than median lobe.

Female. Similar to male in most features except elytral spines and tubercles reduced in size and lateral areas of the elytral declivity greatly inflated.

Type Material. Holotype: male. CHINA: Jiangsu, Nanjing, Yuhuatai; sweetgum 1980.4.20 Lianying Liu coll. ( NMNH)

Paratypes: CHINA: Jiangsu, Nanjing ; host: sweetgum 1979.6 Zuting Tang Coll. ( NMNH, 2) . CHINA: Shanghai, ex. Liquidambar styraciflua , 5 May 2016 Lei Gao Coll , ( NZMC, 3) (Specimen catalog numbers: IOZ (E) 229118 [male]; IOZ (E) 229119–229120 [females]) . CHINA: Shanghai, Jinshan District , ex. L. styraciflua , 26 April 2016 Lei Gao Coll. ( MSUC, 4; NMNH, 1; UF, 2; FU, 2; RABC, 2; SNUC, 2).

Etymology. Acanthotomicus suncei (pronuncation SOON-(t)SUH-EE). After warlord Sun Ce (175–200 A.D.) who conquered the Wu territory which became the state of Eastern Wu (222–280 A.D.) and where Shanghai would eventually develop.

Given its potential economic and ecological impacts in North America, “sweetgum inscriber” is suggested as a common name. “Inscriber” describes the beetle’s behavior of etching the bark and sapwood with egg niches and larval galleries ( Figs. 6 & 7 ) and also distinguishes it from other engraver beetles ( Ips DeGeer, 1775 , Orthotomicus Ferrari, 1867 , and Scolytus Geoffroy, 1762 ).

Notes. DNA was extracted from a specimen of A. suncei and partial cytochrome oxidase I and 28S genes were sequenced (Genbank: COI, MH350029 ; 28S, MH350030 ). These sequences were added to an existing Ipini data set and reanalyzed with the same Bayesian settings following the protocols in Cognato (2013). The resulting tree was nearly identical to the original tree ( Fig. 3 in Cognato 2013) and differed in the placement of an Ips species. A. suncei grouped with the majority of Oriental species including A. spinosus , A. sp. 1/Sarawak, and A. sp. 3/Thailand, and this group had a 0.99 posterior probability. Acanthotomicus suncei was sister to A. sp. 1/Sarawak, and A. sp. 3/ Thailand but the posterior probability was low at 0.73. These species differ morphologically from A. suncei by the presence of long spines (> 3x basal width) on the lateral margin of the elytral declivity.

Damage to host trees. The known hosts of this bark beetle are limited to sweetgum trees, including L. styraciflua and L. formosana . Since the first damage report, more cases of the infested trees were discovered in Shanghai and adjacent Jiangsu Province ( Figs. 8 ). As the original host L. formosana is widely distributed in southern China, the possible distribution range of A. suncei might be larger than currently known. Potentially the upper bound timber-based economic losses to plantation owners may reach $151.9 million if this bark beetle is accidentally introduced to the US ( Susaeta et al. 2017).

Figures

FIGURE 6. Acanthotomicus suncei sp. n. male in situ. (Imaged by You Li)

FIGURE 7. Egg gallery and eggs of Acanthotomicus suncei sp. n.

FIGURE 8. Dead sweetgum trees due to infestation of Acanthotomicus suncei sp. n. in a tree nursery, Shanghai, China.

FIGURES 1–5. 1. Acanthotomicus suncei sp. n. male. 1. Dorsal view. 2. Lateral view. 3. Frontal view. 4. Antenna. 5. Eytral declivity.