Mosquito repellent efficacy of Australian Blue Cypress Callitris intratropica essential oil and its topical formulation under laboratory and field conditions

Mosquito repellents are important for personal protection against nuisance and potentially infectious mosquito bites. Repellent activity of Australian Blue Cypress (ABC) essential oil and a commercially formulated skin lotion containing ABC oil were compared with 20% DEET (N, N-diethyl-3methylbenzamide) and evaluated against mosquitoes under laboratory and field conditions in North Queensland, Australia. Using the arm-in-cage method, the following cumulative doses of ABC oil in ethanol were tested; 0.5%, 1.5%, 3%, 5%, 7.5% and 10.5% against female Aedes aegypti. In the field, 2.5%, 5% and 10% of diluted ethanolic ABC oil were tested using the human landing catch method. We observed a dose-dependent increase in protection with diluted ABC oil approaching 80% at high concentrations. While some protection was afforded, mosquito landing and probing was still recorded immediately after application (laboratory) for both ABC essential oil and skin lotion. Protection declined from 80 - 70% and 93 - 50% for 20% ABC oil (laboratory) and 10% ABC oil (highest dose, field), respectively. For the formulated product, protection declined from 85 - 75% in the laboratory and from 63 - 50% in the field. To conclude, both ABC essential oil and the formulated skin lotion provided moderate protection against mosquito bites, which decreased soon after application.