Geographic ranges of parthenogenetic animals often differ from those of their sexual conspecifics, providing valuable information about evolutionary histories. We studied the geographic distributions of sexual and parthenogenetic forms of the weevil Scepticus insularis (Roelofs) (Coleoptera, Curculionidae) on Honshu, Shikoku, and Kyushu Islands, Japan. We collected Scepticus insularis at 18 sites in the northern half of Honshu; sequenced 633 bp of the mitochondrial ND2 (NADH dehydrogenase subunit 2) gene for 102 Honshu beetles; and constructed a ML gene tree based on these sequences and sequences previously reported for 104 conspecific beetles from Hokkaido of known reproductive mode. The ND2 haplotypes fell into two distinct clades (I and II) separated by 9.5% nucleotide sequence divergence. The haplotypes from all parthenogenetic females on Hokkaido and those from all-female populations on Honshu invariably belonged to clade I, whereas sexual females on Hokkaido and some of the females in male/female populations on Honshu belonged to clade II. Haplotypes of males were in clade II, except for two Hokkaido males having a clade-I haplotype. Excluding these two enigmatic males, we treated individuals with clade-I haplotypes as parthenogenetic, and those with clade-II haplotypes as sexual. Parthenogenetic beetles were widespread throughout Hokkaido and central and northern Honshu, whereas sexuals were found only in three separate areas on Hokkaido and one on Honshu, often sympatrically with parthenogens. The distribution of S. insularis is congruent with the pattern termed geographic parthenogenesis.