Trophobiotic organ and perianal structures in aphid genus Stomaphis WALKER (Aphididae, Lachninae)

Stomaphis Walker is an obligatorily myrmecophilous, tree-trunk feeding aphid genus, having many peculiar features in its morphology. One poorly studied trait is its perianal anatomy, with suspected existence of trophobiotic organ and intriguing tubercles near abdominal segment VIII. Tubercles on rear end of abdomen in Stomaphis were considered to be marginal tubercles, structure typical of aphids. Only after their investigation under scanning electron microscope they revealed to possess a very rough surface, consisting of many protuberant, sclerotic scales with finger-like processes. Analysis and comparison with other aphids suggests, that these structures - perianal tubercles - may be considered remnants of abdominal sternite IX, atrophied in aphids. Due to their similarity to the surface of cauda of non myrmecophilous aphids, they are suspected to serve as sort of auxiliary caudas, protecting from sticky secretions of aphids e. g. honeydew or mucus while giving birth or ovipositing in confined space. A very well developed trophobiotic organ in this genus has been shown to exist for the first time.