Probable Tritonymphal Sexual Dimorphism in Alycus roseus (Bimichaeliidae: Acariformes: Acari)

Grandjean's 1942, 1943, observations on the presence of eugenital setae in nymphs of three species of Bimichaelia are reviewed. New data are presented on the presence of eugenital setae in tritonymphs of Alycus roseus Koch. In A. roseus, it is suggested that male-forming tritonymphs possess two pairs of eugenital setae, and female-forming tritonymphs lack eugenital setae. The presence of eugenital setae in nymphs of species of Bimichaeliidae is hypothesized to represent an ontogenetic acceleration, a derived condition.