Observations on the bionomics of the sheep body louse (Damalinia ovisM)

Abstract

Experimental observations are recorded on the bionomics of Damalinia ovis on the sheep and in vitro. The optimal conditions for in-vitro rearing of D. ovis are 36.5°C. and 70-90 per cent, relative humidity when a mixture of skin scurf and baker's yeast is used as food. Under these conditions the life cycle closely approximates the estimated life cycle on the sheep. The incubation period is 9-10 days; the three nymphal instars are completed in 7, 5, and 9 days respectively; the preoviposition period is approximately 3 days, making a cycle of 34 days from egg to egg. The lice and their eggs are very susceptible to changes in temperature. The areas of heaviest infestation are along the mid-dorsal line and down the sides of the sheep. Individual sheep differ considerably in their susceptibility to artificial and to natural infestations. Sheep in poor condition tend to have the heaviest infestations, which are retained throughout the year. There is a pronounced seasonal fluctuation in populations of D. ovis, the heaviest infestation occurring in the period from June to September.