Asiagomphus pacificus
Creators: name: Kompier, Tom
Publisher: name: Zenodo
Year: 2018
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Odonata
Gomphidae
Asiagomphus
Asiagomphus pacificus

description: Asiagomphus pacificus (Chao, 1953)
(Figs. 4c–d, 5b, 6b, 7b, 8c, 10g –h, 13d)
Asiagomphus sp.: Wilson (1999) pp. 34–36, figs. 19–20;
Asiagomphus pacificus: Wilson (2005) pp. 131–132, figs. 14a–d [records from Guangxi, China]; Wilson & Xu (2009) pp. 12– 13, figs. 2a–d [comparison with A. hainanensis, reappraisal of historic records of A. hainanensis from Guangdong, China, overview of records from literature].
[For extensive overview of literature with records of this species, see Chao (1990), Wilson (1999, 2005) and Wilson & Xu (2009)].
Material examined: 1 ♂ Cao Bang Prov., northern Vietnam, 19-V-2015, TK leg.; 1 ♀, Bac Kan Prov., northern Vietnam, 24-VI-2014, TK leg.; 1 ♀, Cao Bang Prov., northern Vietnam, 6-VI-2018, TK leg.
Additional records based on field observations by TK: 4 ♂♂, Cao Bang Prov., northern Vietnam, 19-V- 2015; 3 ♂♂, same location, 20-V-2015; 1 ♂, same location, 18-VI-2015; 20 ♂♂ 3 ♀♀, same location, 6-VI-2018.
Differential diagnosis. For differences between Asiagomphus pacificus and A. hainanensis see the discussion below. Asiagomphus pacificus can be separated from all other Vietnamese species by the longitudinal markings along the dorsal carina of the S2–6.
Habitat and ecology. In Cao Bang Province the species occurred at a medium-sized river, with sandy and pebbly substrates and larger rocks in a forested valley close to Cao Bang City. Males perched in the sun on larger rocks in the stream or on pebble beaches by the side of the river, whereas females where found perched on vegetation a little removed from the stream. The female in Bac Kan Province was found at a shallow rocky stream, over a pebble substrate in patchy degraded forest between cleared hills close to Ba Be NP, perched over the stream in bushes at head height. In Cao Bang it occurred together with Asiagomphus acco and in Bac Kan with A. auricolor.
Discussion. There has been considerable confusion regarding the identity of two very similar Asiagomphus species with longitudinal markings along the dorsum of the abdomen that occur in southern China: A. pacificus and A. hainanensis. Wilson (1999) recounts the confusion surrounding the identity of A. hainanensis from Hong Kong described by Asahina, first (1966) as A. hainanensis and later (1988) reidentified as A. septimus (Needham, 1930). Wilson (2005) and Wilson & Xu (2009) discussed the differences between the very similar A. pacificus and A. hainanensis, focusing on differences of body structure and patterning: “[A. pacificus is] very similar to A. hainanensis Chao, which has more extensive yellow coloration on the sides of the synthorax, a pair of quadrate spots on the labrum and is generally a less robust insect. The labrum of pacificus is entirely black” (Wilson 2005, p. 132) and “ Asiagomphus pacificus is significantly larger and slightly bulkier species than A. hainanensis Chao and its males feature a uniformly straight occipital margin without any small spines. Its antehumeral stripe may be complete or interrupted in the middle […] and its labrum is entirely black” (Wilson 2009, p. 13). Based on these differences, Wilson identified specimens from Guangxi and Guangdong as A. pacificus. Mr. Wen-Chi Yeh (in litt.) pointed out that male specimens from Taiwan of these two species are often difficult to reliably separate, although dorsal stripes in A. pacificus tend to be more parallel-sided and more weakly connected to the collar, whereas in A. hainanensis the dorsal stripes are more broadly connected to the collar stripes and attenuate upwards. Their caudal appendages and secondary genitalia are not distinctly different. My observations of other Asiagomphus species show that the presence or absence of small quadrate spots on the labrum may vary within a species, and so does size. The observed males in Cao Bang Province moreover displayed both parallel-sided dorsal stripes more weakly connected to the collar and more upwardly attenuated dorsal stripes broadly connected to the collar. However, the identity of my specimens, which also have all black labrum, is further supported by the spines adjacent to the lateral ocelli in the females. Mr. Wen-Chi Yeh (in litt.) commented that although the differences between their vulvar laminae do not provide a reliable help to identification, at least in Taiwan females of both species can be reliably separated on the basis of their head structures. Like my specimens, A. pacificus on Taiwan has one spine between each lateral ocellus and the seam of the compound eye and another at the posterior end of the ridges shielding the lateral ocelli posteriorly. It has therefore four prominent spines around the ocelli. Even though my specimens have a small spine on the occipital ridge not seen in the Taiwanese specimens, this strongly supports the identification of the Vietnamese material as A. pacificus. This is in line with the conclusion by Wilson (2005) and Wilson & Xu (2009), although they used different characters to support their conclusion, that Chinese material from Guangxi and Guangdong also concerns A. pacificus.
description: Published as part of Kompier, Tom, 2018, The genus Asiagomphus in Vietnam, with descriptions of three new species, and first descriptions of the male of Asiagomphus auricolor (Fraser, 1926) and of the female of Asiagomphus reinhardti Kosterin & Yokoi, 2016 (Odonata: Gomphidae), pp. 301-330 in Zootaxa 4462 (3) on page 318, DOI: 10.11646/zootaxa.4462.3.1, http://zenodo.org/record/1441611