Variation in tick community across different control systems, habitats, seasons and environmental factors in a mixed cattle/wildlife ranch: Imire game reserve, Zimbabwe.

Abstract

An assessment of spatial and temporal variation in tick community diversity, abundance, sex ratio and age structure across habitats, seasons and tick sweeper types at Imire Ranch was carried out from March to September 2015. The study primarily aimed at establishing the efficacy of two chemically-treated tick sweepers (buffalo and cattle) in controlling free-living tick populations in a mixed cattle/wildlife ranch. A total of 5,124 ticks were recorded over the study period. Rhipicephalus appendiculatus was the dominant tick species, comprising 98.8% of adult ticks. Rhipicephalus evertsi, Haemaphysalis leachi, Hyalomma truncatum and Hyalomma rufipes comprised 0.92%, 0.16%, 0.05% and 0.11% of adult ticks, respectively. A single genus (Rhipicephalus) was recorded at nymphal stage and two (Rhipicephalus and Amblyomma) at larval stage, with Rhipicephalus being the most abundant. Tick abundance was at a peak during the hot-wet season and density greater in woodlands than in grasslands. There was a significant difference in the efficacy of the two sweepers with 4,274 ticks recorded in the buffalo-swept section and 850 in the cattle-swept section. Tick species richness was also higher in the buffalo-swept section (5) than in the cattle-swept area (3). H. truncatum and H. rufipes were only recorded in the buffalo-swept section. The efficiency of buffalo as a sweeper was lower in woodlands than in grasslands and much lower during the hot-wet season. In contrast, cattle were more efficient in woodlands and highly inefficient in the hot-dry season. Densities of all tick developmental stages (larvae, nymphs and adults) were significantly higher under buffalo sweeping, and were significantly different across seasons. Adult ticks were mostly abundant during the hot-wet season, while larvae and nymphs peaked during the cold-dry and hot-dry seasons, respectively. Tick larva and adults were more abundant in woodlands than grasslands, while nymphs where higher in grasslands. The tick community showed minor variation in sex ratio, with females being more abundant than males in R. appendiculatus and H. truncatum, while R. evertsi and H. rufipes were dominated by males. Haemaphysalis leachi had an equal number of males and females. Sex ratio was influenced by type of habitat, sweeper and season. There was weak correlation between tick density and grass sward height and non-linear relationship between tick abundance and soil moisture, temperature, grass height and mat depth. Canonical correspondence analysis showed an association of Rhipicephalus larva with sites with high sward height and high soil moisture, while Rhipicephalus nymph was associated with high humidity sites. Adult tick species were associated with sites with high mat depth, and they quested under low temperature. Among adult ticks, only R. evertsi and R. appendiculatus ii preferred sites with high humidity. The study revealed that, even though acaricide-treated cattle are effective in controlling free-living ticks, the same cannot be said with buffalo. The difference is attributed to variations in stocking density and host susceptibility to infestation. An integrated tick control strategy that considers stocking rate, season and habitat type is recommended as an effective tick control strategy for cattle /wildlife mixed ranches.