Acaricidal activity of essential oils from five endemic conifers of New Caledonia on the cattle tick Rhipicephalus (Boophilus) microplus.

The aim of the present study was to demonstrate acaricidal activity on the cattle tick Rhipicephalus (Boophilus) microplus of essential oils from endemic conifers of New Caledonia in the context of the development of natural alternatives. Acaricidal activity of essential oils extracted from resin and heartwood of five endemic conifers of New Caledonia (Araucaria columnaris, Agathis moorei, Agathis ovata, Callitris sulcata, and Neocallitropsis pancheri) was evaluated on 14- to 21-day-old Rhipicephalus microplus tick larvae using the Larval Packal Test bioassay. A first screening with 5% dilute solution was carried out and the oils with 100% of mortality at this rate were diluted until no activity was shown. The heartwood oils of the two Cupressaceae were the most active with LC50 value of 0.65% for C. sulcata and 0.55% for N. pancheri while resin oil of A. columnaris (LC50=1.62%) was the most active of the Araucariaceae family. Negative control (ethanol) was not toxic to the larvae. The chemical composition of essential oil from resin of A. columnaris was analyzed by gas chromatography-mass spectrometry. The essential oil was characterized by high level of sesquiterpene hydrocarbons and oxygenated sesquiterpenes and was composed mainly of aromadendrene (23.1%) and bicyclogermacrene (16.0%). In order to compare different plant resources in a sustainable program of natural acaricide, an "essential oil efficiency EOE" can be measured as the ratio between the yield of extraction and LC50 value. This study shows that A. columnaris (EOE=2.36) and N. pancheri (EOE=3.51) could provide valuable and effective natural acaricides for control of the cattle tick R. microplus.