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.
