Comparative mosquitocidal and repellence activities of essential oil, nanoemulsion and main terpenes of Deverra tortuosa against Aedes albopictus with insights into the non-target effects

Abstract

There is an urgent and renewed interest in searching for effective and green pesticides to control mosquitoes. In this framework, the essential oil (EO) of the plant Deverra tortuosa was hydrodistilled, and analysed using gas chromatography-flame ionisation detection (GC-FID) and gas chromatography-mass spectrometry (GC-MS). Dillapiole (40.2%), elemicin (8.1%), and myristicin (6.3%), phenylpropanoids, and sabinene (4.3%) a common monoterpene, were found to be the major EO components. The oil nanoemulsion (ONE) was developed adopting a green protocol, and then characterised. The EO, ONE, and terpenes, particularly the phenylpropanoids possessed considerable mosquitocidal bioactivity against the Asian tiger mosquito, Aedes albopictus. A percentage of 100% larval mortality was recorded when insects were treated with a concentration of 40 μL/mL of ONE after 24 hours of treatment, while double of this concentration from EO and dillapiole was required to achieve the same activity. The LC50’s against larvae ranged between 7.6 and 60.7 μL/mL. For adults, LC50’s ranged between 6.4 and 50.9 μL/L. At sub-lethal concentrations (0.625-5.0 μL/cm2), EO materials significantly repelled Ae. albopictus, where a concentration of 5.0 μL/cm2 of EO and ONE provided 100% protection for up to180 min. As a proposed mechanism of action, the EO materials considerably inhibited the activity of acetylcholinesterase (AChE). The test materials were safe for the mosquitofish, Gambusia affinis, a common larvivorous fish, and Eisenia fetida earthworm. Test materials were also safe for the white albino rat in an oral bioassay at a limit dosage of 3500 mg/kg b.wt. The findings support the use of the EO, nanoemulsion, and phenylpropanoids of D. tortuosa as environmentally benign natural mosquitocodes to control Ae. albopictus.