Revision of the Metallactus humeralis species-group (Coleoptera: Chrysomelidae: Cryptocephalinae)

Nine species of Griburius Haldeman, 1849 and three species of Metallactus Suffrian, 1866, previously regarded as valid, together with two taxa previously treated as synonyms, are revised and critically discussed. According to the recent new diagnosis of Metallactus, all treated taxa are assigned to this genus. The following nomenclatural changes and synonymies are proposed: Metallactus corruscans (Suffrian, 1866) comb. nov. (= Scolochrus tripudians Suffrian, 1866 syn. nov.); Metallactus callens (Suffrian, 1866) comb. nov.; Metallactus diabolicus (Suffrian, 1866) comb. nov.; Metallactus fallax (Suffrian, 1866) stat. restit., comb. nov. (= Metallactus polymorphus Suffrian, 1866 syn. nov.); Metallactus humeralis (Stål, 1857) comb. nov.; Metallactus leucopygus (Suffrian, 1866) comb. nov.; Metallactus quadrillum (Suffrian, 1866) comb. nov.; Metallactus triguttatus (Fabricius, 1801) comb. nov. (= Cryptocephalus perlatus (Olivier, 1808) syn. nov.). Metallactus nigroornatus (Stål, 1857) and Metallactus flavopustulatus (Stål, 1857) are confirmed as valid species. Pachybrachis pustuliger (Stål, 1857) is confirmed as a junior synonym of Metallactus nigroornatus. Type series of all treated species were traced and a lectotype is designated for each of them. Redescriptions of all the species are provided. Additionally, Metallactus acaciaesp. nov. from Bolivia, Metallactus atripennissp. nov. from Brazil, Metallactus australissp. nov. from Argentina, Metallactus cuiabanussp. nov. from Bolivia and Brazil, Metallactus flavoapicalissp. nov. from Brazil, Metallactus flavosuturalissp. nov. from Argentina, Bolivia and Paraguay, Metallactus juliaesp. nov. from Argentina, Brazil and Paraguay, Metallactus konstantinovisp. nov. from Costa Rica and Panama, Metallactus nigrobrunneus sp. nov. from Brazil, Metallactus ornaticollis sp. nov. from Brazil, Metallactus panatahuasp. nov. from Peru, Metallactus seminiger sp. nov. from Argentina, Bolivia, Brazil, Paraguay, Metallactus tacanasp. nov. from Bolivia are described as new to science. Illustrations and distributional data of all the treated species are provided. Pending a future phylogenetic analysis of the genus, all taxa are provisionally assigned to the same morphologically coherent assemblage, here referred to as Metallactus humeralis species-group. Scolochrus (= Griburius) leucurus was originally described (Suffrian, 1866) as belonging to the same species group revised here. However, its type series appears to be lost, consequently, its taxonomic validity and its possible relationship with the species treated in the present study remain unconfirmed.