Pigmentation associated with oogenesis in the biting fly Culicoides variipennis (Diptera: Ceratopogonidae): light and electron microscopy.

Abstract

Females of Culicoides variipennis produce externally visible pigment granules that accumulate in their abdomens during oogenesis. Such granules are useful to categorize females as nulliparous or parous. Electron- and light-microscopy studies showed that the pigment granules are located primarily in large epidermal cells underlying the cuticle and 1st layer of squamous epidermal cells of blood-fed females and also are abundant in the tissues beneath the outer epidermis. Pigment granules also were observed along basement membranes. In non-blood-fed females some pigment granules were present, but they were widely scattered, usually were not present in the cells beneath the cuticle and squamous epidermal cells, and seldom were observed in the tissues beneath the outer epidermis. More endoplasmic reticulum was observed near pigment granules in blood-fed than in non-blood-fed females. Granules were present in the gut tissues of male flies and appeared to be similar to those observed in female flies. The density of granules in male flies was similar to that observed in non-bloodfed females.