Sex pheromones inCulicoides nubeculosus (diptera, ceratopogonidae): Possible sites of production and emission

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Abstract
This study was performed on virgin females ofCulicoides nubeculosus to determine sites of production and emission of sex pheromone. The ventral abdominal surface is the site of emission of the pheromone. Morphologically there is evidence of the presence of abdominal atrichial areas. The abdominal areas, eight per segment (four ventral and four dorsal), are covered by a cuticle devoid of micro- and macrotrichiae. The dorsal and ventral areas differ considerably in their structure. The dorsal atrichial areas have an unperforated cuticle covering a normal epidermis, whereas the ventral atrichial areas have a cuticle perforated by numerous tubular structures, with a loosely organized procuticle and no underlying epidermal cells. A pair of voluminous cells with the classical ultrastructural characteristics of enocytes is invariably located in the vicinity of the ventral atrichial areas. These cells undergo ultrastructural modifications tending towards involution according to the age of the insects, being correlated with the decrease in pheromone emission by older females. The hypothesis is put forward that enocytes are involved in pheromone production.