First report of exocrine epithelial glands in oestroid flies: The tachinid sexual patches (Diptera: Oestroidea: Tachinidae)

Sexual patches are abdominal areas identifiable by modified setation, present in the males of several groups of Tachinidae (Diptera). We comparatively studied more than 40 species belonging to 24 genera representative of subfamilies known to bear these organs, using light microscopy and scanning (SEM) and transmission (TEM) electron microscopy. We provide a detailed characterization of the fine structure of the setae and microtrichia composing these sexual patches and of the underlying epithelium. Study of abdominal sections showed that, close to the patch area, the epidermis forms a thick layer composed of numerous secretory units of strictly associated cells, ending at the level of cuticular pores at the base of the setae. We hypothesize a secretory function of these structures. The segmental pattern of the sexual patches across the Tachinidae is defined and predictable.We note that almost all the segmental patterns share the presence of sexual patches on abdominal tergite 4, underscoring the diversity of male sexual specializations that occur on the fourth abdominal segment of muscomorph flies.