Quadrus ( Zera ) difficilis (Weeks, 1901)

Zhang, Jing, Cong, Qian, Shen, Jinhui, Song, Leina & Grishin, Nick V., 2023, Genomic analysis reveals new species and subspecies of butterflies, The Taxonomic Report of the International Lepidoptera Survey 11 (6), pp. 1-63 : 34

Quadrus ( Zera) difficilis (Weeks, 1901) is confirmed as a species distinct from Quadrus ( Zera) zera (A. Butler, 1870)

Although Quadrus ( Zera) difficilis (Weeks, 1901) ( type locality in Bolivia) is treated as a distinct species and not a subspecies of Quadrus ( Zera) zera (A. Butler, 1870) ( type locality in Venezuela), on the Butterflies of America website (Warren et al. 2023), this taxonomic opinion has not been substantiated numerically. Genomic sequencing of several specimens of both taxa reveals prominent genetic differentiation between them ( Fig. 32), e.g., Fst /COI barcode difference of 0.30/2.7% (18 bp), thus confirming Quadrus ( Zera) difficilis (Weeks, 1901) as a species-level taxon.