Repellency and toxicity of a CO2-derived cedarwood oil on hard tick species (Ixodidae)

Abstract

The repellency and toxicity of a CO 2 -derived cedarwood oil (CWO) was evaluated against actively questing unfed nymphs of four species of hard ticks: Amblyomma americanum (L.), Dermacentor variabilis (Say), Ixodes scapularis Say, and Rhipicephalus sanguineus (Latreille). Using a vertical climb bioassay for repellency, nymphs of these species avoided a CWO-treated filter paper in proportional responses to treatment concentrations. At 60 min of exposure, I. scapularis nymphs were most sensitive with 50% repellency concentration (RC 50 ) of 19.8 µg cm −2 , compared with RC 50 of 30.8, 83.8 and 89.6 µg cm −2 for R. sanguineus, D. variabilis and A. americanum , respectively. Bioassays determined the lethal concentration for 50% (LC 50 ) and 90% (LC 90 ) mortality of nymphs exposed to CWO in treated vials after 24- and 48-h exposure. After 24 h exposure, the LC 50 values were 1.25, 3.45 and 1.42 µg cm −2 and LC 90 values were 2.39, 7.59 and 4.14 µg cm −2 for D. variabilis , I. scapularis and R. sanguineus , respectively, but had minimal effect on A. americanum . After 48 h exposure, the LC 50 values were 4.14, 0.78, 0.79 and 0.52 µg cm −2 , and LC 90 values were 8.06, 1.48, 1.54 and 1.22 µg cm −2 for A. americanum , D. variabilis , I. scapularis and R. sanguineus , respectively. The repellency of CWO on tick species decreased with time. The repellency and toxicity bioassays demonstrated concentration-dependent responses of tick nymphs to the oil, indicating the potential of the CO 2 -derived cedarwood oil be developed as an eco-friendly repellent and/or acaricide.

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