Armpit squeaks: first recorded sounds, video, and images of the stridulatory apparatus in two parasitic flat bark beetles (Coleoptera: Passandridae)

Stridulation is an important sound production mechanism in many groups of insects but is less well-known in beetles (Coleoptera). Recently a new sound production mechanism was documented in Passandridae but not recorded acoustically. In this study, we aimed to directly capture the bioacoustics and morphology of two North American species of Passandridae for the first time in order to better understand their behavior. We investigated whether both species possess a stridulatory apparatus and if their stridulations differ in audio characteristics, as they belong to different genera, building on observations from previous studies. We recorded stridulation patterns of Catogenus rufus (Fabricius, 1798) and Taphroscelidia linearis (LeConte, 1863) and imaged their stridulatory apparatuses using scanning electron microscopy. The two species’ stridulatory organs differed in shape and size and produced sounds with vastly different wavelength ranges and amplitudes. The number of periods and repeated stridulations also differed. We discuss possible uses and purposes of these stridulatory behaviors.