A natural barrier: tick-repellent potential of a spruce-derived volatile blend against Hyalomma excavatum and Ixodes ricinus

Ixodes ricinus and Hyalomma excavatum are two widely dispersed vectors of pathogens, including those that cause Lyme disease and Crimean-Congo haemorrhagic fever in the human population.Recently developed, plant-derived, mosquito-repellent blends have shown promise against other vector clades, and this study assesses these blends as potential tick repellents.Blends of (+)-borneol, bornyl acetate, eugenol, isoeugenol and camphor were assessed in two formats: blends 3 and 4. Ticks were assessed using the moving object bioassay (Ixodes) or a dual-choice behavioural assay (Hyalomma).Both blends were compared against negative controls and four commercially available synthetic repellents: N,N-diethyl-3-methylbenzamide (DEET), 2-(2-hydroxyethyl)-1-methylpropylstyrene 1-piperidine carboxylate) (Picaridin), 3-(N-n-butyl-N-acetyl)-amino-propionic acid ethyl ester (IR3535) and p-menthane-3,8-diol (PMD).Results demonstrate the efficacies of blends 3 and 4; moreover, both were more effective than the commercial repellents (P < 0.05).Blend 3 was marginally more effective than blend 4, and differences in the repellent action were noted for each of the tick species, suggesting broadspectrum vector-repellent activities, irrespective of life strategy.Overall, this work demonstrates the clear potential of blends 3 and 4 as tick repellents that offer an improved vector response over currently available commercial repellents.Furthermore, that the same repellent blends are capable of tick repellency in addition to mosquito repellency, offers the potential for widely dispersed usage across a range of integrated vector management strategies.