MOLECULAR AND MORPHOLOGICAL CHARACTERS DISCRIMINATE SITOPHILUS-ORYZAEAND SITOPHILUS-ZEAMAIS (COLEOPTERA, CURCULIONIDAE) AND CONFIRM REPRODUCTIVE ISOLATION

The Rice Weevil, Sitophilus oryzae (L.), and the maize weevil, S. zeam ais Motschulsky, are sibling species of grain weevils that are usually distinguished by grain preferences and subtle differences in morpholo gy. Previous findings of successful laboratory hybridization, genetic similarity of allozymes and chromosomes, and identity of aggregation p heromones raised questions about the validity of S. oryzae and S. zeam ais as reproductively isolated biological species. We used molecular t echniques to test the hypothesis that individuals assigned as S. oryza e or S. zeamais by morphological criteria represent members of 2 disti nct gene pools, and hence are reproductively isolated species. Weevils from 18 different localities, which were collected from Africa, Austr alia, Asia, the south Pacific, and North America, were studied. All in dividuals were scored for the presence or absence of morphological cha racters that have been used historically for species determination. In most cases, determinations for the same individual were not consisten t, depending on the morphological character used. The polymerase chain reaction (PCR) was used on the same specimens to analyze randomly amp lified polymorphic DNA (RAPD-PCR) markers and to amplify selectively r egions of mitochondrial DNA for analysis of restriction site polymorph isms with restriction endonucleases (RFLP-PCR). Both methods yielded m arkers that were consistently associated with either presence or absen ce of specific genitalic characters in both males and females. This co rrelation of molecular markers with genitalic morphotypes nas consiste nt in all specimens studied, whether collected sympatrically from the same farms or from widely separated geographic populations, and suppor ts a model of 2 reproductively isolated species. Other morphological c haracters involving pronotal punctures proved unreliable as correlates with genetic markers and are not useful for species diagnosis.