Oogenesis in Culicoides Brevitarsis Kieffer (Diptera: Ceratopogonidae) and the Development of a Plastron-Like Layer on the Egg.

Abstract

In C. brevitarsis the mature egg was 290 ¼m long, average fecundity was 31.3, and duration of oogenesis 30-50 h at 24-26ºC. When the first blood meal was consumed oocytes ranged from stage No to I, and 95.8% of females were mated; after a partial blood meal fewer oocytes were initiated and even fewer matured. It is highly likely that C. brevitarsis is anautogenous. Oocytes develop through the same stages as other Culicoides. Chorion developed well below the sheath in late stage IV, causing a reduction in width of oocytes at maturation. Ansulae develop in the space between the sheath and chorion by outward sclerotization, possibly along pore canals; they vary from tall (8-9 ¼m) and broad on the concave surface to short (5-6 ¼m) and narrow on the convex surface; those on the concave surface probably act as a plastron. The sheath surrounding the stage IV oocyte is destroyed during maturation. The secondary oocyte commences development when the primary is at stage III, and its development is arrested at either stage N or I almost simultaneously with the primary oocyte completing development. Development of the secondary oocyte is initiated but not controlled by development of the primary in the same ovariole.