Development of a behavioral assay for testing essential oil repellency with Aedes aegypti mosquitoes

Abstract

Abstract In the following methods article, an essential oil is implemented in a behavioral assay to function as a spatial repellent. The purpose is to ascertain its effectiveness in repelling the vector mosquito, Aedes aegypti (Diptera: Culicidae) based on exposure to volatiles, not contact. A modified dual-choice chamber system was developed to test the efficacy of an essential oil in the presence of an attractant or activator (carbon dioxide). The modified system is composed of 3 glass chambers arranged linearly with 2 metal gates that connect the chambers. The gates can be opened to release mosquitoes from the central chamber and then closed to isolate responding mosquitoes into the treatment or control end chambers. Host-seeking mosquitoes responsive to host stimuli were pre-selected for use in assays to reduce variability. The assay allows for rapid estimation of repellency as each assay is only 10 minutes. Movement of individual mosquitoes is recorded by counting the total number in each chamber. Repellency is determined by calculating the repellent spatial activity index following the guidelines by WHO. The choice chamber assay detected the aversive behavior of thyme oil against three populations of Aedes aegypti. The Vero and Pernambuco populations had higher repellent spatial activity indices compared to the Manatee population. This choice chamber assay system can be used to test any spatial repellent. Additionally, this system may be used to test the repellent properties for other flying host-seeking insects besides mosquitoes. Data gathered from these assays will contribute to entomological knowledge of behavioral cues and responses to spatial repellents.