Mosquito Repellent Efficacy of Australian Blue Cypress Callitris intratropica Essential Oil and a Topical Formulation under Laboratory and Field Conditions

Abstract

ABSTRACT. Mosquito repellents are important for personal protection against nuisance and potentially infectious mosquito bites. Repellent activity of Australian blue cypress essential oil (EO) and a commercially formulated skin lotion containing blue cypress EO (topical formulation) were compared with 20% DEET (N, N-diethyl-3 toluamide) against mosquitoes under laboratory and field conditions in North Queensland, Australia. On a volunteer’s forearm, 1 mL of candidate material was applied to approximately 600 cm2 of exposed skin. When blue cypress EO was applied at various concentrations (0.5%–10.5%), it did not fully prevent mosquito landing or biting. However, a dose–dependent increase, approaching 80% protection, was observed at high EO concentrations. On the basis of these results, three concentrations (5%, 10%, and 20%) of blue cypress EO were selected for complete protection time (CPT) experiments. Topical formulation (undiluted) was also included in CPT experiments. Although some protection was afforded, mosquito landing/probing were still recorded immediately after application for both blue cypress EO and its topical formulation. Specifically, protection declined for blue cypress EO from 80% to 70% (laboratory) and from 93% to 50% (field) within 1 hour. For topical formulation, protection declined from 85% to 75% in the laboratory and from 63% to 50% in the field. In comparison, DEET maintained a 100% protection throughout the testing period of up to 1 h, and there was no landing/probing observed in volunteers who had applied DEET. To conclude, both blue cypress products provided some protection against mosquito bites, which decreased soon after application.