Not sure about id. Appendage drawings in the Theischinger and Hawking guide make me think maybe Austroargiolestes calcaris, but general appearance more like Austroargiolestes icteromelas. I would appreciate some tips to tell apart males of the two species.
A mature male A. calcaris would have the powdery pruinescence on the thorax. In this immature male, the shape and extent of the thoracic markings can be used to distinguish it from A. icteromelas, but it can be a very difficult call.