AbstractA study was made between 1967 and 1971 at Edinburgh University and at EAVRO, Muguga, of the variability in feeding performance of all three instars of Rhipicephalus appendiculatus Neum., with a view to better prediction of transmissions of Theileria parva. Variability could be definitely ascribed to factors within the ticks only when vigour was reduced after prolonged storage and when mating opportunity was withheld from attached females. Lower environmental temperatures prolonged engorgement, but it was arguable whether this effect was produced through the tick or through the host. All other sources of variability arose from influences within the host. The most significant of these were recognised in responses by rabbits in which resistance had been induced by successive infestations. Resistance was manifested by prolonged engorgement, by a reduction in numbers engorged and in degree of repletion, and by an increasing severity in host reaction. Three resistance mechanisms were suggested by host reactions—one appearing at the earliest stages of attachment, a second with the deposition of cement, and a third at the start of salivation. Each varied in efficacy, and each was capable of arresting an infestation. Cumulative and synergistic responses were ascribed to interactions between these mechanisms. Storage periods, sizes of infestations and sex ratios of R. appendiculatus were standardised within routine procedures, and abundant records of previous and subsequent performances on rabbits and cattle are presented for comparison and reference. Comparison of feeding performances on different animals suggests that cattle, buffalo, eland, waterbuck and oryx are as satisfactory as hosts as the rabbit, whereas Thomson's gazelle, wildebeest, sheep and goat are less so. Immature instars successfully completed engorgement on mongoose, cane rat, genet, domestic fowl and spur-fowl.
Acquisition and transmission of Theileria parva by vector tick, Rhipicephalus appendiculatus