Internal female reproductive anatomy and genital interactions during copula in the yellow dung fly, Scathophaga stercoraria (Diptera : Scathophagidae)

Insect genitalia have been extensively studied for taxonomic purposes, but functional anatomy has rarely been examined. We report here on the detailed internal anatomy of the reproductive tract of female yellow dung flies (Sc athophaga stercoraria) and the mechanics of copula and sperm transfer. Fema le dung flies have paired accessory glands, three spermathecae (one singlet and one doublet), each with its own narrow duct, a large muscular bursa co pulatrix, which is met by the common oviduct dorso-anteriorly, and paired l ateral oviducts and ovaries. The bursa is lined internally with a thick cut icle. During copula and while ejaculating, the male aligns the gonopore wit h the spermathecal duct entrances to the bursa and pinches the female's abd omen at approximately this point. Sperm packing in the spermathecae appears quite orderly, and structurally the sperm appear typical of many insects. Aedeagus withdrawal appears to remove some bursal sperm. The results are di scussed in relation to other Diptera.