The distribution of the eggs of Mammalian Lice on their hosts. 3. The distriubtion of the eggs of Damalinia ovis (L) on the sheep.

Abstract

The eggs of Damalinia ovis (L.) are attached to the wool and hair fibres of the sheep and have a vertical and lateral distribution, i.e. they may be laid at different distances from the skin and their distribution over the body of the sheep may vary. The vertical distribution of the newly laid eggs of D. ovis is determined by the distance to which the temperature zone suitable for oviposition extends from the skin. This is regulated mainly by skin temperature, skin topography, the depth of the air blanket trapped within the fleece, and atmospheric temperature. Usually the eggs are laid within 1/4 in. of the skin. The factors which influence the lateral distribution are the presence of suitable fibres and temperatures for oviposition. Eggs are not laid on the bare areas of the body because fibres are absent. There are, however, few bare areas on the sheep. The bases of certain hairs on the face, legs, and axilla and inguinal regions are too large in diameter for oviposition but mingled with them are many fibres which are suitable. As there are no areas on the sheep which are entirely covered with hairs of unsuitable diameter for oviposition, fibre diameter has little influence on the lateral distribution of the eggs of D. ovis. When sheep are exposed to low atmospheric temperatures, the skin temperature of the extremities falls below that at which D. ovis can oviposit. Skin temperature is the main factor which determines the lateral distribution of the eggs of D. ovis on the sheep.