Revision of North American Agabus (Coleoptera: Dytiscidae): the Semivittatus-Group

Larson, D; Wolfe, R

ABSTRACT: The Agabus semivittatus-group is revised. The group, which is restricted to temperate North America, contains six species: Agabus semivittatus LeConte, which is almost transcontinental; Agabus johannis Fall in peninsular Florida; Agabus astrictovittatus new species along the Atlantic coast from New York to northern Florida and Alabama; Agabus stagninus (Say) along the Atlantic coast from New York to Florida and along the Gulf of Mexico coast to Louisiana; Agabus flavovittatus new species with a wide distribution east of the Great Plains, from southern Ontario to Mississippi and eastern Texas but not along the Atlantic coast; and Agabus texovittatus new species in Texas. Agabus stagninus and A. flavovittatus hybridize in southeastern Pennsylvania. The placement of Agabus texanus Sharp as a junior synonym of A. semivittatus is confirmed. A lectotype is designated for Agabus spilotus LeConte (= A. semivittatus). A neotype is designated for A. stagninus. A key to species is presented and, for each species, the following information is provided: description; illustrations of taxonomically important characters; morphological measurements on selected population samples; notes on relationships, variation, and ecology; and a map of collection localities. A cladistic analysis of the relationships of the group within Agabus indicated that the americanus-, spinipes-, and confusus-groups belong to the same clade as the semivittatus-group and that the seriatus-group is sister to this clade. Within the semivittatus-group, there are three well-defined subgroups as follows: A. semivittatus; A. johannis and A. astrictovittatus; and A. stagninus, A. flavovittatus, and A. texovittatus.