Fine structure of the foveal glands and foveae dorsales of the American dog tick, Dermacentor variabilis (Say)

Abstract

The ultrastructure of the foveae dorsales and pheromone glands (foveal glands) of both feeding and unfed female Dermacentor variabilis (Say) was studied. Each pore of the fovea contains a pore tube, with cells surrounding a lumen that can be opened or closed. Each pore tube extends below the fovea and expands to form a cone-shaped ampulla, into which a duct of the foveal gland is inserted. Each duct is lined with microvilli, except near its insertion into the ampulla where the lumen is lined with a brush border. In the feeding female, numerous vesicles and lipid droplets accumulate in and around the ducts. However, in the unfed female, the ducts are free of vesicles or droplets. A nerve, the foveal nerve, occurs in the vicinity of the ducts. Neurosecretory vesicles occur in some of the nerve fibers in the feeding tick. Microorganisms, of unknown identity, were found near the ducts of the pheromone gland in feeding females, but not in unfed females. The secretory lobes of the pheromone glands, representing the major part of these organs, contain large cells which appear to comprise one type. In the feeding female, lipid droplets of varying size occur in vesicles or, more frequently, free in the cytoplasms. The may be clustered or scattered throughout large areas of the cell cytoplasm. Accumulations of vesicles and lipid droplets are especially abundant at the ends of the cells, near the junction with the ducts, where they may occur in a single large membrane-bound enclosure. In the unfed female, the lipid droplets occur only within vesicles, distributed more or less uniformly throughout the gland cells.