Taxonomic Studies of the Ground Beetle Subgenus Rhagadus Motschulsky (Coleoptera: Carabidae: Pterostichus): Unraveling the “Female Holotype Problem” Using External Geometric Morphometrics and Novel Male Genital Morphology

Clarifying the identity of type specimens without information and developing novel procedures for this task are important issues in taxonomy. Because female insects frequently lack taxonomically useful morphological characters, their taxonomic assignment is challenging without sufficient locality information. Using the cryptic species complex previously treated as “Pterostichus (Rhagadus) polygenus Bates” as a model, this study presents a novel procedure based solely on morphological data for the taxonomic assignment of female type specimens that lack sufficient locality information. Without a priori species hypotheses, males were divided into morphotypes based on the morphology of the endophallus, a genital structure that has recently been found to be useful in the taxonomy of insects, particularly Coleoptera. Then, geometric morphometrics of the pronotum followed by discriminant analysis were conducted using females obtained from the same localities as the males (not including female type specimens). The obtained discriminant function unambiguously assigned all female type specimens to the morphotypes, including those without sufficient locality information, resulting in the following Japanese Rhagadus Motschulsky species: Pterostichus microcephalus (Motschulsky) ( = Pterostichus kimurai Morita syn. nov.), Pterostichus negylopus sp. nov. (type locality: Tokyo, Hachiôji-shi, Todorimachi), Pterostichus nimbatidius (Chaudoir), Pterostichus polygenus ( = Pterostichus brittoni Habu, Pterostichus harponifer Tanaka, both syn. nov.), Pterostichus takaosanus Habu ( = Pterostichus freyellus Jedlička, Pterostichus komiyai Morita, both syn. nov.), Pterostichus thorectes Bates ( = Pterostichus latemarginatus (Straneo), Pterostichus mundatus Jedlička, Pterostichus straneoi Habu, Pterostichus satsumanus Habu, all syn. nov.), and Pterostichus thorectoides Jedlička ( = Pterostichus ishiii Morita, Kurosa, and Mori syn. nov.). A morphological phylogeny of Japanese and Korean Rhagadus species was constructed, and their differentiation process is discussed. In addition, based on the observed genital morphology, the possible functions of male and female genitalia are discussed in terms of sexual conflict. Pterostichus glabripennis Jedlička from China was removed from Rhagadus based on type examinations.