Spatial and temporal distributions of parasites: can wild and domestic ungulates avoid African tick larvae?

Infestation of a new host is a crucial stage in the life-cycle of parasites, and the possibility that hosts avoid infesting contact depends, in part, on the predictability of infestation risk. Immature free stages of ticks (Acari, Ixodidae) have limited mobility and survival in the vegetation and strongly depend on host behaviours for their infestation. We studied spatial and temporal distributions of the larvae of 2 major groups of African risk species in a ranch in Zimbabwe. No difference in the abundance of Rhipicephalus evertsi evertsi larvae was found among vegetation types and during most of the seasonal cycle, and no reliable indicator of their presence on a given site was identified. Rhipicephalus appendiculatus/Rhipicephalus zambeziensis larvae are mainly found during the cool dry season, in vegetation types situated close to permanent water holes or dominated by Acacia trees, which provide key forage resources for ungulates; and several indicators of their presence were identified. For both tick groups, spatial and temporal distributions of the larvae result in an optimized contact with ungulate hosts: R. e. evertsi larvae are unpredictable and thus unavoidable by hosts, whereas R. appendiculatus/R. zambeziensis larvae are predictable but also unavoidable because they are associated with key-resources for ungulates.