Comparison of Postembryonic Organization of the Genital Segments in Trichoceridae, Tipulidae, and Anisopodidae (Diptera, Nematocera)

Abstract

The number of abdominal segments in Tipulomorpha and Bibionomorpha larvae and aduts is discussed. For Nematocera, the most primitive number of abdominal segments in both male and female larvae is nine. Reduction of the IX abdominal segment and its subsequent fusion with the VIII segment occurs in different phyletic lines in Nematocera and might have evolved several times. In Trichocera spp. nine abdominal segments are present. In the genital segments the main interrelationships in the position of the anus and some main innervation areas, especially the ventral lobes, and the derivatives of the genital primordia were followed during postembryonic reorganization by studying variously stained serial sections from all developmental stages from the first larval instar to the adult stage. Homologies between male and female derivatives of the IX segment genital primordium were established for Trichoceridae. The trichoceroid male claspers and female ovipositor were found to be of sternal origin and highly specialized structures. They appear to be unique features of the Tipulomorpha. Postembryonic development in Limonia nubeculosa Meigen, 1804 and Sylvicola cinctu (Fab‐ricius, 1787) was studied in the same way. In Limonia males the trichoceroid functional system for grasping is present. In Anisopodidae (Sylvicola), another functional system for grasping has been evolved by the male, which only includes primordial derivatives. In the adults, fusion of the VIII and IX segments prevents development of outer clasping organs or special structures for egg guidance.