Laothoe populeti subsp. caucao Zolotuhin, 2018

SYN. & STAT. NOV. Zolotuhin (2018) (STI 21919) distinguished Laothoe caucao from Laothoe populeti and Laothoe populi based on several minor characters of the habitus and male genitalia, in addition to respective DNA barcode divergences of 2.4% and 3.45%. In terms of the habitus, L. caucao was said to differ mainly in the shape of the forewing antemedial band and the extent of the basal red-brown basal spot of the hindwing. Examination of 14 specimens from the Greater Caucasus in NHMUK, as well as two from the type locality (Tiflis, = Tbilisi]), revealed considerable individual variation in size, ground colour and wing pattern, with some specimens approaching Laothoe populi and others essentially identical to Laothoe [populeti] populeti. As for other species of the Laothoe populi group, differences in the male genitalia are limited to the form and number of the cornuti on the phallus vesica: in caucao, there was said to be a single basal needle-shaped large cornutus (although several are visible in Zolotuhin, 2018: fig. 4), with a small, sparse group of smaller distal cornuti and a weak apical lobe. However, these differences in this structure are relatively minor; indeed, Kitching & Cadiou (2000) (STI 18788) commented that there is considerable intraspecific variation in cornuti shape in Laothoe populi, and that in this species, they are at best indicative of subspecies differentiation. The same is considered here to apply to populations of Laothoe populeti. Regarding the DNA barcode divergence, Řezáč (2018) (STI 21910) commented in his study on Rhodoprasina that in that genus “intraspecific divergences are of the order of 4% [and] differences below 2%, unless supported by conspicuous traits in habitus and the structure of the genitalia, cannot be considered significant, even at subspecies level”. This seems to be generally true of many Smerinthini that do not feed as adults and thus, in the absence of such morphological differences, the divergence of 2.4% from populeti would indicate subspecies differentiation at best. Taken together, they provide no justification for treating Laothoe caucao as a species separate from Laothoe populeti but rather as a subspecies, Laothoe populeti caucao. There is also a potential issue over the identity of the type population of caucao. Zolotuhin (2018: fig. 2) illustrated a tree (presumably a neighbour-joining tree, though this is not stated) of samples derived from BOLD in which five from Armenia and two from Georgia form two distinct clusters that he identified as populeti and caucao (respectively BINs AAC0913 and ABX0813). These samples are doubtless those from which he derived his divergence figures. Zolotuhin (2018) then stated that among other specimens from further south in the Lesser Caucasus was a [female] specimen from Vaik [Vayk], Armenia, illustrated by Danner et al. (1998: colour plate 8, figure 11) (STI 17787), that he identified as caucao. However, in BOLD, one of the five samples from Armenia (BC-EMEM1180), a male, has identical data but falls into the BIN identified as Laothoe populeti populeti. The two DNA barcoded specimens of Laothoe populeti caucao (BIN ABX0813) come from Tusheti, within the Greater Caucasus. However, if Laothoe populeti caucao is restricted to the Greater Caucasus, and Laothoe populeti populeti occurs from the northern slopes of the Lesser Caucasus south into Turkey, Iraq, Iran and SW Turkmenistan, then a question mark must hang over the population from the type locality of Laothoe populeti caucao near Tbilisi, as this location could be interpreted as being on the northern edge of the range of populeti or the southern edge of the range of caucao. Furthermore, at the time of capture of the holotype of Laothoe populeti caucao (i.e., 1907), “Tiflis” may well have referred to the entire Tiflis Governate (https://en.wikipedia.org/wiki/Tiflis_Governorate), which included parts of the ranges of both subspecies. So, given that morphology is a very poor guide to subspecies assignment in this region, the true identity of Tbilisi specimens (and thus Laothoe populeti caucao itself) must await the results of DNA barcoding studies of moths from this area.