Origin and transformation of the in-flight wing-coupling structure in Psocodea (Insecta: Paraneoptera)

Many four-winged insects have mechanisms that unite the forewings and hindwings in a single plane. Such an in-flight wing coupling apparatus may improve flight performance in four-winged insects, but its structure is variable among different insect groups. The wings of bark lice (Insecta: Psocodea: "Psocoptera") also have an in-flight wing coupling apparatus, but to date, its morphology has not been studied in detail. In this study, we examined the wing-coupling structure in representative species of the three suborders of bark lice (Trogiomorpha, Troctomorpha, and Psocomorpha) and inferred its origin and transformation. We conclude that the main component of the psocodean wing coupling apparatus evolved once in the common ancestor via modification of cuticular structures at the apex of the forewing CuP vein. Morphological differences in components of the coupling structures are phylogenetically informative at the intraorder level and include an autapomorphy that characterizes Troctomorpha and a synapomorphy that supports a sister relationship between Troctomorpha and Psocomorpha.