Sexual dimorphism in external scent efferent system of metathoracic scent glands in Aradidae: First evidence within Heteroptera

The morphology of the external scent efferent system of the metathoracic scent gland was studied in detail in three Aradus species, A. betulae (Linnaeus, 1758), A. cinnamomeus Panzer, 1806, and A. ribauti Wagner, 1956 (Heteroptera: Aradidae) using scanning electron microscopy. The ostiole is slit-shaped and poorly developed, the peritreme is not present, and the evaporatorium consists of ridges and grooves that are directed radially from the ostiole. This inconspicuous external scent efferent system could represent an ancestral condition in the Aradidae. The microsculpture of the cuticle of the evaporatorium is highly species-specific. In A. betulae, the ridges and grooves are more distinct in males than in females, the microsculpture pattern of the evaporatorium is more highly developed in males than females, and the most distinct sculpture is present on the ostiole margin in females; in A. cinnamomeus, there are fewer distinct differences between males and females in the sizes of the ridges and shape of the ostiole margin, and the microsculpture pattern of the evaporatorium is identical in both sexes; and in A. ribauti, the size of the ridges and grooves are identical in both sexes, and there are only small differences in the microsculpture pattern. The sexual dimorphism in the external scent efferent system of the metathoracic scent glands in these three species represents the first report of this dimorphism in the Heteroptera.