Plagiometriona emarcida (Boheman, 1855) and Plagiometriona forcipata (Boheman, 1855) (Coleoptera: Chrysomelidae: Cassidinae), a single species differing in larval performance and adult phenotype

Matings frequently observed between the tortoise beetles Plagiometriona forcipata (Boheman, 1855 Boheman, CH. 1855. “Monographia Cassididarum”. In Tomus Tertius, 543Stockholm: Holmiae.  [Google Scholar]) and Plagiometriona emarcida (Boheman, 1855 Boheman, CH. 1855. “Monographia Cassididarum”. In Tomus Tertius, 543Stockholm: Holmiae.  [Google Scholar]), in the State of Rio de Janeiro, Brazil, led us to compare the ecology, life history and genetics of these two morphologically distinct species. Host plant censuses revealed P. emarcida was about five times more abundant, while populations of both species responded in parallel to climate. Laboratory-reared immature P. forcipata took 2 days longer to complete development and showed higher mortality rates. No differences were detected in ovipositional behaviour, genitalia morphology or in sex ratio of offspring. The adult offspring of field-caught females of both species contained individuals with both species' elytral patterns. Finally, nearly identical cytochrome oxidase I sequences obtained from individuals of each species suggest that they are a single polymorphic species. Based on these observations and the examination of type material we propose the new synonymy: Plagiometriona forcipata?=?P. emarcida, syn. nov.