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Sequences for nearly complete 18S rRNA and partial 16S rRNA genes were determined for sixteen species representing twelve calyptrate families. Two unique insertions are present in expansion regions of the 18S rDNA in nycteribiids. Alignments containing other dipteran rRNA genes provided good resolution at higher taxonomic level: monophyly of Calyptratae is well supported. While both 16S and 18S rDNA matrices produce unstable topologies within Calyptratae when analysed separately, their combination results in a tree with several robust and well supported nodes. Of three superfamilies recognized in recent classifications, the Hippoboscoidea is well supported by 16S rDNA and by combined matrices. The representatives of Muscoidea, Musca sp. and Antipoda sp., display a tendency to cluster within Oestroidea. The comparison of secondary structures of two variable regions indicates that Sarcophagidae are related to Calliphoridae rather than to Tachinidae.

The utility of a mitochondrial DNA (mtDNA) fragment of about 1100 bp (including partial COI and COII sequences and tRNALeu) for evolutionary studies in Muscoidea is discussed. The species investigated are Scathophaga stercoraria, Microprosopa pallidicauda and Trichopalpus fraterna (family Scathophagidae), Musca domestica (Muscidae), Lasiomma seminitidum (Anthomyiidae) and Fannia armata (Fanniidae). Comparisons were made with published mtDNA sequences of Drosophila, Anopheles and three Calliphoridae species. The molecular phylogeny obtained here matches the classical morphological taxonomy reasonably well. This varies considerably, however, at different taxonomical levels. At a high taxonomic level, there is a clear separation between the Nematocera and the Brachycera, but the Calyptratae-Acalyptratae division is not always supported. At a lower taxonomic level, all species belonging to the same family are well grouped, but at an intermediate level, within the Calyptratae, it is impossible to clearly separate the Muscoidea and Calliphoridae, preventing a firm conclusion on the phylogenetic relationships among Muscoidea families. The entire COI sequence of S. stercoraria, as well as other mtDNA sequences (including the proximal portions of the COI gene, tRNATrp, tRNACys and tRNATyr genes) in Muscoidea species, are also presented and discussed.

Larval fat body persists, as spherical particles, in most Diptera at the time of adult emergence. The present study and reports in the literature indicate its presence in 25 species of muscoid flies but not in the buffalo fly. the horn fly. or tsetse. In an investigation involving the dissection of female buffalo flies. Haematobia irritans e.xigua de Meijere. for age determination based on the state of the ovaries, it was found that even newly-emerged flies lacked the larval fat body characteristic of recently emerged specimens of other higher Diptera. This was taken as a possible indication of a special physiological feature in these economically important flies, and so further observations were made on the occurrence at adult emergence of larval fat body in other higher Diptera. Larval fat body, described and illustrated (as “‘pupal fat body’”) by Anderson (1964). is quite different from adult fat body. It consists of a large number of tiny, solid spheres, usually somewhat opalescent, lying loose in the abdominal haemocoel in both sexes. Following eclosion, decreasing amounts may be found for several days in the body of the adult fly. Once it has disappeared, similar fat body is not found again during the lifetime of the fly. The species known to have larval fat bodies persisting in the adult (Table) cover a wide taxonomic range in the Muscoidea. No remnants of the larval fat body are observed in the abdomen of newly-emerged H. i. exigua, though there may be a variable amount of normal adult fat body. The closely related horn fly, H. irritans irritans (L.) likewise lacks larval fat body at eclosion (R. L. Harris pers. comm.), nor is there any mention of larval fat body in the literature on tsetsef (Glossina Wiedemann), and P. A. Langley (pers. comm.) has confirmed from his own experience that it is not found in adult flies of this genus. Persistent larval fat body carries over various food reserves from larva to adult (Thomson 1975), and there is no clear indication as to why it should not persist in adult Haemalobia and Glossina. When found it occurs equally in both sexes, and its presence or absence is thus not likely to be connected with reproductive physiology. It is unlikely to be a reflection of any special features of larval nutrition, for although the Glossina larva is nourished entirely by the parent female, which has access to ample blood meals, the Haematobia larva lives in the dung of bovines. as do several other Muscidae in which larval fat bodies persist.