The life cycle of Psorergates ovis Womersley, the itch mite of sheep.

Abstract

The life cycle of Psororgatos ovis is completed in 5-6 weeks, and there are six stages : the egg, larva, protonymph, doutonymph, tritonymph, and the male or female adult. All stages are found under the stratum corneum, but adults and occasional tritonymphs are also found on the surface of the skin. Only the adult is motile and is responsible for the spread of infestation over the body of sheep. Adult mites transferred most readily to cloths which were placed next to the skin, which indicated that they primarily are responsible for transference of infestation from sheep to sheep. Adults did not leave the skin rapidly; at 20¦C, they survived away from sheep for only 24-48 hr at R.H. 92 and 100% and they died of desiccation within 24 hr at R.H. 54 and 75%. These findings suggest that natural transference of infestation is mainly by adults when the fleece is short, which would explain the slow spread of infestation which has been observed in the field.