Systellus mentaweicus

Diagnosis
Body chocolate brown, matt, with yellowish bifid setae on head along anterior margin, on longitudinal raised parts between sulci and underside, mesorostrum at sides and rostral apophyses at lateral surface

Distribution
Borneo, Sumatra, Peninsular Malaysia, Thailand.

Biology
Most specimens of Systellus mentaweicus examined in this paper were collected in light traps. However, one of us (MM) has observed several individuals of this species in or around an ant nest at Ulu Gombak in Selangor, Peninsular Malaysia. During the night of 9 May 2005, a male was found walking on a fallen tree branch (maximum 30 cm diameter, probably fallen about two weeks earlier), with several Camponotus (Tanaemyrmex) sp. ants walking around it. The following day, at nighttime, MM found a female exposing her head from a nest entrance of the same ant on the same branch. Several ants went in and out the nest entrance, seemingly without paying any attention to the beetle. The nest entrance would have been situated about 20 m above the ground, where the branch was attached to the tree trunk before falling down. The next morning, MM whittled the branch to examine the ant nest, and five brentid adults were found walking slowly around the nest, together with one queen ant, 30 worker ants and about 50 ant larvae and cocoons. When the nest was exposed to light, the ants ignored the beetles and carried their brood outside the nest very quickly. At least six beetles were living in this small colony, which measured only 30 × 3 cm in area. Though no interaction between the beetles and the host ants was observed, the high number of brentid specimens in the nest, the morphological modifications of the head, and the slow motion of the beetles together suggest that this species is integrated into the ant society, as observed for the wellstudied eremoxenine Amorphocephala coronata (Germar, 1817) (e.g., Torossian 1966). No larvae of eremoxenines were found inside the nest. Sforzi and Bartolozzi (2004, p. 826: Appendix 4) listed all the brentid host ant associations reported in literature up until 2004. This is the first host ant record for the genus Systellus.