Phylogenetic Importance of Immature Stages: Solving the Riddle of Exeretonevra Macquart (Diptera: Xylophagidae)

Abstract

Exeretonevra Macquart is a small genus of flies (Diptera) belonging to the suborder Brachycera endemic to Australia. The classification of Exeretonevra has been extremely unstable; the genus has been placed in 3 of the 4 brachyceran infraorders at various times since it was described in 1846. Misplacements were a result of reliance on convergent characters of wing venation or plesiomorphic features of the adult. Synapomorphies critical to the classification of Exeretonevra remained unavailable for 150 yr because the larval stages were unknown. Here we describe egg and larval morphology of Exeretonevra angustifrons Hardy, and provide biological information on these life history stages. We also provide a detailed treatment of external anatomy of the adult and describe some aspects of adult biology. Larval characteristics and reinterpretation of adult morphology clearly show that Exeretonevra belongs to the family Xylophagidae, subfamily Coenomyiinae. A scanning electron microscope study of the paired bare areas present posterolaterally on the first abdominal tergite suggests that these areas are associated with, and provide an outlet for, a glandular product. The Xylophagidae is the sole member of the infraorder Xylophagomorpha, which are predominantly distributed in the northern hemisphere. Exeretonevra is the only Australian representative of this infraorder, and this lineage is likely to have existed on the continent since the Mesozoic. The distribution of larval habitats across xylophagid genera suggests at least 2 evolutionary transitions in the family between soil and rotting wood.