VERTICAL MIGRATION OF ADULT IXODES-RUBICUNDUS, THE KAROO PARALYSIS TICK (ACARI, IXODIDAE)

Mortality due to Karoo paralysis amongst livestock is of considerable economic importance in South Africa. Indications are that the extent o f vertical migration Of adult ticks, to reach questing positions on gr asses, is influenced by sudden climatic changes. Such influences as we ll as selection of questing substrates were investigated under control led conditions. Vertical migration of adult Ixodes rubicundus on coppe r rods was determined in a square metal arena within a closed glass co ntainer in a room in which temperature and light could be controlled. Significantly more female and male ticks migrated vertically on 1.5 mm diameter rods than on 4.0 mm rods and on 450 mm long rods than on 100 mm rods. More ticks of both sexes migrated vertically at RH >80% than at RH <50% and at 12-degrees-C than at 21-degrees-C. More female than male and more older than younger ticks migrated vertically in all exp eriments. The results of this study contribute towards an understandin g of the epidemiology of Karoo paralysis.