Laothoe populetorum (Staudinger, 1887) [Invalid]

SYN. & STAT. REV. Proposed as a [geographical] variety of Smerinthus populi. Synonymized with Amorpha populi populeti by Rothschild & Jordan, 1903, Novit. zool. 9 (suppl.): 335. Raised to species status by Danner, Eitschberger & Surholt, 1998, Herbipoliana 4 (1): 109. Resynonymized with Laothoe populi populeti by Kitching & Cadiou, 2000, Hawkmoths of the world: 53. Reinstated as a species by Eitschberger, 2002, Neue ent. Nachr. 53: 155. Resynonymized with Laothoe populi as a subspecies by Kitching and Rougerie et al., 2018, Biodivers. Data J. 6: e22236. Reinstated as a species by Zolotuhin, 2018, Eversmannia 54: 7. Described as a geographical variety of Smerinthus populi, and later synonymized with Amorpha populi populeti by Rothschild & Jordan (1903) (STI 19807), Laothoe populi populetorum was raised to species status by Danner, Eitschberger & Surholt (1998) (STI 17413) based mainly on differences in size, the distal field of cornuti on the vesica and egg chorion morphology. Kitching & Cadiou (2000) (STI 18788) reviewed these characters and concluded that they provided insufficient evidence for species status and synonymized populetorum once more with Laothoe populi populeti. In reinstating populetorum once more as a species, Eitschberger (2002) (STI 17730) simply asserted the revived status and provided no new counterarguments. However, study of a small number of DNA barcode sequences has shown that populetorum was only ≈2.5% different from Laothoe populi populi and Laothoe populi iberica, and that all these were much more divergent (≈ 4%) from Laothoe populeti. However, major morphological differences from Laothoe populi were lacking and so Kitching & Rougerie et al. (2018) (STI 21830) resynonymized populetorum as a subspecies with Laothoe populi. Zolotuhin (2018) (STI 21919) reiterated the differences proposed by Danner, Eitschberger & Surholt (1998) (STI 17413) as well as noting some other small differences in wing pattern. He also noted a DNA barcode divergence of 2.35% between populetorum and populi, “что доказывает его видовую самостоятельность” [“which proves its species independence”]. However, regarding DNA barcode divergences in Smerinthini, 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 divergences of 2.35% from [populi] populi would indicate subspecies differentiation at best. Taken together, there is thus no justification for treating Laothoe populetorum as a species separate from Laothoe populi and it is here once again treated as a subspecies thereof, Laothoe populi populetorum.