Taiwanese ambrosia beetle (Eccoptopterus formosanus) and midst ambrosia beetle (Eccoptopterus intermedius)

NEWS - Two xyleborine ambrosia beetles, Taiwanese ambrosia beetle (Eccoptopterus formosanus Lin, Sittichaya & Smith, sp. nov.) and midst ambrosia beetle (Eccoptopterus intermedius Sittichaya, Lin & Smith, sp. nov.) described from Taiwan and Thailand based on DNA sequences (COI and CAD) and morphological characteristics.

Eccoptopterus Motschulsky 1863 is the earliest described xyleborine ambrosia beetle (Coleoptera: Curculionidae: Scolytinae). Victor Ivanovich Motschulsky assigned the name to the monotypic genus and a new species, E. sexspinosus Motschulsky 1863, described from Burma.

Currently 14 species and subspecies have been described of which 4 are: E. drescheri Eggers 1940, E. limbus Sampson 1911, E. spinosus (Olivier, 1800) and E. tarsalis Schedl 1936. Eccoptopterus is easily distinguished by its autapomorphically enlarged metatibiae and metatarsi.

Based on specimens collected as part of a survey of xyleborine ambrosia beetles in Thailand and Taiwan, researchers have found variations in Eccoptopterus specimens that suggest the potential for a new species.

E. formosanus female, 2.56−2.64 mm long (mean = 2.61 mm; N = 4), 2.13−2.17× as long as wide (mean = 2.14×; N = 4). Medium body size, declivital armature composed of a pair of major spines on declivital summit and 2–4 minor denticles unevenly spaced on each lateral margin; protibiae slender, broadest at apical 1/3, outer margin armed with six or seven moderated socketed denticles; scutellum broadly linguiform; elytra tapering laterally.

Bred from Elaeocarpus sylvestris (Lour.) Poir. (Elaeocarpaceae), Lithocarpus hancei (Benth.) Rehder, Quercus glauca Thunb. ex Murray (Fagaceae), Sapium discolor Muell.-Arg. (Euphorbiaceae), Trema orientale (L.) Blume (Cannabaceae) with a diameter of about 4.8–6.2 cm in Taiwan. The radial entrance gallery leads to several branches in various planes without enlarged brood chambers.

E. intermedius female, 1.70−1.90 mm long (mean = 1.80 mm; N = 6), 2.03−2.38× as long as wide (mean = 2.13×; N = 6). Small body size, declivital armature composed of a pair of major spines at interstriae 3 on declivital summit and four minor spines unevenly spaced on each lateral margin, declivity covered with flattened scale-like setae; protibiae slender, broadest at apical 1/3, outer margin armed with four or five moderated socketed denticles, elytra tapering laterally.

Formosa is the old name of the island of Taiwan, referring to the location of the type collection with a distribution in Nantou County). L. inter + medius = in the middle. The name refers to the morphological character of the species which is intermediate between E. limbus and E. spinosus. Distribution in Chiang Mai, Lamphun, Tak, Ubon Ratchathani provinces (Thailand).

The differences in COI and CAD sequences between the new species (E. formosanus, E. intermedius) and E. limbus, E. spinosus sensu lato and the junior synonym E. gracilipes are greater than the suggested species boundaries for these genera. Geographically separated morphological characters also show variation in the degree of elytral constriction and density of declivital setals.

E. intermedius is more similar to E. limbus than to E. spinosus but some characters are intermediate. E. intermedius differs from E. limbus by its smaller size, shorter elytra (elytra: pronotum), only four minor spines on the declivital margin, and more slender protibiae. It differs from E. spinosus by its hair-like declivital seta and only one pair of major spines and more slender protibiae.

E. formosanus is more similar to E. spinosus than to E. limbus. E. formosanus differs from E. spinosus in lacking the second and third major spines on the declivital margin and the declivital surface is densely covered with long, thick setae. It differs from E. limbus in having a smaller body size, tapering elytra and a declivital margin with 2–4 minor denticles.

Original research

Sittichaya W, Lin C-S, Smith SM, Pornsuriya C, Cognato AI (2024). Two new species of Eccoptopterus Motschulsky, 1863 ambrosia beetle from Taiwan and Thailand (Coleoptera, Curculionidae, Scolytinae, Xyleborini). ZooKeys 1217: 247-262, DOI:10.3897/zookeys.1217.129707

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