Ophyroglena sp (Ciliata : Oligohymenophora) in Caenis luctuosa (Ephemeroptera : Caenidae)

Sampling of mayfly nymphs belonging to Caenis luctuosa (Ephemeroptera, Caen idae) revealed that 5% were infected by an enormous number of ciliates of t he genus Ophryoglena. Free moving ciliates were recognisable by observing t he host animals in vivo under a stereomicroscope. The ciliates lived in the hemolymph and penetrated the wing pads and trochanteral junctions of the l egs. After their removal from the host body, some specimens were reared in Petri dishes. Ophryoglena sp, formed cysts and failed to survive more than two days. In order to test the effect of the parasites on the host tissues, the ovarioles of some healthy and parasitised specimens were examined unde r TEM. Parasitic castration depends upon an early degeneration of the folli cle cells, which were unable to envelope the egg within a firm epithelium. Eggs were blocked in their early phase of maturation since the integrity an d activity of the follicular epithelium is essential for the ensuing synthe sis of the egg envelopes (vitelline and chorionic layers). The low rate of parasitized mayflies hampers a full understanding of the life cycle of this ciliate and of its modality of spreading.