On the horns of a dilemma: toward a better understanding of the <i>Monacon</i> species (Hymenoptera: Perilampidae) of Borneo

A new species of Monacon is described from Borneo based on digital images, COI sequences and X-ray microtomography. The natural history of this primary parasitoid is documented and its host, a pinhole borer or ambrosia beetle, is documented with digital images and a COI sequence. The X-ray microtomography revealed that the frontal horn that is characteristic of the genus Monacon is not simply a cuticular process, but is associated with tissues, and may have a sensory function.