Population dynamics of ticks on Ankole cattle in five ecological zones in burundi and strategies for their control

Abstract

Tick populations were observed on Ankole (Sanga type Bos indicus x Bos taurus) cattle at monthly intervals over periods of 2–3 years in 4 ecological zones (Gatumba (830-m alt., 789-mm rain); Gitega (1671-m alt., 1122-mm rain); Kirundo (1420-m alt., 1076-mm rain) and Gihofi (1260-m alt., 1225-mm rain)) of Burundi, Central Africa. Concurrently, observations were made on the development and survival of Rhipicephalus appendiculatus in pastures at each location. Ticks were also counted on cattle in a fifth, high altitude zone (Ijenda, 2191-m alt., 1549-mm rain) for a period of 2 years. Rainfall was monomodal at all sites and fell between September and May. The species composition and total numbers of ticks infesting cattle in the 5 ecological zones varied. The most common species recorded were R. appendiculatus, Boophilus decoloratus and Amblyomma variegatum. The highest average number of adult females of the above species completing engorgement daily was 29 R. appendiculatus at Kirundo, 13 B. decoloratus at Ijenda and A. variegatum at Gitega. The regions differed slightly in their overall level of tick infestation, as measured by the average numbers of adult female ticks of all species engorging daily, i.e. Kirundo (34), Gatumba (27), Gitega (26), Ijenda (21) and Gihofi (11). Adults of A. variegatum exhibited the strongest seasonal pattern of feeding, with peaks early in the wet season. Non-climatic factors were apparently important in determining the relative numbers of A. variegatum in different regions. Development times of the free-living stages of R., appendiculatus in pastures varied between locations, taking 3 weeks for engorged larvae, 4–7 weeks for nymphs and 6–9 weeks for oviposition and egg development. Engorged larvae and nymphs suffered the least mortality while egg hatching was reduced in the dry season. Fifty percent of unfed larvae survived 1.5–3 months, nymphs 3–5 months and adults 16 months. Parasitic ticks completed engorgement more successfully when attached in preferred sites on the host's body. Computer simulations were used to estimate the proportional reduction in numbers of R. appendiculatus from dipping strategies with different timing, duration and efficiency. Strategies of 3-months duration, with the start timed to coincide with the period of adult feeding activity, were economically the most efficient. Computer simulations suggested that the annual cattle migration from the highlands to the lowlands in the dry season was important in limiting the size of tick populations. These results were taken into account when designing a policy to make the best use of the country's resources.