Aspects of the bio-ecology of the biting louse, Damalinia Limbata

English: Biting lice are well known ecto-parasites of vertebrates. Most wild and domesticated animals have one or more louse species, living on them. Although lice are a source of irritation to the host, they are not generally considered as economically important because they do not cause much physical damage. The sheep biting louse (Damalinia avis) has, however, been shown to cause losses in wool production and quality. Damalinia limbata are ecto-parasites on Angora goats and can cause the same type of losses to the farmer as the sheep biting louse. Very little research has been done on these lice and their impact on mohair production can therefore not be objectively assessed. The objectives of the current study were to investigate aspects of the biology and distribution of D. limbata and to promote more effective and economical management of these lice on commercial farms. The following were investigated: (1) Aspects of the morphology of D. limbata and D. avis. (2) Environmental temperatures prevalent on the body of Angora goats. (3) The number of nymphal instars of D. limbata. (4) Seasonal changes in the populations of D. limbata. (5) The influence of D. limbata on the body mass of Angora goats and the production and quality of mohair, as well as the efficacy of different control methods. Field experiments were conducted on the farm Preezfontein (29°50'S, 25° 19'E), situated 10 km from the town Fauresmith, about 130 km southwest of Bloemfontein in the south-western Free State. The veld type of this area is defined as 'False Upper Karoo' and falls in the Karoo biorne. The Free State is a summer rainfall region with an average precipitation of 450-500 mm per annum, with hot summers and cold winters and droughts occurring regularly. D. limbata and D. avis were compared using general morphological characters, morphometric measurements of various body regions and placement of dorsal and ventral abdominal sclerites. D. limbata has a more robust appearance than D. avis. Females of both D. limbata and D. avis were on average 1.611 mm long and the males had average lengths of 1.378 mm and 1.255 mm, respectively. Male D. ovis had solid dorsal plates where as D. limbata males had dorsal plates, which were transversally split, on segments IV and V. Temperature studies, on the micro-habitat of D. limbata, showed that the temperature against the skin of an Angora goat is relatively constant at approximately 35°C. All attempts to establish a laboratory colony of D. limbata were unsuccessful. D. limbata was found to have three nymphal instars before reaching adulthood. Instar 1 had average head-capsule widths and lengths of 0.252 mm and 0.202 mm, respectively. The second and third instars had head-capsule widths of 0.364 mm and 0.467 mm and lengths of 0.305 mm and 0.425 mm respectively. The louse populations increased during spring and early summer, peaking in mid summer. Mid winter shearing seemed to have a greater impact on the louse populations than mid summer shearing. D. limbata moves around the body of Angora goats, being more abundant on the ventral areas of the body during summer and more evenly dispersed over the body during winter. It was found that D. limbata does not have an adverse influence on the body mass of Angora goats, but does adversely affect mohair production and quality. The average loss in mohair production was 12 % and individual losses of as much as 25 % were recorded, representing substantial financial losses to the farmer. D. limbata was effectively controlled by Deltamethrin when applied as either a backline treatment or as a lateral application with a Tikspray applicator.