An oil extracted from the leaves of a tropical shrub Ocimum suave was found to repel as well as kill all stages of the tick Rhipicephalus appendiculatus. In an in vitro bioassay for the larvae, the LC50 of the oil in liquid paraffin was 0.024%. A 10% solution was found to kill all immatures and more than 70% of adults feeding on rabbits. Rabbits were protected for 5 days against attaching larvae using a 10% solution. Preliminary experiments undertaken with cattle kept in the field suggest that the oil may have potential in tick control, and a role in integrated tick management.
In an experiment to investigate the effect of the tick parasitoid, Ixodiphagus hookeri, on tick numbers on cattle, 150000 parasitoids were released over a period of 1 year in a field where ten cattle infested with multiple tick species were kept. Amblyomma variegatum was reduced from 44 to two ticks per animal while Rhipicephalus appendiculatus increased over the time of parasitoid release. During the time of release 51% of the nymphs of A. variegatum collected from the animals were parasitized. The recovery of the parasitoids after the releases were stopped was only 9%. The total numbers of A. variegatum remained low up to 1 year after the parasitoid release was stopped. This study gives an insight into how I. hookeri could be used strategically for the management of A. variegatum on small-scale farms.
In a study to develop anti-tick pastures, the climbing behaviour of Rhipicephalus appendiculatus on Melinis minutiflora (molasses grass) was investigated. Experiments were done with cut green stems of grass, grass dried in the shade, grass dried in sunshine, grass washed in solvent and grass growing in a study plot. In all cases a common pasture grass, Pennisetum clandestinum (Kikuyu grass), was used as control. All instars of the tick avoided climbing on the green M. minutiflora whereas most larvae, nymphs and adults climbed on the control green P. clandestinum grass. More ticks climbed on the stems dried in the sunshine than on air-dried grass. Acetone was found to be the best of 5 solvents used to extract the tick-repellent substance. Possibilities of using M. minutiflora as part of an integrated tick control package are discussed.
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