Biological effects of Lippia alba essential oil against Anopheles gambiae and Aedes aegypti

Abstract

Background the management of mosquito resistance to chemical insecticides and the biting behaviour of some species are motivating the search for complementary and/or alternative control methods. The use of plants is increasingly considered as a sustainable biological solution for vector control. The aim of this study was to evaluate the biological effects of the essential oil (EO) of Lippia alba against Anopheles gambiae and Aedes aegypti mosquitoes. Methods phytochemical compounds were identified by GC-MS. Knockdown and mortality were determined according to the WHO test tube protocol. Contact irritancy was assessed by observing the movement of mosquitoes from a treated WHO tube to a second untreated tube. Non-contact repellency was assessed using a standardised high-thtoughput screening system (HITSS). Blood meal inhibition was assessed using a membrane feeding assay treated with EO. Results the EO was identified as the citral chemotype (geranial + neral) and it is composed mainly of geranial (26.79%), neral (19.07%) and geraniol (14.52%). The essential oil gave 100% KD60 in both species at a concentration of 1%. Mortalities of 100% were recorded with An. gambiae and Ae aegypti at concentrations of 1% and 5% respectively. The highest proportions of females escaping during the contact iritancy test were 100% for An. gambiae at 1% concentration and 94% for Ae. aegypti at 2.5% concentration. The 1% concentration produced the highest proportions of repelled mosquitoes in the non-contact repellency tests: 76.8% (An. gambiae) and 68.5% (Ae. aegypti). The blood meal inhibition rate at a dose of 10% was 98.4% in Ae. aegypti but only 15.5% in An. gambiae. Conclusion the citral chemotype of L. alba EO has highly interesting biological effects in both species that make it a potentially good candidate for its use in mosquito control. The results obtained in this study encourage the further evaluation of L. alba essential oils from other localities and of different chemotypes.