Pseudagrion perfuscatum, Lieftinck, 1937

Pseudagrion perfuscatum View in CoL and P. pilidorsum

At Borneo Island P. perfuscatum occurs in West Kalimantan, Brunei and Sarawak, and probably East Kalimantan although the number of published observations especially from the latter area is low ( Dow et al. 2024). The records of P. perfuscatum published from Sabah need to be verified (R.A. Dow, pers. comm.). Pseudagrion pilidorsum appears to be much scarcer and observations are restricted to the north and east of Borneo. Records are published from East Kalimantan, Sabah, and Sarawak ( Dow 2006, Dow & Reels 2008, Dolný et al. 2011, Steinhoff et al. 2019, Dow et al. 2021, Dow & Singa 2022). Both species are almost identical in morphology of the male cercus, and they share the red face including a completely red frons—a character that sets them apart from all other species of the Pseudagrion red-group. Typical males of P. perfuscatum ( Figs 163, 164) can be easily separated from P. pilidorsum ( Figs 165, 166) by the more extensive black on the dorsum of the head, the broader black humeral stripe (lacking in P. pilidorsum ), the dorsum of S1–2 being largely black (red in typical P. pilidorsum ), and the presence of dense pruinosity on the pterothorax and the basal two abdominal segments (lacking in P. pilidorsum ). However, there are also specimens in which these characters are less strongly expressed making the identification difficult. An example of a specimen with intermediate characters is shown in Bartá & Dolný (2013: 87) as P. pilidorsum . This male does have S1–2 dorsally black, a comparatively dark vertex (pro perfuscatum ), and the humeral suture is only partly black (pro pilidorsum ). Similarities are present in the male pictured in Fig. 167: in this individual the ground colour of the pterothorax is more reddish-brown with pruinosity up to interpleural suture (both pro perfuscatum ), but lacking a black stripe at humeral suture as well (pro pilidorsum ). Unfortunately the dorsum of S1–2 as well as the pattern of the head is not clearly visible in this photo, although it seems to be less black dorsally at the respective abdominal segments than it is usually in P. perfuscatum . However, P. pilidorsum and P. perfuscatum are very closely related, and developed a complex hybridization zone in the northeast of Sarawak and probably in East Kalimantan and parts of Sabah (R.A. Dow, pers. comm.). Many Bornean populations appear somewhat intermediate and additional taxonomic research of the Pseudagrion red-group in Borneo, including molecular studies, is needed to clarify the situation.