On-host behavioural interactions between adult rhipicephalus appendiculatus and characterisation of the mediating pheromones
Bramuel, Khaemba Wafula
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Rhipicephalus appendiculatus (Brown Ear tick) is an efficient vector of Theileria parva the aetiological agent of East Coast fever (ECF) in cattle. Currently, ECF threatens about 28 million cattle in eastern, central and southern Africa. Control of this tick has largely depended on synthetic acaricides. The use of these chemicals for tick control has however, been compromised by increased cases of tick resistance, high cost of the acaricides and concerns over environmental pollution as a result of extensive use of the acaricides. There have been calls therefore, for alternative tick control approaches that minimise or eliminate the use of synthetic acaricides. Pheromone aided tick control can be one such an approach. Effective use of pheromones in controlling ticks however, demands an understanding of the ticks’ behaviour and the identity of the pheromone(s) mediating these behaviours. This study sought to understand the on-host behavioural interactions between adult R. appendiculatus ticks and to characterise the pheromone(s) mediating these behaviours. The findings show that female R. appendiculatus attach readily on the host even in the absence of male ticks. After feeding for at least 4 days, female ticks not only attract sexually mature males for copulation but also attract and induce the attachment of unfed males. GC-MS analyses of SPME trapped tick volatiles from 5 days fed R. appendiculatus females showed the presence of phenol, p-cresol and 2,6 dichlorophenol in the ratio 11:5:6. All the three phenols and their blends were found attractive to unfed male R. appendiculatus ticks in a two choice climbing assay. P-cresol at a concentration of 2.5ng/μl exhibited the highest relative percentage attractancy (50.41 ± 1.88) among the individual compounds tested. A blend consisting of 5.5ng/μl phenol and 2.5ng/μl p-cresol exhibited the highest relative percentage attractancy (50.90 ± 1.77) among the blends tested. 2,6-dibromophenol, an analogue of the identified phenols was also found attractive to the unfed male ticks with a concentration of 5.0 ng/μl exhibiting the highest relative percentage attractancy (37.90 ± 2.76) among the 2,6-dibromophenol doses tested. Behavioural interactions in this tick species could thus be simply mediated by phenols. Male ticks seem to play a critical role on the repletion time and engorged mass of the female ticks. The time and the physiological state of the males (partially fed or unfed) at the time they join females on the host had an impact on the females’ engorged mass and repletion time. Females that attached on the host the same day with males attained an engorged mass of 402.60 ± 37.30 mg and reached repletion in 10.47 ± 0.36 days. 5-Days feeding females that were accompanied on the host by 5-days fed males attained an engorged mass of 237.22 ± 22.28 mg and reached repletion in 11.17 ± 0.23 days while those 5-days feeding females that were accompanied by unfed males attained an engorged mass of 387.90 ± 32.42 mg reaching repletion in 13.40 ± 0.34 days. These findings lay some ground work for deploying the brown ear tick’s pheromone in its control especially so by targeting the male tick which appears to play a critical role in the successful feeding of the female.