Abstract
The abundance and sex ratio of four species of water mites: Parafissicepheus africanus (Mazen, 1979), and Cheiroseiulus crassipes, C. spinosus, C. punctum (Ramadan, 1998) which inhabit the roots of the aquatic plant Eichhornia. crassipes, were studied. The first species belongs to suborder Cryptostigmata, while the other three species belong to suborder Mesostigmata. The present data showed that the cryptostigmatid mite was more predominant than the mesostigmatid ones. Also, the total density of the four species was higher in winter than in spring. Most of the investigated ecological factors had no significant effect on the present studied species. On the other hand, the high values of dissolved oxygen were consistent with the density peaks of the present studied mites. The sex ratio was nearly equal among the three mesostigmatid mites with a slight bias towards females during most of the collection months. However, there was a sharp female increase over the males in the cryptostigmatid mite, P. africanus.