Circumscription of the sclerolobii group of Amblycerus Thunberg (Coleoptera, Chrysomelidae, Bruchinae) with descriptions of four new species and a revision of the species groups of the genus

The seed-beetle <i>Amblycerus</i> Thunberg, 1815 the second most diverse genus of Bruchinae (Chrysomelidae) in the Western Hemisphere, is organized into groups of species, as many others in the subfamily. The main objective of this work is to delimit the group <i>sclerolobii</i>, here established as composed by five described species, <i>A. sclerolobii</i> Ribeiro-Costa, 2000, <i>A. kingsolveri</i> Ribeiro-Costa, 1993, <i>A. marinonii</i> Ribeiro-Costa, 1993, <i>A. manauara</i> Ribeiro-Costa, 2000, <i>A. tachigaliae</i> Kingsolver, 1976 and four new species: <i>A. biacutus</i> Ribeiro-Costa, <b>sp. nov.</b>, <i>A. falcorostrus</i> Ribeiro-Costa & Morse, <b>sp. nov</b>., <i>A. morsei</i> Ribeiro-Costa, <b>sp. nov.</b> (type localities: Brazil: Amazonas, Manaus) and <i>A. truncatus</i> Ribeiro-Costa, <b>sp. nov.</b> (type locality Brazil: Mato Grosso, Sinop). Therefore, including these new species 70 Brazilian species of <i>Amblycerus</i> were recorded. <i>Amblycerus bicolor</i> (Pic, 1927) previously considered to belong to this group is excluded and placed as incertae sedis. The <i>sclerolobii</i> group is distributed mainly in the Brazilian Amazonia biome, consuming <i>Tachigali</i> Aubl., <i>Dinizia</i> Ducke, and <i>Stryphnodendron</i> Mart. seeds (Fabaceae). Diagnoses are presented for this group and for ten species (including <i>A. bicolor</i>), and descriptions for the four new ones, an identification key for the nine species, colored photographs of external morphology, and detailed male genitalia illustrations for all the species studied. Due mainly to previously broad contributions on the taxonomy of <i>Amblycerus</i> that resulted in many species groups, we also present a revised study of this intrageneric taxonomic level. From 37 species groups now we update to 32 groups with a total of 96 species assigned to them. Finally, a detailed systematic study of some specific groups is also suggested before mergence.