Ecology and phenology of cattle ticks in Zambia: development and survival of free-living stages.

A study on development and survival of free-living stages of three important cattle ticks in Zambia, Amblyomma variegatum Fabricus, Boophilus decoloratus Koch, and Rhipicephalus appendiculatus Neumann, was carried out to complement studies on seasonal dynamics of parasitic stages. Different instars of engorged ticks were exposed under quasi-natural conditions according to the season in which they occur naturally. Generally, development rates of all stages of the three species were related to temperature, whilst the duration of survival was influenced mainly by rainfall and consequent relative humidity. Observations on the effect of age and climate on the behaviour of ticks on pastures were also made. Both A. variegatum and R. appendiculatus completed only one generation per year. In A. variegatum, engorged females detaching early in the adult season (August to October) undergo morphogenetic diapause. Adults of R. appendiculatus emerging between August and October enter a period of behavioural diapause before becoming active in December. These mechanisms effectively synchronize the life-cycles of these two univoltine species. The one-host tick, B. decoloratus, is able to complete three to five generations each year with no indication of seasonal synchronization.