A physiological age-grading system for female Hydrellia pakistanae Deonier (Diptera: Ephydridae)

Abstract

Abstract The female reproductive system of Hydrellia pakistanae Deonier was described by dissecting individuals of known ages and describing changes in relation to number of eggs oviposited. Female H. pakistanae have meroistic ovaries, in that specialized nurse cells or trophocytes (nutritive cells associated with the eggs) are present within each ovariole, and of the polytrophic subtype because nurse cells closely accompany each developing egg, or oocyte. The reproductive system includes two ovaries, each consisting of 8 or 10 tube-like ovarioles. The ovariole can be divided into two distinct areas: a distal germarium, which produces the follicles, and a more proximal vitellarium, which houses the developing follicles. Each ovariole is surrounded by an ovariole sheath and houses several developing follicles, a term referring to the ova (yolk and surrounding cells; i.e., the egg), nurse cells, and surrounding epithelium. Within an ovariole, the follicle proximate to the lateral oviduct is the most mature with each subsequent, more distal follicle becoming less mature. All ovarioles within an ovary are connected via the lateral oviducts, while the common oviduct connects the ovaries to each other. The spermatheca and accessory glands branch off the common oviduct. Sperm stored in the spermatheca fertilize eggs as they pass through the common oviduct. Based on this information the continuum of ovarian maturation was divided into three nulliparous and four parous stages. The nulliparous stages are classified based on degree of ovariole segmentation and maturity of the most proximal follicle while follicle relic quantity and appearance is mainly used to separate the parous classes. Limited field sampling demonstrated the possibility of using this system to assess reproductive health of wild populations.