A review of the Malagasy species of the genus Trigonochilus Brenske (Coleoptera: Scarabaeidae: Rutelinae: Adoretini) with description of a new species

Abstract

Africa and Madagascar have a large and diverse fauna of the chafers of the ruteline beetle tribe Adoretini (Ohaus 1912, 1918). Many nominal taxa from Madagascar are still poorly known and many new ones were described recently (Akhmetova & Montreuil 2010; Montreuil 2010, 2013; Montreuil & Frolov 2014; Frolov & Montreuil 2018). One of the poorly known Adoretini taxa is the genus Trigonochilus Brenske, 1896. Trigonochilus was proposed to accommodate the East-African species T. coriaceus Brenske, 1896, based on the enlarged and curved metatibiae and a short, spur-like process of the labrum (Brenske 1896). Arrow (1901) noted that the enlarged metatibiae of this species (described from a single male) is a secondary sexual character and added another species to this genus, T. politus Arrow, 1901, from Angola. These species were revised by Krikken (1979). Fairmaire (1903) described Adoretus oedipus from Madagascar (without any precise locality) and noted its enlarged metatibia and the shape of the labrum similar to that in Trigonostonum Burmeister, 1844. Fairmaire was apparently unaware of the Brenske’s and Arrow’s works as he did not discuss the possible affinities of A. oedipus with Trigonochilus species. Ohaus (1912) moved A. oedipus to Trigonochilus after examination of the type series but he did not discuss the characters of the species in detail as well as its distribution on the island. Therefore, the genus Trigonochilus Brenske comprised three species described so far, two from Africa and one from Madagascar.