The ecology of Lice on sheep. 5. The influence of heavy rain on populations of Linognathus ovillus

Abstract

Exposure of nymphal and adult Damalinia ovis (L.) to 100% R.H. at 37°C did not increase the death rate but immersion for 6 hr in water followed by exposure to 40% R.H. was sufficient to kill all nymphs and adults. Immersion of only 1 hr was fatal for 50-100% when followed by exposure of 7.5-24 hr to 90% R.H. Eggs continued to develop under water at 37°C and an appreciable mortality occurred only after 7 days immersion. Exposure to relative humidities of over 90% killed hatching eggs. When the fleece of a sheep infested with D. ovis is soaked by rain it may take many hours to dry and there is a resultant mortality of nymphal and adult lice and hatching eggs. In the region where the experiments were carried out, sheep were soaked periodically by thunderstorms in the autumn. The irregular mortalities of lice on different sheep was reflected 6 months later, when the lousiest sheep were shown to be those which were not soaked in the previous autumn.