Published online by Cambridge University Press: 10 July 2009
A method is described for studying the life-cycle of Melophagus ovinus. The female ked matures in 6 to 7 days and the male in 10 to 11 days. Copulation takes place 16 hours after emergence and the first pupa is deposited by the female about 13 days after its emergence. The second and successive pupae are deposited at intervals of seven to eight days. The pupal stage covers 20 to 26 days (an average of 22·5 days for 28 observations). The life-cycle is completed in 33–36 days. Experimental conditions did not affect the duration of the various stages observed in the life-cycle.
An investigation of the periodic fluctuations in the infestation of a flock of Welsh sheep showed that the degree of infestation is influenced by the transference of keds between the sheep. Before lambing, keds are transferred from hoggs to two- to three-year old ewes and, after lambing, from ewes to lambs. The peak infestation of ewes and hoggs occurs before lambing. The maximum infestation of lambs occurs before shearing. At shearing the majority of adult keds and pupae are removed with the fleece. Adults surviving after shearing are killed at dipping. Depending on the nature of the dip, re-infestation results from pupae hatching in fleece or by the transference of keds from infested sheep coming into contact with the dipped flock. Keds disappear from the fleece through being devoured by the sheep, by the activity of insectivorous birds and through natural death. The transference of keds between sheep is achieved through contact and occurs readily when the ked is on the surface of the fleece. The vertical migration of the insect in the fleece is controlled by temperature and is not influenced by light.
The distribution of pupal and adult stages of M. ovinus in the fleece of lambs, hoggs and ewes is given. The position of attachment to the pupae is controlled by the depth of the fleece, deposition occurring on the wool fibres at a point where the temperature is suitable for their development. The age of the sheep influences the distribution of the ked, young sheep being more susceptible than older animals. In a flock, the higher infestation of hoggs compared to older ewes may be due to the higher initial infestation of the hoggs after dipping. Open fleeced sheep are more susceptible to ked infestation than tight fleeced sheep.