The ecology of lice on sheep. 1. The influence of skin temperature on populations of Linognathus pedalis (Osborne).

Abstract

Female Linognathus pedalis (Osborne) were exposed to temperatures of 22, 25, 30, 36, and 40°C. Nost eggs were laid at 36°C but none at 22°C. Eggs were exposed to 22, 25, 30, 33, 36, 38, and 40°C and hatched only at 33, 36, and 38°C. Most eggs hatched at 36°C. At 36°C, however, few eggs were laid at 100 per cent. R.H. and the majority of eggs exposed to even 92 per cent. R.H. failed to hatch. Thus, high humidities could reduce the number of eggs which are laid and which hatch on the legs of sheep even if the temperature near the skin is favourable. When sheep were exposed to atmospheric temperatures near 28°C the temperatures near the skin of the body were higher than 38°C, and conditions cool enough for the maintenance of L. pedalis populations were found only on parts of the legs. On exposure to cold, the temperature near the skin of the legs fell and remained too cold for oviposition and egg development during several hours of exposure. However, it was also found that the resultant temperatures near the skin of the legs of the same sheep and of the legs of different sheep could differ greatly. Thus, those legs on which temperatures near the skin are above 30°C for the longest periods may become most heavily infested. These findings offer a possible explanation of observed differences in the numbers of L. pedalis on the legs of sheep.