Abstract
Dichloromethane (DCM) extract of garlic (Allium sativum Linn.) bulbs was assessed for its repellent effect against the hard tick, Hyalomma rufipes (Acari: Ixodidae) using two tick behavioural bioassays; Type A and Type B repellency bioassays, under laboratory conditions. These bioassays exploit the questing behaviour of H. rufipes, a tick that in nature displays ambush strategy, seeking its host by climbing up on vegetation and attaching to a passing host. One hundred microlitres (100 µL) of the test solution containing DCM extract of garlic bulbs and DCM at concentrations of 0.35%, 0.7% or 1.4% w/v were evaluated. DCM only was used for control. Tick repellency increased significantly (R2 = 0.98) with increasing concentration (40.03% – 86.96%) yielding an EC50 of 0.45% w/v in Type B repellency bioassay. At concentration of 1.4% w/v, the DCM extract of garlic bulbs produced high repellency index of 87% (male ticks) and 87.5% (female ticks) in the Type A repellency bioassay. Only 4% avoidance of male ticks or female ticks was recorded in the Type B repellency bioassay. In the corresponding controls, the mean numbers of non-repelled male or female ticks were 80% and 41 males or 38 females of 50 ticks in the Type A and Type B repellency bioassays, respectively. The variations in the results could be attributed to the difference in tick repellent behaviours that were assessed by the two repellency bioassays; the Type A repellency bioassay assessed repellent effect of garlic extracts without discriminating between deterrence and avoidance whereas the Type B repellency bioassay only assessed avoidance response. Generally, DCM extract of garlic was repellent against H. rufipes, albeit weak tick repellency was obtained in the Type B repellency bioassay. Furthermore, this study established that the tick repellent activity of garlic extracts is predominantly by deterrence.
Highlights
Tick bites and tick-borne diseases resulting from encounters with ticks are widespread; for example, in South Africa, there are reports of ixodids such as Hyalomma and Amblyomma feeding on humans (Estrada-Pẽna & Jongejan 1999; Horak et al 2002)
In the Type A repellency bioassay, fewer ticks were observed on test filter papers than on control filter papers at all concentrations of DCM extract of garlic (Figure 1)
A noteworthy observation is that no significant difference was found between male and female responses at all concentrations of DCM extract of A. sativum
Summary
Tick bites and tick-borne diseases resulting from encounters with ticks are widespread; for example, in South Africa, there are reports of ixodids such as Hyalomma and Amblyomma feeding on humans (Estrada-Pẽna & Jongejan 1999; Horak et al 2002). There is mounting interest in the use of alternative and environmentally friendly arthropod pest control agents such as plant-based repellents (Kaaya 2003; Pålsson & Jaenson 1999). Allium sativum L. is attracting interest from researchers as a potential source of tick repellent, especially following a report that the consumption of garlic protected soldiers exposed to ticks from tick bites under field conditions (Stjernberg & Berglund 2000). There are many anecdotes and ethnobotanical claims suggesting that garlic extracts repel pest of arthropod origin (Karunamoorthi & Hailu 2014). Very few studies have scientifically validated these claims and most of the scientific investigations involving garlic repellent activities have been directed towards insects (Birrenkott et al 2000; Kianmatee & Ranamukhaarachchi 2007; Sritabutra et al 2011)
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