The beetle Brontispa longissima (Gestro) (Coleoptera: Chrysomelidae) is a serious invasive pest of the coconut palm, Cocos nucifera I., in Southeast Asia and the Pacific region. Genetic analysis is essential to ecological and evolutionary study of such invasive species. We therefore conducted molecular analyses by using partial sequences (1044 bp) of the mitochondrial cytochrome oxidase subunit I (COI) genes of B. longissima collected from several locations. We found two monophyletic groups: one distributed over a limited area (Australia, Papua New Guinea, Samoa, and Sumba Island; referred to as the Pacific group) and the other collected from a wide area of Asia and the Pacific region (referred to as the Asian group). We compared the biological and morphological traits of the two groups. We found that insects in the Pacific group had a shorter developmental time from hatching to adult emergence, produced fewer eggs, and had a larger adult body size than insects in the Asian group. Elytral color patterns did not differ between the two groups. Our interpopulation crosses produced significantly fewer progeny than intrapopulation crosses, suggesting that B. longissima represents two cryptic species.