Larval structure of Passalus gravelyi and sexual dimorphism in Passalid larvae.
Adult passalids produced sounds of 7 basic structural types in at least 13 different behavioral contexts. A given type in a particular behavioral context may be termed a "signal". A total of 31 signals were recorded from 57 species. The presence of the same basic signals in both New World tribes suggests an early origin of the fundamental repertoire. The 14-signal repertoire of Odontotaenius disjunctus (Ill.) is larger than previously known for any arthropod and more extensive than those of many vertebrates. The large repertoire is associated with a high level of sociality. Dendroctonus beetles, similarly highly social, also have a large repertoire with some signals resembling those of passalids. Convergence in sound signals and social behavior may derive from occupation of similar microhabitats (tree trunks).